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ATEL # 2003; L. Prat, J. Rodriguez (CEA Saclay, France), M. Cadolle Bel (ESA/ESAC, Spain), S. Corbel, M. Coriat, A. Goldwurm (CEA Saclay, France), E. Kuulkers (ESA/ESAC, on behalf of the INTEGRAL Galactic Bulge monitoring team), J. Tomsick (SSL, USA)
on 2 Apr 2009; 11:04 UT
Distributed as an Instant Email Notice (Transients)
Password Certification: Lionel Prat (email@example.com)
Subjects: X-ray, Gamma Ray, Request for Observations, Binaries, Black Holes, Transients
We report renewed activity of the Black-Hole Candidate IGR J17098-3628 (Atel #444, Chen et al. 2008, Capitanio et al. 2009) seen with the INTEGRAL/IBIS/ISGRI instrument during INTEGRAL Key Programme observations of the Galactic Centre (revolution 789, from 2009-03-30T14:14 to 2009-03-31T11:11). The source is detected in the 20-40 keV mosaic image at 10 sigmas, with a rate of 1.8±0.2 cps (about 11 mCrab) for an effective exposure time of 73 ksec. It is also detected at 5.2 sigmas in the 40-80 keV band, with a rate of 0.8±0.2 cps (about 10 mCrab). It is not detected at higher energies.
The source was not detected by INTEGRAL during previous observations of the field between 2008-09-18 and 2009-03-12. The upper limit on the flux at the source position during this period, with pointings of similar exposure, is about 0.5 mCrab. Between 2009-03-12 and 2009-03-30, Galactic Bulge observations give a typical 3 sigma upper limit of about 7 mCrab in the 18-40 keV band. At lower energies, the RXTE/ASM ligntcurve show a possible activity since 2009-03-25, in the 3-9 keV band.
The ISGRI spectrum can be represented by a simple power law model with photon index 2.05±0.35 (reduced chi squared 0.86, d.o.f. 9) with a model flux of F(20-200 keV) = 2.7E-10 erg/cm**2/sec. The spectral model is compatible with the Hard State spectrum of black hole candidates. Therefore, the new detection of IGR J17098-3628 at high energies and the spectral state inferred from the INTEGRAL spectrum suggest that the source is now entering a new outburst.
INTEGRAL will continue to observe this region regularly in the coming weeks, as part of its Key Programs. We encourage follow-up observations of this source at all wavelengths.