IGR J17191-2821: a new hard X-ray transient detected by INTEGRAL

The IBIS/ISGRI instrument aboard INTEGRAL discovered a new hard X-ray source during the INTEGRAL Key Programme observations of the galactic bulge region conducted from 2007 March 2 at 13:22 to March 4 at 05:21 UTC. The new source, IGR J17191-2821, is located 5.2 degrees above the galactic plane at (RA,DEC) = (259.77,-28.35) (J2000) with an accuracy of 2.5 arcmin.

The source is clearly detected in the 20-40 keV band mosaic image of this observation with a significance of 10.4 sigma and an average flux of 8.9 +/- 0.9 mCrab. The source is not detected in any single science window - each lasting about 2.7 ksec - and thus there is no clear sign of strong variability within this observation.

The source was also not detected in the image mosaics of the preceding Key Programme observations of the same region. In the 40-80 keV band, IGR J17191-2821 is marginally detected at the 4-sigma level with a flux of 5.8 +/- 1.4 mCrab. We cannot constrain the flux in the 3 to 20 keV energy band, because the source is well within the JEM-X field of view in only one science window, where it is not detected.

According to Simbad, there are two known sources within the IBIS/ISGRI position uncertainty: a soft X-ray ROSAT survey source 1RXS J171909.4-282041 at a distance of 1.4 arcmin and an infrared source IRAS 17159-2819 located 1.6 arcmin away. We further note the presence at a distance of 0.83 deg of the unidentified EGRET source 3EG J1717-2737 located at (RA,DEC)=(259.30,-27.63) with an uncertainty of 0.64 deg (95% confidence).

INTEGRAL will continue to observe this region in the coming days and we encourage follow-up observations of this source at all wavelengths.