Hard X-ray variability of active galactic nuclei
Abstract
Aims:Active Galactic Nuclei are known to be variable throughout the electromagnetic spectrum. An energy domain poorly studied in this respect is the hard X-ray range above 20 keV.
Methods: The first 9 months of the Swift/BAT all-sky survey are used to study the 14-195 keV variability of the 44 brightest AGN. The sources have been selected due to their detection significance of >10 σ. We tested the variability using a maximum likelihood estimator and by analysing the structure function.
Results: Probing different time scales, it appears that the absorbed AGN are more variable than the unabsorbed ones. The same applies for the comparison of Seyfert 2 and Seyfert 1 objects. As expected the blazars show stronger variability. 15% of the non-blazar AGN show variability of >20% compared to the average flux on time scales of 20 days, and 30% show at least 10% flux variation. All the non-blazar AGN which show strong variability are low-luminosity objects with L(14{-195 keV)} < 1044 erg s-1
Conclusions: Concerning the variability pattern, there is a tendency of unabsorbed or type 1 galaxies being less variable than the absorbed or type 2 objects at hardest X-rays. A more solid anti-correlation is found between variability and luminosity, which has been previously observed in soft X-rays, in the UV, and in the optical domain.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- December 2007
- DOI:
- 10.1051/0004-6361:20078355
- arXiv:
- arXiv:0709.2230
- Bibcode:
- 2007A&A...475..827B
- Keywords:
-
- galaxies: active;
- galaxies: Seyfert;
- X-rays:;
- galaxies;
- surveys;
- Astrophysics
- E-Print:
- 9 pages, 7 figures, accepted for publication in A&