H1743-322 in stable outburst phase

ATel #1779; C. Ricci (ISDC), M. Caballero-Garcia (IoA Cambridge), V. Beckmann (ISDC), J. M. Miller (Univ. Michigan), E. Kuulkers (ESA/ESAC)
on 12 Oct 2008; 10:26 UT
Credential Certification: Volker Beckmann (Volker.Beckmann@obs.unige.ch)

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The Galactic black-hole candidate and X-ray transient H 1743-322 has reached a stable high flux outburst after activity in hard X-rays had been reported by INTEGRAL (Kuulkers et al. 2008, ATel #1739; Prat et al. 2008, ATel #1745) and in the radio domain by ATCA (Corbel et al. 2008, ATel #1766).

Here we report about recent observations performed by INTEGRAL during the on-going outburst. Observations were performed from 2008-10-10T05:19 until 2008-10-10T11:19 and from 2008-10-10T21:34 until 2008-10-11T21:57. The source showed only 5% variability in the 20-40 keV band at a flux level of 170 mCrab during these observations, and thus we analysed the combined data set.

The spectrum, based on 86.4 ksec JEM-X1 (3-20 keV), 80.4 ksec IBIS/ISGRI (20-200 keV), and 84.1 ksec SPI (25-200 keV) data, can be represented by an absorbed model for Comptonization of soft photons by a hot plasma (compTT; Titarchuk et al. 1994). The model includes the plasma temperature T_e of the hot corona, the optical depth tau of this plasma, and the temperature T_0 of the soft photon spectrum. Because the spectrum starts at 3 keV, T_0 is not well constrained by the data and has been fixed to 100 eV. The model fit resulted in NH = 1.8 +- 1.5 10^22 1/cm**2, kT_e = 39 +-1 keV, and tau = 1.2 +- 0.1 for plane geometry. The compTT model gives a reduced chi-squared of 1.1 (3% systematics added to the spectra).
The flux of the source in outburst, based on the model described above, is f(3-20 keV) = 1.0e-9 erg/cm**2/sec and f(20-200 keV) = 2.1e-9 erg/cm**2/sec.

The evolution of the outburst of H1743-322 will be followed by INTEGRAL through the Galactic Bulge monitoring program (Kuulkers et al. 2007, A&A 466, 595).