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IGR J06074+2205 is a Be X-ray Binary

ATel #959; J. A. Tomsick (SSL/UC Berkeley and CASS/UCSD), S. Chaty (CEA Saclay), J. Rodriguez (CEA Saclay), R. Walter (ISDC), P. Kaaret (Univ. of Iowa)
on 7 Dec 2006; 18:09 UT
Credential Certification: John A. Tomsick (jtomsick@ucsd.edu)

Subjects: X-ray, Binary, Black Hole, Neutron Star, Transient, Variables

Referred to by ATel #: 1018

The X-ray source IGR J06074+2205 was discovered using data from observations made by INTEGRAL in 2003 February. (Chenevez et al. 2004, ATEL#223). Two different sources in the 2 arcminute INTEGRAL error circle have been suggested as possible counterparts. The first is the radio source NVSS J060718+220452 (Pooley et al. 2004, ATEL#226; Pandey et al. 2006), while the second possible counterpart is a Be star (Halpern & Tyagi 2005, ATEL#682; Masetti et al. 2006). In order to localize the X-ray source and determine the correct counterpart, we obtained a 5 ks observation with the Chandra X-ray Observatory on 2006 December 2. A 0.3-8 keV Chandra image shows only one bright source in the INTEGRAL error circle at a position of R.A. = 06h 07m 26s.62, Decl. = +22d 05' 47".6 (equinox 2000.0, uncertainty = 0".6). This source is only 0".5 from the Be star, confirming that IGR J06074+2205 is a Be X-ray binary. No X-ray source is detected at the location of the suggested radio counterpart. Further evidence that the Chandra and INTEGRAL sources are the same comes from our spectral analysis that shows that the Chandra source is very hard. Its spectrum can be described by an absorbed power-law with a column density of N_H = (6+/-2) x 10^22 cm^-2 and a photon index of 1.3+/-0.8 (90% confidence errors). The absorbed 0.3-10 keV flux of the source is 2 x 10^-12 ergs/cm^2/s, which is about a factor of 60 lower than the 5-7 mCrab flux reported at the time of its discovery (ATEL#223). Such variability is consistent with the behavior of Be X-ray binaries.