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

ATel #8881; N. Degenaar (Cambridge), R. Wijnands (UvA), M. T. Reynolds, J. M. Miller (Michigan), J. A. Kennea (PSU), N. Gehrels (GSFC), G. Ponti (MPE) and D. Haggard (McGill), on behalf of a larger collaboration
on 30 Mar 2016; 09:01 UT
Credential Certification: Nathalie Degenaar (degenaar@ast.cam.ac.uk)

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Regular monitoring observations of the Galactic center with the Swift/XRT reveal renewed activity of the transient neutron star low-mass X-ray binary GRS 1741-2853. This known thermonuclear X-ray burster is located ~10 arcmin NW of Sgr A*. It is first detected during a ~1 ks PC-mode observation performed on 2016 March 23, at a net count rate of ~0.015 counts/s. Five subsequent observations obtained between March 24 and 28 show that the source brightened to ~0.25 counts/s, indicating that it is entering a new outburst.

An averaged spectrum extracted from three PC-mode observations performed between March 26 and 28 (during which the source was detected at similar count rates), can be described by an absorbed power-law model with a photon index of 1.7+/-0.5 and a hydrogen column density of (1.6+/-0.4)E23 cm-2 (using tbabs with wilm abundances and vern cross-sections). The inferred 2-10 keV unabsorbed flux is ~8.7E-11 erg/cm2/s, which corresponds to a luminosity of ~5.4E35 erg/s for a distance of 7.2 kpc (Trap et al. 2009).

GRS 1741-2853 is frequently active; previous outbursts were detected during the Swift/XRT Galactic center monitoring campaigns in 2006, 2007, 2009, 2010, and 2013 (Degenaar & Wijnands 2009, 2010; Degenaar et al. 2013). The outbursts typically last a few weeks and reach a 2-10 keV luminosity of ~1E35-1E37 erg/s (Degenaar et al. 2015).

In addition to GRS 1741-2853, we detect ongoing activity from the transient neutron star low-mass X-ray binary AX J1745.6-2901 (which has been active since mid-July 2013; Degenaar et al. 2013, 2015; Ponti et al. 2015), and the new transient Swift J174540.7-290015 (which was first detected in early-February 2016; ATels #8684, #8689, #8729, #8737, #8746, #8793). We do note that the XRT count rate of both these sources has decreased by a factor of ~2 over the past month. Daily X-ray observations of the Galactic center with Swift are ongoing.

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
Degenaar et al. 2013, IAU conf. proc. 303, 315
Degenaar et al. 2015, JHEA 7, 137
Ponti et al. 2015, MNRAS 446, 1536
Trap et al. 2009, A&A 504, 501