Fast X-ray timing and spectroscopy at extreme count rates · HTRS 2011 Fast X-ray timing and...
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HTRS 2011 Fast X-ray timing and spectroscopy at extreme count rates 7-11 February 2011, Champ´ ery, Switzerland Abstract Book
Transcript of Fast X-ray timing and spectroscopy at extreme count rates · HTRS 2011 Fast X-ray timing and...
HTRS 2011
Fast X-ray timing andspectroscopy at extreme
count rates
7-11 February 2011, Champery, Switzerland
Abstract Book
List of papers
I Invited contributions 11
1 The High Time Resolution Spectrometer aboardthe International X-ray ObservatoryDidier Barret . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2 Multiwavelength high-time resolution observationsPiergiorgio Casella . . . . . . . . . . . . . . . . . . . . . . . . 14
3 Relativistic jets from Galactic accreting binarysystemsStephane Corbel . . . . . . . . . . . . . . . . . . . . . . . . . 15
4 M/R constraints from NS Iron lineMaria Diaz Trigo . . . . . . . . . . . . . . . . . . . . . . . . . 16
5 What Thermonuclear X-ray Bursts can tell us aboutNeutron StarsMaurizio Falanga . . . . . . . . . . . . . . . . . . . . . . . . . 17
6 General properties of magnetars and observationaldevelopments at high energiesWim Hermsen . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
7 Fitting a self-consistent physical model to the powerspectral density of XTE 1550-564Adam Ingram . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
8 Present and Future of Magnetar bursting/outburstingstudiesGianLuca Israel . . . . . . . . . . . . . . . . . . . . . . . . . . 20
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9 Status of IXO and the ESA Cosmic Visions Pro-grammeDavid Lumb . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
10 New results on the X-ray spectra of thermonu-clear burstsCole Miller . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
11 Relativistic Disk Reflection in Stellar-Mass BlackHolesJ. M. Miller . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
12 M/R constraints from accreting Millisecond Pul-sars and cooling stage of X-ray burstsJuri Poutanen . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
13 Testing the No-Hair Theorem with Observationsof Astrophysical Black HolesDimitrios Psaltis . . . . . . . . . . . . . . . . . . . . . . . . . 25
14 The Properties of High Frequency QPOs and theirConnection to the Physical Properties of BlackHolesRon Remillard . . . . . . . . . . . . . . . . . . . . . . . . . . 26
15 Black Hole Spin Measurements via X-ray Contin-uum SpectroscopyJames Steiner . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
16 Lense-Thirring PrecessionLuigi Stella . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
17 Timing of XRBs in the HTRS eraPhil Uttley . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
18 X-ray variability of black holes on all mass scalesSimon Vaughan . . . . . . . . . . . . . . . . . . . . . . . . . . 30
19 Cooling of accretion-heated neutron starsRudy Wijnands . . . . . . . . . . . . . . . . . . . . . . . . . . 31
20 HTRS Performance Simulations
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Jorn Wilms . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
II Oral contributions 33
1 Timing black-hole binaries: status and prospectsTomaso Belloni . . . . . . . . . . . . . . . . . . . . . . . . . . 35
2 Undetectable, intermittent, and detectable mil-lisecond X-ray oscillations of accreting neutronstars in LMXBsStratos Boutloukos . . . . . . . . . . . . . . . . . . . . . . . . 36
3 Epicyclic frequencies and QPOsMichal Bursa . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
4 Time lags as a constrain on the accretion disc ge-ometry in BHXRBsPablo Cassatella . . . . . . . . . . . . . . . . . . . . . . . . . 38
5 Can a ”propelling” disc stay trapped near co-rotation?Caroline D’Angelo . . . . . . . . . . . . . . . . . . . . . . . . 39
6 Living in a LOFTMarco Feroci . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
7 Systematic Uncertainties in the Spectroscopic Mea-surements of Neutron-Star Masses and Radii fromThermonuclear X-ray BurstsTolga Guver . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
8 Signatures of superfluid neutron star dynamicsBrynmor Haskell . . . . . . . . . . . . . . . . . . . . . . . . . 42
9 Broad iron emission lines in the intermediate stateof black-hole transientsBeike Hiemstra . . . . . . . . . . . . . . . . . . . . . . . . . . 43
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10 Detectors for fast X-ray spectroscopy, timing andimagingPeter Lechner . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
11 Spectral and timing features in the ultra-compactX-ray binary 4U 0614+091Oliwia Madej . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
12 Kilohertz Quasi-Periodic Oscillations as a tool toprobe the neutron-star interior and gravitationalfieldMariano Mendez . . . . . . . . . . . . . . . . . . . . . . . . . 46
13 Fast variability as a tracer of states and state-transitions in black holesTeo Munoz-Darias . . . . . . . . . . . . . . . . . . . . . . . . 47
14 GRAVITAS: General Relativistic Astrophysics ViaTiming and SpectroscopyKirpal Nandra . . . . . . . . . . . . . . . . . . . . . . . . . . 48
15 Oscillation-Phase-Resolved Spectroscopy in the IXOEraJoey Neilsen . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
16 A newly discovered accreting pulsar in Terzan 5Alessandro Papitto . . . . . . . . . . . . . . . . . . . . . . . . 50
17 Constraining the mass and moment of inertia ofneutron stars from quasi-periodic oscillations inX-ray binariesJerome Petri . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
18 The pertinence of Jet Emitting Discs in Micro-quasarsPierre-Olivier Petrucci . . . . . . . . . . . . . . . . . . . . . . 52
19 The Advanced X-ray Timing Array (AXTAR)Paul Ray . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
20 A non-magnetar Soft Gamma Repeater
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Nanda Rea . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
21 Theoretical disk spectra and BH spin determina-tionAgata Rozanska . . . . . . . . . . . . . . . . . . . . . . . . . . 55
22 Kilohertz quasi-periodic oscillations and broad ironemission lines as a probe of strong-field gravityAndrea Sanna . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
23 HIFI - A High Framerate Imager for GRAVITASAlexander Stefanescu . . . . . . . . . . . . . . . . . . . . . . . 57
24 All-Sky Monitoring of Variable Sources with FermiGBMColleen Wilson-Hodge . . . . . . . . . . . . . . . . . . . . . . 58
25 The complete sample of type-I X-ray bursts in thelow-mass X-ray binary 4U 1636-53 with RXTEGuo-Bao Zhang . . . . . . . . . . . . . . . . . . . . . . . . . . 59
III Poster contributions 61
1 Preliminary concept of modern X-ray timing mis-sionVadim Arefiev . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
2 The 2008 outburst of the new X-ray transientXTE J1719-291Montserrat Armas Padilla . . . . . . . . . . . . . . . . . . . . 64
3 How the fast X-ray timing at extreme count rateswill constrain the equation of state of the densematter from the burst oscillations of the neutronstarsRomain Artigue . . . . . . . . . . . . . . . . . . . . . . . . . . 65
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4 kHz QPO studies with IXO - Testing the MovingHotspots ModelMatteo Bachetti . . . . . . . . . . . . . . . . . . . . . . . . . 66
5 Re Analysis of Timing Parameters of OAO 1657-415Altan Baykal . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
6 Time lags in 4U 1608-52Marcio Guilherme Bronzato de Avellar . . . . . . . . . . . . . 68
7 Flame spreading velocity in Type I X-ray burstsYuri Cavecchi . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
8 The COSPIX mission : focusing on the energeticand obscured UniversePhilippe Ferrando . . . . . . . . . . . . . . . . . . . . . . . . 70
9 Phase lags and cyclotron lines in 4U 0115+63Carlo Ferrigno . . . . . . . . . . . . . . . . . . . . . . . . . . 71
10 Supergiant Fast X-ray Transients and other wind-fed accretors - testing with the Corbet diagramSergei Grebenev . . . . . . . . . . . . . . . . . . . . . . . . . 72
11 Aperiodic X-ray variability studies of the blackhole candidate MAXI J1659-152Maithili Kalamkar . . . . . . . . . . . . . . . . . . . . . . . . 73
12 Pulse profile variations in GX 1+4Peter Kretschmar . . . . . . . . . . . . . . . . . . . . . . . . . 74
13 Dipping and Absorption in the stellar wind in GX301-2Ingo Kreykenbohm . . . . . . . . . . . . . . . . . . . . . . . . 75
14 Pulse-phase spectroscopy as a tool for the studyof X-ray pulsarsAlexander Lutovinov . . . . . . . . . . . . . . . . . . . . . . . 76
15 On the nature of low frequency quasi periodic os-cillations: a variability study of the BHC GX 339-4
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Sara Motta . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
16 X-ray bursts and burst oscillations from the slowlyspinning X-ray pulsar IGR J17480-2446Sara Motta . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
17 Spectroscopy of the Pulsar-like White Dwarf AEAquarii from Chandra and Swift-XRT DataBosco Oruru . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
18 On the time evolution of the lower kHz QPO in4U 1608-52Stephane Paltani . . . . . . . . . . . . . . . . . . . . . . . . . 80
19 A filter wheel for the HTRSStephane Paltani . . . . . . . . . . . . . . . . . . . . . . . . . 81
20 Central Engines of GRBsTsvi Piran . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
21 INTEGRAL and the unified model of AGNClaudio Ricci . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
22 Type I and type II X-ray bursts of the RapidBurster as seen by SwiftGloria Sala . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
23 A Catalogue of X-ray bursters detected by JEM-X on board INTEGRALCelia Sanchez-Fernandez . . . . . . . . . . . . . . . . . . . . . 85
24 Simulations of the performance of the HTRS onIXOChristian Schmid . . . . . . . . . . . . . . . . . . . . . . . . . 86
25 Measuring strong magnetic fields of neutron starswith the next-generation of X-ray instrumentsGabriele Schonherr . . . . . . . . . . . . . . . . . . . . . . . . 87
26 Investigating the disc-jet coupling in accreting com-pact objects by studying the “radio quiet” sourcesPaolo Soleri . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
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27 XTE J1752-223: A broad band X-ray spectral in-vestigation combined with timing studiesHolger Stiele . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
28 X-ray bursting neutron star atmosphere modelsValery Suleimanov . . . . . . . . . . . . . . . . . . . . . . . . 90
29 Magnetized neutron star atmospheres: beyondthe cold plasma approximationValery Suleimanov . . . . . . . . . . . . . . . . . . . . . . . . 91
30 Extreme-value analysis of the X-ray emission ofCygnus X-1Maria Suveges . . . . . . . . . . . . . . . . . . . . . . . . . . 92
31 Synchrotron self-Compton model for optical/X-ray correlation in black hole X-ray binariesAlexandra Veledina . . . . . . . . . . . . . . . . . . . . . . . . 93
32 Fast variability of gamma-ray emission from su-permassive black hole binary OJ 287Ievgen Vovk . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
33 The Digital Data Processing Unit for the HTRSon board IXOHenning Wende . . . . . . . . . . . . . . . . . . . . . . . . . . 95
34 LATE POSTER:Are the two peaks of the Cathedral QPO real har-monics?Jerome Rodriguez . . . . . . . . . . . . . . . . . . . . . . . . 96
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I Invited contributions
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1 The High Time Resolution Spectrometer aboardthe International X-ray Observatory
Didier BarretRavera, Laurent; Bodin, Pierre; Amoros, Carine; Boutelier, Martin; Glorian,Jean-Michel; Godet, Olivier; Orttner, Guillaume; Lacombe, Karine; Pons,Roger; Rambaud, Damien; Ramon, Pascale; Ramchoun, Souad; Biffi, Jean-Marc; Belasic, Marielle; Cledassou, Rodolphe; Faye, Delphine; Pouilloux,Benjamin; Motch, Christian; Michel, Laurent; Lechner, Peter H.; Niculae,Adrian; Strueder, Lothar W.; Distratis, Giuseppe; Kendziorra, Eckhard;Santangelo, Andrea; Tenzer, Christoph; Wende, Henning; Wilms, Joern;Kreykenbohm, Ingo; Schmid, Christian; Paltani, Stephane; Cadoux, Franck;Fiorini, Carlo; Bombelli, Luca; Mendez, Mariano; Mereghetti, Sandro
CESR/IRAP, Toulouse
The High Time Resolution Spectrometer (HTRS) is one of the six focal planeinstruments of the International X-ray Observatory (IXO). The HTRS is theonly instrument matching the top level mission requirement of handling aone Crab X-ray source with an efficiency greater than 10%. It will provideIXO with the capability of observing the brightest X-ray sources of the sky,with sub-millisecond time resolution, low deadtime, low pile-up (less than2% at 1 Crab), and CCD type energy resolution (goal of 150 eV FWHM at 6keV). The HTRS is a non-imaging instrument, based on a monolithic arrayof Silicon Drift Detectors (SDDs) with 31 cells in a circular envelope anda X-ray sensitive volume of 4.5 cm2 x 450 µm. As part of the assessmentstudy carried out by ESA on IXO, the HTRS was studied by a consortiumled by CNES and CESR. In this paper, we will describe the expected per-formance of the HTRS, as assessed through Monte Carlo simulations. Wewill illustrate the instrument capabilities.
