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Transcript of Uddipan KASI Talk
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Properties of
High Mass X-ray Binary Pulsars :
emphasis on the Stellar Windof the companion
Uddipan Mukherjee (T.I.F.R., India)
Advisor : Prof. Biswajit Paul (T.I.F.R. & R.R.I., India)
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Outline of the Talk
X-ray Binaries : Pulsars & High Mass X-ray Binaries
Stellar Winds
Detectors & Analysis
Orbital Phase Spectroscopy of HMXBs
4U 1538-52
GX 301-2 OAO 1657-415
Vela X-1
Be/X-ray binary 3A 0535+262 in quiescence
Spectral studies in the high and low states
Cen X-3
2S 0114+650 Future Work
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What are X-ray binaries?
Most bright X-ray
sources are in binaries
Compact object issucking material fromthe other star
Systems composed of 2 stars
The other star iscalled the companion
Binaries
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According to the nature of the companion
If Mcomp
≤ Msun
Low Mass XRBs
If Mcomp
> Msun
High Mass X-ray Binaries
Classification of XRBs
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Compact object is a NS with strongmagnetic field (1012 G)
Matter can only move following themagnetic field lines
Accumulation of plasma on the NSis called Accretion
X-rays make way out the magneticfield in a narrow beam
X-ray pulsars
The radiation is in pulses and theNS is an X-ray pulsar
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High Mass X-ray Binaries
HMXRB contain supergiants (O &B) as companion & a NS(or a BH : Cyg X-1)
Companion is very bright (104 –105 × Lum of Sun)
Companion can be viewed in IR, optical or UV
NS can only be seen in X- rays
Most HMXRB are X-ray pulsars
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As the supergiant expands, it increases in
brightness
The outer layers of its atmosphere push outa stream of particles
NS can pick up some of these particles andstart accretion in X rays
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What is a supergiant ?
Brightest & largest kind of stars
Radii : 20 to several hundred times of Sun
Red (Betelguese) Blue (Rigel)
Both types can explode as Supernovae
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Red Giant
Star of at least 15 solar mass & exhausting H
He - C burning expands even larger
Red Supergiant
Emanates a vigorous Stellar Wind
Lose extended atmospheres
smaller, hotter Blue Supergiants
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What are Stellar Winds ?
Stars emit not only radiation but also particles
The emission of particles is called the Stellar Wind
Continuous phenomena, not episodic outbursts
In a star like the sun, the wind arises from the corona
In hotter stars, the high radiative flux, drives the wind
Primarily by means of line scattering
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2 important parameters of a Stellar Wind derived fromobservations :
Mass Loss Rate : M & Terminal Velocity : v∞
A star like Sun loses about 10-14 solar mass yr-1
from winds blowing with 700 km s-1
Hot luminous stars exhibit stronger winds blowing
at speeds up to 2000 km s-1
And loses up to 10-5 solar mass yr-1 via winds
They are important to know the mechanism of wind generation
•
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Line Driven Winds
Winds of luminous hot stars are driven by absorption in spectral lines
Hot stars emit bulk of their radiation in UV
Radiative acceleration in the winds of hot stars
mainly by the absorption & re-emission of UV photons
resonance lines of ions of abundant elements
C, N, O & Fe-group elements
Winds from quasars may also be radiation driven
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Resonance line of N IV 765 Å
N+++ ion absorbing it increases its velocity by (h mc) cm s-1
To accelerate a single N+++ ion to the terminal velocity of 2000 km s-1 ,
we need 5
absorptions
In a plasma, momentum shared with other constituents
Hence, on an average : 1011
absorptions per ion to boost the velocityto the terminal value
The terminal velocity of a wind is reached within a few stellar radii
For example
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To solve the Eqn. Of Motion for a stationary,
time independent wind
Assumptions :
Photosphere as a point source : radiation in the radialdirection
A photon emitted from the photosphere is absorbed by aline transition in the wind in only a narrow interactionregion
The wind is isothermal and behaves like a perfect gas
Then, the solution is :
v(r) = v ∞(1 – R/r)0.5
where R is the stellar radius
S o b o
l e v A
p p
r o x i m a
t i o n
Velocity Profile of Line Driven Winds
CAK Wind Profile
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Observations & Analysis
● To go above the Earth's atmosphere ●
Possible via balloons, rockets & satellites● Data from ASCA, BeppoSAX, Chandra,
RXTE & XMM-Newton
X-rays from Stars
Satellite
Image Spectrum Light Curve
X-ray emissionmechanisms !!
