J/ApJ/853/150 Spectral analysis of low-mass X-ray binaries (Sonbas+, 2018)
A Study of low-mass X-ray binaries in the low-luminosity regime.
Sonbas E., Dhuga K.S., Gogus E.
<Astrophys. J., 853, 150 (2018)>
=2018ApJ...853..150S 2018ApJ...853..150S
ADC_Keywords: Binaries, X-ray; Black holes; Stars, neutron; X-ray sources
Keywords: methods: data analysis; stars: black holes; stars: neutron;
X-rays: binaries
Abstract:
A recent study of a small sample of X-ray binaries (XRBs) suggests a
significant softening of spectra of neutron star (NS) binaries as
compared to black hole (BH) binaries in the luminosity range
1034-1037erg/s. This softening is quantified as an anticorrelation
between the spectral index and the 0.5-10keV X-ray luminosity. We
extend the study to significantly lower luminosities (i.e., ∼a few
x1030erg/s) for a larger sample of XRBs. We find evidence for a
significant anticorrelation between the spectral index and the
luminosity for a group of NS binaries in the luminosity range
1032-1033erg/s. Our analysis suggests a steep slope for the
correlation i.e., -2.12±0.63. In contrast, BH binaries do not
exhibit the same behavior. We examine the possible dichotomy between
NS and BH binaries in terms of a Comptonization model that assumes a
feedback mechanism between an optically thin hot corona and an
optically thick cool source of soft photons. We gauge the NS-BH
dichotomy by comparing the extracted corona temperatures, Compton-y
parameters, and the Comptonization amplification factors: the mean
temperature of the NS group is found to be significantly lower than
the equivalent temperature for the BH group. The extracted Compton-y
parameters and the amplification factors follow the theoretically
predicted relation with the spectral index.
Description:
We started with an initial sample of 52 low-mass X-ray binaries
(LMXBs) for which there were either Chandra or XMM-Newton
observations. The majority of these systems (23 black holes (BHs) and
23 neutron star (NS) respectively) are transient, low-to-moderate
accreting sources. The sample also included two microquasars and four
LMXBs with an uncertain nature. Of these, we identified 40 sources
with distance information so that we could establish a luminosity
scale. As a preliminary step, we extracted spectra for all these
systems in order to identify sources with reasonable signal-to-noise
ratios and sufficient counts in the 0.5-10keV energy band to allow for
further detailed spectral analysis. Our final sample consists of 27
LMXBs (15 BH and 12 NS binaries respectively) for which we present a
detailed spectral analysis. The entire data sets are taken from the
Chandra and XMM-Newton archives.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 109 104 Total number of observations analyzed for the sample
of low-mass X-ray binaries (LMXBs)
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See also:
B/chandra : The Chandra Archive Log (CXC, 1999-2014)
B/xmm : XMM-Newton Obs. Log (XMM-Newton Science Operation Center, 2012)
J/ApJ/376/161 : X-ray spectra of bursting neutron stars (Madej+, 1991)
J/ApJ/719/L79 : BH spin-orbit misalignment in Galactic XRBs (Fragos+, 2010)
J/ApJ/800/17 : Mass-transfer sequences in 16 Galactic LMXBs (Fragos+, 2015)
J/A+A/587/A61 : BlackCAT, stellar-mass BHs. (Corral-Santana+, 2016)
J/ApJS/222/15 : WATCHDOG: Galactic BHXBs all-sky database (Tetarenko+, 2016)
J/A+A/606/A130 : List of 1254 X-ray bursts (in't Zand+, 2017)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 2 A2 --- Type Binary type (BH=Black hole or NH=Neutron star)
4- 22 A19 --- Name Name of the source
24- 34 I11 --- ObsID [95/744870201] ObsID number
36 A1 --- f_ObsID [CX] Facility flag of the ObsID
(X=XMM or C=Chandra)
38- 44 F7.3 ks Exp [2.5/138.5] Exposure time
46- 50 F5.3 cm-2 GalNH [0.01/1.8] Galactic extinction
52- 57 F6.3 cm-2 IntNH [0.01/11.6]? Intrinsic extinction
59- 64 F6.3 cm-2 e_IntNH [0.001/1]? Error in IntNH
66- 73 E8.2 10-7W Lum [2.5e+30/1.7e+37] Source 0.5-10 keV luminosity
in erg/s units
75- 81 E7.2 10-7W e_Lum [5e+29/8e+35] Error in Lum
83- 86 F4.2 --- SpInd [0.3/5.8] Spectral index
88- 91 F4.2 --- e_SpInd [0.01/1] Error in SpIndex
93- 97 F5.2 keV Tin/kTbb [0.1/4.0]? Temperature
99-103 F5.2 keV e_Tin/kTbb [0.01/0.2]? Error in Tin/kTbb
105-109 F5.3 --- chi2 [0.4/2.8] Model χ2 fit
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 31-Oct-2018