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2 Multiwavelength high-time resolution observa-tions
Piergiorgio Casella
School of Physics & Astronomy, University of Southampton, UK
The study of X-ray variability in X-ray binaries has represented - and stillis - one of the most powerful tools to study the accretion flow in the vicin-ity of compact objects. The advent of new instrumentation during the lastdecade has made possible to extend high time resolution astronomy to op-tical and infrared wavelengths. This has opened new exciting windows, asthe novel technique of echo-tomography, which allows us to map the binarygeometry, and the study of the fast-variable emission from relativistic jets,which provides unprecedented insights on the geometry and the Physics ofthe jets themselves. This field is at its dawn, but it is already showing itslarge potential. I will quickly review the state of the art, and show howhaving an X-ray timing satellite flying in the near future will be crucial tofully harness the great potential of these techniques.
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3 Relativistic jets from Galactic accreting binarysystems
Stephane Corbel
Univ. Paris Diderot & CEA Saclay
In the past decade, several considerable achievements have been reachedin the field of Galactic accreting binary systems, especially in light of theextreme variability of their relativistic jets. These jets are now known toexist in at least three different favours: the self absorbed compact jets inthe hard state, the transient and discrete ejection events associated with thestate transitions, and the emission associated with the interaction of the jetswith the interstellar medium.
Althought their phenomenology is now rather well established, theiremission and contribution to the total energy budget of microquasars is stillthe subject of active debates. In this review, I will present the most relevantobservations concerning our understanding of relativistic jets in accretingsystems, discussing in particular some open issues.
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4 M/R constraints from NS Iron line
Maria Diaz TrigoC. Ng, M. Cadolle Bel, S. Migliari
ESO, ESA
The recent claim of broad skewed iron lines from neutron star low-massX-ray binaries has opened the exciting possibility of determining an upperlimit to the radius of the neutron star, the most difficult parameter to obtainin order to constrain their equation of state.
With the aim of studying further this possibility, we performed a sys-tematic analysis of XMM-Newton archival observations of bright neutronstar low-mass X-ray binaries (LMXBs).
We performed a detailed data analysis taking into account the systematiceffects that arise as a consequence of the high count rates present in theobservations of these sources. The properties of the iron lines differed fromprevious published analyses due to either incorrect pile-up corrections ordifferent continuum parameterization. Most important, we could fit the Feline with a simple Gaussian component for all the sources. The lines didnot show the asymmetric profiles that were interpreted as an indication ofrelativistic effects in previous analyses of these LMXBs. I will present theresults of the outlined study and discuss the implications of these results forthe origin of broad Fe lines in LMXBs.
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5 What Thermonuclear X-ray Bursts can tell usabout Neutron Stars
Maurizio Falanga
ISSI, Bern
Some of the most extreme conditions of the universe exist in neutron stars,as these stars are very dense, have magnetic fields, and sometimes spin veryrapidly and emit intense radiation. Many aspects of extreme physics can bestudied only by observing and understanding neutron stars, as these prob-lems cannot be addressed by doing experiments in laboratories. One suchproblem is the lack of knowledge of the nature of dense cold matter at theneutron star cores, and only the accurate measurements of the mass, ra-dius, and spin period of a neutron star can resolve this. A promising wayto measure these stellar properties is to study type I X-ray bursts, whichare produced by thermonuclear burning of matter accumulated on the sur-faces of accreting neutron stars. This is because, these intense bursts, whichsometimes exhibit timing features (such as bursts oscillations from the stellarsurfaces) and may show surface spectral features, contain detailed informa-tion about the neutron stars. Moreover, X-ray bursts can be helpful forconstraining the stellar atmospheric parameters, and for understanding thethermonuclear flame spreading under extreme physical conditions that existon neutron star surfaces. In this talk, I will review our current knowledgeof type I X-ray bursts and address questions on the observational future.
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6 General properties of magnetars and observa-tional developments at high energies
Wim Hermsen
SRON Netherlands Institute for Space Research, Utrecht
The magnetar model has been proposed by Thompson and Duncan firstto explain the enigmatic behavior of Soft Gamma-ray Repeaters (SGRs)and later also that of Anomalous X-ray Pulsars (AXPs). Many of the(out)bursting, timing and spectral characteristics of these objects can beexplained with this model proposing rotating neutron stars with extremelystrong magnetic fields (in excess of 1014 Gauss). This strong magnetic fieldbeing the source of the energy required to explain the observed high lumi-nosities. Even persistent emission is found to be 1-3 orders of magnitudemore luminous at X-ray energies below 10 keV, as well as for an apparentlydifferent component above 10 keV, than can be explained with rotationalenergy loss. However, there is no agreed model scenario for the productionof the high-energy emission in the magnetospheres of magnetars. In this re-view I will concentrate on the observational characteristics at high-energiesincluding new constraints on the production of the non-thermal emissionabove 10 keV.
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7 Fitting a self-consistent physical model to thepower spectral density of XTE 1550-564
Adam IngramChris Done
Durham University Physics Department
The variability properties of Black Hole Binaries (BHBs) have been stud-ied for well over 20 years and a very detailed phenomenological picture hasbeen developed, particularly of the properties of the Power Spectral Den-sity (PSD). However, the underlying physical processes that generate thevariability are very poorly understood, especially low frequency Quasi Peri-odic Oscillations (QPOs). I describe a model that asociates the QPO withLense-Thirring Precession of the hot inner flow and show how this processis affected by fluctuations in mass accretion rate which themselves generatebroadband variability power. This causal connection between physical pro-cesses allows me to define a full, self-consistent model of the PSD which Ifit to data from the 1998 outburst of XTE 1550-564. This is the first everattempt to fit a physical model of the PSD to data.
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8 Present and Future of Magnetar bursting/out-bursting studies
GianLuca Israel
Osservatorio di Roma, Monte Porzio Catone
In the latest few years the study of X/Gamma-ray flashes, long bursts, out-bursts and giant flares from mangetars has opened new horizons in the field,through the study of the neutron star structure, magnetic field propertiesand the physical mechanism(s) responsible for their emission. The detectionof QPOs during giant flares impacted on the NS equation of states and onthe possibility of constraining them (in the future). The study of intermedi-ate flares gave us an important tool for the study of a magnetically trappedfireball and on the different species of photons (E-mode and O-mode polar-ized ones) responsible for the timing and spectral properties of bursts. Itsapplication resulted in an independent measurement of the distances and themagnetic field strengths of bursting magnetars. The long-term monitoringof outbursts from magnetars allowed, for the first time, to test new spectralmodels obtained through a detailed calculation (Montecarlo) of the photonradiative transfer into a ”twisted” magnetosphere. All these studies are ex-pected to be boosted in the future thanks to the capabilities of a number ofproposed high energy missions, such as IXO, NHXM, LOFT, etc.
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9 Status of IXO and the ESA Cosmic Visions Pro-gramme
David Lumb
SRE-SA ESTEC, Noordwijk
The overall status of the ESA CV programme is described.The progress ofIXO towards the down selection milestone in the Cosmic Visions programmeis reviewed. Lessons learned in the industrial assessment study and technicalreviews are presented. Continuation studies at ESA into high effective areatelescopes suitable for high time resolution X-ray astronomy missions arebriefly reviewed.
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10 New results on the X-ray spectra of thermonu-clear bursts
Cole MillerStratos Boutloukos, Frederick Lamb, Ka-Ho Lo
University of Maryland, Department of Astronomy, College Park
X-ray burst spectra have long been used to estimate neutron star masses andradii. These estimates assumed that burst spectra are accurately describedby the model atmosphere spectra developed over the last two decades. Thesemodel atmospheres have small scale heights and predict spectra that deviatesignificantly from Planck spectra. Fits of the Planck function to these spec-tra give temperatures significantly higher than the effective temperature.Using RXTE data, we measured X-ray spectra during several bursts withgreater precision than previous measurements and compared these measure-ments with the spectra predicted by existing model atmospheres. We foundthat the spectra predicted by existing model atmospheres were strongly in-consistent with these new, high-precision measurements, whereas a simpleBose-Einstein spectrum is fully consistent with them. These results indicatethat burst atmospheres are more extensive and have lower densities and moreuniform temperatures than existing model atmospheres, with spectra thatreflect saturated Comptonization. If the emission from burst atmospheresis efficient, the measured spectra imply fluxes ∼ 3-5 times the Eddingtonflux from ∼ 20-30% of the stellar surface. We discuss the implications of ourresults for determinations of neutron star masses and radii and the advancesin modeling burst atmospheres that have occurred since we first reportedthese results.
These results are based on research supported by NSF grant AST0708424at Maryland and by NSF grant AST0709015 and the Fortner Chair at Illi-nois.
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11 Relativistic Disk Reflection in Stellar-Mass BlackHoles
J. M. Miller
The University of Michigan
The X-ray spectra of stellar-mass black holes reveal the clear signatures ofrelativistic disk reflection. This takes the form of a skewed iron emission line,and a characteristic reflection ”hump” at higher energy. The latter feature isan important confirmation of the interaction and dynamical effects impliedby the iron line, and is particularly well observed in stellar-mass black holes.The degree to which the line and reflection hump are skewed is a sensitivediagnostic of the spin of the central black hole. At present, spins havebeen measured in a dozen systems using fits to relativistic disk reflectionspectra, and the future for such efforts is particularly bright. This talk willreview recent progress and discuss means by which a new mission with largecollecting area and high thoughput can make major advances.
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12 M/R constraints from accreting Millisecond Pul-sars and cooling stage of X-ray bursts
Juri PoutanenValery Suleimanov, Mike Revnivtsev, Klaus Werner
Astronomy Division, Department of Physics, University of Oulu
I will review the recent works on the analysis and theoretical interpretationsof the pulse profiles of accreting X-ray millisecond pulsars. The emission inthese pulsars is produced at hot spots in the accretion shocks near magneticpoles. The radiation spectrum can be described as a blackbody like from theneutron star surface and hard Comptonized emission from the shock. Thepulse profiles can be described by the combined action of the relativisticeffects such as Doppler effect, relativistic aberration and gravitational lightbending. Theoretical pulse profiles can be fitted to the data and constraintson the neutron star parameters can be obtained.
Thermal emission during X-ray bursts is a powerful tool to determineneutron star masses and radii, if the Eddington flux and the apparent ra-dius in the cooling tail can be measured accurately, and distances to thesources are known. We propose here an improved method of determiningthe basic stellar parameters using the data from the cooling phase of long,photospheric radius expansion bursts covering a large range of luminosities.For this purpose, we computed a large set of atmosphere models for burstluminosities varying by two orders of magnitude and for various chemicalcompositions and surface gravities. We show that the variation of the inversesquare root of the apparent blackbody radius with the flux, observed duringthe photospheric radius expansion bursts from a number of sources at lowaccretion rate is entirely consistent with the theoretical expectations of thecolor-correction factor evolution. However, for bursts happening at higheraccretion rates the observed evolution is inconsistent with theory, implyingthat accretion strongly disturbs the neutron star atmosphere. These find-ings have profound implications for the recent claims on determination ofthe neutron star radii and masses from such bursts. Our method allows usto determine both the Eddington flux and the ratio of the stellar apparentradius to the distance much more reliably.
