ON THE SPIN PERIOD DISTRIBUTION IN Be/X-Ray BINARIES

Cheng, Zhongqun; Shao, Yong; Li, Xiang-Dong

doi:10.1088/0004-637x/786/2/128

Cited by 53 publications

(64 citation statements)

References 62 publications

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“…2.1.2) implies an unexpectedly short orbital period of P orb ∼ 4 days for a canonical 1.4 M neutron star companion. For P orb ∼ 20 days, consistent with the commonly found lower bound for Be X-ray binaries (Cheng et al 2014), we would infer a companion mass of ∼2.5 M , with any longer period strongly favouring a black hole, apparently excluded by the detection of X-ray pulsations 10 . Preliminary Monte-Carlo analysis following the methodology of Sana et al (2013) appears to favour a lower-mass companion with a short period.…”

Section: Vfts 399 In Contextsupporting

confidence: 85%

“…These systems are overwhelmingly comprised of OeBe stars (∼O9-B2 V-III; Negueruela & Coe 2002;McBride et al 2008) orbited by neutron stars and have periods 20 days P orb 400 days and eccentricities 0.1 e 0.9 (Cheng et al 2014). The interplay between orbital phase and the intrinsically variable circumstellar disc leads to complex, variable X-ray emission (e.g.…”

Section: Understanding the X-ray Emissionmentioning

confidence: 99%

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The VLT-FLAMES Tarantula survey

Clark

Bartlett

Broos

et al. 2015

A&A

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Context. The stellar population of the 30 Doradus star-forming region in the Large Magellanic Cloud contains a subset of apparently single, rapidly rotating O-type stars. The physical processes leading to the formation of this cohort are currently uncertain. Aims. One member of this group, the late O-type star VFTS 399, is found to be unexpectedly X-ray bright for its bolometric luminosity − in this study we aim to determine its physical nature and the cause of this behaviour. Methods. To accomplish this we performed a time-resolved analysis of optical, infrared and X-ray observations. Results. We found VFTS 399 to be an aperiodic photometric variable with an apparent near-IR excess. Its optical spectrum demonstrates complex emission profiles in the lower Balmer series and select He i lines − taken together these suggest an OeBe classification.The highly variable X-ray luminosity is too great to be produced by a single star, while the hard, non-thermal nature suggests the presence of an accreting relativistic companion. Finally, the detection of periodic modulation of the X-ray lightcurve is most naturally explained under the assumption that the accretor is a neutron star. Conclusions. VFTS 399 appears to be the first high-mass X-ray binary identified within 30 Dor, sharing many observational characteristics with classical Be X-ray binaries. Comparison of the current properties of VFTS 399 to binary-evolution models suggests a progenitor mass 25 M for the putative neutron star, which may host a magnetic field comparable in strength to those of magnetars. VFTS 399 is now the second member of the cohort of rapidly rotating "single" O-type stars in 30 Dor to show evidence of binary interaction resulting in spin-up, suggesting that this may be a viable evolutionary pathway for the formation of a subset of this stellar population.

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Section: Vfts 399 In Contextsupporting

confidence: 85%

Section: Understanding the X-ray Emissionmentioning

confidence: 99%

The VLT-FLAMES Tarantula survey

Clark

Bartlett

Broos

et al. 2015

A&A

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“…5 we plot the maximum and minimum fluxes (F max and F min ) and the derived ratio (variability factor) for the SMC BeXRB pulsars versus their spin period. As shown by Cheng et al (2014), short-period (<40 s) pulsars show on average higher maximum luminosities than long-period pulsars. This is demonstrated by the rather loose anti-correlation of maximum flux with spin period in the upper panel of Fig.…”

Section: Population Statisticsmentioning

confidence: 83%

“…Knigge et al (2011) discussed the bimodal distribution of the spin period with two maxima at around 10 s and between 100 s to 1000 s in terms of two populations of X-ray pulsars produced by two types of supernovae. As an alternative explanation, Cheng et al (2014) proposed that the spin period distribution is the result of two different accretion modes. To elaborate on this question, we collected maximum and minimum fluxes (or upper limits when lower) reported for the SMC BeXRBs in the literature and entered them in our catalogue.…”

