Swift Observations of GRS 1739-278 in Outburst
ATel #9541; J. Neilsen (MIT), S. Motta (Oxford), G. Ponti (MPE), M. Coriat (IRAP), R. Fender (Oxford), S. Corbel (CEA Saclay)
on 24 Sep 2016; 19:03 UT
Credential Certification: Joey Neilsen (jneilsen@space.mit.edu)
Subjects: X-ray, Request for Observations, Black Hole, Transient
Following the report of an increased flux from the black hole candidate GRS 1739-278 in INTEGRAL observations of the Galactic Center (ATel #9517), we triggered a Swift monitoring campaign to track the evolution of this new outburst. We are grateful to Neil Gehrels and the Swift team for rapidly executing our first observation.
Swift observed the source starting on 2016-09-21 at 23:18:58 UT, with a good exposure time of 972 seconds. Using the tools available at http://www.swift.ac.uk/user_objects (Evans et al. 2009, MNRAS, 397, 1177), we extracted a light curve and spectrum. GRS 1739-278 is clearly detected, with an average count rate of 2.55 count s^-1, and exhibits ~20% variability over the course of the observation. The online spectral analysis tool indicates that the spectrum is consistent with an absorbed power law with photon index 1.44 +/- 0.27 and total hydrogen column density (3.3 +/- 0.6) x 10^22 cm^-2 (assuming Anders and Grevesse (1989) abundances and using the phabs absorption model). The absorbed 0.3-10 keV flux is (2.1 +/- 0.2) x 10^-10 erg s^-1 cm^-2. Our results are consistent with a black hole in the hard state.
Swift will continue to monitor the evolution of the outburst for the next 40 days. In addition, we have triggered a coordinated Chandra/HETGS, NuSTAR, and JVLA campaign, which will provide further details on the behavior of the accretion flow, jet, and any other outflows launched by the black hole. The first Chandra observation will begin on 2016-09-24 20:40:59 UT, and will last 30 ks. Observations at other wavelengths are strongly encouraged.