For 4U 1724-307, we find a lower limit on the neutron star radius of 13km, independently of the chemical composition. These results suggest thatthe matter inside neutron stars is characterized by a stiff equation of state.
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13 Testing the No-Hair Theorem with Observa-tions of Astrophysical Black Holes
Dimitrios Psaltis
Astronomy and Physics Departments, The University of Arizona
The Kerr spacetime of spinning black holes is one of the most intriguingpredictions of Einstein’s theory of general relativity. The special role thisspacetime plays in the theory of gravity is encapsulated in the no-hair theo-rem, which states that the Kerr metric is the only realistic black-hole solu-tion of the vacuum field equations. Recent high-energy observations of blackholes have secured our understanding of their basic properties while open-ing up new opportunities for devising tests of the Kerr metric. In this talkI will show how timing and spectroscopic observations of accreting black-holes with future instruments can lead to the first direct test of the no-hairtheorem.
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14 The Properties of High Frequency QPOs andtheir Connection to the Physical Properties ofBlack Holes
Ron Remillard
MIT, Cambridge
The properties of high-frequency QPOs in black hole binaries are reviewedincluding their conditions of occurrence, frequency stability, amplitude spec-tra, and correlations with low-frequency QPOs. The circumstantial argu-ments that such QPOs may constrain the mass and spin of black holes aresummarized. Updates are given for the 3:2 frequency ratio for pairs of QPOsseen in some sources, and for the relationship between QPO frequency andblack hole mass. Comments are offered for the inadequacies of current con-cepts for the oscillation mechanism and for prospects to make advances withnew X-ray instrumentation.
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15 Black Hole Spin Measurements via X-ray Con-tinuum Spectroscopy
James Steiner
Harvard-Smithsonian Center for Astrophysics, Cambridge
A remarkable property of an astrophysical black hole is that it is completelydescribed by just its mass and spin. Our research group is dedicated to mea-suring these two fundamental properties of the black hole primaries foundin X-ray binary systems. We measure spin by modeling the thermal X-raycontinuum spectrum that originates in the innermost regions of the accre-tion disk. We fit for the disk’s inner radius, which we identify with theinnermost stable circular orbit (ISCO) predicted by GR. By measuring thisradius in concert with optical estimates for the black hole mass, and theorbital inclination angle and distance of the system, we uniquely determinea black hole’s spin. I will present an overview of our spin measurements anddiscuss progress which would be enabled with a large collecting area HTRS.
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16 Lense-Thirring Precession
Luigi Stella
INAF - Osservayorio Astronomico di Roma
The effects of Lense-Thirring precession and, more generally, frame draggingare expected to be important in the motion of matter close to spinningcompact objects. I will concentrate on phenomena that can probe in situthe very strong gravitational field and single out Lense-Thirring precessionin the close vicinity of accreting neutron stars and black holes: these arethe fast quasi periodic oscillations in the X-ray flux of these objects. Theexpected magnitude of Lense-Thirring/frame dragging effects in the regionswhere these signals originate are large and thus their detection does not posea challenge; rather it is the interpretation of these phenomena that needsto be corroborated through deeper studies and observations with very largeeffective area X-ray instruments.
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17 Timing of XRBs in the HTRS era
Phil Uttley
School of Physics and Astronomy, University of Southampton
I will review the future potential of the combination of high throughput,time-resolution and spectral-resolution which is offered by future instru-ments like the HTRS. I will start by highlighting what is already possiblewith the fast-timing modes and soft response of current CCD detectors. Inparticular, XMM-Newton’s EPIC-pn is opening up new capabilities in com-bined spectral-timing measurements, allowing us to measure the causal linksbetween the power-law continuum and the disc thermal and reflection com-ponents in X-ray binaries. The much greater throughput offered by futuremissions will push these measurements deep into the regime of light-crossingtimes for the innermost radii in these systems, enabling reverberation map-ping and even Doppler tomography of the inner disc. These observationswill provide direct measurements of disc radii in km, not just relative unitssuch as Gravitational radii. Together with the ability to probe the coherencetimes of the highest-frequency
29
18 X-ray variability of black holes on all mass scales
Simon Vaughan
University of Leicester
We will review the similarities in X-ray variability properties of the differ-ent types of luminous accreting black holes, namely those in X-ray bina-ries (XRBs), Active Galactic Nuclei (AGN), and also Ultra-luminous X-raysources (ULXs).
If strong gravity dominates the dynamics of the inner accretion flowsaround black holes then an elementary consequence is scale invariance: manyimportant aspects of accretion onto supermassive black holes (M > 106
Msun) in AGN should be fundamentally the same as for stellar mass blackholes (M ∼ 10 Msun) in XRBs. (And similarly for ULXs.) Over the past fewyears we have revealed many remarkable similarities in the X-ray variabilityof nearby AGN and BH XRBs, supporting the idea of ’black hole unification.’
In parallel with these X-ray advances, studies of transient radio jetsfrom XRBs have led to the development of a scheme that unifies jet pro-duction with accretion state. Relativistic jets must be launched from theregion of strong-field gravity, and so scale invariance implies this accretionstate/jet unification scheme should extend to AGN. From these results anew paradigm is emerging in which accretion mode, X-ray spectrum, high-frequency timing properties and jet production for both XRB ’states’ andAGN ’types’ may be unified into a single framework for the activity cyclesof accreting black holes.
We will discuss the present state of comparative work on X-ray behaviourof luminous accreting black holes (from the ,XMM-Chandra-Suzaku era),with particular emphasis on the results of a recent ∼600 ks XMM-Newtonobservation of the prototypical low-mass Seyfert 1 galaxy NGC 4051. Timepermitting, we will attempt to outline some of the possibilities for exploringand exploiting the differences and similarities between the BH types usingfuture, high throughput and fast timing X-ray missions.
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19 Cooling of accretion-heated neutron stars
Rudy Wijnands
Astronomical Institute “Anton Pannekoek”, University of Ams-terdam
Neutron stars in X-ray binaries are heated due to the accretion of matteronto their surfaces. When the accretion stops the deposited heat is partlyradiated away from the surface as thermal radiation. By studying this ra-diation and how it various over time (i.e., how the surfaces cool down) newinsights in the properties of the crust and the core of neutron stars havebeen obtained in the last decade. I will summarize what we have learnedso far about the behavior of neuron star matter, what the uncertainties stillare in our understanding, and how we can make progress in the future usingmore optimized observing strategies and new upcoming and planned X-raysatellites.
31
20 HTRS Performance Simulations
Jorn Wilms
Remeis-Sternwarte and ECAP, University of Erlangen-Nuremberg
The very high count rates that will be obtained with future X-ray satellitespose a significant challenge for the prediction of their performance. Over thepast years we have developed a set of software tools for such performancepredictions that is easily adaptable for most pixel-based X-ray detectorsplanned. These simulations take into account all relevant phenomena dis-torting the measured signals. Amongst others, these phenomena includeenergy pile up, i.e., the detection of more than one photon in the same de-tector pixel during one read-out cycle, and pattern pile up, i.e., detectionof two photons in adjacent pixels in a pattern that resembles that causedby charge splitting of a single higher energetic photon. Here, we presentresults of simulations of such observations for the IXO-HTRS and -WFI aswell as other planned future instruments and discuss the challenges that theanalysis of data from these instruments will present.
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II Oral contributions
33
1 Timing black-hole binaries: status and prospects
Tomaso Belloni
INAF-OAB
The low-frequency (0.1-10 Hz) variability of black-hole binaries is now wellsampled and its basic characteristics are known. Interpretations which takeinto account also the spectral distribution are being put forward and needto be compared with existing observations in order to plan future ones.I will present a summary of the current status of our knowledge of sourcestates and related timing features, and discuss the future prospects in view offuture planned and proposed missions. I will also examine the current statuson HFQPOs and their possible connection with kHz QPOs in neutron-starsystems.
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2 Undetectable, intermittent, and detectable mil-lisecond X-ray oscillations of accreting neutronstars in LMXBs
Stratos BoutloukosFrederick Lamb, Ka Ho Lo, Coleman Miller
University of Tuebingen, Theoretical Astrophysics
Accretion-powered X-ray oscillations have been detected in only 14 of about130 accreting neutron stars in LMXBs. Three such stars produce detectableoscillations only intermittently. We show that the absence of detectableoscillations from most LMXBs, and the intermittent detection of oscillationsin a few, can both be explained if the emitting regions of accreting neutronstars with millisecond spin periods typically have small inclinations relativeto the spin axis and move in response to changes in the accretion flow.This nearly-aligned moving spot model is consistent with the small observedamplitudes and nearly sinusoidal waveforms of most accreting millisecondX-ray pulsars, and the large, rapid phase variations of several.
These results are based on research supported by NASA grant NAG 5-12030, NSF grant AST0709015, and funds of the Fortner Endowed Chair atIllinois, and by NSF grant AST0708424 at Maryland.
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3 Epicyclic frequencies and QPOs
Michal Bursa
Astronomical Institute, Czech Academy of Sciences
The idea that observed HFQPOs arise as a manifestation of some sort oforbital motion in the accretion flow has a number of supporting arguments.The omnipresent signature of a special 3:2 ratio in HFQPO frequencies ledto the idea of a resonance between two modes of disk epicyclic frequenciesand still today that idea represents one of the most favourite explanations ofthe phenomenon. The talk will review some observational facts and resultsthat have been obtained within the epicyclic resonance theory and drawdown some ideas about directions of the future research with respect tohigh precision timing measurements.
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4 Time lags as a constrain on the accretion discgeometry in BHXRBs
Pablo CassatellaP. Uttley, J. Wilms, J. Poutanen
University of Southampton
Timing analysis in the last few decades has proven successful to give aninsight into the accretion geometry and emission mechanisms in black holeX-ray binaries. In particular, time lags show that the hard X-ray emis-sion usually lags the soft emission, and papers like Kotov et al (2001) haveaddressed this issue.
While there is evidence that the variability originates in the disc, thanksto the propagation of fluctuations throughout the disc and to a centralcorona, it has also been observed that the central X-ray emission is in-tercepted by the disc in its outer regions, possibly in a flared geometry, andthis can contribute to the observed lags vs frequency.
Here we show a reflection model that can be used within XSPEC or ISISto concurrently fit both lags vs frequency and mean spectrum, and constrainthe geometry of the reflecting disc. We will show a few examples using fastmode observations of black hole binaries with XMM-Newton.
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5 Can a ”propelling” disc stay trapped near co-rotation?
Caroline D’AngeloHenk Spruit
Anton Pannekoek Institute/MPA Garching
A strong stellar magnetic field significantly alters the behaviour of an ac-cretion disc around the star. In particular, at low accretion rates it is oftenassumed that the interaction between the field and the disc will expel thegas out of the disc in an outflow rather than allow it to accrete onto thestar – a state known as the ”propeller regime”. However, recent work hassuggested that if the disc is truncated close to the co-rotation radius (wherethe star’s spin frequency equals the Keplerian frequency of the disc) thedisc-field interaction will mostly confine the gas, preventing it from escapingfrom the disc. The interaction changes the density profile of the disc, andcan completely halt accretion onto the star without producing an outflow.In turn, this forces the inner edge of the disc to stay trapped close to theco-rotation radius even when there is no net mass flow through the disc,so that the disc never moves into the true propeller regime. In my talk Iwill explain how a trapped disc can form and show how this can sometimesresult in bursts of accretion onto the star, such as have been observed aslow-frequency QPOs in X-ray pulsars SAX J1808.4-3658 and NGC 6440 X-2. Finally, I will discuss how trapped discs could also be responsible for theweak recurrent outbursts seen in NGC 6440 X-2 and IGR J00291+5934.
