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Correlated X-ray/optical variability in the quasar MR 2251−178
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Arévalo, P., Uttley, P., Kaspi, S., Breedt, E., Lira, Paulina and McHardy, Ian M. (2008) Correlated X-ray/optical variability in the quasar MR 2251−178. Monthly Notices of the Royal Astronomical Society, Vol. 389 (No. 3). pp. 1479-1488. doi:10.1111/j.1365-2966.2008.13719.x ISSN 00358711.
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Official URL: http://dx.doi.org/10.1111/j.1365-2966.2008.13719.x
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.
| Item Type: | Journal Article | ||||
|---|---|---|---|---|---|
| Divisions: | Faculty of Science, Engineering and Medicine > Science > Physics | ||||
| Journal or Publication Title: | Monthly Notices of the Royal Astronomical Society | ||||
| Publisher: | Wiley | ||||
| ISSN: | 00358711 | ||||
| Official Date: | 2008 | ||||
| Dates: |
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| Volume: | Vol. 389 | ||||
| Number: | No. 3 | ||||
| Page Range: | pp. 1479-1488 | ||||
| DOI: | 10.1111/j.1365-2966.2008.13719.x | ||||
| Status: | Peer Reviewed | ||||
| Publication Status: | Published | ||||
| Access rights to Published version: | Restricted or Subscription Access |
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