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)
Subjects: Radio, Infra-Red, X-ray, Gamma Ray
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