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6 Living in a LOFT
Marco FerociLuigi Stella (INAF/OAR Rome) on behalf of the LOFT consortium
INAF/IASF, Rome
LOFT (Large area Observatory For x-ray Timing) is an innovative missionconcept for the next generation of X-ray timing experiments, being submit-ted to the ESA Call for Medium size missions. Recent developments in thefield of Silicon detectors allowed us to design a realistic observatory devotedto X-ray timing studies with an effective area above 10 m2, in the energyrange 2-30 keV, with an energy resolution between 200 and 500 eV. Such anexceedingly large area (20 times RXTE/PCA), with a time resolution bet-ter than 10 µs, will enable unprecedently fast and accurate time variabilitystudies related to accreting collapsed objects (e.g. fast coherent pulsationsand QPOs). The scientific payload is complemented by a coded-mask widefield monitor based on similar detectors. In this paper we will present themission concept, the payload design and the expected performance.
40
7 Systematic Uncertainties in the SpectroscopicMeasurements of Neutron-Star Masses and Radiifrom Thermonuclear X-ray Bursts
Tolga GuverDimitrios Psaltis, Feryal Ozel
University of Arizona
Low mass X-ray binaries that show thermonuclear X-ray bursts are excel-lent targets for constraining the equation of state of neutron star matter.We make use of time resolved, high count rate X-ray spectra to measurethe Eddington limit and the apparent radii of neutron stars, which we thenuse to determine the masses and radii. In an effort to asses the system-atic uncertainties in these measurements, we have analyzed archival RXTEobservations of 447 X-ray bursts observed from 12 X-ray sources. I willpresent the results of this analysis and discuss the potential uncertaintiesintroduced by systematic effects on the mass and radius measurements. Iwill also discuss the strategies for understanding and reducing systematicerrors using future X-ray missions that combine good timing and spectralresolution with the ability to observe high count-rate sources.
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8 Signatures of superfluid neutron star dynamics
Brynmor Haskell
Astronomical Institute ”Anton Pannekoek”, University of Ams-terdam
Neutron stars offer a unique opportunity to probe a wealth of physical ef-fects that cannot be studied in terrestrial laboratories. Not only do theyallow us to gain insight on the state of matter at extreme densities, butalso to study the dynamics of large scale superfluid components of the star.However theoretical neutron star models are highly uncertain and disentan-gling the signature of different effects in the data can be very challenging. Iwill discuss recent theoretical developments in superfluid NS modeling andhow the use of high precision X-ray observations, also combined with radioand possibly, in the future, with gravitational wave (GW) observations, canconstrain models and shed light on different phenomena. In particular Iwill discuss the dynamics of accreting millisecond X-ray pulsars, which havebeen proposed as interesting GW sources, and how cooling observations inthe X-ray, combined with precision radio data (and GW observations fromnext generation interferometers), can constrain glitch models and furtherour understanding of NS superfluidity.
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9 Broad iron emission lines in the intermediatestate of black-hole transients
Beike HiemstraMariano Mendez, Chris Done, Maria Diaz Trigo, Diego Altamirano, Pier-giorgio Casella
Kapteyn Astronomical Institute, University of Groningen
Simultaneous XMM-Newton and RXTE observations of the new X-ray tran-sient and black-hole candidate XTE J1652-453 have revealed a very strongand broad iron emission line in its X-ray spectrum. The source was observedin the hard-intermediate state in the decline of the 2009 outburst.
The line has an equivalent width of ∼450 eV, which makes it amongthe strongest ever detected in a black-hole candidate. The line profile isconsistent with being produced by reflection off the accretion disk, and isbroadened by relativistic effects close to the black hole. Assuming that theaccretion disk is truncated at the innermost stable circular orbit, the blackhole in XTE J1652-453 has a spin parameter of ∼0.5. The high ionizationparameter and the best-fitting line energy of 6.97 keV are consistent withhighly ionized iron, which in turn can explain the high equivalent width sincethe fluorescence probability is increased due to the lack of Auger destruction.
Given that the source was observed in a spectral state where spectral andtiming properties are changing on short timescales, studying the line profileand its underlying continuum in the intermediate state needs to be done inshort exposures. To do so, we need an instrument like the High Time Reso-lution Spectrometer, since its large collecting area, high time resolution andmoderate spectral resolution will allow us to have sufficient good statisticsand data to study short-term variations in the line and continuum.
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10 Detectors for fast X-ray spectroscopy, timingand imaging
Peter LechnerP. Majewski, A. Niculae, H. Soltau, L. Strueder, A. Stefanescu, J. Treis
PNSensor & MPI-HLL, Munchen
For high time resolution spectroscopy and imaging in X-ray astronomy twodetector concepts have been developed: multi-channel Silicon Drift Detec-tors and DePFET Active Pixel Sensors. The Silicon Drift Detector (SDD) isdedicated for timing and spectroscopy. This sensor concept combines a largesensitive area with a small output capacitance guaranteeing high energy res-olution and high count rate capability. To obtain a uniform count rate overthe array the sensor is placed out of focus. The formats and areas of the SDDcells can be adapted to the telescope’s radial intensity distribution. E.g. theHTRS instrument on IXO is based on a monolithic multi-channel SiliconDrift Detector (SDD) with 31 cells in a circular envelope and a sensitivevolume of 4.5cm2 x 450µm. It has been designed to operate at count ratesexceeding 1 million per sec with an energy resolution of 150 eV (FWHM at6 keV), a time resolution of 10 micro-second, and a dead time and pile-upon the percent level.
The DePFET (Depleted P-channel Field Effect Transistor) structurecombines the functionalities of sensor and integrated amplifier. It is thebasic cell of an Active Pixel Sensors for X-ray imaging and spectroscopywith Fano-limited energy resolution and high efficiency from 100 eV to 20keV. For a row-by-row readout of the pixel matrix dedicated control andreadout ASICs have been developed. With a format of e.g. 100 x 100 pixelsframe rates of more than 10.000 per second are possible. Representativeprototypes with a format of 256 x 256 pixels are currently under test.
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11 Spectral and timing features in the ultra-compactX-ray binary 4U 0614+091
Oliwia MadejP.G. Jonker
SRON, Netherlands Institute for Space Research, Utrecht
We have studied the ultra-compact X-ray binary 4U 0614+091, which is apromising target for the High Time Resolution Spectrometer (HTRS). Itis a bright source (L∼3x1036 erg/s) consisting of a neutron star orbitingaround a carbon-oxygen or oxygen-neon-magnesium white dwarf with anorbital period of around 50 min. We recently discovered an emission featureat ∼0.7 keV in this source. We interpret this feature as a relativisticallybroadened reflection line of O VIII Ly alpha, caused by X-rays reflected offthe accretion disc in the strong gravitational field close to the neutron star.This is the first time that a broad fluorescent O VIII Ly alpha line is seenin the X-ray binary. This source also shows strong kHz quasi-periodic oscil-lations (QPOs). By modeling the relativistically broadened oxygen line andsimultaneously measuring kHz QPOs we can obtain two independent mea-surements of the inner radius of the accretion disc. Since 4U 0614+091 showstransitions from low flux to high flux, using HTRS we will be able to trackthe changes of the inner radius of the accretion disc obtained from modelingthe oxygen line and measuring the QPOs. Hence, we can investigate thecorrelation between the two. In this way we will be able to test theoreticalmodels for relativistically broadened reflection lines and kHz QPOs.
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12 Kilohertz Quasi-Periodic Oscillations as a toolto probe the neutron-star interior and gravita-tional field
Mariano Mendez
Kapteyn Astronomical Institute, University of Groningen
The expected timescale of variability close to the surface of a neutron staris of the order of a millisecond or less. The discovery of the kilohertz quasi-periodic oscillations (kHz QPOs) in neutron-star low-mass X-ray binariesprovided the first direct evidence of such variability. These QPOs wereimmediately recognized as a powerful tool to probe the dynamics of matterand the properties of the gravitational field in the vicinity of neutron stars,as well as the neutron-star interior.
After 15 years of observations with the Rossi X-ray Timing Explorer, wehave collected a wealth of data on these QPOs, and a number of patternshave emerged, including correlations of the QPO properties with propertiesof other types of variability and source parameters (e.g., energy spectra orneutron-star spin). Notwithstanding, the mechanism that produces the kHzQPOs remains elusive. While several models have been proposed, none ofthem can consistently explain the richness of this phenomenon.
Perhaps the most outstanding question that remains is whether theseQPOs reflect the Keplerian, or other General-Relativistic, frequency whenmass orbiting in an accretion disc plunges onto the neutron-star surface.There are two promising avenues to address this question: Energy-dependenttime lags and simultaneous measurements of kHz QPOs and iron lines.
In this talk I will discuss these two possibilities in light of the capabilitiesof current and future X-ray missions.
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13 Fast variability as a tracer of states and state-transitions in black holes
Teo Munoz-DariasMotta, S., Belloni, T. M.
INAF- Osservatorio Astronomico di Brera
I present a new tool to study the different accretion regimes present in blackhole transients by focusing solely on the evolution of the rms-flux relationalong their outburst. This technique enables an accurate identification ofthe various accretion states without using spectral information. I will showthe results obtained by applying this method to several black hole transients.The hard, soft and the two intermediate states can be clearly identified bythis simple technique, and marked transitions are observed between them.I will also show that black holes seem to follow a specific flux-variabilityrelation when type-B oscillation are present in their power density spectra.I will finally discuss on the physical implications of this method and thepotentials that it offers for future studies of black hole transients using hightime resolution instruments.
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14 GRAVITAS: General Relativistic AstrophysicsVia Timing and Spectroscopy
Kirpal Nandra
Max-Planck Institut fur extraterrestriche Physik
GRAVITAS is an X-ray observatory, designed and optimised to address theESA Cosmic Vision theme of “Matter under extreme conditions”. It is sub-mitted as a response to the call for M3 mission proposals. The conceptcentres around an X-ray telescope of unprecedented effective area, whichwill focus radiation emitted from close to the event horizon of black holesor the surface of neutron stars. To reveal the nature and behaviour of mat-ter in the most extreme astrophysical environments, GRAVITAS targets akey feature in the X-ray spectra of compact objects: the iron Kα line at∼ 6.5 keV. The energy, profile, and variability of this emission line, and theproperties of the surrounding continuum emission, shaped by GR effects,provide a unique probe of gravity in its strong field limit. Among its primetargets are hundreds of supermassive black holes in bright Active GalacticNuclei (AGN), which form the perfect laboratory to help understand thephysical processes behind black hole growth. Accretion plays a fundamen-tal role in the shaping of galaxies throughout cosmic time, via the processof feedback. Modest (∼sub-arcmin) spatial resolution will therefore deliverthe necessary sensitivity to extend high quality X-ray spectroscopy of AGNto cosmologically-relevant distances. Closer to home, ultra-high count ratecapabilities and sub-millisecond time resolution will enable the study of GReffects and the equation of state of dense matter in the brightest X-ray bi-naries in our own Galaxy, using multiple probes, such as the broad iron line,the shape of the disk continuum emission, quasi-periodic oscillations, rever-beration mapping, and X-ray burst oscillations. Despite its breakthroughcapabilities, all enabling technologies for GRAVITAS are in a high state ofreadiness. It will use ultra light-weight X-ray optics and a focal plane detec-tor based on silicon technology. The baseline launcher will be a Soyuz-Fregatto place GRAVITAS into a low-inclination, low-earth orbit, providing lowand relatively stable background.