Section: Population Statisticsmentioning

confidence: 99%

High-mass X-ray binaries in the Small Magellanic Cloud

Haberl

Sturm

2016

A&A

157

176

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Aims. The last comprehensive catalogue of high-mass X-ray binaries in the Small Magellanic Cloud (SMC) was published about ten years ago. Since then new such systems were discovered, mainly by X-ray observations with Chandra and XMM-Newton. For the majority of the proposed HMXBs in the SMC no X-ray pulsations were discovered as yet, and unless other properties of the X-ray source and/or the optical counterpart confirm their HMXB nature, they remain only candidate HMXBs. Methods. From a literature search we collected a catalogue of 148 confirmed and candidate HMXBs in the SMC and investigated their properties to shed light on their real nature. Based on the sample of well-established HMXBs (the pulsars), we investigated which observed properties are most appropriate for a reliable classification. We defined different levels of confidence for a genuine HMXB based on spectral and temporal characteristics of the X-ray sources and colour-magnitude diagrams from the optical to the infrared of their likely counterparts. We also took the uncertainty in the X-ray position into account. Results. We identify 27 objects that probably are misidentified because they lack an infrared excess of the proposed counterpart. They were mainly X-ray sources with a large positional uncertainty. This is supported by additional information obtained from more recent observations. Our catalogue comprises 121 relatively high-confidence HMXBs (the vast majority with Be companion stars). About half of the objects show X-ray pulsations, while for the rest no pulsations are known as yet. A comparison of the two subsamples suggests that long pulse periods in excess of a few 100 s are expected for the "non-pulsars", which are most likely undetected because of aperiodic variability on similar timescales and insufficiently long X-ray observations. The highest X-ray variability together with the lowest observed minimum fluxes for short-period pulsars indicate that in addition to the eccentricity of the orbit, its inclination against the plane of the Be star circum-stellar disc plays a major role in determining the outburst behaviour. Conclusions. The large population of HMXBs in the SMC, in particular Be X-ray binaries, provides the largest homogeneous sample of such systems for statistical population studies.

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“…In addition to individually interesting sources, the known population of the Magellanic Clouds is as comprehensive as the Galactic sample and ideally suited for statistical studies, e.g. to determine the NS spin distribution (Knigge et al 2011;Cheng et al 2014), the relation to the star-formation history (Antoniou et al 2010), and the faint end of the X-ray luminosity function (Shtykovskiy & Gilfanov 2005;Sturm et al 2013c), and to find and constrain the population of Be/white dwarf systems (Kahabka et al 2006;Sturm et al 2012;Li et al 2012; Morii et al 2013). …”

Section: Introductionmentioning

confidence: 99%

Discovery of SXP 265, a Be/X-ray binary pulsar in the Wing of the Small Magellanic Cloud★

Sturm

Haberl

Vasilopoulos

et al. 2014

Monthly Notices of the Royal Astronomical Society

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We identify a new candidate for a Be/X-ray binary in the XMM-Newton slew survey and archival Swift observations that is located in the transition region of the Wing of the Small Magellanic Cloud and the Magellanic Bridge. We investigated and classified this source with follow-up XMM-Newton and optical observations. We model the X-ray spectra and search for periodicities and variability in the X-ray observations and the OGLE I-band light curve. The optical counterpart has been classified spectroscopically, with data obtained at the SAAO 1.9 m telescope, and photometrically, with data obtained using GROND at the MPG 2.2 m telescope. The X-ray spectrum is typical of a high-mass X-ray binary with an accreting neutron star. We detect X-ray pulsations, which reveal a neutron-star spin period of P s = (264.516 ± 0.014) s. The source likely shows a persistent X-ray luminosity of a few 10 35 erg s −1 and in addition type-I outbursts that indicate an orbital period of ∼146 d. A periodicity of 0.867 d, found in the optical light curve, can be explained by non-radial pulsations of the Be star. We identify the optical counterpart and classify it as a B1-2II-IVe star. This confirms SXP 265 as a new Be/X-ray binary pulsar originating in the tidal structure between the Magellanic Clouds.

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ON THE SPIN PERIOD DISTRIBUTION IN Be/X-Ray BINARIES

Cited by 53 publications

References 62 publications

The VLT-FLAMES Tarantula survey

The VLT-FLAMES Tarantula survey

High-mass X-ray binaries in the Small Magellanic Cloud

Discovery of SXP 265, a Be/X-ray binary pulsar in the Wing of the Small Magellanic Cloud★

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