Expected number of supergiant fast X-ray transients in the Milky Way

Ducci, L.; Doroshenko, V.; Romano, P.; Santangelo, A.; Sasaki, M.

doi:10.1051/0004-6361/201424215

Cited by 15 publications

(16 citation statements)

References 52 publications

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“…These types of outbursts are frequently observed in supergiant HMXBs (see Reig 2008;Ducci et al 2014, and references therein), and the so-called supergiant fast X-ray transient (SFXT, Negueruela et al 2008) events are shorter X-ray flares that occur as part of much longer outburst events, which can last several days (Sidoli et al 2008;Romano et al 2011Romano et al , 2014a. The mechanism by which Type II outbursts and SFXT flares are produced is not certain, although eruptions from the donor star or changes in the stellar wind properties may contribute to the observed Xray variability (Ducci et al 2014, and references therein). LMXBs also exhibit strong X-ray variability, which is frequently accompanied by spectral changes that are driven by the structure of the inner accretion disk (Lewin et al 1997;Maccarone 2003;Asai et al 2012).…”

Section: Model Ii: Agn + Persistent Xrbs + Variablementioning

confidence: 93%

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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Section: Model Ii: Agn + Persistent Xrbs + Variablementioning

confidence: 93%

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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“…There may be a significant population of these sources in the Magellanic Clouds that have yet to be discovered. For example, Ducci et al (2014) estimate the number of Galactic SFXTs at 37 +53 −22 , suggesting that the SFXTs constitute a large subclass of XRBs with supergiant companions.…”

Section: Introductionmentioning

confidence: 99%

Star formation history and X-ray binary populations: the case of the Large Magellanic Cloud

Antoniou

Zezas

2016

Mon. Not. R. Astron. Soc.

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In the present work we investigate the link between high-mass X-ray binaries (HMXBs) and star formation in the Large Magellanic Cloud (LMC), our nearest star-forming galaxy. Using optical photometric data, we identify the most likely counterpart of 44 X-ray sources. Among the 40 HMXBs classified in this work, we find 33 Be/X-ray binaries, and 4 supergiant XRBs. Using this census and the published spatially resolved star-formation history map of the LMC, we find that the HMXBs (and as expected the X-ray pulsars) are present in regions with starformation bursts ∼6-25 Myr ago, in contrast to the Small Magellanic Cloud (SMC), for which this population peaks at later ages (∼25-60 Myr ago). We also estimate the HMXB production rate to be equal to 1 system per ∼ 43.5 × 10 −3 M yr −1 or 1 system per ∼143 M of stars formed during the associated star-formation episode. Therefore, the formation efficiency of HMXBs in the LMC is ∼17 times lower than that in the SMC. We attribute this difference primarily in the different ages and metallicity of the HMXB populations in the two galaxies. We also set limits on the kicks imparted on the neutron star during the supernova explosion. We find that the time elapsed since the supernova kick is ∼3 times shorter in the LMC than the SMC. This in combination with the average offsets of the HMXBs from their nearest star clusters results in ∼4 times faster transverse velocities for HMXBs in the LMC than in the SMC.

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“…In the latter case, both the accretion torque and the equilibrium spin period deviate from those in the traditional spherical wind accretion model. This subsonic accretion model has been applied to account for the observational characteristics of some long-spin period X-ray pulsars including GX 1+4 (González-Galán et al 2012), 4U 1954+31 (Martin et al 2011), SXP 1062(Popov & Turolla 2012, X Per (Lutovinov et al 2012), and GX 301-2 (Postnov et al 2015), as well as supergiant fast X-ray transients (Shakura et al 2014), which are a subclass of HMXBs characterized by sporadic X-ray flares with peak luminosities ∼10 36 -10 37 erg s −1 (Ducci et al 2014). However, a study on the global feature of HMXBs in this model is still lacking.…”

Section: Introductionmentioning

confidence: 99%

Can the Subsonic Accretion Model Explain the Spin Period Distribution of Wind-Fed X-Ray Pulsars?

Shao

2016

ApJ

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Neutron stars in high-mass X-ray binaries (HMXBs) generally accrete from the wind matter of their massive companion stars. Recently, Shakura et al. suggested a subsonic accretion model for low-luminosity (<4×10 36 erg s −1 ), wind-fed X-ray pulsars. To test the feasibility of this model, we investigate the spin period distribution of wind-fed X-ray pulsars with a supergiant companion star, using a population synthesis method. We find that the modeled distribution of supergiant HMXBs in the spin period-orbital period diagram is consistent with observations, provided that the winds from the donor stars have relatively low terminal velocities (1000 km s −1 ). The measured wind velocities in several supergiant HMXBs seem to favor this viewpoint. The predicted number ratio of wind-fed X-ray pulsars with persistent X-ray luminosities that are higher and lower than 4×10 36 erg s −1 is about 1:10.

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Expected number of supergiant fast X-ray transients in the Milky Way

Cited by 15 publications

References 52 publications

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

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

Star formation history and X-ray binary populations: the case of the Large Magellanic Cloud

Can the Subsonic Accretion Model Explain the Spin Period Distribution of Wind-Fed X-Ray Pulsars?

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