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15 Oscillation-Phase-Resolved Spectroscopy in theIXO Era
Joey NeilsenRon Remillard, and Julia C. Lee
Center for Astrophysics, Cambridge
We present the first phase-resolved analysis of a variability class in GRS1915+105 that combines the broadband timing and spectral capabilitiesof RXTE with Chandra’s superb spectral resolution. We demonstrate thatrapid changes in the broadband X-ray spectrum can cause significant changesin the ionization, structure, and density of accretion disk winds on timescalesof 5 seconds or less. Yet recent results indicate that spectral lines may varyon even shorter timescales during quasi-periodic oscillations. With next-generation X-ray facilities, which will easily track individual QPO waves, itwill be possible to determine precisely how emission and absorption featuresrespond to quasi-periodic oscillations in the X-ray lightcurve. Therefore,using our phase-resolved spectral analysis of GRS 1915+105 as an example,we discuss the enormous potential of QPO-phase-resolved spectroscopy withnext-generation X-ray instruments, including reverberation mapping and de-tailed measures of nearby plasma conditions on sub-second timescales. Inthis way, future observations of QPOs will provide sensitive, powerful probesof the physical processes that link accreting black holes and their environ-ments. With the capabilities of IXO, GRAVITAS, and LOFT, this physicswill be routinely accessible not just in GRS 1915+105, but also in black holeX-ray binaries across the galaxy.
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16 A newly discovered accreting pulsar in Terzan 5
Alessandro PapittoS. Motta, A. Riggio, A. D’Aı, T. Di Salvo, R. Iaria, L. Burderi, T. Belloni
Universita di Cagliari
The 90.5 ms accreting pulsar, IGR J17480-2446, has been recently discoveredin the globular cluster Terzan 5. The analysis of the Doppler shifts inducedby the orbital motion reveal how the neutron star belongs to a ∼ 21.3 hrbinary system with a companion star mass between 0.4 and 1 M�. From thepresence of pulsations at different accretion rates we constrain the magneticfield to lie within ∼ 2 108 and ∼ 2.4 1010 G. Together with the value of theneutron star spin period, such an estimate puts this source in the still poorlysampled population of slow, possibly mildly recycled, accreting pulsars thusmaking it an extremely intriguing scientific case. The presence of a ∼ 815Hz QPO possibly allows also to test the theories that interpret these featuresin terms of Keplerian rotation in the inner parts of the accretion disc.
IGR J17480-2446 also shows several type I X-ray bursts. For the firsttime burst oscillations are observed at a relatively low frequency, indicatinghow fast rotation is not a necessary ingredient for their appearance. As thesource shows bursts with a recurrence time down to few minutes it also offersan almost the fundamental opportunity to follow the variations of the burstsenergetics with the mass accretion rate, across a wide range of parameters.
50
17 Constraining the mass and moment of iner-tia of neutron stars from quasi-periodic oscil-lations in X-ray binaries
Jerome Petri
Observatoire Astronomique de Strasbourg
Neutron stars are the densest objects known in the Universe. Being thefinal product of stellar evolution, their internal composition and structureis rather poorly constrained by measurements.
It is the purpose of this paper to put some constrains on the mass andmoment of inertia of neutron stars based on the interpretation of kHz quasi-periodic oscillations observed in low mass X-ray binaries.
We use observations of high-frequency quasi-periodic observations (HF-QPOs) in low mass X-ray binaries (LMXBs) to look for the average mass andmoment of inertia of neutron stars. This is done by applying our parametricresonance model to discriminate between slow and fast rotators.
We fit our model to data from ten LMXBs for which HF-QPOs havebeen seen and the spin of the enclosed accreting neutron star is known.For a simplified analysis we assume that all neutron stars possess the sameproperties (same mass M∗ and same moment of inertia I∗). We find anaverage mass M∗ ≈ 2.0 − 2.2M�. The corresponding average moment ofinertia is then I∗ ≈ 1 − 3 × 1038 kg m2 ≈ 0.5 − 1.5 (10 km)2M� whichequals to dimensionless spin parameter a ≈ 0.05 − 0.15 for slow rotators(neutron stars with a spin frequency roughly about 300 Hz) respectivelya ≈ 0.1−0.3 for fast rotators (neutron stars with the spin frequency roughlyabout 600 Hz).
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18 The pertinence of Jet Emitting Discs in Micro-quasars
Pierre-Olivier PetrucciFerreira J., Henri G., Malzac J., Cabanac C.
Laboratoire d’Astrophysique de Grenoble
Very broad band observations of microquasars, from radio to X-rays, haverevealed the strong connection between accretion and ejection processes inthese objects. Not only their radiative outputs are a complex combinationof accreting and expelling components but jets appear to play also a crucialrole in the dynamics and the energetics of these systems.
Based on the complete calculation of the full accretion-ejection set ofequations, we present a model that aims at explaining the spectral statesand variability behaviors of BH binaries as well as their spectral evolutionduring outbursts. In our view, the accretion flow is pervaded by a largescale magnetic field of bipolar topology. In the hard state, the field is largeenough for a new class of accretion flow to set in where most of the re-leased accretion power feeds self-collimated jets. Such a Jet Emitting Disc(JED) has dynamical properties quite different from both the standard andadvection dominated discs. The hot branch of solutions has all the charac-teristics of the so-called ”hot corona” generally invoked in XrB sytems in theLow/Hard states. We will detail the energetics and radiative expectationsof our model and show their good agreement with those observed in CygnusX-1, the proptotype of microquasars. The nature of the X-ray variabilityis also investigated by assuming an oscillating hot plasma at the jet basiswhose temperature varies locally through the propagation of a magnetosonicwave. The variable comptonized spectra are computed through monte-carlosimulation and comparison to observations will be discussed.
52
19 The Advanced X-ray Timing Array (AXTAR)
Paul RayDeepto Chakrabarty, Colleen Wilson-Hodge for the AXTAR Collaboration
Naval Research Laboratory, Washington
AXTAR is a NASA MIDEX mission concept for X-ray timing of compactobjects that combines very large collecting area, broadband spectral cov-erage, high time resolution, highly flexible scheduling, and an ability torespond promptly to time-critical targets of opportunity. It is optimizedfor submillisecond timing of bright Galactic X-ray sources in order to studyphenomena at the natural time scales of neutron star surfaces and blackhole event horizons, thus probing the physics of ultradense matter, stronglycurved spacetimes, and intense magnetic fields. AXTAR’s main instrumentis a collimated, thick Si pixel detector with 2-50 keV coverage and over 3square meters effective area. For timing observations of accreting neutronstars and black holes, AXTAR provides at least a factor of five improve-ment in sensitivity over the RXTE PCA. AXTAR also carries a sensitivesky monitor that acts as a trigger for pointed observations of X-ray tran-sients in addition to providing high duty cycle monitoring of the X-ray sky.We review the science goals and technical concept for AXTAR and presentinitial results from a preliminary mission design study at the MSFC Ad-vanced Concepts Office.
53
20 A non-magnetar Soft Gamma Repeater
Nanda Rea
Intitut de Ciencies de l’Espai (ICE-CSIC, IEEC), Barcelona
I will report on the discovery of a Soft Gamma Repeater with a magneticfield in line with that of the normal pulsar population. This discovery opensthe possibility of many normal pulsars hiding an internal magnetar-activity.
54
21 Theoretical disk spectra and BH spin determi-nation
Agata RozanskaJ. Madej, M. Gancarczyk
N. Copernicus Astronomical Centre, Warsaw
In my talk I will present angle-dependent, broad-band theoretical spectrafrom accretion disks around stellar black hole. In our numerical calculations,full radiative transfer of irradiated disk atmospheres was solved includingeffects of Compton scattering, free-free and all important bound-free transi-tions of 10 main elements. Moreover, we included the fundamental series ofiron lines from helium-like and hydrogen-like ions, and fluorescent Kα andKβ lines from low ionized iron. Our results show, that emission lines of ironcan be observed only if heating by external X-rays dominates over thermalprocesses in hot disk atmospheres. Irradiated disks are usually brighter inX-ray continuum when seen edge on, and fainter when seen face on. Theshapes of theoretical multitemperature disk component and iron Kα line areextremely important in black hole spin determination. I will discuss howthe disk hardening factor and iron line complex affect the spin of a blackhole.
55
22 Kilohertz quasi-periodic oscillations and broadiron emission lines as a probe of strong-fieldgravity
Andrea SannaMariano Mendez, Diego Altamirano, Tomaso Belloni
Kapteyn Astronomical Institute, Groningen
Kilohertz quasi-periodic oscillations (kHz QPOs) and broad iron emissionlines are thought to be produced at the inner edge of an accretion disk aroundneutron stars in low mass X-ray binary systems (LMXBs). The frequency ofkHz QPOs and the width of iron lines strongly suggest that these phenomenatake place just few kilometers above the surface of the neutron star and hencethey should probe the strong gravitational field around these stars. BothQPO variability and iron line hold the promise of searching for signatures ofstrong-field general relativity, e.g. the ISCO or Lense-Thirring precession.Here I present new results of the kHz QPOs in the transient neutron starLMXB XTE J1701- 462, and the kHz QPOs and the broad iron line in thepersistent neutron star LMXB 4U 1636-53. In XTE J1701 we find that,contrary to previous claims, properties of the kHz QPO are probably notuniquely determined by the geometry of the space-time. In 4U 1636 we findthat there is a complex relation between kHz QPOs and properties of theiron line, which is difficult to explain if both phenomena reflect propertiesof the same region in the accretion disk.
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23 HIFI - A High Framerate Imager for GRAVI-TAS
Alexander Stefanescu
Max-Planck-Institut Halbleiterlabor, Munchen
GRAVITAS is a proposed X-ray observatory, designed and optimised toaddress the Cosmic Vision theme of ”Matter under extreme conditions”. Itwill have a X-ray mirror system optimized for a very high effective area atthe Fe Kα line, and will utilize the resulting statistics to do time-resolvedspectroscopy with excellent timing resolution and at high count-rates. HIFIis a high frame-rate imager for GRAVITAS. Using an advanced Active PixelSensor array based on DEPFET macropixels, it will be able to offer imagingwith excellent energy resolution, while a massively parallel read-out willallow extremely high frame-rates. The APS of HIFI offers very flexibleread-out modes, allowing the imager to cope with the flux of bright X-raybursts. Despite its breakthrough capabilities, all enabling technologies forGRAVITAS and HIFI are already in a high state of readiness.
57
24 All-Sky Monitoring of Variable Sources withFermi GBM
Colleen Wilson-Hodgefor the GBM Pulsar and Earth Occultation teams
NASA/MSFC, Huntsville
Using the Gamma ray Burst Monitor (GBM) on Fermi, we monitor thetransient hard X-ray/soft gamma ray sky. The twelve GBM NaI detec-tors span 8 keV to 1 MeV, while the two BGO detectors span 150 keV to40 MeV. We use the Earth occultation technique to monitor a number ofsources, including X-ray binaries, AGN, and solar flaring activity. Our mon-itoring reveals predictable and unpredictable phenomena such as transientoutbursts and state changes. With GBM we also track the pulsed flux andspin frequency of accretion powered pulsars using epoch-folding techniques.Highlights from the Earth Occultation and Pulsar projects will be presentedincluding our recent surprising discovery of variations in the total flux fromthe Crab. Searches for quasi-periodic oscillations and X-ray bursts are alsopossible with GBM all-sky monitoring capabilities. With these results weshow how crucial an all-sky monitor is for any future X-ray timing mission.