Any Periodicities ??
Position
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RXTE – PCA : Large Area (1000 sq. cm. @ 6 keV)
Broad Energy Band (2 – 60 keV)Time Resolution : 1 sEnergy Res : 18% @ 6.0 keV
A very brief description
ASCA : 0.4 – 10 keV
Energy Res : 2% @ 6 keV Area : 100 sq. cm. @ 6 keV
BeppoSAX : 0.1 – 10 keV
Energy Resolution : 8% @ 6.0 keV Area : 150 sq. cm. @ 6 keV
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........Continued
Chandra :
ACIS : 0.1 – 10 keV
HETG : Energy Res : 0.5% @ 6 keV Area : 30 sq. cm. @ 6 keV
XMM-Newton :
PIC : 0.1 – 15 keV Area : 800 sq. cm. @ 6 keV (PN)
Energy Res : 2% @ 6 keV
Both have high earth orbits which helps toprovide long, continuous observations
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A Glimpse of the Spectral Analysis
Assume a model for the incident spectrum
Generally for pulsars : power law (PL), black-body (BB) &
high energy cut-off describe their continuum
Any emission lines are modeled as gaussian features
Exponential line of sight absorption
Incident spectrum + detector response = observed spectrum
try to match the observed spectrum by varying the parameters of
the assumed model
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Lineof sight
NS Eccentricorbit
Stellar Wind
4r2(r)v(r) = M
NH = ∫(x)dxX : path
Schematic diagram for HMXB pulsars
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What we have done ............
Evaluated the Column Densities by a numerical integration along the line of sight from the NS to the observer at infinity as the NS traversed the
elliptical orbit
CAK velocity profile was assumed
The observer was on a diferent plane than the orbit
An assumed inclination angle was taken
Binary parameters , Mass-loss rate & Terminal velocity were known
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Our Work
Part I
U. Mukherjee & B. Paul 2004, A&A,427, 567
U. Mukherjee et al., 2006a
U. Mukherjee, B. Paul & S. Naik,2006b
i i h h fl i i d
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4U 1538-52 : a nice system with smooth outflowing wind
Properties
Orbital Period 3.73 d
Eclipse duration 0.6 d
Eccentricity 0.18
Distance 5.5 kpc
X-ray Luminosity 1036 erg s-1
Companion Star : B-type supergiant (Parkes et al. 1978)
Mass-loss rate 10-6 solar mass yr-1
v ∞
: 1000 km s-1
Pulse Period 529 s
Thus, it is a suitable candidate to study the windstructure of the companion star
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Observations : We had proposed toobserve the source with RXTE-PCA
P.I. : Prof. B. Paul
from 2003-07-31 to 2003-08-07
out-of-eclipse phases for 2 binary orbits
25 data segments : exposure of (1.5 – 6.0) ks
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Set III
1998-07-29 to 1998-08-01 with
BeppoSAX covering one binary orbit
40 data segments : exposure of
1.7 – 4.0 ks
Set II
1997-01-01 to 1997-01-05 with
PCA
14 datasets : (1.5 – 10.0) ks
on-source time
.....supplemented with archival data
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Spectral Analysis
Backgrnd sub source spectra in 3 – 20 keV
Model : P L + exp Cut-Off + line-of-sightexp absp + gaussian @ 6.4 keV
All spectral parameters kept free for 2003dataset
Line centre and width frozen for 1997dataset
MECS and LECS data fitted in (1.8 – 10.0)keV & (0.3 – 4.5 ) keV
No high-energy cut-off for SAX
The soft excess at 0.1 keV was too faint
(0.8 – 1.5) : RXTE & (0.6 – 1.3) : SAX
LECS
MECS
RXTE-PCA
Spectral Parameters
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Spectral Parameters
(1.0 – 1.5), lack of any
binary phase modulation
Similarly forE
c: RXTE-PCA 14 keV
& Ef 7 keV
Slightly different from Ec 16
keV &E
f 10 keV : BeppoSAX (Robba et
al. 2001)
Fluorescent Fe--line fluxmeasured with the averagespectrum taken over 2 -- 3 ks
Does not show any considerable variation along the orbit
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Variation of Column Density with orbital phase
Column density : smooth variation over the orbitalphase
Model is consistent withobservations
2 HMXB pulsars showedsimilar increase in columndensity pattern near eclipse :
X1908+075 (Levine et al.2004) & SMC X-1 (Woo et al.
