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

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

galaxies: active
0035-8711
1479-1488
Arévalo, P.
16a262f1-5692-423c-83f4-a61364f9f958
Uttley, Philip
db770bd7-d97e-43f5-99d4-a585bccd352a
Kaspi, S.
2ee9658d-8799-49b8-994c-b8979fbbd9a0
Breedt, Elme
8a142b4e-67c2-4d4e-a7d5-9d179a63b2ec
Lira, P.
f209900c-34b4-4225-b87a-d53855819b7f
McHardy, I.M.
4f215137-9cc4-4a08-982e-772a0b24c17e
Arévalo, P.
16a262f1-5692-423c-83f4-a61364f9f958
Uttley, Philip
db770bd7-d97e-43f5-99d4-a585bccd352a
Kaspi, S.
2ee9658d-8799-49b8-994c-b8979fbbd9a0
Breedt, Elme
8a142b4e-67c2-4d4e-a7d5-9d179a63b2ec
Lira, P.
f209900c-34b4-4225-b87a-d53855819b7f
McHardy, I.M.
4f215137-9cc4-4a08-982e-772a0b24c17e

Arévalo, P., Uttley, Philip, Kaspi, S., Breedt, Elme, Lira, P. and McHardy, I.M. (2008) Correlated X-ray/optical variability in the quasar MR?2251?178. Monthly Notices of the Royal Astronomical Society, 389 (3), 1479-1488. (doi:10.1111/j.1365-2966.2008.13719.x).

Record type: Article

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.

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Published date: 26 July 2008
Keywords: galaxies: active

Identifiers

Local EPrints ID: 144533
URI: https://eprints.soton.ac.uk/id/eprint/144533
ISSN: 0035-8711
PURE UUID: 76772544-ae2c-4fbe-9988-21393fc514d4

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Date deposited: 24 May 2010 11:32
Last modified: 28 Oct 2019 21:42

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