IGR J07597-3842 - A new INTEGRAL source with candidate counterparts in the radio, IR and X-ray bands

ATel #261; P. R. den Hartog, W. Hermsen, L. M. Kuiper, J. J.M. in 't Zand (SRON Utrecht), C. Winkler (ESA/ESTEC Noordwijk), A. Domingo (LAEFF Madrid)
on 29 Mar 2004; 13:36 UT
Credential Certification: P.R. den Hartog (Hartog@sron.nl)

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We report the detection of a new hard X-ray source in 2.2 Msec of exposure on the Vela region as accumulated by INTEGRAL during June/July and November/December 2003. The position is R.A. = 7h 59m 43.5s, Decl. = -38o 42' 36s (Eq. J2000) with an error of 2'. It was detected at a 12-sigma significance level with the INTEGRAL IBIS/ISGRI detector in the 20-60 keV energy band. The source spectrum can be described by a simple power law with photon index 1.8+/-0.3 (Red. Chi^2 = 0.9, 6 dof) and flux 2.4 mcrab.

Archival searches/analyses provided possible counterparts at different wavelengths. The ROSAT source RXH J075942.0-384355 at the position R.A. = 07h 59m 42.0s ,Decl. = -38o 43' 56.0" (systematic error 6") is 1.4' from the INTEGRAL centroid position. The flux between 0.1 and 2.4 keV is 1.35 E-11 erg s-1 cm-2. Consistent with the ROSAT position we found a 1.4-GHz radio counterpart (R.A. = 07h 59m 41.8s; Decl. = -38o 43' 53"; 5" error) in the NVSS archive with a peak flux of 3.8 mJy, and an IRAS point source, IRAS 07579-3835, of 2.4e-1 Jy at 25 microns. Another ROSAT source, RXH J075959.2-384102, located 3.4' from the INTEGRAL position, is a less likely candidate counterpart.

The BeppoSAX Wide Field Cameras serendipitously observed the field around IGR J07594-3843 during roughly 250 observations over its 1996-2002 operational life. The total net exposure time is 3.5 Msec. The exposure per half year up to 2001 varies between 80 (2nd half 2001) and 900 ksec (second half 1996). Never was a source detected in a single observation, with upper limits ranging mostly between roughly 7 and 70 mCrab, nor in accumulations over half a year, with upper limits ranging between 1.0 and 3 mCrab (2-28 keV). However, a 7 sigma detection was obtained when combining all data, with a flux in the 2-9 keV band of 1.0 mCrab. The source position R.A.= 07h 59m 42.8s Decl. = -38o 43' 54s (3.6' at 99% confidence) is 0.2' from RXH J075942.0-384355 and 3.4' from RXH J075959.2-384102.

Both, the ROSAT and BeppoSAX-WFC flux values are within the errors consistent with the extrapolation of the power-law spectrum fitted to the INTEGRAL data points.

The nature of IGR J07597-3842 is unclear. The radio and IR candidate counterparts suggest an AGN, but a Galactic origin cannot be ruled out.