GRS 1758-258 not detected at hard X-rays
ATel #9625; K. Pottschmidt (NASA-GSFC/UMBC), W. Eikmann, I. Kreykenbohm, J. Wilms, M. Hirsch, M. Kuehnel (all ECAP-FAU), B. H.G. Rodrigues (Itajuba), F. Krauss (UvA), R. Soria (ICRAR-Curtin/Sydney), V. Grinberg (MIT), D. M. Smith (UCSC), M. Cadolle Bel (MPCDF), J. A. Tomsick (UCB), A. Bodaghee (GSCU), E. Kuulkers (ESA-ESAC) on behalf of the INTEGRAL Galactic bulge monitoring team, E. Kalemci (Sabanci), J. M. Miller (Michigan)
on 14 Oct 2016; 18:01 UT
Credential Certification: Katja Pottschmidt (email@example.com)
Subjects: X-ray, Black Hole
Referred to by ATel #: 9890
The Galactic black hole candidate GRS 1758-258 is usually found in the
hard state but has been known to enter soft states in which the
spectrum changes from a power-law to a thermal disk without
substantial changes in bolometric luminosity (Soria et al., 2011,
MNRAS 415, 410). The most extended soft state to date was observed in
2000-2002 (Smith et al., 2001, ApJ 554, L41). The soft states are
associated with a strong drop in flux above 3 keV (Pottschmidt et al.,
2006, A&A 452, 285; Soria et al., 2011, MNRAS 415, 410). Recent
observations of the source show the strongest drop in flux since the
The Swift BAT 15-50 keV light curve of GRS 1758-258 shows a rapid
decline in flux over the past ~50 days and the source has not been
detected during the past ~15 days
( http://swift.gsfc.nasa.gov/results/transients/GRS1758-258/ ).
The source has been extensively covered by the INTEGRAL Galactic bulge
monitoring-, Galactic Center monitoring-, and our GRS 1758-258 TOO
observation program from 2016 August 17 onward. INTEGRAL ISGRI
confirms the rapid flux decline over this time range. Selected values
in the 20-40 keV energy band are 69+/-3 mCrab (8.7+/-0.3 cps) on 8/17,
24+/-2 mCrab (3.0+/-0.2 cps) on 9/2, and 15+/-1 mCrab (1.9+/-0.2 cps)
on 9/27. Selected values in the 40-80 keV energy band are 74+/-4 mCrab
(4.8+/-0.3 cps) on 8/17 31+/-2 mCrab (2.0+/-0.2 cps) on 9/2, and
13+/-2 mCrab (0.9+/-0.1 cps) on 9/27.
GRS 1758-258 has not been detected by ISGRI since 2016 September 30.
During the most recent INTEGRAL Galactic Center observation on 2016
October 11, with an effective exposure of 4.4 ks, upper limits of 0.4
cps and 0.5 cps were obtained in the 20-40 keV and 40-80 keV energy
Additional observations are encouraged.