Correlated X-ray/optical variability in the quasar MR 2251-178

Arevalo, P; Uttley, P.; Kaspi, S; Breedt, E; Lira, P; MCHARDY, IM

Abstract

Emission from active galactic nuclei is known to vary strongly over time over a wide energy band, but the origin of the variability and especially of the interband correlations is still not well established. Here we present the results of our X-ray and optical monitoring campaign of the quasar MR 2251-178, covering a period of 2.5 years. The X-ray 2-10 keV flux is remarkably well correlated with the optical B, V and R bands, their fluctuations are almost simultaneous with a delay consistent with 0 d and not larger than 4 d in either direction. The amplitude of variations shows an intriguing behaviour: rapid, large amplitude fluctuations over tens of days in the X-rays have only small counterparts in the optical bands, while the long-term trends over hundreds of days are stronger in the B band than in X-rays. We show that simple reprocessing models, where all the optical variability arises from the variable X-ray heating, cannot simultaneously explain the discrepant variability amplitudes on different time-scales and the short delays between X-ray and optical bands. We interpret the variability and correlations, in the optically thick accretion disc plus corona scenario, as the result of intrinsic accretion rate variations modulating both X-ray and optical emission, together with reprocessing of X-rays by the accretion disc. © 2008 RAS.

Más información

Título según WOS: Correlated X-ray/optical variability in the quasar MR 2251-178
Título según SCOPUS: Correlated X-ray/optical variability in the quasar MR 2251-178
Título de la Revista: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volumen: 389
Número: 3
Editorial: OXFORD UNIV PRESS
Fecha de publicación: 2008
Página de inicio: 1479
Página final: 1488
Idioma: English
URL: http://mnras.oxfordjournals.org/cgi/doi/10.1111/j.1365-2966.2008.13719.x
DOI:

10.1111/j.1365-2966.2008.13719.x

Notas: ISI, SCOPUS