1995)
They may also have isotropic wind pattern from thecompanion stars
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4U 1538-52 has a moderate X-ray luminosity : 1036 erg s-1
No significant perturbation in the stellar wind acceleration
4U 1700-37 (Haberl et al. 1989), 4U 1907+09 (Robertset al. 2001) & GX 301-2 (Leahy 1991, Pravdo & Ghosh2001) :
a simple spherical wind is not sufficient to explain thecolumn density profile
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Conclusions for 4U 1538-52
Continuum X-ray spectrum is hardly affected by the NSrevolution
NH
shows a smooth variation over the orbital phase
A spherically symmetric stellar wind from the companion star mayproduce the observed orbital dependence of N
Hfor certain range of
the orbital inclination
Orbital phase resolved NH
measurements can be an
independent way to estimate the orbital inclination,especially for non-eclipsing binaries
GX 301 2 t ith l i d t t
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GX 301-2 : a system with clumpy wind structure
• Orbital period ~ 41.5 d
• Eccentricity ~ 0.46
• Distance ~ 5.3 kpc
• X-ray Luminosity ~ 1035--37 erg s-1
• Companion Star : B-type Supergiant (Parkes et al. 1980)
• Mass-loss Rate ~ (3-10) × 10-6 solar mass yr -1
• v
∞~ 400 km s-1
• Pulse Period ~ 680 s
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So, a large mass-loss rate & unusually low wind
velocity result in formation of clumped blobs of matter
Also, a large absorption column density is created
Thus, a variable luminosity & an eccentric orbit provide
a good site to probe the wind structure of the companion
A hi l RXTE Ob ti
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Archival RXTE Observations
Set I : from 1996-10-05 to 1996-15-06 :
17 data segments
did not cover 0.85 - 0.98 phases
useful obs duration : 34 ks
Set II : from 2000-12--10 to 2000-19-11 :
39 data segments
almost a full phase coverage
useful obs duration : 262 ks
Choice of the spectral model
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Choice of the spectral model
Her X-1 : Endo et al. (2000) : absorption had two components
One component absorbs the entire spectrum while the otherabsorbs it partially
Spectrum fitted : Partial Covering Absorption Model (PCAM)
PCAM : 2 different power laws with same photon index butdifferent normalisations & absorbed by different column densities
Endo et al. (2002) & Saraswat et al. (1996) : ASCA spectra of GX 301-2 with the PCAM + Fe K-alpha, K-beta emission lines and anFe absorption edge
The Chandra-HEG spectra of GX 301-2 was also fitted with the PCAM
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A broad compton back-scattered peak @ 6.3 keV (660 eV FWHM) in the Chandra spectrum (Mukherjee & Paul, 2003& Watanabe et al. 2003)
For RXTE, we used the model used by Endo et al. (2002) + ahigh energy exponential cut-off
The back-scattered peak was not included in the RXTEspectrum due to the moderate energy resolution
Chandra
Wavelength (Ang)
C o u n
t s
/ s / A
n g
6.3 keV
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RXTE Spectral Results
Almost all datasets : goodReduced between 0.6 and 1.6for 44 degrees of freedom (d.o.f.)
The fits with poor Reduced
showed wavy residuals with dips
around 10, 20 and 30 keV
Not Clear if it is a systematicphenomenon for this source
Systematic deviations at 20 &40 keV observed with Beppo-SAX also (Orlandini et al. 2000)
Poor
Good
The Continuum Parameters
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10 spectral parameters varied : NH1
NH2, , the 2 normalizations, the 2iron line intensities, edge depth, E
c
& Ef
5 kept frozen : the iron-lineenergies & their FWHM along with
the edge energy (at the values of Mukherjee & Paul 2003)
Photon Index
Cut-off Energy
e-folding energy
No remarkable change in thecontinuum parameters
Ec, E
f & are more or less
consistent with the previouslymeasured values (White et al.1983; Orlandini et al. 2000).
The Continuum Parameters
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Geometry of the GX 301-2/Wray 977 system (from Pravdo & Ghosh 2001)
Variation of the Column Densities
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Considerable increase in column density near periastron; but also a substantialscatter in the values at intermediatephases
NH1
NH2
Large variation throughout the binary orbit(from 1022 to 1024 H atoms cm-2) seems to beone of the characteristics of the X-rayspectrum of GX 301--2
The large variations of NH1 & NH2 at allorbital phases indicate clumpiness of thestellar wind at different size scales.
