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          Institute: MPI für Astronomie     Collection: Publikationen_mpia     Display Documents

ID: 710182.0, MPI für Astronomie / Publikationen_mpia
Active galactic nucleus X-ray Variability in the XMM-COSMOS survey
Authors:Lanzuisi, G.; Ponti, G.; Salvato, M.; Hasinger, G.; Cappelluti, N.; Bongiorno, A.; Brusa, M.; Lusso, E.; Nandra, P. K.; Merloni, A.; Silverman, J.; Trump, J.; Vignali, C.; Comastri, A.; Gilli, R.; Schramm, M.; Steinhardt, C.; Sanders, D.; Kartaltepe, J.; Rosario, D.; Trakhtenbrot, B.
Date of Publication (YYYY-MM-DD):2014
Title of Journal:The Astrophysical Journal
Issue / Number:2
Start Page:id. 105 (14 pp)
Audience:Not Specified
Abstract / Description:We used the observations carried out by XMM in the COSMOS field over 3.5 yr to study the long term variability of a large sample of active galactic nuclei (AGNs) (638 sources) in a wide range of redshifts (0.1 < z < 3.5) and X-ray luminosities (1041 < L 0.5-10 <1045.5). Both a simple statistical method to assess the significance of variability and the Normalized Excess Variance (\sigma ^{2}_{rms}) parameter were used to obtain a quantitative measurement of the variability. Variability is found to be prevalent in most AGNs, whenever we have good statistics to measure it, and no significant differences between type 1 and type 2 AGNs were found. A flat (slope -0.23 ± 0.03) anti-correlation between \sigma ^{2}_{rms} and X-ray luminosity is found when all significantly variable sources are considered together. When divided into three redshift bins, the anti-correlation becomes stronger and evolving with z, with higher redshift AGNs being more variable. We prove, however, that this effect is due to the pre-selection of variable sources: when considering all of the sources with an available \sigma ^{2}_{rms} measurement, the evolution in redshift disappears. For the first time, we were also able to study long term X-ray variability as a function of M BH and Eddington ratio for a large sample of AGNs spanning a wide range of redshifts. An anti-correlation between \sigma ^{2}_{rms} and M BH is found, with the same slope of anti-correlation between \sigma ^{2}_{rms} and X-ray luminosity, suggesting that the latter may be a by-product of the former. No clear correlation is found between \sigma ^{2}_{rms} and the Eddington ratio in our sample. Finally, no correlation is found between the X-ray \sigma ^{2}_{rms} and optical variability.
Free Keywords:galaxies: active; X-rays: galaxies; X-rays: general
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astronomie
Identifiers:ISSN:0004-637X %R 10.1088/0004-637X/781/2/105
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