X-ray variability of SDSS quasars based on the SRG/eROSITA all-sky survey

Monthly Notices of the Royal Astronomical Society. 2024. Vol. 528. No. 4. P. 5972–5989.

S. A. Prokhorenko, S. Yu. Sazonov, Gilfanov M. R., S. A. Balashev, Bikmaev I. F., Ivanchik A. V., Medvedev P. S.

We examine the long-term (rest-frame time scales from a few months to ∼20 years) X-ray variability of a sample of 2344 X-ray bright quasars from the SDSS DR14Q Catalogue, based on the data of the SRG/eROSITA All-Sky Survey complemented for ∼7% of the sample by archival data from the XMM-Newton Serendipitous Source Catalogue. We characterise variability by a structure function, SF2(Δt). We confirm the previously known anti-correlation of the X-ray variability amplitude with luminosity. We also study the dependence of X-ray variability on black hole mass, MBH, and on an X-ray based proxy of the Eddington ratio, λX. Less massive black holes prove to be more variable for given Eddington ratio and time scale. X-ray variability also grows with decreasing Eddington ratio and becomes particularly strong at λX of less than a few per cent. We confirm that the X-ray variability amplitude increases with increasing time scale. The SF2(Δt) dependence can be satisfactorily described by a power law, with the slope ranging from ∼0 to ∼0.4 for different (MBH, λX) subsamples (except for the subsample with the lowest black hole mass and lowest Eddington ratio, where it is equal to 1.1 ± 0.4).

Keywords: рентгеновское излучение, аккреция, аккреционные диски, active galactic nuclei, квазары, сверхмассивные черные дыры, accretion, accretion discs, quasars: supermassive black holes, X-rays: galaxies