Reactivation of IGR J17464-3213 in hard X-rays
ATel #189; S. A.Grebenev (IKI, Moscow), A. A.Lutovinov (IKI, Moscow), R. A.Sunyaev (IKI, Moscow/MPA, Garching)
on 16 Sep 2003; 13:58 UT
Credential Certification: A.Lutovinov (aal@hea.iki.rssi.ru)
Subjects: X-ray, Gamma Ray, Black Hole, Transient
Referred to by ATel #: 198
On the basis of recent INTEGRAL observations we report on reactivation
of the Galactic black hole candidate IGR J17464-3213 (=H1743-322) in
the hard X-ray band.
The source flared up as an X-ray nova in the end of March (ATEL #132)
remains bright in soft E < 15 keV X-rays (ATEL #180). We regularly
detected it with the JEM-X monitor during last 1.5 months while
INTEGRAL performed deep obsevations of the Galactic center
region. However with the hard X-/gamma-ray telescope IBIS we succeeded
to detect this source on only September 9 for the first time. The
flux measured during this and subsequent days was strongly variable on
a time scale of hours with the mean level of about 15 mCrab in both
15-40 keV and 40-100 keV bands and with the peak values of 25-35
mCrab. The detailed analysis of the combined IBIS/JEM-X spectrum
measured during one of such strong flares (on September 12) has shown
the presence of two distinct components: a soft one which could be
fitted by a multicolor disk model with kT_in ~ 1.04 keV for the fixed
N_H = 2.5 x 10^{22} cm^{-2} (or a black-body model with kT ~ 0.81 keV,
cf. with ATEL #180) and a hard power-law tail with the photon index of
about 2.2 extended without cut-off to at least 80 keV. It is likely
that the source is in process of steady transition to the hard
spectral state.