INTEGRAL and Swift/XRT observations of IGR J19405-3016

2009 
Aims. IGR J19405-3016 is reported in the 3rd IBIS catalog as one of its lowest significance sources (similar to 4.6 sigma under an exposure of about 371 ks). This leads to a caveat in multi-wavelength studies, although the source was identified in the optical as a Seyfert 1. The currently available INTEGRAL data on the source have increased to an exposure time of similar to 1376 ks, which stimulates us to investigate the reality of this source again by using all the available data from INTEGRAL and Swift/XRT. Methods. We analyzed all available observations carried out by the International Gamma-Ray Astrophysics Laboratory (INTEGRAL) on IGR J19405-3016. The data were processed by using the latest version OSA 7.0. In addition, we analyzed all the available Swift/XRT data on this source. Results. We find that IGR J19405-3016 has a detection significance of similar to 9.4 sigma in the 20-60 keV band during the observational period between March 2003 and March 2008. This 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. We analyzed the Swift/XRT observations on IGR J19405-3016 as well, and find that the spectrum can be fitted with a simple power law model. 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) with a column density fixed at 8.73 x 10(20) atoms/cm(2). Such a photon index is consistent with the mean value 1.98 (dispersion 0.27) obtained from Swift/BAT AGN samples at 14-195 keV. The spectral slope of IGR J19405-3016 is softer than the average spectral slope found elsewhere. A similar discrepancy is found with other results regarding Seyfert 1 AGNs. A possible explanation for 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.
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