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25 The complete sample of type-I X-ray burstsin the low-mass X-ray binary 4U 1636-53 withRXTE
Guo-Bao ZhangMariano Mendez, Diego Altamirano, Tomaso Belloni and Jeroen Homan
Kapteyn Astronomical Institute, University of Groningen
Type-I X-ray bursts are due to unstable burning of H and He on the surfaceof accreting neutron stars in low-mass X-ray binaries (LMXBs). One ofthe best studied sources of X-ray bursts is the LMXB 4U 1636-53. Here wepresent a complete analysis of all X-ray bursts of this source observed to date(300 at the time of writing) with the Rossi X-ray Timing Explorer (RXTE).Using the bolometric light curves of individual bursts we found that about96% of the bursts show single-peaked profiles, whereas about 4% show amulti-peaked profile. All the multi-peak bursts in this source took placewhen 4U 1636-53 occupied a relatively narrow region in the colour-colourdiagram (CCD), corresponding to a relatively high (inferred) mass-accretionrate. As the source moves from the island state to the banana state onthe CCD, both burst duration and recurence time decrease. From fits totime-resolved spectra, we found that about 20% of the single-peaked burstsare photospheric radius-expansion (PRE) bursts, whereas non of the multi-peaked burst is a PRE burst. We also found that on average the X-ray burstsin 4U 1636-53 do not follow the L ∼ T4 relation. We did a statistical studyof the fitted blackbody temperature of X-ray bursts at different flux levelsduring the cooling phase of X-ray bursts. The distribution of blackbodytemperature for different type of burst show significant differences at lowflux level, where the average temperature in hard non-PRE bursts is higherthan in PRE and soft non-PRE bursts. We calculated the colour correctionfactor (fc) as a function of luminosity for different bursts, and found thatfc in hard non-PRE bursts is larger than in PRE and soft non-PRE burstsat the same luminosity level. From the timing analysis we found oscillationsappear both in PRE and no-PRE bursts, but mostly when the source is inthe soft state.
59
III Poster contributions
61
1 Preliminary concept of modern X-ray timing mis-sion
Vadim ArefievM. Pavlinsky, M.Revnivtsev
Space Research Institute, Moscow
We present concept of new X-ray timing mission proposed for Russian spaceprogram. The preliminary study includes the main scientific tasks for the X-ray timing mission, requirements for scientific payload and spacecraft. Themission will concentrate on X-ray variability study of bright black holes andneutron stars. These objects can give unique information for both stronggravity and nuclear physics. The study of accretion flows variability mecha-nism is essential to successful interpretation of X-ray data and unambiguousdetermination of fundamental parameters of compact objects. The main in-strument of the observatory is large area X-ray timing spectrometer.
63
2 The 2008 outburst of the new X-ray transientXTE J1719-291
Montserrat Armas PadillaN.Degenaar, R.Wijnands
Astronomical Institute Anton Pannekoek
During the last decade a new population of X-ray transients have beendiscovered. They show anomalously low peak luminosities (2-10 keV) of 1034
to 1036 ergs/sec. A large fraction of them is expected to harbor accretingneutron stars and black holes in binaries systems. These very faint X-raybinaries provide new regimes to study accretion onto compact objects, andtherefore they could challenge our understanding of accretion physics andbinary evolution models.
We present the 2008 outburst of the new X-ray transient XTE J1719-291, which was observed with the Chandra, Swift, XMM-Newton and RXTEsatellites. The spectra are consistent with a power law model affected byinterstellar absorption. The photon index has values between 2 and 2.8, andthe peak luminosity is 7 x 1035 ergs/sec for an assumed distance of 8 kpc.The X-ray spectrum softens along the outburst (i.e., while the luminositydecreases), which is not typically seen in X-ray transients. We derive aduty cycle of 1 per cent, from which we estimate a long-term time averageaccretion rate of ∼10−13 M/yr.
64
3 How the fast X-ray timing at extreme countrates will constrain the equation of state of thedense matter from the burst oscillations of theneutron stars
Romain ArtigueDidier Barret
CESR/IRAP, Toulouse
We show that detailed modeling of burst oscillations can be an extremelypowerful probe of neutron star structure (M,R), and thus the equation ofstate of ultra-dense matter. M and R are encoded in the shape of the os-cillations resulting from spin modulation of the thermonuclear burst fluxfrom the neutron star. We have developed an expanding hot spot modelfor X-ray burst oscillations, taking into account all relativistic effects affect-ing photon trajectories from the neutron star surface to the observer. Wehave then simulated several data sets (for an assumed M, R and hot spotgeometry and emission pattern) with the statistics currently achieved withthe RXTE/PCA and the one expected from a more advanced mission interm of count rate. We first show that thanks to the improved statistics,the harmonic content of the signal (whose amplitude relates directly to theasymmetry of the waveform) will be detected by this new mission. Using alibrary of theoretical light curves, we have the
65
4 kHz QPO studies with IXO - Testing the Mov-ing Hotspots Model
Matteo Bachetti
Centre d’Etude Spatiale des Rayonnements Toulouse
According to the moving hot spots hypothesis, kHz quasi-periodic oscilla-tions (kHz QPOs) are originated at the surface of the star from the move-ment of hot spots formed during accretion. In this scenario, the lower peakcorresponds to hot spots created by the funnel flow in a hot region around themagnetic pole and moving around it, while the upper peak to hot spots cre-ated through instabilities closer to the equatorial zone, moving at a greatervelocity than the polar ones. This model predicts that if the star is notalmost perfectly aligned (misalignment angle much smaller than the polarhot region), the same movement originating the lower kHz QPO should alsoproduce a dimmer feature at the frequency of the star. Low and high fre-quency phenomena should also be correlated, the red noise being influencedby the duration and frequency of appearance of the hot spots.
The unprecedented collecting area of IXO, increasing the count rate bya factor of ∼ 10 with respect to RXTE, would be an extraordinary tool tostudy the light curves of LMXBs and look for features at the frequency ofthe star in observations where the lower QPO is present. Moreover, it wouldhelp study LMXB variability on shorter timescales, helping the investigationof the short-term coherence of QPOs and correlations between high and low-frequency phenomena.
66
5 Re Analysis of Timing Parameters of OAO 1657-415
Altan Baykal
Physics Department, Middle East Technical University
Using the new orbital parameters of OAO 1657-415, archival data of RXTEobservations are analysed. We investigate the spin up/down rate and X-rayflux correlations and re-evaluated the torque noise power density spectra.
67
6 Time lags in 4U 1608-52
Marcio Guilherme Bronzato de AvellarMendez, Mariano; Sanna, Andrea; Horvath, Jorge
Instituto Astronomico, Geofısico e de Ciencias Atmosfericas , SaoPaulo
In binary systems with a neutron-star (NS) primary and a low-mass sec-ondary star that fills its Roche lobe, accretion onto the NS proceeds via adisk that extends very close to the surface of the NS. X-ray emission fromthe disk and the NS surface carries information about the geometry of space-time around the NS. The so-called kilohertz quasi-periodic oscillations (kHzQPOs) are one of the tools that can be used to study this. kHz QPOs arefluctuations in the X-ray emission of these systems, with frequencies between300 and 1200 Hz, comparable to the orbital frequency 5 km above a 10-kmand 1.4 solar mass NS, and are thought to be produced at (or close to) theinner edge of the accretion disk.
Since (part of) the high-energy radiation from the surface of the NS isreprocessed an re-emitted at lower energies in the accretion disk, one canconstrain the size of emitting region measuring the time lags between low-and high-energy photons on the time scales of the kHz QPOs. We studiedthe system 4U 1608-52, in which the kHz QPOs change from 540 to 1060Hz. If these QPOs come from the inner edge of the accretion disk, the timelags should change with frequency, as the inner disc radius changes. We finda significant dependence of the time lags with energy, but a weak (if any)dependence with frequency.
We use these results to constrain the location at which these QPOs areproduced.
68
7 Flame spreading velocity in Type I X-ray bursts
Yuri CavecchiBraithwaite, Watts & Levin
Sterrenkundig Instituut Anton Pannekoek, Amsterdam
High resolution timing analysis of Type I Burst lightcurves has revealed thepresence of oscillations in their intensity. There is evidence of a relation be-tween the frequencies of such oscillations and the spinning frequency of theNS, which in turn can be used to deduce information regarding the EOS.Thus, properly modelling such phenomena could give deep insight into thestructure of ultra dense matter, as well as into other processes linked to therotation of NS, such as i.e. gravitational wave emission. We will present re-sults from simulations of ignition and propagation of thermonuclear burningon the surface of an accreting NS, focusing on the dependence of the velocityof the burning front on physical parameters like conductivity and spinningfrequency of the NS, as well as implications for future timing instruments.
69
8 The COSPIX mission : focusing on the ener-getic and obscured Universe
Philippe Ferrandoon behalf of the COSPIX consortium
Irfu / Service d’Astrophysique, CEA Saclay
Tracing the formation and evolution of all supermassive black holes, includ-ing the obscured ones, and understanding how black holes influence theirsurroundings, and how matter behaves under extreme conditions, are rec-ognized as key science objectives to be addressed by the next generation ofinstruments. These are the main goals of the COSPIX proposal, made toESA in the context of its call for selection of the M3 mission. In addition,COSPIX, will also provide key measurements on the non thermal Universe,particularly in relation to the question of the acceleration of particles, aswell as on many other fundamental questions as for example the energeticparticle content of clusters of galaxies.
COSPIX is proposed as an observatory operating from 0.1 to ∼ 100 keV.The payload features a single long focal length focusing telescope offering aneffective area close to ten times larger than any scheduled focusing mission at30 keV, an angular resolution better than 20 arcseconds in hard X-rays, andpolarimetric capabilities. The COSPIX design extensively builds-on resultsobtained these last years in the studies of missions like Simbol–X and IXO.
In this paper, we will describe the science objectives of the mission, itsbaseline design, and its performances, as proposed to ESA.
70
9 Phase lags and cyclotron lines in 4U 0115+63
Carlo FerrignoM. Falanga, E. Bozzo
ISDC, University of Geneva
Highly magnetized pulsars accreting matter in a binary system are brightsources in the X-ray band (0.1–100 keV). Despite the early comprehension ofthe basic emission mechanism, their spectral energy distribution is generallydescribed by phenomenological or simplified models. We propose a study ofthe energy dependent pulse profiles of the high mass X–ray binary pulsars4U 0115+63 to unveil the role of cyclotron resonant scattering in the pulseprofile formation. We analyze archival BeppoSAX and RXTE data of sixlong observations of the bright phase of the giant outburst occurred duringspring 1999 in the energy range 2–50 keV, and study the energy dependencyof the pulse profiles by means of a cross correlation technique. We alsodevelop a geometrical model of the column emission to motivate our findings.We find that the pulse profiles are significantly shifted and distorted incorrespondence of the cyclotron scattering absorption features and this canbe at first approximation explained by a variation of the angular dependentpattern of the radiation emitted by the column. The complex dependencyon angle and energy of the beam originating in the accretion column is farfrom being satisfactorily understood, our analysis reveals that the resonancein the cross section of electrons in the strong magnetic field of this objectsplays an important role, never explored in detail from this point of view.Data with high S/N at lower luminosity and a more sophisticated theoreticalmodel will contribute significantly to the comprehension of the the X-rayemission in the strong gravitational and radiative fields of neutron stars.
71
10 Supergiant Fast X-ray Transients and other wind-fed accretors - testing with the Corbet diagram
Sergei Grebenev
Space Research Institute, Moscow
Supergiant wind-fed X-ray binaries and Be-systems occupy different regionsin the Pspin-Porbit diagram (known as the Corbet diagram). The previousattempts to explain this diagram were not fully satisfactory. We proposea new explanation for the observed dependences which takes into accountthe fact that the accretting matter in such systems has smaller angularmomentum than the Keplerian one. We review properties of the SupergiantFast X-ray Transients recently discovered with INTEGRAL and note thattheir location at the Corbet diagram can be a key to understanding of theaccretion mechanism responsible for their outbursts.
