1E1740.7-2942 and KS1741-293
ATel #257; S. A.Grebenev (IKI, Moscow), M. G.Revnivtsev (IKI, Moscow & MPA, Garching), R. A.Sunyaev (IKI, Moscow & MPA, Garching)
on 24 Mar 2004; 17:46 UT
Distributed as an Instant Email Notice Request For Observations
Credential Certification: M. Revnivtsev (mikej@mpa-garching.mpg.de)
Subjects: X-ray, Request for Observations, Black Hole
1E1740.7-2942, one of the most peculiar persistent hard X-/gamma-ray
sources in the Galaxy, a black-hole candidate and a microquasar, was
not detected with INTEGRAL during deep Open Program observations of
the Galactic center field carried out on March 12-16, 2004.
The 3-sigma upper limits for the flux were 1.7 mCrab and 3.1 mCrab in
the 17-40 and 40-100 keV, respectively, indicating that the flux
dropped at least 20-30 times of its usual level. Such behaviour is
similar to the remarkable ``long-term switch-off'' of the source in
1991-1992. The switch-off gives us a unique chance for studying this
source in quiescence. We encourage observations of the source in IR
and radio bands, as well as in soft X-rays (to check the possibility
of the transition to the soft spectral state).
The only hard X-ray source in the few-degrees neighbornhood of Sgr A*
remains currently the burster KS1741-293 which demonstrates the hard
Crab-like spectrum extended to at least 100 keV.