Peak between 0.1 and 0.2 was expected
since the line of sight passes through thedensest parts of the wind
Thus it is clear that the observed variationin column density cannot be explained by aspherically symmetric CAK wind only
Comparison with the Models
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2 models put forward to explain the NH
variation
Leahy (1991), from TENMA data, proposes a
spherically symmetric stellar wind + linear gasstream
The peak near periastron was fitted when thegas stream was introduced (see right, Leahy1991)
A gas stream can be due to the dynamicaleffect of the neutron star on the companionwind and the effect would be strongest atperiastron
Pravdo & Ghosh (2001), proposed the existence
of an equatorially enhanced circumstellar disk about Wray 977
The model describes two interactions of the NSwith the disk which gives rise to the two peaks inthe column density
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Model calculations are very different from the observed variation with the RXTE-PCA data
There are probably strong inhomogeneties in the wind thatare causing large fluctuations in the column densities
Almost throughout the binary orbit the Covering Fractionremains high
Indicates the presence of clumpy inhomogeneous material
A spherical wind plus + stream fitted the variation in columndensity for 4U 1907+09 (Roberts et al. 2001)
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Covering Fraction (CF)
defined as :
Norm2 / (Norm1+Norm2) ;
Norm1 and Norm2 arerespectively the normalizationsof the two power-laws
CF remains substantially high almost throughout theorbit which means thatthere is dense and clumpy material present throughout
Iron-line Flux & Equivalent Width
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2 iron lines show large increases in flux near periastron and a possible smallincrease near 0.1 (at least for 1996)
The peak near periastron (phase 0.9) is not very evident in the 1996 data due tothe lack of enough observations
Fluxes for both lines in the intermediate phases show a more or less steady value
EQW has a clear correlation with NH2
, with considerable scatter
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Makino et al. (1985) & Endo et al. (2002) have showedthat a correlation between N
H
& EQW exists in GX 301--2
Endo et al. (2002) discusses that the EQW increasesmonotonoically with the column density as long asthe fluorescing plasma is optically thin and fully surrounds the pulsar
The scatter seen in our correlation may be due to theclumpiness of the reprocessing material
For small values of the NH, the EQW is constant
This can happen if the fluorescing material does notsurround the pulsar completely
Conclusions for GX 301-2
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Conclusions for GX 301-2
PCAM describes the X-ray spectrum well throughout thebinary orbit
Column Densities measured are very high with a large variation indicating a clumpy nature of the stellar wind
Correlation of the Fe-line EQW with NH2
suggests that
most of the Fe-line is produced by the local clumpymatter
Both the models do not clearly explain our results
OAO 1657-415 & Vela X-1 : orbital phase dependentt
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spectroscopy
OAO 1657-415 Vela X-1 Orbital Period (d) : 10.44 8.96 Eclipse (d) : 1.7 2.0
eccentricity : 0.1 0.1
Distance (kpc) : 6.4 2.0
X-ray Luminosity (erg s-1) : 1037
Companion Star : B Supergiant B Supergiant
Pulse Period (s) : 38 283
Vela X-1 has fluctuations of luminosities to the order of 10%
These 2 comparable pulsars provide a good opportunity tostudy their stellar winds through spectral variability
Observations
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OAO 1657-415 :
RXTE archival data from1997-10-31 to 1997-11-11 :
26 obs On-source time : 1--18 ks
Fairly good coverage of theorbit
Most purposes, pulsar was inthe eclipsed state
Also, we have analysed theMECS obs on 2001-08-14 for104 ks
Vela X-1 :
RXTE archival data from 2005-01-01 to 2005-01-09 : 38 obs On-source time : 2--18 ks
PCU0 had lost the propane layer,hence we did not use its data inany further analysis
For a very high luminosity pulsarlike Vela~X-1, this is not a majorissue
The dataset does not provide acomprehensive orbital coverage,i.e. it lacks data for the 0.4--0.7
orbital phase duration
Spectral Models
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Quite similar to that used for GX 301-2
MECS spectrum of OAO 1657-415 best fitted withPCAM + 2 gaussian lines, at 6.5 keV (narrow) &@ 7.0 keV
Initial RXTE values of the parameters for theiteration : From MECS fit
Similarly for Vela X-1 : Same model + only one
gaussian line worked best
RXTE is a non--imaging instrument
& OAO 1657-415 under the Galactic ridgeemission
So, explicitly incorporate the ridge background asa separate spectral component : Raymond-Smithplasma + power-law with appropriatenormalizations (Valinia & Marshall 1998)
For the RXTE spectra : systematics to the tune of
1%
OAO 1657-415 Vela X-1
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Continuum
OAO 1657-415 Vela X-1
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C o v
e r i n
g
F r a c
t i o
n
C o v e r i n g
F r a c t
i o n
ColumnDensity
&
CoveringFraction
An Concl sions ??
