Post on 28-Dec-2015
Pharos:distant beacons as cosmological probes
Fabrizio Fiore, Fabrizio Nicastro INAF-OAR, Martin Elvis SAO
The “Pharos” of Alexandria, oneof the Seven Wonders of the ancient world, was the tallestbuilding on Earth (120m). Its mysterious mirror, which reflection could be seen more than 55 km off-shore fascinated scientists forcenturies.
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The fate of baryons
Lyclouds
WH
HG green ~10
red ~104
The warm intergalactic mediumThe warm intergalactic medium
Cen et al. 2005
Hellsten et al. 1998 ApJ, 509, 56
OVIII
OVII
IGM density
IGM temperature
IGM metallicity
The warm intergalactic mediumDave’ et al 2000
Cen et al. 2005
Cen et al. 2005
Cen et al. 2005
Cen et al. 2005
•HRC/LETG 63 ksec on 21mCrab source
•R=400
•~700 counts/resolution element.
•PKS2155-304 z=0.116 blazar & Cal. target.
•Strong detection of OVII ,
•NeIX K
•Weaker detection of OVIII K
•EW 10-20 mA
•FUSE detection of OVI 2s->2p
•All lines at z~0, -135 km s-1 from FUSE
Detection of the Local Warm IGMby Chandra: PKS2155 line of sight
OVII
NeIX OVIII
Nicastro et al. 2002 ApJ
Detection of Warm IGM
by Chandra: Mark421 line of sight The highest S/N grating The highest S/N grating spectrum ever!spectrum ever!
40-60mCrab source yielded2500 counts per resolution el.at 0.6 keV!
Fluence of 10Fluence of 10-4-4 erg cm erg cm22!!
First detection of warm First detection of warm IGM at z>0IGM at z>0
OVII(z=0.011) EW=0.05eVOVII(z=0.027) EW=0.03eV 10101515 cm cm-2-2 NVII(z=0.027) EW=0.05eV Nicastro et al. 2005
Cen et al. 2005
Ωb(NOVII>7x1014 cm-2)• Mkn 421 (2 Filaments.): z=0.03
• Combined Mkn421+1ES1028+511 (3 Filaments):
Consistent with missing =2.5 0.4
%107.21
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(Nicastro et al., 2005, Nature, 433, 495; Steenbrugge et al., 2006, in prep.)
Physics and Astrophysics of the Warm IGM
• How many lines? The baryon density at low redshift
• How is the Warm IGM heated? shocks? -> R>=6000
• What is the history of the heating? mirrors decline of Lyman forest? -> z=1- 2 X-ray forest
• Did chemical enrichment trace heating? tracks star formation rates? -> R>=6000
• Does the `X-ray forest’ redshift structure match
CDM predictions? trace later formation of large scale structures
-> z=0.1-1 X-ray forest
Reducing Uncertainties•GOALGOAL: Reduce : Reduce bb and d and dNN/dz uncertainties /dz uncertainties down to down to fewfew % from current (+140,-70) % % from current (+140,-70) %
Needs 100 to Needs 100 to 1000 1000
Detections!Detections!
•Resolve Warm IGM line widths:
50 km s-1, R = 6000
•Span 0<z<2 for OVII, OVIII:
(OVIII K18.97A; OVIII Ka = 22.09A)
i.e. 18 - 66A, 0.19 keV 0.7 keV minimum
• Extra line diagnostics:
NeIX (13.69A) : 0.31 - 0.92 keV
CVI (33.73A) : 0.13 - 0.38 keV
weak lines need high resolving power
Warm IGM Spectroscopy Goals
FWHM= 20 km s-1
Chandra LETG OVII
FUSE OVI
goal
FWHM= 660 km s-1
51014 cm-2
The minimum detectable EW scales with the square root of E. Since the rest frame EW scales with (1+z)EWobs and since for gratings E scales with E-1, the minimum detectable rest frame EW is nearly constant with z. • Similar column densities can be probed with gratings in the z range 0-2
Physics and Astrophysics of the Warm IGM
• How many lines? The baryon density at low redshift
• How is the Warm IGM heated? shocks? -> R>=6000
• What is the history of the heating? mirrors decline of Lyman forest? -> z=1- 2 X-ray forest
• Did chemical enrichment trace heating? tracks star formation rates? -> R>=6000
• Does the `X-ray forest’ redshift structure match
CDM predictions? trace later formation of large scale structures
-> z=0.1-1 X-ray forest
How was the Warm IGM heated?Thermal broadening of O linesis ~50 km/s at T=4106 K
Fang et al 2002
Hydrodynamic simulations show that reasonable warm intergalactic gas turbulence may be of ~100 km s-1 up t0 200 km/s (implying a resolution of 1500-3000 to resolve these lines and measure the Doppler term b.
