Transition of H 1743-322 to the HIMS/SIMS confirmed and preliminary spectral fit results

ATel #1813; M. D. Caballero-Garcia (IoA, Cambridge), J. M. Miller (U. of Michigan), C. Ferrigno (ISDC/IAAT), V. Beckmann (ISDC)
on 26 Oct 2008; 15:50 UT
Credential Certification: Maria D. Caballero-Garcia (mcaballe@ast.cam.ac.uk)

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We present the results of preliminary spectral fits to the third 130 ksec INTEGRAL ToO observation of H 1743-322 (see ATEL #1779 and ATEL #1798), obtained between 2008-10-23T00:43 and 2008-10-24T14:48. We made joint spectral fits to spectra obtained with the JEM-X (5-20 keV), IBIS/ISGRI (18-200 keV) and SPI (25-200 keV) instruments.

The spectrum is no longer described by a purely absorbed thermal Comptonization model of seed photons from the inner disk. We obtained very bad statistics, i.e. reduced chi-squared of 3, 3.4 for 112, 109 d.o.f. for compTT (Titarchuk et al. 1994) and compPS (Poutanen & Svensson, 1996) models, respectively. This would indicate that the source has left the LH state in which was during 1st (ATEL #1779) and 2nd TOO (#1798) observations. The spectrum is best described by an absorbed cut-off powerlaw at high energies plus a multicolor disk black body (diskbb; Mitsuda et al. 1984) at lower energies. We obtained a reduced chi-squared of 1.9 for 110 d.o.f (2 % systematics added to the spectra), constraining the cross-calibration factors of the instruments to reasonable values (1, 1+-20% and 1+-50% for JEM-X, ISGRI and SPI, respectively). We froze the column density to NH = 1.8 10^22 1/cm**2 and obtained a high value for the inner disk temperature around 1 keV, a photon index of 2.06+-0.02 and a cut-off in the range of 20-30 keV. The photon index in the range of 1.5-2.5 corresponds to the HIMS/SIMS in the classification scheme of Homan & Belloni (2005) and Belloni (2005).

The unabsorbed flux of the source, based on the model described above, is f(3-20 keV) = 1.8E-09 erg/cm**2/sec and f(20-200 keV) = 1.4e-9 erg/cm**2/sec, thus constant and decreased by 50 % in the 3-20 and 20-200 keV energy ranges, respectively, with respect to the previous TOO (ATEL #1798).

In the same FOV there are two active sources: 1) XTE J1701-407, which shows a simple power law spectrum with photon index 2.6+-0.3, thus softer than reported in ATEL #1791, and flux(20-100 keV) = 1.8e-10 erg/cm**2/sec; 2) SAX J1753.5-2349 (see ATEL #1810), which shows also a power law spectrum with photon index 2.1+-0.4 and flux(20-100 keV) = 7e-11 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).