INTEGRAL/IBIS observations of the Galactic center region at the epoch of the short Fermi/LAT flare

ATel #3170; M. Fiocchi (IASF-Rome/INAF), C. Sanchez-Fernandez (ESA/ESAC Madrid Spain), L. Natalucci (IASF-Rome/INAF), E. Kuulkers (ESA/ESAC Madrid Spain), A. Bazzano(IASF-Rome/INAF), A. J. Bird (School of Physics and Astronomy, Univ. of Southampton), E. Bozzo (ISDC), J. Chenevez (DTU Space, Denmark), C. Ferrigno (ISDC), V. Sguera (IASF-Bologna/INAF), C. Tchernin (ISDC)
on 16 Feb 2011; 17:40 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Lorenzo Natalucci (Lorenzo.Natalucci@iasf-roma.inaf.it)

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The Galactic Center was in the IBIS/ISGRI field-of-view during the epoch of the gamma-ray flare observed recently by Fermi/LAT (ATEL#3162). During the 20s interval of the flare IBIS/ISGRI did not detect any emission from SAX J1747.0-2853, located at ~10degrees off-axis, with a 3sigma upper limit of ~250mCrab in the 20-60 keV band.
We have also analyzed two separate time slots of 6 and 7 pointings, respectively: (a) 2011 Feb. 10, 11:41-18:41 UT, and (b) 2011 Feb. 12, 04:09-10:09 UT. The retrieved data belong to the near-real time INTEGRAL archive.
The first period includes the gamma-ray flare, the second one was selected because the source position was most optimal, i.e., about 6-8 degrees off-axis, the closest to the Galactic center region. The second slot is only a few hours apart from the Swift/XRT observation of SAX J1747.0-2853 (ATEL #3163), during which very bright emission from this source was reported.
SAX J1747.0-2853 was not detected in the IBIS/ISGRI images produced in the range 20-60 keV and we find 3 sigma upper limits of 6 mCrab for period (a) and 4 mCrab for period (b). Conversely, during a 10.4 ks period including the XRT observation, we have an indication of faint activity of the source found by comparing with the images taken with periods (a) and (b). However, since the source is blended and located only 9.5 arcmin from 1E1743.1-2852, we cannot claim for a clear detection.
We note that in both periods IBIS/ISGRI detects emission from a region consistent with the position of the transient X-ray burster SAX J1750.8-2900. The average flux is 14.5 +/- 1.2 mCrab (20-60 keV) during both periods and the 90% c.l. position error is 2.2 arcmin.
The IBIS survey catalog version 4 (Bird et al. 2010, ApJS 186, 1) lists a candidate transient source (classified as "blended"), IGR J17507-2856, at about 5' from the position of SAX J1750.8-2900. IGR J17507-2856 is a faint source known to appear sporadically in the survey maps. Within the limits of our analysis both sources are compatible with the observed site of emission, although our results are suggesting that the detected source is most probably SAX J1750.8-2900. For this detection, we encourage follow-up observations to identify the source of emission seen with IBIS/ISGRI.
Finally, we thank the ISDC for providing us the results of their quick look analysis.