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INTEGRAL observations of the BHC IGR J17091-3624 in outburst

ATel #3159; Capitanio F. (INAF/IASF-Roma), Tramacere A. (ISDC), Del Santo M. (INAF/IASF-Roma), Bozzo E. (ISDC), Watanabe K. (FGCU), Caballero I. (CEA-AIM Saclay), Chenevez J. (DTU Space, Denmark) , Paizis A. (INAF/IASF-Milano), Pottschmidt K. (UMBC/NASA GSFC), Sanchez-Fernandez C. (ESA/ESAC, Spain), Sguera V. (INAF/IASF-Bologna), Tarana A. (INAF/IASF-Roma)
on 11 Feb 2011; 14:21 UT
Credential Certification: Melania Del Santo (melania.delsanto@iasf-roma.inaf.it)

Subjects: X-ray, Binary, Transient

Referred to by ATel #: 3167, 3203, 3225, 3229, 3230, 3232, 3266, 3299, 3913, 4773

During the monitoring of the RX J1712.7-3946 region (PI. R. Terrier), INTEGRAL observed the currently ongoing outburst of the BHC IGRJ17091-3624 (Atels #3144, #3148, #3150). These observations were performed from 2011 Feb. 07 at 11:53 to 2011 Feb. 08 at 18:56 (UTC). The source was detected by IBIS/ISGRI (effective exposure time 65.3 ks) at a significance level of 96 sigma and 74 sigma in the 20-40 keV and 40-80 keV energy bands, respectively. The source was simultaneously observed by the JEM-X telescope (effective exposure time 5.5 ks) and detected at a significance level of 12 sigma in the 3-10 keV energy range.

The combined ISGRI+JEMX2 spectrum (5-300 keV) is well described (chi2/dof=14.8/14) by an absorbed cut-off power law model (the absorption column density was fixed to 1.1E22 cm-2, Atel #3148). We found a photon index of 1.4 (+/-0.1) and a high energy cutoff of 110(-27,+47) keV (all uncertainties are at 90% c.l.). The estimated unabsorbed flux of the source is:

9.4(-1.7,+0.8)E-10 erg/cm2/s (5-20 keV)

2.0(-0.5,+0.1)E-9 erg/cm2/s (20-200 keV).

The fit parameters and the lack of a prominent blackbody suggest that the source is in the hard state. Further INTEGRAL observations of the field of view around IGR J17091-3624 are currently being performed and more are planned to take place from Feb. 19-22, and again from March 1st to 3rd.

We thank the ISDC for the results of their quick look analysis.