High-mass X-ray binaries in the Milky Way

Walter, R.; Lutovinov, A.; Bozzo, E.; Tsygankov, Sergey S.

doi:10.1007/s00159-015-0082-6

Cited by 228 publications

(237 citation statements)

References 511 publications

(599 reference statements)

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“…The cut-off of the power-law at high energies is usually measurable only when a broad-band spectrum extending up to 20-30 keV is available (see, e.g., Walter et al 2015, and references therein). The 1-10 keV X-ray flux was measured by using the pegpow model in xspec, in order to have values not dependent from the largely variable absorption column densities and the uncertainties that arise when the spectra are de-absorbed after the fit in xspec.…”

Section: Xmm-newton Data Reduction and Analysismentioning

confidence: 99%

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The accretion environment of supergiant fast X-ray transients probed withXMM-Newton

Bozzo

Bernardini²,

Ferrigno

et al. 2017

A&A

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Context. Supergiant fast X-ray transients are a peculiar class of supergiant X-ray binaries characterized by a remarkable variability in the X-ray domain, widely ascribed to the accretion from a clumpy stellar wind. Aims. In this paper we performed a systematic and homogeneous analysis of the sufficiently bright X-ray flares observed with XMMNewton from the supergiant fast X-ray transients to probe spectral variations on timescales as short as a few hundred of seconds. Our ultimate goal is to investigate if SFXT flares and outbursts are triggered by the presence of clumps and eventually reveal whether strongly or mildly dense clumps are required. Methods. For all sources, we employ a technique developed by our group already exploited in a number of our previous papers, making use of an adaptive rebinned hardness ratio to optimally select the time intervals for the spectral extraction. A total of twelve observations performed in the direction of five SFXTs are reported, providing the largest sample of events available so far. Results. Using the original results reported here and those obtained with our technique from the analysis of two previously published XMM-Newton observations of IGR J17544-2619 and IGR J18410-0535, we show that both strongly and mildly dense clumps can trigger these events. In the former case, the local absorption column density may increase by a factor of ≫3, while in the latter case, the increase is only by a factor ∼2-3 (or lower). An increase in the absorption column density is generally recorded during the rise of the flares/outbursts, while a drop follows when the source achieves the peak flux. In a few cases, a re-increase of the absorption column density after the flare is also detected, and we discovered one absorption event related to the passage of an unaccreted clump in front of the compact object. Overall, there seems to be no obvious correlation between the dynamic ranges in the X-ray fluxes and absorption column densities in supergiant fast X-ray transients, with an indication that lower densities are recorded at the highest fluxes. Conclusions. The spectral variations measured in all sources are in agreement with the idea that the flares/outbursts are triggered by the presence of dense structures in the wind interacting with the X-rays from the compact object (leading to photoionization). The lack of correlation between the dynamic ranges in the X-ray fluxes and absorption column densities can be explained by the presence of accretion inhibition mechanism(s). Based on the knowledge acquired so far on the SFXTs, we propose a classification of the flares/outbursts from these sources to drive future observational investigations. We suggest that the difference between the classes of flares/outbursts is related to the fact that the mechanism(s) inhibiting accretion can be overcome more easily in some sources compared to others. We also investigate the possibility that different stellar wind structures, rather than clumps, could provide the means to temporarily overcome the...

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Section: Xmm-newton Data Reduction and Analysismentioning

confidence: 99%

“…The largest dynamic range in luminosity recorded so far is that of the SFXT prototype IGR J17544-2619, reaching a factor of ∼10 6 . For comparison, the classical SgXBs display a typical dynamic range of 100 (Walter et al 2015).…”

Section: Introductionmentioning

confidence: 99%

The accretion environment of supergiant fast X-ray transients probed withXMM-Newton

Bozzo

Bernardini²,

Ferrigno

et al. 2017

A&A

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“…Systems with persistently high X-ray luminosities (above 10 35 erg s −1 ) are produced when the radius of the donor star fills its Roche lobe, and mass transfer to the compact object becomes dominated by the tidal stream between the two components (e.g., Roche lobe overflow, RLOF). Although these sources can achieve luminosities up to ∼10 40 erg s −1 , lower luminosities of a few 10 36 erg s −1 are frequently observed in Galactic sources (e.g., Vela X-1; see Walter et al 2015, and references therein) and in SMC pulsar-HMXBs (Laycock et al 2010). However, most XRBs in the Milky Way and SMC produce very low X-ray luminosities (∼10 33 erg s −1 ).…”

