J/ApJ/738/128 RXTE observations of 4U 1728-34 (Seifina+, 2011)
On the constancy of the photon index of X-ray spectra of 4U 1728-34 through all
spectral states.
Seifina E., Titarchuk L.
<Astrophys. J., 738, 128 (2011)>
=2011ApJ...738..128S 2011ApJ...738..128S
ADC_Keywords: Binaries, X-ray ; Equivalent widths
Keywords: accretion, accretion disks - black hole physics - stars: neutron -
radiation mechanisms: non-thermal - stars: individual (4U 1728-34)
Abstract:
We present an analysis of the spectral properties observed in X-rays
from neutron star X-ray binary 4U 1728-34 during transitions between
the low- and high-luminosity states when the electron temperature
kTe of the Compton cloud monotonically decreases from 15 to 2.5keV.
We analyze the transition episodes from this source observed with
BeppoSAX and RXTE satellites. We find that the X-ray broadband energy
spectra of 4U 1728-34 during all spectral states can be modeled by a
combination of a thermal (blackbody-like) component, a Comptonized
component (which we herein denote as COMPTB), and a Gaussian
component. Spectral analysis using this model provides evidence that
the photon power-law index Γ is almost constant
(Γ=1.99±0.02) when kTe changes from 15 to 2.5keV during
these spectral transitions.
Description:
We analyzed the available data obtained with RXTE (Rossi X-ray timing
explorer; Bradt et al. 1993A&AS...97..355B 1993A&AS...97..355B), which were found in the
time period from 1996 February to 2000 July (see also the review by
Galloway et al. 2008, Cat. J/ApJS/179/360). In our investigation we
selected 127 observations made at different count rates (luminosity
states) with a good coverage of rise-decay flare track. We performed
an analysis of RXTE observations of 4U 1728-34 during four years for
eight intervals.
Objects:
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RA (2000) DE Designation(s)
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17 31 57.73 -33 50 02.5 4U 1728-34 = NAME SLOW BURSTER
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table4.dat 139 127 *Best-fit parameters of the spectral analysis of
PCA & HEXTE/RXTE observations of 4U 1728-34 in
the 3-60keV energy range
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Note on table4.dat: The spectral model is wabs*(blackbody+COMPTB+Gaussian),
where NH is fixed at a value 2.73x1022/cm2 (Piraino et al.
2000A&A...360L..35P 2000A&A...360L..35P); color temperatures Ts and TBB are fixed at
1.3 and 0.7keV, respectively (see comments in the text).
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See also:
B/cb : Cataclysmic Binaries, LMXBs, and related objects (Ritter+, 2013)
J/A+A/545/A27 : INTEGRAL/IBIS Galactic Hard X-Ray Survey (Krivonos+, 2012)
J/ApJ/714/1424 : Isolated neutron stars from Rosat and Swift (Turner+, 2010)
J/A+A/523/A61 : INTEGRAL survey of hard X-ray sources (Krivonos+, 2010)
J/A+A/522/A68 : Variable sources detected by INTEGRAL (Telezhinsky+, 2010)
J/ApJS/179/360 : Thermonuclear X-ray bursts observed by RXTE (Galloway+, 2008)
J/A+A/467/585 : Sources detected by ISGRI (Bodaghee+, 2007)
J/A+A/469/807 : Catalogue of Galactic low-mass X-ray binaries (Liu+, 2007)
J/A+A/458/21 : INTEGRAL burst observations of 4U 1728-34 (Falanga+, 2006)
Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 15 A15 --- ObsID Observational identification
17- 25 F9.3 d MJD [50128/51734] Start time (Modified Julian Date)
27- 31 I5 s Exp Exposure time
33- 38 F6.1 ct/s Rate Count rate, background corrected (1)
40- 44 F5.3 --- alpha Energy index of the Comptonization spectrum
α=Γ-1
46- 50 F5.3 --- e_alpha alpha uncertainty
52- 56 F5.2 keV Te Electron temperature
58- 61 F4.2 keV e_Te Te uncertainty
63- 66 F4.2 [-] logA COMPTB parameter log(A)
67 A1 --- f_logA [b] logA fixed (2)
69- 72 F4.2 [-] e_logA ? logA uncertainty
74- 77 F4.2 --- Ncomp Normalization of the seed photon spectrum
NCOMPTB (3)
79- 82 F4.2 --- e_Ncomp Ncompt uncertainty
84- 87 F4.2 --- Nbb Normalization of the blackbody component
NBB (3)
89- 92 F4.2 --- e_Nbb Nbb uncertainty
94- 97 F4.2 keV Eline Centroid line energy
99-102 F4.2 keV e_Eline Eline uncertainty
104-107 F4.2 --- Nline Normalization Nline to fit the data in the
6-8keV range (3)
109-112 F4.2 --- e_Nline Nline uncertainty
114-116 I3 eV EW Equivalent width of iron line EWline
118-119 I2 eV e_EW EW uncertainty
121-124 F4.2 --- chi2 χ2 fit
126-129 F4.2 --- e_chi2 chi2 uncertainty
131-134 F4.2 pW/m2 F1 Spectral flux for 3-10keV energy range (4)
136-139 F4.2 pW/m2 F2 Spectral flux for 10-60keV energy range (4)
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Note (1): The count rate corresponds to 5PCA units and corrected for background.
Note (2):
b = When parameter log(A)≫1, it is fixed at 1.0, because in any case of
log(A)≫1 a Comptonization fraction f=A/(1+A) is approximately 1 and
variations of A≫1 do not further improve the fit quality. See section 3.
Note (3): Normalization parameters of blackbody and COMPTB components are
in units of L37/d210erg-1/s/kpc2, where L37 is the source
luminosity in units of 1037erg/s (1030W), d10 is the distance to
the source in units of 10kpc, and the Gaussian component is in units
of 10-2xtotal photons/cm2/s in line.
Note (4): Spectral fluxes (F1/F2) in units of x10-9ergs/s/cm2 for
(3-10) and (10-60) keV energy ranges, respectively.
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History:
From electronic version of the journal
(End) Emmanuelle Perret [CDS] 24-May-2013