ESA Science & Technology: A deep INTEGRAL hard X-ray survey of the 3C 273/Coma region

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A deep INTEGRAL hard X-ray survey of the 3C 273/Coma region

Publication date: 15 July 2008

Authors: Paltani, S. et al.

Journal: Astronomy & Astrophysics
Volume: 485
Issue: 3
Page: 707-718
Year: 2008

Copyright: ESO

We present an analysis of the deepest hard X-ray survey to date of about 2500 deg² performed by the IBIS instrument on board INTEGRAL in the 20-60 keV band, with a total exposure time of 4 Ms. We find 34 candidate sources, for which we try to find counterparts at other wavelengths. The ratio of Seyfert 1 to Seyfert 2 is significantly more than the ratio found in the optical. This effect may be explained in the framework of the receding-torus model, but could also be due to absorption columns large enough to affect the 20-60 keV band. None of the predicted Compton-thick objects with 10²⁴ < N_H < 10²⁵ cm^-2 is detected unambiguously; when taking lower limits on N_H into account, the fraction of these objects is found to be lower than 24%. We do not see, but cannot exclude, a relationship between absorption and luminosity similar to what is seen in the 2-10 keV band. Our data suggests the possibility of a lack of objects with 10²¹ <= N_H <= 10²² cm^-2, which could be expected if absorption has two origins, for instance a torus-like structure and the host galaxy. We find that the Log N-Log S diagram of our sources is compatible with those obtained in other surveys in hard X-rays. Compared to models of the AGN population selected in the 2-10 keV band, the Log N-Log S diagram is generally in good agreement, but the N_H distribution is significantly different, with significantly less unabsorbed sources (N_H < 10²² cm^-2) at a given flux limit compared to the models. In this survey, we resolve about 2.5% of the cosmic X-ray background in the 20-60 keV band. -- Remainder of abstract is truncated --

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Last Update: 01 August 2008