IGR J18175-1530: a new hard X-ray transient detected by INTEGRAL

ATel #1248; A. Paizis (INAF-IASF Milano), V. Beckmann (ISDC), D. Gotz (CEA Saclay), L. Sidoli, A. Bazzano, G. Belanger, M. Cadolle-Bel, J. Chenevez, A. De Rosa, E. Kuulkers, M. Falanga, M. Fiocchi, L. Kuiper, J. C. Leyder, S. Mereghetti, S. Piraino, K. Pottschmidt, S. Shaw, J. Tomsick, K. Watanabe, R. Walter, G. Weidenspointner
on 25 Oct 2007; 14:05 UT
Credential Certification: Adamantia Paizis (ada@iasf-milano.inaf.it)

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During the INTEGRAL Key Programme observations of the Galactic Centre (revolutions 599, 600 and 601, from 2007-09-09 to 2007-09-17), the IBIS/ISGRI telescope detected a new hard X-ray transient, IGR J18175-1530, at the position RA = 18 17 34.3, DEC= -15 30 41 (statistical error of 2.5'). The source is detected in the combined data set at 10 sigma in the 20-40 keV band with a rate of 1.5+-0.1 cps (about 9 mCrab) for an effective exposure time of 307 ksec, using OSA7 analysis software. IGR J18175-1530 is detected (6-7 sigma) also in the single revolution sky maps but it is neither detected at a single pointing level (2ksec), nor in the IBIS/ISGRI mosaic images in the 40-100 keV band. IGRJ18175-1530 has been in the IBIS/ISGRI field of view also prior to our detection, in August 2007 (revolutions 594, 595, 596) but was not detected. Unfortunately, IGR J18175-1530 was always too far off-axis (> 9 degrees) to be covered by JEM-X. An XMM-Newton observation of the source position performed on 2003-04-10 did not detect the object. We derive a 3-sigma upper limit of 3.3E-02 cps (0.3-12 keV, EPIC pn) at the source position. Using PIMMS and assuming a Crab-like spectrum with a 1e22cm-2 column density (the total Galactic in the source direction), we derive upper limits of 4e-13 ergs/cm/cm/s and 7e-13 ergs/cm/cm/s for the observed and unabsorbed source flux, respectively. This implies an upper limit to the luminosity of about 1e34 erg/s at 10 kpc. It is interesting to note that the radio source GPSR5 15.308+0.226 (RA = 274.41058, DEC = -15.52519, Becker et al. 1994) is 1.3' away from IGR J18175-1530, well within the IBIS/ISGRI location error (2.5'). INTEGRAL will not be monitoring this region in the next months, follow-up observations are encouraged.