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Any Conclusions ??
The PCAM model appears to be somewhat generic for pulsars which have variable column density, at least
when observed with RXTE/SAX
For highly luminous pulsars, the CAK Model of stellar wind does not suffice to describe the column density variations
Moderately luminous pulsars probably validate the
spherical wind model
The continuum parameters do not show any significant variation over the orbit
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Part II
U. Mukherjee & B. Paul 2005, A&A, 431, 667
Be/X-ray Binaries
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Courtesy : Negueruela
Circumstellat Disc
Formation not clear
Probably due to rapid rotation
Be stars : major subclass of the B stars
Be means a non-supergiant star of spectral class Bwhich shows emission lines
B stars : HeI absorption lines in optical spectrum
High Temp : He loses 1 e
He II Absorption lines : O stars : hottest of all stars
Accretion Barrier ?
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Be phenomenon is episodic transient
No outburst NS in quiescence
Low accretion rate : rm
> rc
Centrifugal Barrier exists
X-ray transients like 4U 0115+63 (Campana et al. 2001withBeppoSAX) &
GRO J1744-28 (Wijnands et al. 2002 with Chandra) in quiescencewith luminosities of 1033 erg s-1
Also been thought to be in the centrifugally inhibited regime
3A 0535+262 : Accretion and pulsations
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during quiescence
The transient pulsar :
Magnetic Field : 1013 G
Pulse Period : 104 s
Orbital Period : 111 days
Optical Companion : O9.7IIIe Be star
Orbital Geometry
3 obs with the Beppo-SAX on
2000 Sep 4 (5:14 UT) : A
Oct 5 (00:42 UT) : B &
2001 Mar 5 (22:52 UT) : C
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Distance of 2 kpc for this system (Steele et al. 1998)
The 2--10 keV X-ray luminosities measured from the threeobservations are in the range of (1.5-4.0) 1033 erg s-1,
We detected pulsations in C down to 2 1033 erg s-1
At this accretion rate the system is expected to be in the
centrifugally inhibited regime
Useful on-source times for A, B & C : 32 ks, 39 ks & 51 kseach for MECS and 19 ks, 30 ks & 43 ks for LECS
Data from only two of the MECS detectors were available
Timing Analysis
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MECS light curves with res : 1.0 s
Average Count Rate for A & B 0.04 count s-1
For C 0.09 count s-1
Only C showed coherent pulsations103.41 s
Another period : 101.57 s whenperiod search over a wider rangebetween (101--105) s
Long term pulse period history rulesout 101.57 s
Probably arose due to the windowfunction of the light curve
Extracted 5 separate light-curves each
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with data only with avg count rate lessthan 0.15 , 0.125 , 0.1 count s-1, 0.08 &0.06 count s-1 respectively
Detection of pulsations down to anaverage count rate of less than0.08 count s-1
But pulse profile for 0.06 count s-1 showspulsations (last panel)
Pulse profiles are background subtracted
Pulse Fraction = [(Maximum - Minimum)/Maximum] 50%
Thus it is fair to conclude that pulsationsexist for C down to at least a count rate of 0.06 count s-1
Spectral Analysis
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Spectra fitted with PL or BB + exp. line of sight absp
BB does not fit A, B or C : red > 2.0
PL + exp. line of sight absp fits A, B well but not C
PL + BB + exp. line of sight absp fits C well
BB temp : 1.33 keV
Radius of BB 0.1 km
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The BB component !!
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Quite different from the soft excess usually observed in some binary X-raypulsars (Yokogawa et al. 2000, Paul et al. 2002)
In general modeled as a BB with temp 0.1 keV and the area of theemitting region 1015 -16 sq. cm.