If the temperature of the gas can be constrained through OVI, OVII and OVIII line ratios the measure of b can provide information on the heating history of the gas. For example, if the gas were shock heated one would expect that the gas temperature is proportional to the square of the gas sound speed, which in turn should be proportional to the gas turbulence.
By measuring b and T it would be possible to check this idea and to provide tests and constraints to hydrodynamic models.
Constellation-X SWG Sept 2002
Gamma-ray Bursts
BATSE all sky GRB map (http://f64nsstc.nasa.gov/batse/grb/skymap)
• GRBs come from distant (z>1) explosions
• Brighter than Crab Nebula for a few minutes
•brightest GRB fluence
= 10-5 erg cm-2 (1min-12hr)
= 10 Msec (4months) observing brightest z~2 quasar, flux: 10-12 erg cm-2 s-1
GRBs are best `lighthouses’ to study intervening matter
Stupor CoeliStupor Coeli
Greatest Lighthouses of the Universe
BeppoSAX GRBM+WFC Frontera et al. 2000 Fiore et al. 2000
Assuming F(2-10)@30sec/Fpeak(50-300)=0.01 and a power law decay with =-1.3
GRBs are the best path Fiore et al 2000 ApJL, astro-ph/0303444
• Most GRB have X-ray afterglows, a few can be very bright (fluence> 1x10-5 erg s-1 )
•brightest z~0.5-1 quasars (0.5 mCrab) take 2 weeks to gather same fluence
•1-2 GRB/yr at fluence>1x10-5 erg/cm2
= 1 Msec obs of a half mCrab AGN
•40 GRB/yr at fluence>1x10-6 erg/cm2
=100 ksec of a half mCrab AGN
resolve lines, detect faint lines
• 100 GRB/yr at fluence>1x10-7 erg/cm2
detect X-ray forest
But … Swift will tell….!
44 GRB localized by Swift BAT
8 GRB localized by BSAX WFC,Extrapolated from 30sec to 100 sec, 2.4 hrassuming =-1.3
100 sec
2.4 hr
Primary Targets: GRB Afterglows; Secondary Targets: QSOs, Blazars
Pharos Concept
• Goal: R=6000 (50 km s-1) soft (<1 keV) X-ray spectroscopy• Cosmological driver: measure baryon density at low z• Physics driver: resolve thermal widths of X-ray lines• Astronomy driver: resolve internal galaxy motions
Gamma-ray Burst (GRB) afterglows may produce many more X-ray photons than any other high redshift source (i.e. quasars).
Requires acquisition within 10 minutes of GRB
1 minute goal, as Swift
Constellation-X SWG Sept 2002
Pharos: Rapid X-Ray-rich GRB Trigger & Location
0.1-1 keV (5-10” mirror): short focal length
reduces moment of inertia, I=mR2
(factor 25 for 2 m vs. 10 m)
• Problem: require <1armin location + acquisition in 0.5-1 minutes and require quasi-4coverage: conflicting goals
• Solution: trigger in the 5-30 keV with 2 1-D Coded Masks
TriggerTrigger
5-30 keV ‘light’
ASM Coded Mask 1’ localization in
0.5-1 s
Rapid rough slewRapid rough slew to 1’ location
Fine slewFine slew to <1 arcmin position
X-ray spectrometer starts to take data R>5000 @ 0.5 keV:
Out-of-plane Reflection Gratings
GRB trigger must be on-board & autonomous: 5-30 keV triggers X-ray rich
t=0 st=1-15 s
t=30 s
SuperAGILE in short
1-D Coded Masks
Collimator
Si μ-strip Detectors
Energy Range 15-40 keV
Energy Resolution
7-8 keV FWHM
Geometric Area 1360 cm2
Max Effective Area
280 cm2
Field of View (ZR) 2 x (68° x 107°)
Angular Resolution
6 arcmin (on-axis)
Source Location Accuracy
2-3 arcmin
for bright sources
Point Source Sensitivity
10 mCrab
(50 ks, on axis)
Timing Accuracy 5 μs
Imposed by AgileCosta, Feroci & the Super-Agile Coll.
