A Census of AGN with INTEGRAL
Abstract
Most cosmic accretion onto supermassive black holes is obscured by gas and dust that absorbs all but the hardest X-ray photons. A complete census of AGN is possible with a hard X-ray survey like the one we are carrying out with INTEGRAL in the XMM-LSS field. This survey offers an important constraint on the demographics of heavily obscured AGN; an important and complementary constraint is provided by the X-ray background, but because it is an integral constraint, the number of Compton-thick sources is degenerate with their hard X-ray intensities. Our ultra-deep INTEGRAL survey offers a direct constraint on the number of Compton-thick sources and thus on the normalization of the reflection component. To date, we have obtained and analyzed 2.2 Msec of the 3 Msec allotted time, detecting roughly a dozen AGN at high significance. Most are previously catalogued Seyfert galaxies and all are local (z<0.1). At most two are Compton-thick AGN, fewer than predicted by some models for the X-ray background. This discrepancy implies a higher efficiency for reflection in individual sources. The statistics can be improved significantly - to nearly 50 AGN - by adding 7 Msec to the INTEGRAL exposure and co-adding 10 Msec of Swift BAT data, which will probe evolution to z 0.1.
- Publication:
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AAS/High Energy Astrophysics Division #10
- Pub Date:
- March 2008
- Bibcode:
- 2008HEAD...10.3502U