Hickox, Narayan and Kallman (2004) have exploredthe physical origin of this so called “soft excess”
For sources with luminosity < 1036 erg s-1, it may be due to emission byphotoionized or collisionally heated diffuse gas, or thermal emission fromthe surface of the NS
This soft BB comp resembles that of 4U 0352+309 (Coburn et al. 2001)
& RX J0146.9+6121by Palombara & Mereghetti (2006)
This BB comp. has been attributed to polar cap emission
Conclusions
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For all the 3 obs, A, B & C : accretion is expected to becentrifugally inhibited
Detection of pulsations in C at these low flux levels indicatesthat some matter may have leaked through onto the NS
surface
When the emission is non-pulsating, the X-ray spectrum isPL type
Origin of an additional BB component in the pulsedobservation is not very clear though it seems to be essentialin fitting the spectra
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Part III
U. Mukherjee & B. Paul, 2006c
U. Mukherjee & B. Paul, 2006, J. Astrophys. Astr., 27, 37
B. Paul, H. Raichur & U. Mukherjee,2005, A&A, 442, L15
Centaurus X-3 : Any reason behind the high-low states ?
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Detailed spectral analysis of the out of eclipse obs
with ASCA, BeppoSAX, Chandra, XMM-Newton & RXTE
in its different intensity states
High & low states have separate domains of
From RXTE : NH
has a ceiling in the high states
Low states have high EQW
Compare our results with that of LMC X-4 & Her X-1
Properties of Cen X-3
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Ps 4.8 s
Porb
2.1 d
D 8 kpc (Krzeminski 1974).
O-type supergiant V779 Cen Companion (Krzeminski 1974).
V779 Cen radius of 12 R S
& M 17-19 MS(Hutchings et al.
1979).
QPOs at 40 mHz (Takeshima et al. 1991; Audley et al. 1996)strengthen the case for the presence of an accretion disk
Broadband (0.12-100) keV out-of-eclipse pulse-phase-
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Broadband (0.12 100) keV out of eclipse pulse phaseavg spec generally described by :
an abs PL + a broad Fe emission line @ 6.7 keV +cut-off @ 14 keV (Santangelo et al. 1998, Burderi etal. 2000)
Soft excess < 1 keV : BB with kT 0.1 keV (Burderi et al. 2000)
Cyclotron resonant feature @ 28 keV
B (2.4-3.0) 1012 G (Santangelo et al. 1998)
1.5 – 3.0 keV
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RXTE-ASM in different energy bands shows that Cen X-3 has aflux 40 times more in the bursting state as compared to the lowstate (Paul, Raichur & Mukherjee 2005)
Also, the low and high states last between a few to upto 110 dwithout having any periodicity
3.0 – 5.0 keV
5.0 – 12.0 keV
Not only Cen X 3 but several other X ray
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Not only Cen X-3, but several other X-rayPulsars show long term X-ray intensity
modulations
Her X-1 & LMC X-4 show periodic X-ray
intensity variations, modulated at theirsuperorbital periods
Cen X-3 does not possess any such periodicbehaviour at all
There are complex X-ray spectral changesassociated with the intensity modulations at the
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associated with the intensity modulations at thesuperorbital periods of Her X-1 & LMC X-4
(Naik & Paul 2003, 2004)
Broad band X-ray spectrum of Cen X-3 is more or
less similar to these pulsars
It is pertinent to explore the spectral changes of
this pulsar corresponding to its different intensity states
Observations
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80 obs with RXTE from 1996 to 2000 covering the various
intensity states
2 obs. With BeppoSAX on 1999-06-24 (High) & 2000-06-06(Low)
XMM-Newton observed Cen X-3 on 2002-08-01 in the Low state
The obs with ASCA was on 1993-06-24 (Low)
With Chandra on 2000-12-30 (High)
All the observations were chosen in the out-of-eclipse state
Observation Log
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Continuum fitted with line of sight absp. + PL + a cut-off
In addition, a cyclotron absorption feature was also added
Fe-emission lines @ 6.4 keV, 6.67 keV and 6.95 keV were also included in the form of gaussian lines
The centre energies were fixed to the laboratory values and thewidths of the gaussian lines were fixed to that obtained with theXMM-Newton PN spectra respectively
All the other parameters were allowed to vary
A systematic uncertainty of 1.0% was added to the spectralchannels
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For flux < 6.0 10-10 erg cm-2 s-1, thereseems to be a correlation between theCont. Flux &
The spectrum becomes harder at lowerflux levels
At a flux level > 2 10-9 erg cm-2 s-1,0.8 < < 1.3
Chandra (H)
SAX (H)
SAX (L)
ASCA (L)
XMM (L)
Naik & Paul (2003) have reported fromRXTE th t LMC X 4 i d ib d i th
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RXTE that LMC X-4 is described in the
