INTEGRAL/IBIS detection of the onset of the outburst of the black hole binary H1743-322

ATel #4418; Victoria Grinberg (Remeis/ECAP/FAU), Jerome Rodriguez (CEA SAp/LAb, AIM, Saclay), Joern Wilms (Remeis/ECAP/FAU), Marion Cadolle Bel (ESA/ESAC), Alexander Popp (Remeis/ECAP/FAU), Katja Pottschmidt (CRESST/GSFC/UMBC), Tomaso Belloni (INAF/OAB, Italy), Sara Motta (INAF/OAB, Italy & ESA/ESAC), Arash Bodaghee (SSL/UC Berkeley), John Tomsick (SSL/UC Berkeley)
on 24 Sep 2012; 21:33 UT
Credential Certification: Joern Wilms (j.wilms@sternwarte.uni-erlangen.de)

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We report on the onset of the outburst of the black hole binary H1743-322 (IGR J17464-3213) as detected by INTEGRAL during the recent monitoring of Swift J174510.8-262411.

The source was detected in INTEGRAL/ISGRI data covering MJD 56190.471-56191.372 (part of INTEGRAL revolution 1213) with 8.3 mCrab in the 20-40 keV band and 11.1 mCrab in the 40-80 keV band.

The flux increased to 24.1 mCrab (20-40 keV) and 38.9 mCrab (40-80 keV) in MJD 56191.724-56192.163 (part of INTEGRAL revolution 1214) and H1743-322 was detected in the 80-150 keV range at 53 mCrab.

In the data of MJD 56192.164-56193.044 (part of revolution 1214) the source has further brightened to 37.5 mCrab in the 20-40 keV band, 52.1 mCrab in the 40-80 keV band and 64.4 mCrab in the 80-150 keV band. At this time, a 4.3 sigma detection at 65 mCrab was possible in the 150-300 keV band. The source spectrum at this point can be described by a power law with a high energy cutoff with a the photon index of ~1.5 and a cutoff energy of ~100 keV.

The Jem-X soft X-ray coverage is sparse, resulting in 3-7keV upper limits of 11mCrab and 17mCrab in revolutions 1213 and 1214, respectively.

The evolution of the INTEGRAL fluxes and the spectral shape indicates that the source is in a hard state, typical for the onset of an outburst of transient black hole binaries.

Observations of the source with all-sky monitors confirm this conclusion: An increase in the 15-50 keV flux by a factor of > 5 within the last week as compared to the previous quiescence of the source can also be seen in the Swift/BAT data (http://swift.gsfc.nasa.gov/docs/swift/results/transients/weak/IGRJ17464-3213/). A transient warning has been issued by the MAXI transient alert system on 2012-09-24 13:01:12.

INTEGRAL observation of the source will continue and will be augmented by soft X-ray coverage with Swift. We encourage further observations of this intriguing source in other wavelengths.