Swift BAT 100-Month Supergiant Fast X-Ray Transient Catalog
Short Name:
SWBATSFXT
Date:
07 Mar 2025
Publisher:
NASA/GSFC HEASARC
Description:
Supergiant Fast X-ray Transients (SFXTs) are High Mass X-ray Binaries (HMXBs) that are defined by their hard X-ray flaring behavior. During such flares they reach peak luminosities of 10<sup>36</sup> - 10<sup>37</sup> erg/s for a few hours (in the hard X-ray), i.e., much shorter timescales than those characterizing Be/X-ray binaries. The authors have investigated the characteristics of bright flares (detections in excess of 5 sigma) for a sample of SFXTs and their relation to the orbital phase. They have retrieved all Swift/BAT Transient Monitor light curves, and collected all detections in excess of 5 sigma from both daily- and orbital-averaged light curves in the time range from 2005 February 12 to 2013 May 31 (MJD 53413 - 56443). The authors also considered all on-board detections as recorded in the same time span and selected those within 4 arcminutes of each source in their sample and in excess of 5 sigma. This table contains the catalog of over a thousand Burst Alert Telescope (BAT) flares from 11 SFXTs, down to 15-150 keV fluxes of ~6 x 10<sup>-10</sup>erg/cm<sup>2</sup>/s (daily timescale) and ~1.5 x 10<sup>-9</sup>erg/cm<sup>2</sup>/s (orbital timescale, averaging ~800s) and spanning 100 months. The great majority of these flares are unpublished. This population is characterized by short (a few hundred seconds) and relatively bright (in excess of 100 milliCrab, 15-50 keV) events. In the hard X-ray, these flares last in general much less than a day. Clustering of hard X-ray flares can be used to indirectly measure the length of an outburst, even when the low-level emission is not detected. In their paper, the authors construct the distributions of flares, of their significance (in terms of sigma) and their flux as a function of orbital phase, to infer the properties of these binary systems. In particular, they observe a trend of clustering of flares at some phases as P_orb increases, as consistent with a progression from tight, circular or mildly eccentric orbits at short periods, to wider and more eccentric orbits at longer orbital periods. Finally, the authors estimate the expected number of flares for a given source for their limiting flux and provide the recipe for calculating them for the limiting flux of future hard X-ray observatories. The BAT observes 88% of the sky daily, on average, so it is ideally suited to detect flaring in hard X-ray sources. Since 2005-02-12, the BAT Transient Monitor (Krimm et al. 2013, ApJS, 209, 14) has been providing near real-time light curves in the 15-50 keV energy range of more than 900 sources with a mean variance for one-day mosaics of 5.3 milliCrab. Several flares from SFXTs are regularly caught every year by the BAT Transient Monitor (BATTM). The catalog contains a total of 1117 flares from 11 SFXT sources (the only other confirmed SFXT, IGR J11215-5952, never triggered the BAT: see Section 2.2 of the reference paper for more information about this source). They are divided into 46 BAT triggers (bat_subsample_flag = 'T', 43 in outbursts), 126 daily-averaged BATTM light curves (bat_subsample_flag = 'D'), 267 orbital-averaged BATTM light curves (bat_subsample_flag = 'O'), and 678 on-board detections (bat_subsample_flag = 'B'). For each flare, the time of the occurrence, duration, flux, and significance are reported. Given the cut in sigma applied to the available BATTM and on-board detections, this catalog is a flux-limited sample of flares. Assuming a Crab-like spectrum (power-law of photon index 2.15), 5 sigma detections for one day and an average orbit typically correspond to fluxes of 5.98 x 10<sup>-10</sup> and 1.46 x 10<sup>-9</sup> erg cm<sup>-2</sup> s<sup>-1</sup>, respectively, in the 15-150 keV band (or 3.38 x 10<sup>-10</sup> and 8.24 x 10<sup>-10</sup> erg cm<sup>-2</sup> s<sup>-1</sup> in the 15-50 keV band). This table was created by the HEASARC in August 2015 based on the union of <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/A+A/562/A2">CDS Catalog J/A+A/562/A2</a> files sample.dat (the properties of the confirmed SFXTs) and table4.dat (the catalog of the 1117 flares detected by the Swift BAT from 11 of the 12 confirmed SFXTs). This is a service provided by NASA HEASARC .