High state with 0.7 < <1.0 & Low state with < <
Thus for both these pulsars, a separate
range of values of may be designatedfor the low and high flux statesrespectively
Variation of NH
shows a few instances of high
to moderate values at low flux levels
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For higher flux levels (> 2 10-9 erg cm-2 s-1),
there seems to be a ceiling of 4 1022 cm-2
For both there appears to be a lot of
scatter in their values as obtained with thePCA for intermediate flux levels
ASCA (L)SAX (L)
XMM (L) SAX (H)Chandra (H)
Variation of NH
does not quite pesent a very
conspicuous picture either
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co sp cuous p ctu e e t e
Her X-1 shows an increase in NH
by almost 2
orders of magnitude in its low state comparedto its high state over its 35-d superorbitalperiod (Naik & Paul 2003)
On the other hand, LMC X-4 does not show anychange in N
Halong its superorbital period
(Lang et al. 1998)
Hence we find that Cen X-3 shows resultswhich are in between these two extremes
Fe-line fluxes against (7 - 25)keV PCA Flux does not showany systematic trend (see figureright)
SAX (H)
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Large & considerable scatter atall flux levels for all the 3 lineintensities
EQW of the Fe-lines show a
reasonable trend (bottom panel,right)
For low fluxes, the values of EQW are quite high (a fewhundred eVs, especially for
Fe-K )
Then decreasing to acquire amore or less steady value of 100 eV for higher fluxes(> 6 10-9 erg cm-2 s-1)
ASCA
( )
SAX (L)
Chandra
XMM
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LMC X-4 Her X-1
Naik & Paul, 2003
A similar variation of the EQW with continuum flux was seen in case of LMC X-4 & Her X-1
All the 3 sources show very high values of the EQW in the lowstates whereas during the high states, no significant change is seen
Unlike LMC X-4 & Her X-1, Cen X-3 does not show anyglobal dependence of the iron-line intensities with thecontin m fl
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continuum flux
Low states : it may seem Fe-line intensity has somepositive correlation with the continuum intensity, but
High states : no such dependence
LMC X-4 & Her X-1 : a clear correlation between thefluxes at high states, indicating the production of theiron line near the continuum X-ray source
Picture for Cen X-3 is far more intricate & itsuggests that not all the Fe-line is produced closeto the pulsar
Inference
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Our work attempts to compare the X-ray
observational results for Cen X-3 in both its highand low states with that of Her X-1 & LMC X-4
It is more or less established that Her X-1 &LMC X-4 have an warped accretion disk which isbelieved to be accounting for their flux behaviour
However spectral results obtained by us are notfully in corroboration with that measured for thethe other 2 pulsars
Hence, based on these results it seems difficult toput forward the same reasoning for the flux
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behaviour in case of Cen X-3 as for the other two
Obscuration in the low states is present for
Cen X-3 (cases of high NH)
But that is not the only criterion to unequivocallyattribute the presence of high/low states to thewarped accretion disk
Ogilvie and Dubus (2001) : LMC X-4 & Her X-1 are 2possible candidates to show a super periodicity while
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possible candidates to show a super-periodicity whileCen X-3 is unlikely to exhibit such
Numerical simulations of the evolution of theprecessing accretion disks in XBPs :
Iping & Petterson (1990) propose for Cen X-3
a precessing accretion disk could describe a partof its aperiodic X-ray flux variability
Day & Stevens (1993), based on EXOSAT data :
th t l t tt f di k
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the central source accretes matter from a disk
which is fed by an X-ray excited wind emanatingfrom the companion
Scope for further theoretical and observationalwork in this direction remains open
Especially extensive orbital coverage at lower
energies with detectors of the genre of Chandra& XMM-Newton as well as a detailed broad bandcoverage
BeppoSAX
Model : PL + BB + a gaussian line
High
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Model : PL + BB + a gaussian lineas additive comp. & an abs along
the line of sight as the multipl.comp.
Both the high and low state spectrawere well fitted
A broad Fe-emission line @6.65 keV
Presumably the blend of theHe-like triplet of Fe XXV
EQW (High) : 877 eV
EQW (Low) : 116 eV
Low
Model as used by
ASCA
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Model as used byBurderi et al. (2000)
Fixed both the 6.44keV and 6.96 keV lines along with theirwidths as given in
Burderi et al. (2000) Red. : 1.47 for267 d.o.f.
