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Decrease in flux of H 1743-322 and preliminary spectral fit results

ATel #1798; M. D. Caballero-Garcia (IoA, Cambridge), J. M. Miller (University of Michigan), Volker Beckman, Simona Soldi (ISDC, Geneva University), on behalf of a larger collaboration team
on 21 Oct 2008; 21:19 UT
Credential Certification: Maria D. Caballero-Garcia (mcaballe@ast.cam.ac.uk)

Subjects: X-ray, Gamma Ray, AGN, Binary, Black Hole, Gamma-Ray Burst, Nova, Neutron Star, Quasar, Soft Gamma-ray Repeater, Star, Transient, Variables, Pulsar

Referred to by ATel #: 1808, 1810, 1813

We present the results of preliminary spectral fits to the second 130 ksec INTEGRAL ToO observation of H 1743-322 (see ATEL #1779), obtained between 2008-10-17T20:59 and 2008-10-19T10:17. We made joint spectral fits to spectra obtained with the JEM-X (5-20 keV), IBIS/ISGRI (18-200 keV) and SPI (23-200 keV) instruments.

We applied the 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 5 keV, T_0 is not well constrained by the data and has been fixed to 100 eV. We froze the column density to NH = 1.8 10^22 1/cm**2. We notice a change in the coronal properties, in the form of both heating and decrease of the opacity (i.e. kT_e = 90 +-4 keV, and tau = 0.6 +- 0.03, for plane geometry). This model gives a reduced chi-squared of 1.5 for 11 d.o.f. (2 % systematics added to the spectra).

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) = 3.5e-9 erg/cm**2/sec, decreased by 10 % and 15 %, respectively, with respect the previous TOO (ATEL #1779).

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).