Three Years of Monitoring GRS 1758-258: an Extremely Hard X-Ray Source near GX 5-1

Details Three Years of Monitoring GRS 1758-258: an Extremely Hard X-Ray Source near GX 5-1 Three Years of Monitoring GRS 1758-258: an Extremely Hard X-Ray Source near GX 5-1

Dec 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993apj...418..844g&link_type=abstract

Astrophysical Journal v.418, p.844

Physics

26

Black Hole Physics, Galaxy: Center, X-Rays: General

Scientific paper

One of the hardest X-ray sources in the vicinity of the Galactic center, GRS 1758-258, has been monitored by the GRANAT/SIGMA above 35 keV since 1990 spring. The hardness of the observed spectrum (clearly detected up to ˜200 keV) suggests considering GRS 1758-258 to be a black hole candidate. The range of flux variations on a time scale of about a year, observed by SIGMA, corresponds to factor of more than 10. During all observations in 1990 it was one of the two brightest sources within a few degrees of the Galactic center (1E 1740.7-2942 was another one) with 40-150 keV flux at the level of ˜90 mCrab, while in 1991 fall its flux had declined below the SIGMA detection limit (<9 mCrab, 3 σ upper limit). The source reappeared in 1992 fall with 40-150 keV flux at the level of ˜30 mCrab. The long-term light curve of GRS 1758-258 and its 35-300 keV spectral properties, observed by SIGMA during 3 years, are quite similar to the light curve and spectra of 1E 1740.7-2942, suggesting a similar nature of these two brightest sources in the 6° neighborhood of the Galactic center.

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