INTEGRAL and Swift/XRT observations of IGR J19405-3016

Abstract

Aims. IGR J19405-3016 is reported in the 3rd IBIS catalog as one of its lowest significance sources (∼4.6σ 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 ∼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 ∼9.4σ 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 × 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.