Section: Model Ii: Agn + Persistent Xrbs + Variablementioning

confidence: 99%

The Effect of Variability on X-Ray Binary Luminosity Functions: Multiple-Epoch Observations of NGC 300 With Chandra

Binder

Gross

Williams

et al. 2017

ApJ

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We have obtained three epochs of Chandra ACIS-I observations (totaling ∼184 ks) of the nearby spiral galaxy NGC 300 to study the logN -logS distributions of its X-ray point source population down to ∼2×10 −15 erg s −1 cm −2 in the 0.35-8 keV band (equivalent to ∼10 36 erg s −1 ). The individual epoch logN -logS distributions are best described as the sum of a background AGN component, a simple power law, and a broken power law, with the shape of the logN -logS distributions sometimes varying between observations. The simple power law and AGN components produce a good fit for "persistent" sources (i.e., with fluxes that remain constant within a factor of ∼2). The differential power law index of ∼1.2 and high fluxes suggest that the persistent sources intrinsic to NGC 300 are dominated by Roche lobe overflowing low mass X-ray binaries. The variable X-ray sources are described by a broken power law, with a faint-end power law index of ∼1.7, a bright-end index of ∼2.8-4.9, and a break flux of ∼8×10 −15 erg s −1 cm −2 (∼4×10 36 erg s −1 ), suggesting they are mostly outbursting, wind-fed high mass X-ray binaries, although the logN -logS distribution of variable sources likely also contains low-mass X-ray binaries. We generate model logN -logS distributions for synthetic X-ray binaries and constrain the distribution of maximum X-ray fluxes attained during outburst. Our observations suggest that the majority of outbursting X-ray binaries occur at sub-Eddington luminosities, where mass transfer likely occurs through direct wind accretion at ∼1-3% of the Eddington rate.

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“…SFXTs are associated with early-type supergiants, making them a subclass of HMXBs. Their X-ray properties were quickly recognized as a challenge to the accretion models: apparently, SFXTs share similar properties (donor spectral type, orbital geometry, neutron star spin periods) to classical persistent HMXBs hosting supergiant stars, except for their extremely variable X-ray behaviour (see, e.g., Sidoli 2013;Walter et al 2015).…”

Section: Introductionmentioning

confidence: 99%

XMM-Newton and NuSTAR Simultaneous X-Ray Observations of IGR J11215-5952

Sidoli

Tiengo

Paizis

et al. 2017

ApJ

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We report the results of an XMM-Newton and NuSTAR coordinated observation of the Supergiant Fast Xray Transient (SFXT) IGR J11215-5952, performed on February 14, 2016, during the expected peak of its brief outburst, which repeats every ∼165 days. Timing and spectral analysis were performed simultaneously in the energy band 0.4-78 keV. A spin period of 187.0 (±0.4) s was measured, consistent with previous observations performed in 2007. The X-ray intensity shows a large variability (more than one order of magnitude) on timescales longer than the spin period, with several luminous X-ray flares which repeat every 2-2.5 ks, some of which simultaneously observed by both satellites. The broad-band (0.4-78 keV) time-averaged spectrum was well deconvolved with a double-component model (a blackbody plus a power-law with a high energy cutoff) together with a weak iron line in emission at 6.4 keV (equivalent width, EW, of 40±10 eV). Alternatively, a partial covering model also resulted in an adequate description of the data. The source time-averaged X-ray luminosity was 10 36 erg s −1 (0.1-100 keV; assuming 7 kpc). We discuss the results of these observations in the framework of the different models proposed to explain SFXTs, supporting a quasi-spherical settling accretion regime, although alternative possibilities (e.g. centrifugal barrier) cannot be ruled out.

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High-mass X-ray binaries in the Milky Way

Cited by 228 publications

References 511 publications

The accretion environment of supergiant fast X-ray transients probed withXMM-Newton

The accretion environment of supergiant fast X-ray transients probed withXMM-Newton

The Effect of Variability on X-Ray Binary Luminosity Functions: Multiple-Epoch Observations of NGC 300 With Chandra

XMM-Newton and NuSTAR Simultaneous X-Ray Observations of IGR J11215-5952

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