INTEGRAL and Swift/XRT observations of IGR J19405-3016

IGR J19405-3016 is reported in the 3rd IBIS catalog as being one of its lowest significance sources (~4.6 sigma under an exposure of about 371 ks). This leads to a caveat in multi-wavelength study although the source was identified in optical as a Seyfert 1. The currently increased INTEGRAL data stimulate us to investigate the reality of this source. We analyze all available observations carried out by INTEGRAL and Swift on IGR J19405-3016. We find that IGR J19405-3016 has a detection significance of ~ 9.4 sigma in the 20-60 keV band during the observational period between March 2003 and March 2008. Thus confirms a real source detection reported previously. The source position and error location are therefore updated. The source is found to be constant over years at the hard X-rays. Over the three XRT observations, the source flux varied by up to 39% from the average, and the spectrum is generally soft. The combined XRT/ISGRI spectrum is well fitted with a simple power law model (photon index 2.11+-0.03). Such a photon index is well consistent with the mean value 1.98 (dispersion 0.27) as obtained from Swift/BAT AGN samples at 14-195 keV. The spectral slope of IGR J19405-3016 is larger than the average spectral slope found by Molina et al. (2009). A similar discrepancy is found with the results of Beckmann et al. (2009) regarding Seyfert 1 AGNs. A possible explanation of this simple spectral description may be that the low level of the column density allows for the `true' spectrum to appear at soft X-rays as well.
Comment: Astronomy and Astrophysics, in press