Swift identifications of two INTEGRAL sources

ATel #2557; J. Rodriguez (CEA/SAp-AIM, Paris), A. Bodaghee, J. A. Tomsick (SSL, Berkeley)
on 14 Apr 2010; 08:53 UT
Credential Certification: Jerome Rodriguez (jrodriguez@cea.fr)

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We report the results of Swift/XRT (0.2-10 keV) and UVOT (UVW2 filter) observations of the fields of new INTEGRAL sources recently reported in the 4th IBIS catalog in the 20-40 keV and 40-100 keV energy ranges (Bird et al. 2010). The Swift XRT and UVOT data analysis methods are described in Rodriguez, Tomsick and Bodaghee 2010 A&A (in press, arXiV 1003.3741).

IGR J13045-5630 has an unknown source type as reported in the 4th IBIS catalog. The XRT exposure is 1671 s in photon counting mode. We found a 3.9 sigma source in the X-ray image within the IBIS error box. The source coordinates are R.A.=13h 04m 31.5s and Dec.=-56deg 30' 54.8" (+- 6.6" at 90% confidence, galactic coordinates l=304.74732, b=6.31038).

The XRT error box contains a single UVOT source with a magnitude m=19.1 +- 0.1 (sys+stat) in the UW2 band. There is no source reported in SIMBAD, 2MASS, 2MASX, and NED at a position compatible with that of XRT. There are, however, 3 sources listed in the USNO B1.0 catalog at positions consistent with that of Swift/XRT. The closest in position to the UVOT source (at 1.2") is USNO B1.0 0334-0372825, that has m_I=12.6 m_R=13.0 m_B=14.4. The XRT spectrum has too few counts (17 net counts) to perform a meaningful spectral analysis.

IGR J13550-7218 also has an unknown type as reported in the 4th IBIS catalog. We found a 4.4 sigma source at R.A.=13h 55m 13.05s and Dec.=-72deg 19' 11.62" (+-5.7" at 90% confidence, galactic coordinates l=307.79251,b=-10.05271).

The XRT error box contains a single UVOT source with a magnitude m=20.0 +- 0.2 (sys+stat) in the UW2 band. The source may possibly be extended but given its faintness we consider the evidence as being only very marginal. There is no source reported in the 2MASS, 2MASX, or NED catalogs. There is a single USNO B1.0 source within the XRT error box that is also compatible with being the optical counterpart to the UVOT source. USNO B1.0 0176-0353892 has m_I=15.6 m_R=15.1 m_B=16.8. Note that inspection of the Digitized Sky Survey IR, R and B images show two possible objects within the XRT error box.

The XRT spectrum only has 24 net counts. A fit with an absorbed power law seems to give a good representation of the spectrum, but the spectral parameters are very poorly constrained, especially the power law index. However, the best fit seems to indicate that the spectrum is significantly absorbed. When allowing all parameters to vary (and constraining Gamma to be between 1.5 and 3), we obtained N_H=19 -9 +8 10^22 cm-2. Gamma however pegged at the highest value allowed. The 0.5-10 keV (absorbed) flux is 2.1e-12 erg/s/cm2.
Although we cannot give a definite classification of this object, its high Galactic latitude, the possible extension of the UVOT counterpart, and the quite absorbed spectrum may indicate an AGN.