The 100-month Swift catalogue of supergiant fast X–ray transients

Journal Article · Fri Feb 17 00:00:00 EST 2023 · Astronomy and Astrophysics

DOI:https://doi.org/10.1051/0004-6361/202244783· OSTI ID:1992266

Romano, P.  ^[1]; Evans, P. A.  ^[2]; Bozzo, E.  ^[3]; Mangano, V.  ^[1]; Vercellone, S.  ^[1]; Guidorzi, C.  ^[4]; Ducci, L.  ^[5]; Kennea, J. A.  ^[6]; Barthelmy, S. D. ^[7]; Palmer, D. M.  ^[8]; Krimm, H. A.  ^[9]; Cenko, S. B.  ^[7]

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1. Istituto Nazionale di Astrofisica (INAF), Merate (Italy). Osservatorio Astrofisico di Brera
2. Univ. of Leicester (United Kingdom)
3. Univ. of Geneva (Switzerland); Istituto Nazionale di Astrofisica (INAF), Roma (Italy). Osservatorio Astronomico di Roma
4. Univ. of Ferrara (Italy); Istituto Nazionale di Fisica Nucleare (INFN), Ferrara (Italy); Istituto Nazionale di Astrofisica (INAF), Bologna (Italy). Osservatorio di Astrofisica e Scienza dello Spazio di Bologna
5. Univ. of Tubingen (Germany); Univ. of Geneva (Switzerland)
6. Pennsylvania State Univ., University Park, PA (United States)
7. NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States)
8. Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
9. National Science Foundation (NSF), Alexandria, VA (United States)

Supergiant fast X-ray transients (SFXTs) are high mass X-ray binaries (HMXBs) displaying X-ray outbursts that can reach peak luminosities up to 10³⁸ erg s^-1 and spend most of their lives in more quiescent states with luminosities as low as 10³²-10³³ erg s^-1. During the quiescent states, less luminous flares are also frequently observed with luminosities of 10³⁴-10³⁵ erg s^-1. The main goal of the comprehensive and uniform analysis of the SFXT Swift triggers presented in this paper is to provide tools to predict whether a transient that has no known X-ray counterpart may be an SFXT candidate. These tools can be exploited for the development of future missions exploring the variable X-ray sky through large field-of-view instruments. We examined all available data on outbursts of SFXTs that triggered the Swift/Burst Alert Telescope (BAT) collected between 2005 August 30 and 2014 December 31, in particular those for which broad-band data, including the Swift/X-ray Telescope (XRT) data, are also available. This work complements and extends our previous catalogue of SFXT flares detected by BAT from 2005 February 12 to 2013 May 31, since we now include the additional BAT triggers recorded until the end of 2014 (i.e. beyond the formal first 100 months of the Swift mission). Due to a change in the mission’s observational strategy, virtually no SFXT triggers obtained a broad-band response after 2014. We processed all BAT and XRT data uniformly by using the Swift Burst Analyser to produce spectral evolution dependent flux light curves for each outburst in the sample. The BAT data allowed us to infer useful diagnostics to set SFXT triggers apart from the general γ-ray burst population, showing that SFXTs uniquely give rise to image triggers and are simultaneously very long, faint, and ‘soft’ hard-X-ray transients. We find that the BAT data alone can discriminate very well the SFXTs from other classes of fast transients, such as anomalous X-ray pulsars and soft gamma repeaters. On the contrary, the XRT data collected around the time of the BAT triggers are shown to be decisive for distinguishing SFXTs from, for instance, accreting millisecond X-ray pulsars and jetted tidal disruption events. The XRT observations of 35 (out of 52 in total) SFXT BAT triggers show that in the soft X-ray energy band, SFXTs display a decay in flux from the peak of the outburst of at least three orders of magnitude within a day and rarely undergo large re-brightening episodes, favouring in most cases a rapid decay down to the quiescent level within three to five days (at most).

• Research Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA); National Aeronautics and Space Administration (NASA); National Science Foundation (NSF)
• Grant/Contract Number: 89233218CNA000001
• OSTI ID: 1992266
• Report Number(s): LA-UR-22-28474; TRN: US2404185
• Journal Information: Astronomy and Astrophysics, Vol. 670; ISSN 0004-6361
• Publisher: EDP Sciences
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
astronomy and astrophysics
x-rays
SFXT
supergiant fast x-ray transients
x-ray astronomy