16 46x46 deg2 “SA”s cover Half Sky
•Current Size and Thickness Imposed by Agile
Presence of Agile anticoincidence limits current sensitivity by 1.5-2
•Only 5.5 kg (can be improved): Integral/IBIS=700 kg; Swift/BAT>100 kg; ISS/MAXI=490 kg
•Current Energy Range: 15-40 keV-Low Energy Threshold halved just doubling the points of read-outs 7-40 keV for free!!-High Energy Threshold increases with thickness
•650 μm Si-thickness + FOV=46x46 deg2 Sensitivity: 1 mCrab in 50 ks (5-10 keV) at 5σ
CHEAP!: 1 M$ to redo itLIGHT!: Total weight ~ 80 kg
X-ray Mirror Area
Baseline mirrorMinimum mirror1200 cm-2 2000 cm-2 60kg (incl. 40%support) 200 kg (incl. 40% support)
•Low energy band allows wide grazing angles (up to 3-4 degrees) and
short focal length: 2-2.5 meters – larger Aeff
•Use Ni coating for E<0.9 keV higher reflectivity than Au
Pharos goal
Citterio & Pareschi
X-ray Gratings
• R=6000 is technically achievable
XMM RGS gratings behind Chandra mirror -> R=5000
(subject to improved facet alignment)• Out-of-plane reflection gratings
give higher dispersion (Cash 1991)• Need 5” FWHM mirror assembly.
Control of grating scattering crucial.
(else wings fill in absorption lines)
5” resolution R=5400!!!
MIT gratings+ HRC efficiency ~25-30%
Calorimeter +Filter efficiency~50%
Figure of Merit: Comparison with other Missions
• No other mission matches R = 6000 in X-rays
WHIM and high z galaxy dynamics unavailable.
• Other missions can still detect WHIM systems in GRBs
Compare a figure of merit:
FoM = Aeff (cm2) x peak x R (0.5 keV) x GFFoM = Aeff (cm2) x peak x R (0.5 keV) x GF
XMM 1RGS # 2100
Chandra LETG # 5000
Chandra HETG # 9000
Swift 1000
Con-X 1 unit # * 123,000
Con-X 4 units # * 500,000
Minimal Pharos 600,000
Baseline Pharos 2,500,000
* assumes R=1000
# for a 4-8hr response time
x 24 for 10 min response
FoM
GF= Gain in Fluence = 1 Pharos,Swift t=10mGF=0.04 Chandra, XMM, Con-X t=4-8hr
Pharos Summary
• GRB afterglows combine 4 themes of
early 21st Century astrophysics: – The most energetic events in the Universe 19971997– The fate of the baryons & large scale structure 19991999– Galaxies in the age of star formation 19971997– The recombination epoch 20002000
• R=6000 X-ray spectroscopy opens up all of these new physics and astrophysics
• A small, short, soft X-ray telescope is enough• Rapid GRB trigger & autonomous slewing essential
Gamma ray bursts: one of the great wonders of the Universe• GRBs combine 4 themes of
early 21st Century astrophysics: – Among the most energetic events in the Universe
1997 11997 1stst GRB redshift (thank to BeppoSAX) GRB redshift (thank to BeppoSAX)– Galaxies in the age of star formation
metal abundances, dynamics, gas ionization, dust– The recombination epoch
2000-200? Gunn-Peterson trough at z~6-?2000-200? Gunn-Peterson trough at z~6-?– The fate of the baryons & large scale structure
1999 Warm IGM simulations1999 Warm IGM simulations
2001 12001 1stst Warm IGM detection (thank to Chandra) Warm IGM detection (thank to Chandra)
Minutes after the GRB event their afterglows are the brightest sources in the sky at cosmological redshift.
Afterglows can be used to probe the high redshift Universe through the study of the intervening matter along the line of sight. Two possible applications:
Galaxies in the age of star-formationthrough high resolution spectroscopy of UV lines
The warm intergalactic mediumthrough high resolution X-ray spectroscopy of highly ionized C,O,Ne lines
GRB01022210 Crab!
Crab
1mCrab i.e. a bright AGN
Galaxies in the Age of Star Formation
Mann et al. 2002 MNRAS, 332, 549
• Star formation in the Universe peaked at z~2
• Studies of z=>1-2 galaxies are biased against dusty environments.
• GRB hosts are normal galaxies
• GRB afterglows will reveal host
Galaxy dynamics, abundances, & dust content at z>1
redshift, (1+z)
sta
r fo
rmat
ion
rate
GRB Hosts
peak of star formation
GRBs also probe normal high z galaxies
X-ray high resolution spectroscopyOptical-near infrared high resolution spectroscopy
GOALS
1- The GRB environment: size and density of the region surrounding a GRB can be constrained by monitoring the absorption line equivalent widths (Perna & Loeb 1998). This can be used to discriminate among competing GRB progenitor scenarios.