2.0 keV Si XIV emission line
Low
Iaria et al. (2005) have
Chandra
Hi h
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analyzed the Chandra-HEG
spectrum in the (6.0 - 7.6)keV & resolved the Fe XXV triplet
We used only the first ordergrating spectra
The zero-order source position determined by examining the HEG/MEGdispersion lines & the data read out streak of the zeroth-order image
We used the same model as of Iaria et al. (2005) but allowed the cont.
params to vary
We froze the centre energies of the triplet and their respective widthsthough we kept the params of the Fe K line thawed
High
XMM-Newton
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The 100 s binned PN-light curve
showed a broad coverage of eclipse,egress and out of eclipse for about 68 ks.
Avg PN count rate was 15 counts s-1
For our spectral analysis, weselected out-of-eclipse dataonly (34 ks onwards)
Out of eclipse
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Si XIV
S XVI Ar XVII+
Ar XVIII
Fe XXVI
Ca XX
Continuum Parameters
(*ASCA (L) & **SAX (H) : from Burderi et al. (2000))
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4U 0114+65 : a luminosity dependentstudy
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Spectral characteristics of the high and low statesof the pulsar 4U 0114+65 with ASCA
Examine the change in the parameters of thespectral model
Compare these spectral characteristics to theresults with other satellites
And with other X-ray pulsars ..........
About the Pulsar ..........
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B1Ia supergiant optical companion
At a distance 7 kpc (Reig et al. 1996)
Crampton, Hutchings & Cowley (1985) reported anOrb Period 11.59 d (optical radial velocity measurements)
Their measurements were not able to distinguish between acircular or elliptical orbit
Corbet et al. (1999) obtained X-ray intensity modulations at aperiod 11.63 d from the long term light curve of RXTE-ASM
X-ray light curve : considerable variability,flaring activity for a few hours (Apparao et al. 1991,Finley et al. 1992)
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Also short-term flickering for minutes (Koenigsbergeret al. 1983)
Presence of a 2.8 hr periodicity observed in the X-ray
light curves from EXOSAT and ROSAT data (Finley et al.1992)
Farrell et al. (2005) reported the detection of a
superorbital period of 30.7 d in this pulsar fromRXTE-ASM
Observations
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Carried out by ASCA on 1997-02-10
Orbital phase0.19
Useful exposure time 25 ks
Total time span between start & end was55 ks (about 5.5% of the orbital period)
GIS : 0.7 – 10.0 keV
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The intensity at the peak of the flare is 12-15 times than the
persistent low level emission
At times, the intensity almost drops down to zero (@ 22 & 32 ks)
High state : 0-18 ks & rest : low state
SIS : 0.5 – 9.0 keV
Bin : 100 s
High
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Low
Most significant difference between thehigh & low state spectra is a change inthe Fe-line flux by a factor similar to thechange in the continuum
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NH
corroborates well with that of RXTE & Ginga
But SAX measures a high NH
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Masetti et al. (2005) reported for (1.5-100.0) keV whereas,we are able to go down to 0.5 keV
Fe emission line @ 6.4 keV was reported with SAX, RXTE,EXOSAT & Ginga
But the line was better detected during the low states
We report the detection of the Fe-line in both the stateswith appreciable EQWs (Table 2)
ASCA has the best spectral resolution in comparison,so the detectability of the Fe line can be supposed tobe most reliable
EQW of the Fe-line is found to increase appreciably in the low
Summarising...........
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EQW of the Fe line is found to increase appreciably in the low
states of several other pulsars like Her X-1 (Naik & Paul 2003),LMC X-4 (Naik & Paul 2004) & SMC X-1 (Vrtilek et al. 2005)
High & low states of these pulsars are ascribed to the super-orbitalperiod precessing warped inner accretion disk
For 4U 0114+65, an abrupt decrease in X-ray flux over a fewthousand secs cannot be assigned to a super-orbital period
Rather, change in lum during our obs may be ascribed to a localchange in the density of the stellar wind
Rise & fall times of 1-2 ks as can be seen in the light curve
An assumed orbital velocity of a few hundred km/s indicatesclumpiness of the stellar wind at a length scale of about 1010-11 cm
Future Work ?!???!!
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Binary Millisecond X-ray Pulsars
Techniques used for HMXBPs can be directly appliede.g. compare the characteristics of 3A 0535+262, to theobservations of BMXPs in quiescence
Furthermore, observations in the optical and IR will be
useful
Pulse Phase Resolved Spectroscopy of