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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.