72
11 Aperiodic X-ray variability studies of the blackhole candidate MAXI J1659-152
Maithili KalamkarD. Altamirano, M. van der Klis, P. Casella, J. Homan, M. Linares
Astronomical Institute ‘Anton Pannekoek’, University of Amster-dam
MAXI J1659-152 is an X-ray transient discovered in September 2010. Thesource was identified as a black hole candidate as it exhibited type C QPOswhile in the hard intermediate state which is very typical of stellar-massblack hole transients. The source also exhibited the harmonic and sub-harmonic of the type C QPO along-with a strong power law noise. Thesource is currently in the soft intermediate state and exhibited type B QPO.In this poster, we will present the results of the aperiodic X-ray variabilitystudies with Rossi X-ray Timing Explorer (RXTE). The QPOs are believedto originate in the region of the disk very close to the black hole and thereforecan help us to understand the behaviour of matter under extreme conditionspresent in the vicinity of compact objects. Though the origin of QPOs isvery poorly understood, their behaviour has been extensively studied inother transient black hole candidate systems. Similar QPOs have been seenin some neutron star systems. An account will be presented of the propertiesof the QPOs in MAXI J1659-152 in comparison to these earlier analyses.
73
12 Pulse profile variations in GX 1+4
Peter KretschmarR. Ruiz Carmona, E. Kuulkers, A. Gonzalez Galan, C. Ferrigno
ESA/ESAC
The symbiotic accreting X-ray pulsar GX 1+4 shows significant changes inits pulse profile together with strong, irregular luminosity variations typicalfor this source class. We present results of a comparative study of profilesobtained over several years with INTEGRAL.
74
13 Dipping and Absorption in the stellar wind inGX 301-2
Ingo KreykenbohmFuerst, F.; Gogus, E.; Belloni, T.; Schmid, C.; Wilms, J.; Pottschmidt, K.;Suchy, S.; Rothschild, R.E.; Kretschmar, P.
Dr. Karl Remeis Observatory & ECAP, Bamberg
We present a detailed study of the absorption and dipping behavior of theaccreting High Mass X-ray Binary GX 301-2 using high quality XMM timingmode data taken during the pre-periastron flare. We accumulate spectrawith an exposure time of the order of 30 seconds and perform pulse phaseresolved spectroscopy on single pulses.
Keeping the continuum parameters fixed, we obtain a light curve ofthe column density NH and the iron line parameters, thus allowing us totrack the evolution of the NH and the iron line with time. By trackingthe NH and iron line with very high time resoultion, we can investigate theabsorbing material in the stellar and its rapid changes This NH lightcurveshows that the density in the stellar wind fluctuates strongly on timescalesof 100 seconds or less.
Analysis of RXTE data shows that the source is also strongly variableoutside the pre-periastron flare: the source exhibits intense flaring as well asdipping activity. The source countrate as recorded by the RXTE/PCA dropsto almost zero during some of the dips in the lightcurve and no pulsations areobserved, whereas the pulsations are clearly visible outside the dip. Similarphenomena have been observed in Vela X-1 (Kreykenbohm et al. 2008,1999).
These remarkable phenomena show that these objects need to be ob-served with IXO with high time resolution to be able to study the absorbingmaterial and the pulsations in detail and thus track structures in the stellarwind. To assess the feasibility of such observations, we perform detailedsimulations of observations of bright sources with the HTRS.
75
14 Pulse-phase spectroscopy as a tool for the studyof X-ray pulsars
Alexander LutovinovS.Tsygankov
Space Research Institute, Moscow
We proposed to use the pulse-phase resolved spectroscopy as a tool for thestudy of the accretion flows structure in X-ray pulsars at different luminosi-ties. Such a comprehensive analysis require a new generation of instrumentswith high timing and spectroscopic capabilities like HTRS. Based on thecurrent results of the analysis of the emission from transient X-ray pulsarsobtained with the RXTE observatory we debated the hypothesis about a ge-ometrical origin of the spectral parameters variations with the pulse phase.We also shown that properties of the fluorescent iron line emission (partic-ularly a variability of its equivalent width on the time scale of the pulseperiod) can be used to investigate the spatial distribution and physical con-ditions of the matter around the compact object as well as in the binarysystem as a whole.
76
15 On the nature of low frequency quasi periodicoscillations: a variability study of the BHCGX 339-4
Sara Motta
Osservatorio Astronomico di Brera
A few distinct types of low-frequency oscillations showing rather differentproperties have been discovered in the X-ray emission of black-hole binaries.An exhaustive classification has not yet been obtained, however, three mainoscillation types stand out in the present scenario. In the past years, it hasbecome clear that the best way to characterize the spectral evolution of anX-ray transient is to produce a Hardness-Intensity Diagram, analogous to astellar CMD but for each source separately. The three types of oscillationsare observed only when the source is in very delimited areas of this dia-gram, with a very clear and well-defined phenomenology. Here I present theanalysis of all the RXTE data of the bright black hole transient GX 339-4,which has shown five complete outbursts. I examine the parameters of theoscillations and compare them with the result of a full spectral analysis ofthe data. The three types display different dependences on the spectral andtiming parameters, further strengthening their different nature.
77
16 X-ray bursts and burst oscillations from theslowly spinning X-ray pulsar IGR J17480-2446
Sara Motta
Osservatorio Astronomico di Brera
The newly discovered 11 Hz accreting pulsar, IGR J17480-2446, located inthe globular cluster Terzan 5, has shown several bursts with a recurrencetime as short as few minutes. The source shows the shortest recurrence timeever observed from a neutron star. We present a study of the morphologi-cal, spectral and temporal properties of 107 of the bursts observed by theRossi X-ray Timing Explorer. The recurrence time and the fluence of thebursts clearly anticorrelate with the increase of the persistent X-ray flux.The ratio between the energy generated by the accretion of mass and thatliberated during bursts indicate that Helium is ignited in a Hydrogen richlayer. Therefore we conclude that all the bursts shown by IGR J17480-2446are Type-I X-Ray bursts.
78
17 Spectroscopy of the Pulsar-like White DwarfAE Aquarii from Chandra and Swift-XRT Data
Bosco OruruP. J. Meintjes
Department of Physics and UFS-Boyden Observatory, Universityof the Free State
The novalike variable AE Aqr is perhaps the best source to study amongaccretion driven systems. It consists of a fast rotating highly magnetic WDorbiting, and accreting material from, a low-mass main sequence compan-ion. It has been observed in almost all wavelengths, with unique charac-teristics which include flares and coherent oscillations. The system is in apropeller state, and most of its emission properties are associated with thepropeller process. We have analysed its X-ray spectra from data observedwith Chandra and the Swift X-ray telescope, and the results show that theX-rays emission in the system has both thermal and non-thermal character-istics. In this presentation, results of the X-ray spectroscopy, based on theconstraints on the emission mechanisms, thermal and non-thermal, will bediscussed.
79
18 On the time evolution of the lower kHz QPOin 4U 1608-52
Stephane PaltaniD. Barret, M. Suveges
ISDC, University of Geneva
We follow the evolution of the lower kHz QPO in the neutron-star X-raybinary 4U 1608-52 over 55 RossiXTE observations, for a total of more than120 ks over 10 years. The evolution is found to differ significantly from apower-law in the sense that it evolves more slowly. The QPO is found tomove symmetrically in frequency space, which implies non-symmetric stepsin radius, if the QPO frequency is determined by the Keplerian frequency ata given distance to the central source. We propose a model of random-walkwith a deterministic frequency drift that is able to reproduce the time seriesproperties of the QPO frequency. If applied to the frequency evolution, theparallel-track model fails to reproduce the power-spectrum properties of thesource flux.
80
19 A filter wheel for the HTRS
Stephane PaltaniFranck Cadoux, Ludovic Genolet
ISDC, University of Geneva
The HTRS requires a filter wheel to perform several important tasks: to pro-tect the detector, to reduce the optical load on the detector when observingoptically bright sources and to place a radioactive source in the optical beamfor calibration purposes. The very compact footprint of the HTRS FPA andits very tight mass budget impose strong constraints on the filter wheel me-chanical envelope and mass. We present here the current design of the filterwheel, together with a full-scale bread-board model of the mechanism.
81
20 Central Engines of GRBs
Tsvi Piran
Racah Institute for Physics
Most GRB models are based on rapid accretion onto a newborn compactobject. An alternative model is based on tapping the rotational energy ofthe compact object. This model has been suggested either for powering theprompt emission or as the source of the ”energy injection” observed in theplateau phase of the afterglow of many GRBs. I examine pros and cons ofthis model as well as the prospects of searching for an observed signaturethat would enable us to distinguish between the two.
82
21 INTEGRAL and the unified model of AGN
Claudio RicciRoland Walter, Thierry Courvoisier, Stephane Paltani
ISDC, University of Geneva
We present the study of the average hard X-ray spectra of a sample of about200 hard X-ray selected radio-quiet Active Galactic Nuclei (AGN) detectedby INTEGRAL. Using all the available IBIS/ISGRI public data (as of May2010), we produced the average stacked spectra of different classes of AGNin the 17-250 keV energy range. The sample consists of 68 Seyfert 1, 38Seyfert 1.5, 77 Compton thin Seyfert 2, 12 Narrow Line Seyfert 1 (NLS1),and 13 Compton thick (CT) Seyfert 2. These subsamples have exposuresup to 45 Ms.
We found that, in agreement with the unified model of AGN, the av-erage spectra of Seyfert 1 and Seyfert 1.5 are consistent, and can be wellrepresented by a cutoff power law with a photon index Γ = 1.9, a cutoff atEc>300 keV, and a reflection parameter of R<0.4.
The spectrum of Compton thin Seyfert 2 shows instead a much greatercurvature, and, when normalized and compared to those of Seyfert 1 andSeyfert 1.5, it presents a strong excess in the 20-60 keV band. We found thatthis excess is due to the contribution of heavily obscured (Nh in the 1-7 1023
cm−2 range) Seyfert 2, which show a reflection dominated spectrum. Theunabsorbed reflector of these objects has an average value of R>1, whichmight imply the existence of partially covering CT clumps in the line ofsight. Taking into account reflection, the spectrum of heavily obscured Sy2has the same continuum of Sy1 and Sy1.5. We will discuss the impact ofthese results on the Cosmic X-ray Background, and on the unified model ofAGN.
83
22 Type I and type II X-ray bursts of the RapidBurster as seen by Swift
Gloria SalaF. Haberl, J. Jose, A. Parikh, W. Pietsch
Univeristat Politecnica de Catalunya, Barcelona
The Rapid Burster (MXB1730-335) is a unique object showing both typeI (thermonuclear) and type II (accretion driven) X-ray bursts. Swift ob-servations obtained during a long outburst in February-March 2009 showintense bursting activity, with bursts intervals between 25 and 200 seconds.During the first observation, most Type II bursts peak at fluxes higher than10−8 erg/s cm2 (L=(1-1.6)x1038 erg/s (1-10 keV)), with the peak intensitydecreasing in the last Swift observations. A Type I burst is observed onMarch 5, showing indications of photospheric radius expansion.
84
23 A Catalogue of X-ray bursters detected by JEM-X on board INTEGRAL
Celia Sanchez-FernandezE. Kuulkers
INTEGRAL Science Operations Center, ESAC
The wide field of view of JEM-X on board INTEGRAL allows concurrentmonitoring of several sources in a single pointing, thus allowing serendipitousdetection of interesting events from any of these targets. Taking advantageof this capability, we have performed a systematic search of Type-I X-raybursts in the light curves of known X-ray bursters.
For this task, all the the public data in the INTEGRAL archive havebeen analyzed. We present here the preliminary results of this work. Intotal, ∼ 70 000 science windows of observations have been analyzed, allow-ing the detection of 2243 Type-I X-ray burst candidates, with short andintermediate durations (≤ 100 sec).
85
24 Simulations of the performance of the HTRSon IXO
Christian SchmidWilms J., Martin M., Kendziorra E., Muck B., Barret D., Rambaud D.
Dr. Karl Remeis-Observatory & ECAP, Bamberg
We present the results of our analysis of the HTRS performance studiedwith a Monte-Carlo simulation of the photon imaging and detection pro-cesses. Based on the effective area of the individual mirror shells in the IXOsilicon pore optics design we have analysed the photon distribution on theHTRS detector at its out-of-focus position taking into account misalignmenteffects according to the instrument alignment requirements. We have stud-ied different pixel geometries and analysed the bright source performancewith respect to pile-up for analog and digital readout electronics.
