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Swift/XRT detects activity of the Galactic center transient GRS 1741-2853

ATel #5246; N. Degenaar, M. T. Reynolds, J. M. Miller (Michigan), R. Wijnands (UvA), J. A. Kennea (PSU) and N. Gehrels (GSFC), on behalf of a larger collaboration
on 3 Aug 2013; 01:38 UT
Credential Certification: Nathalie Degenaar (degenaar@umich.edu)

Subjects: X-ray, Binary, Neutron Star, Transient

Referred to by ATel #: 5332

During regular monitoring observations of the Galactic center with the Swift/XRT (Atel #5006; see link below), we detect a transient X-ray source located ~10 arcmin NW of Sgr A*. It is weakly detected at a 3-sigma level during a ~1.1 ks PC-mode observation performed on 2013 August 1, at a net count rate of ~5E-3 counts/s. Subsequent observations obtained on August 2 (~1.0 ks) show that the source brightened to ~1.5E-2 counts/s. The position of this object is consistent with that of the transient neutron star low-mass X-ray binary and thermonuclear X-ray burster GRS 1741-2853. The Swift observations indicate that this source is entering a new accretion outburst.

Assuming an absorbed power-law model with a photon index of 2 and a hydrogen column density of 1E23 cm-2, the observed XRT count rates translate into 2-10 keV unabsorbed fluxes of ~1E-12 and ~3E-12 erg/cm2/s for August 1 and 2, respectively. For a distance of 7.2 kpc (Trap et al. 2009), the corresponding luminosities are ~6E33 erg/s (August 1) and ~2E34 erg/s (August 2). GRS 1741-2853 has frequently been seen active during the Swift/XRT monitoring campaign of the Galactic center; outbursts were detected in 2006, 2007, 2009 and 2010 (Degenaar & Wijnands 2009, 2010; ATel #2770). These active periods generally have a duration of a few weeks, with typical luminosities in the range of ~1E35-1E36 erg/s (Degenaar & Wijnands 2010).

In addition to GRS 1741-2853, the Swift/XRT observations detect ongoing activity from the transient neutron star low-mass X-ray binary AX J1745.6-2901 (ATels #5222, #5226), and the magnetar SGR J1745-29 (e.g., Kennea et al. 2013).

The Swift Monitoring Campaign website can be found at: http://www.swift-sgra.com

References:
Degenaar & Wijnands 2009, A&A 495, 547
Degenaar & Wijnands 2010, A&A 524, 69
Kennea et al. 2013, ApJ 770, L24
Trap et al. 2009, A&A 504, 501