2- Metal column densities, gas ionization and kinematics These studies have so far relied upon either Lyman Break Galaxies or Damped Lyman Alpha systems. However, it is not clear if these systems are truly representative of the whole high-z galaxy population.
GRB afterglows can provide new, independent tools to study high z galaxies.
Results from low resolution spectroscopy
Savaglio, Fall & Fiore 2002DLAs
High dust depletion
High dust content
Denser clouds
DATA
UVES spectra 3800-9400 A, slit 1”, resolution=42,000
GRB020813: z=1.245 - Exposure of 5000 sec. 24 hours after the GRB; R=20.4, B=20.8
GRB021004: z=2.328- Exposure of 7200 sec. 12 hours after the GRB; R=18.6, B=19
GRB021004
FORS1 R~1000 CIV CIV z=2.296 z=2.328
UVES R=40000
z=2.296 z=2.328
GRB021004 AlIII1854
AlII1670
SiIV1402
SiIV1393
CIV1550
CIV1548
z=2.321 z=2.328
GRB021004 z=2.321 z=2.328
MgII2803
FeII1608
FeII2344
FeII2374
FeII2382
Constellation-X SWG Sept 2002
GRB021004
AlIII1670
SiIV1393
SiIV1402
CIV1548
CIV1550
z=2.296 z=2.298
Constellation-X SWG Sept 2002
GRB021004 z=2.296 z=2.298
MgII2796
MgII2803
FeII1608
FeII2344
FeII2374
FeII2382
Relative abundances in GRB021004
Constellation-X SWG Sept 2002
Comparison with CLOUDY models:
Ionization parameter assuming solar abundances
GRB020813 z=1.2545
MgII2796
MgII2803
FeII2344
FeII2374
FeII2382
FeII2600
Summary
High resolution UVES observations can provide reliable ion column densities.
The GRB021004 higher z systems have much fainter low ionization lines (FeII, MgII) than the GRB020813 systems (and most other GRBs), and strong high ionization lines.
The photoionization results of CLOUDY yield ionization parameters constrained in a relatively small range with no clear trend with the system velocity. This can be interpreted as density fluctuations on top of a regular R-2 wind density profile.
…but this is only the begining!
With Swift we will have many more prompt triggers, say 20/yr during the Paranal night
and we will use the VLT in Rapid Response Mode (10-20 minutes to go on the GRB!)
so .. stay tuned for many more results on GRB host galaxies!
Beacons of the Recombination Era
HST Deep Field (http://www.stsci.edu/ftp/science/hdf/hdf/html)
• Gunn-Peterson trough found in z=6.28 quasar: Epoch of reionization Becker et al., Djorgovski et al.
• Primordial star formation (PopIII) may create 100-1000s Msol `stars’ Madau, Norman et al.
• Quickly produce hypernovae GRBs?
• 10% of GRBs may be at z>6
Bromm & Loeb
First metal production, snapshot of IGM
GRBs may be the only bright z>6 sources
• No quasars at z>>6?
• GRBs a unique probe of recombination epoch?
In the meantime…Swift is due to launch on Sept 2004!!!
Swift will trigger medium resolution R=400@1keV observations with Chandra and XMM-Newton, R=1000@6keV observations with AstroE2
A few events/yr with Fluence10-6 erg cm2
A dozen events/yr with Fluence310-7 erg cm2
Warm IGM:Statistics of OVII lines: first reliable measure of B at low z
Host galaxy ISM:Observations with the calorimeters of AstroE2 will measure: metal column densities, gas ionization parameter, gas dynamics
Rapid GRB Trigger & Location
short focal length reduces moment of inertia, I=mR2
(factor 25 for 2 meters vs. 10 meters)
• Problem: require <1armin location + acquisition in 1-10 minutes and require quasi-4coverage: conflicting goalsconflicting goals
• Solution: divide GRB trigger from location (as on BeppoSAX)
TriggerTrigger
faceted CsI solid 1o in seconds
Rapid rough slewRapid rough slew to 1o location
LocationLocation small X-ray coded mask eg XMM pn chip with 10ox10o fov to obtain arcmin location in a few seconds
Fine slewFine slew to <1 arcmin position
X-ray spectrometer starts to take data
GRB trigger must be on-board & autonomous
~20cm dia
x ~50cm lengtht=0s t=3s t=30s
t=60s
t=40s
Con-X Pros & Cons
• Pros:– Real project: 2010 launchNext new MIDEX launch 200X
– Includes 1-10 keV
+10 -100 keV spectra
• Cons:– 1min vs 12 hr slews– R=6000 vs R~400 or R~2000
– Add GRB trigger/locator
`Christmas tree’ effect