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|Title:||Supergiant fast X-ray transients as an under-luminous class of supergiant X-ray binaries||Authors:||Bozzo, E.
|Issue Date:||2015||Journal:||ADVANCES IN SPACE RESEARCH||Number:||55||Issue:||4||First Page:||1255||Abstract:||The usage of cumulative luminosity distributions, constructed thanks to the long-term observations available through wide field hard X-ray imagers, has been recently exploited to study the averaged high energy emission (>17 keV) from supergiant fast X-ray transients (SFXTs) and classical Supergiant High Mass X-ray Binaries (SgXBs). Here, we take advantage of the long term monitorings now available with Swift/XRT to construct for the first time the cumulative luminosity distributions of a number of SFXTs and the classical SgXB IGR J18027-2016 in the soft X-ray domain with a high sensitivity focusing X-ray telescope (0.3-10 keV). >By complementing previous results obtained in the hard X-rays, we found that classical SgXBs are characterized by cumulative distributions with a single knee around, while SFXTs are found to be systematically sub-luminous and their distributions are shifted at significantly lower luminosities (a factor of ∼ 10-100). As the luminosity states in which these sources spend most of their time are typically below the sensitivity limit of large field of view hard X-ray imagers, we conclude that soft X-ray monitorings carried out with high sensitivity telescopes are particularly crucial to reconstruct the complete profile of the SFXT cumulative luminosity distributions. The difference between the cumulative luminosity distributions of classical SgXBs and SFXTs is interpreted in terms of accretion from a structured wind in the former sources and the presence of magnetic/centrifugal gates or a quasi-spherical settling accretion regime in the latter.||Acknowledgments:||Acknowledgments The authors thank three anonymous referees for their valuable comments and suggestions. E.B. acknowledges support from ISSI through funding for the International Team meeting on Unified View of Stellar Winds in Massive X-ray Binaries (ID 253), during which most of the ideas presented in this paper were developed. PR acknowledges contract ASI-INAF I/004/11/0. LD thanks Deutsches Zentrum fr Luft und Raumfahrt (Grant FKZ 50 OG 1301). The XRT data were obtained through ToO observations (20072012; contracts ASI-INAF I/088/06/0, ASI-INAF I/009/10/0) and through the contract ASI-INAF I/004/11/0 (20112013, PI P. Romano).||URI:||http://hdl.handle.net/20.500.12386/23922||URL:||https://www.sciencedirect.com/science/article/pii/S0273117714007157?via%3Dihub||ISSN:||0273-1177||DOI:||10.1016/j.asr.2014.11.012||Bibcode ADS:||2015AdSpR..55.1255B||Fulltext:||open|
|Appears in Collections:||1.01 Articoli in rivista|
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