Supergiant Fast X-ray Transients (SFXTs) are HMXBs with OB supergiant companions. I review the results of the Swift SFXT Project, which since 2007 has been exploiting Swift's capabilities in a systematic study of SFXTs and supergiant X-ray binaries (SGXBs) by combining follow-ups of outbursts, when detailed broad-band spectroscopy is possible, with long-term monitoring campaigns, when the out-of-outburst fainter states can be observed. This strategy has led us to measure their duty cycles as a function of luminosity, to extract their differential luminosity distributions in the soft X-ray domain, and to compare, with unprecedented detail, the X-ray variability in these different classes of sources. I also discuss the "seventh year crisis", the challenges that the recent Swift observations are making to the prevailing models attempting to explain the SFXT behaviour.
@article{arxiv.1504.07249,
title = {Seven Years with the Swift Supergiant Fast X-ray Transients Project},
author = {P. Romano},
journal= {arXiv preprint arXiv:1504.07249},
year = {2015}
}
Comments
12 pages, 9 figures, 1 table. Review paper for "Swift 10 Years of Discovery" conference. Accepted for Publication in the Journal of High Energy Astrophysics