86
25 Measuring strong magnetic fields of neutronstars with the next-generation of X-ray instru-ments
Gabriele SchonherrP. Kretschmar, J. Wilms, I. Kreykenbohm, F. Schwarm, K. Pottschmidt, R.Rothschild
Astrophysikalisches Institut Potsdam
To date, the only direct method to assess the strong magnetic fields of High-Mass X-ray Binaries containing accreting neutron stars is the observationand analysis of electron cyclotron resonance features (”cyclotron lines”) intheir high-energy X-ray spectra. We discusss how the upcoming area of newobservatories and instrumentation like IXO will change our ”magnetic” viewof those objects.
87
26 Investigating the disc-jet coupling in accretingcompact objects by studying the “radio quiet”sources
Paolo SoleriRob Fender
Kapteyn Astronomical Institute, University of Groningen
The coupling between accretion processes and ejection mechanisms in ac-creting black hole binaries can be investigated by empirical relations betweenthe X-ray/radio and X-ray/optical-infrared luminosities. These correlationsare valid over several orders of magnitude and can connect stellar-mass andsupermassive black holes. Despite these relations were supposed to be uni-versal, many black hole binaries have been found to produce jets that, givencertain accretion-powered luminosities, are fainter than expected from thecorrelations. This shows that black holes with similar accretion flows canproduce a broad range of outflows in power, suggesting that some otherparameters or factors might be tuning the accretion/ejection coupling. Wediscuss whether typical parameters of the binary system, as well as the prop-erties of the outburst, produce any effect on the energy output in the jet. Noobvious dependence is found. We also define a jet-toy model in which thebulk Lorentz factor becomes larger than ∼1 above ∼0.1% of the Eddingtonluminosity. Despite several limits, this model can qualitatively describe thescatter of the X-ray/radio correlation and the ”radio quiet” population. Wealso compare the ”radio quiet” black holes with the neutron stars. We showthat if a mass correction is applied, the possibility that they are statisticallyindistinguishable in the X-ray:radio plane can not be completely ruled out.Our result suggests that some of the outliers could actually be neutron stars.Another possibility is that the disc-jet coupling in the ”radio quiet” blackholes is more similar to the one in neutron stars.
88
27 XTE J1752-223: A broad band X-ray spectralinvestigation combined with timing studies
Holger StieleT. Munoz-Darias, S. Motta, T. Belloni
INAF Osservatorio astronomico di Brera
We report on X-ray monitoring observations of the transient black holecandidate (BHC) XTE J1752-223 with the Rossi X-ray Timing Explorer(RXTE). The source was discovered on 2009 October 23 and during itslow/hard state (LHS), which lasted for at least 25 days, all timing andspectral properties were similar to those of Cyg X-1 during its canonicalhard state (Munoz-Darias et al. 2010, MNRAS 404, L94). The combinedPCA/HEXTE spectra were well fitted by an absorbed broken power lawwith high energy cut off. When RXTE observations were resumed, after anobservational gap due to solar constrains, the source was in the hard inter-mediate state (HIMS), showing type C QPOs. The source evolved throughthe soft intermediate state, characterized by a 5 - 10 % rms variability andtype B QPOs, into the high soft state. In the following it showed severaltransitions between these states. The combined PCA/HEXTE spectra werewell fitted by an absorbed disk black body plus broken power law. After afurther 59 days XTE J1752-223 passed through another HIMS at lower lu-minosity into the LHS. We discuss the different states, including a discussionof the variability diagram, and present the results of our combine spectral(PCA/HEXTE) and timing investigations. In addition, we will discuss theresults of our spectral studies in which we combined RXTE and Swift data.
89
28 X-ray bursting neutron star atmosphere mod-els
Valery SuleimanovJ. Poutanen, K. Werner
IAAT, University of Tuebingen
X-ray bursting neutron stars in low mass X-ray binaries constitute an ap-propriate source class to constrain masses and radii of neutron stars. Wecomputed a necessary for these investigations set of model atmospheres andemergent spectra in a plane-parallel, hydrostatic, and LTE approximationwith Compton scattering taken into account. The models were calculatedfor six different chemical compositions: pure hydrogen and pure helium at-mospheres, and atmospheres with solar mix of hydrogen and helium, andvarious heavy element abundances Z = 1, 0.3, 0.1, and 0.01 Z�. For eachchemical composition the models are computed for three values of surfacegravity, log g =14.0, 14.3, and 14.6, and for 20 values of the luminosity inunits of the Eddington luminosity, L/LEdd, in the range 0.001–0.98. Theemergent spectra of all models are redshifted and fitted by a diluted black-body in the RXTE/PCA 3–20 keV energy band, and corresponding valuesof the color correction.
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29 Magnetized neutron star atmospheres: beyondthe cold plasma approximation
Valery SuleimanovG.G. Pavlov, K. Werner
IAAT, University of Tuebingen
Harmonically spaced absorption features are observed in thermal soft X-rayspectra of some isolated neutron stars. The interpretation of the featuresas quantum resonances of magnetic free-free opacity has been recently sug-gested, and neutron star atmosphere models calculated in the cold plasmaapproximation. This approximation neglects the cyclotron emission of elec-trons at the harmonics of the cyclotron frequency, as well as the Dopplerbroadening of the cyclotron resonances, which may be important even at therelatively low temperatures of neutron star atmospheres. To demonstratethis effect, we calculate models of hydrogen neutron star atmospheres withB ∼ 1010–1011 G (i.e., the electron cyclotron energy Ec,e ∼ 0.1–1 keV) andTeff = 1–3 MK with the thermal cyclotron opacities taken into account.Such conditions are thought to be typical for the so-called central compactobjects in supernova remnants, such as 1E 1207.4–5209 in PKS 1209–51/52.We show that the ”warm plasma effects” are very significant in first threecyclotron harmonics, and they should be taken into account for the properinterpretation of the observed spectra in addition to the quantum oscillationsin the magnetic free-free opacity.
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30 Extreme-value analysis of the X-ray emissionof Cygnus X-1
Maria SuvegesS. Paltani
ISDC Data Centre for Astrophysics, University of Geneva
The multiplicative model of Uttley et al. (2005) for the X-ray emissionfrom X-ray binaries accounts well for the observed global characteristics ofthe time series such as the linear flux-rms relationship and the lognormaldistribution of the fluxes. However, models that are fitted to the bulk ofthe data may not provide satisfactory models for the extreme events in theseries: these might be produced by other unrecognized processes. As themodel of Uttley et al. (2005) implies a well-determined structure of eventsabove high thresholds, we applied methods from extreme-value statistics tocheck whether the same process can be responsible for the extremes in thedata. We first considered the limiting distribution of large events as ex-pected from the model, and compared to that of a model fitted to data fromCygnus X-1. Next, the clustering characteristics of the observed large eventswas compared to what is expected. Both comparisons show that the mul-tiplicative model can indeed generate the observed extreme events, thoughthere are indications of non-stationarity in the baseline level of the processand also of short periods where the observed extreme-value characteristicsare incompatible with the model implications.
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31 Synchrotron self-Compton model for optical/X-ray correlation in black hole X-ray binaries
Alexandra VeledinaJ. Poutanen, I. Vurm
Department of Physics, University of Oulu
Simultaneous optical and X-ray observations of compact objects in low-massX-ray binaries allow us to constrain radiative processes operating in thesesystems. Such observations for the first time were carried out by Motch etal. (1983) for X-ray binary GX 339-4. Although the time resolution of datawas not very good, the authors were first to report on complicated cross-correlation function (CCF) between the two bands, with an anti-correlationpreceding positive correlation. The same structure of CCF was later foundin XTE J1118+480 (Kanbach et al. 2001) and in SWIFT J1753.5-0127(Durant et al. 2008). All these objects are black-hole candidates, however,recently similar CCFs were found for two binaries, Sco X-1 and Cyg X-2,hosting neutron stars (Durant et al. 2010).
The physical nature of the CCF structure is unknown. Number of toymodels were developed to explain such a behavior, most of them include jetsas a source of optical emission. Detailed calculations of resulting CCFs weremade so far only by Malzac et al. (2004), where the optics and the X-raysare fed by magnetic energy reservoir. However, the model has a numberof problems, for example, it is not clear how to maintain such an energeticmagnetized zone. Also in the case of SWIFT J1753.5-0127, the jet seems tobe too faint to contribute to the optical luminosity (Soleri et al. 2010).
We propose a novel model capable of explaining timing properties ofthese objects. We argue that the X-ray emission is produced by synchrotronself-Compton mechanism, which also contributes to the optical luminosity.Small variations in the accretion rate cause changes of parameters of theflow (optical depth, total luminosity), leading to variations in X-rays andoptical luminosities. By simulating spectra for specific parameters, we showthat fluxes in the two bands are anti-correlated. Additional contributionto the optics comes from reprocessing of the X-rays by the outer regionsof the accretion disc. We find that our model is consistent with the CCFsrecently observed from Galactic black holes. From the presence of the dipsin the CCFs, we can estimate the size of the synchrotron-emitting regions,and from the absolute value of the dips we constrain the contribution ofsynchrotron radiation in the optical energy band.
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32 Fast variability of gamma-ray emission fromsupermassive black hole binary OJ 287
Ievgen VovkA. Neronov
ISDC Data Centre for Astrophysics, University of Geneva
We report the discovery of fast variability of gamma-ray flares from blazarOJ 287. This blazar is known to be powered by the binary system of super-massive black holes. The observed variability time scale Tvar < 3 hr is muchshorter than the light crossing time of the more massive (1.8 x 1010 solarmasses) black hole and is comparable to the light crossing time of the lessmassive (2 x 108 solar masses) black hole. This indicates that the observedgamma-ray emission is produced by relativistic jet ejected by the black holeof smaller mass. Detection of gamma-rays with energies in excess of 10 GeVduring the fast variable flares constrains the bulk Lorentz factor of the jet tobe larger than 4. Possibility of the study of the orbital modulation of emis-sion from relativistic jet makes OJ 287 a unique laboratory for the studyof the mechanism(s) of formation of jets by black holes, in particular, ofthe response of the jet parameters to the changes of the parameters of themedium
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33 The Digital Data Processing Unit for the HTRSon board IXO
Henning WendeG. Distratis, C. Tenzer, E. Kendziorra, A. Santangelo
IAAT, University of Tuebingen
The Institute for Astronomy and Astrophysics in Tubingen participatesin the development of two of the IXO instruments - one of them is theHigh Timing Resolution Spectrometer (HTRS). The soft- and hardware forits Data Processing Unit (DPU) is being developed and will be tested inTubingen. We will give a brief overview of the challenges that the DPUfaces, in particular the instrument data rate. The two main solutions tothis problem and thus the primary tasks of the DPU are then presentedin more detail. Reducing the incoming data rate to a value limited by theavailable telemetry rate is achieved in two steps: First the data handlingFPGA will implement several highly configurable detector operation modito reduce the amount of data while enabling the observer to optimize sci-entific output of the observation. The second step is lossless on-board datacompression and intelligent wrapping of the data done by a Leon3 CPU ad-ditionally implemented in the FPGA. We present first simulation results ofthe DPU operations that show the achieved data rate reduction and give anupdate on the development and performance testing of an operational DPUprototype done in Tubingen.
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34 LATE POSTER:Are the two peaks of the Cathedral QPO realharmonics?
Jerome RodriguezP. Variere
CEA Saclay
We present a complete study of the two main peak of the so-called cathedralQPO in XTE J1859+226. While looking at the temporal evolution of thetwo features we show that they do not manifest the same amplitude ofvariations of their power, and do not seem to follow the flux variation inthe same way. We then present their RMS-spectra and show that theydo not have the same shape, slope and cut-off energy. We discuss thesedifferent facts and try to answer the question regarding the genuineness oftheir harmonic relationship.
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