A four-year baseline Swift study of enigmatic X-ray transients located near the Galactic center
Abstract
We report on continued monitoring observations of the Galactic center carried out by the X-ray telescope aboard the Swift satellite in 2008 and 2009. This campaign revealed activity of the five known X-ray transients AX J1745.6-2901, CXOGC J174535.5-290124, GRS 1741-2853, XMM J174457-2850.3 and CXOGC J174538.0-290022. All these sources are known to undergo very faint X-ray outbursts with 2-10 keV peak luminosities of LX, peak 1034-36 erg s-1, although the two confirmed neutron star low-mass X-ray binaries AX J1745.6-2901 and GRS 1741-2853 can also become brighter (LX, peak 1036-37 erg s-1). We discuss the observed long-term lightcurves and X-ray spectra of these five enigmatic transients. In 2008, AX J1745.6-2901 returned to quiescence following an unusually long accretion outburst of more than 1.5 years. GRS 1741-2853 was active in 2009 and displayed the brightest outburst ever recorded for this source, reaching up to a 2-10 keV luminosity of LX 1 × 1037 (D/7.2 kpc)2 erg s-1. This system appears to undergo recurrent accretion outbursts approximately every 2 years. Furthermore, we find that the unclassified transient XMM J174457-2850.3 becomes bright only during short episodes (days) and is often found active in between quiescence (LX 1032 erg s-1) and its maximum outburst luminosity of LX 1036 erg s-1. CXOGC J174535.5-290124 and CXOGC J174538.0-290022, as well as three other very-faint X-ray transients that were detected by Swift monitoring observations in 2006, have very low time-averaged mass-accretion rates of < dot{M} >_long ⪉ 2 × 10-12 M⊙ yr-1. Despite having obtained two years of new data in 2008 and 2009, no new X-ray transients were detected.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- December 2010
- DOI:
- 10.1051/0004-6361/201015322
- arXiv:
- arXiv:1007.0249
- Bibcode:
- 2010A&A...524A..69D
- Keywords:
-
- X-rays: binaries;
- stars: neutron;
- accretion;
- accretion disks;
- Galaxy: center;
- X-rays: general;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- Minor textual revisions according to referee report, accepted for publication in A&