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Simultaneous X-ray and infrared variability in the quasar 3C273 – II. Confirmation of the correlation and X-ray lag

McHardy, Ian and Lawson, Anthony and Newsam, Andrew and Marscher, Alan P. and Sokolov, Andrei S. and Urry, C. Megan and Wehrle, Ann E. (2007) Simultaneous X-ray and infrared variability in the quasar 3C273 – II. Confirmation of the correlation and X-ray lag. Monthly Notices of the Royal Astronomical Society, 375 (4). pp. 1521-1527. ISSN 0035-8711.

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The X-ray emission from quasars, such as 3C273, is generally agreed to arise from Compton scattering of low-energy seed photons by relativistic electrons in a relativistic jet oriented close to the line of sight. However, there are a number of possible models for the origin of the seed photons. In Paper I (McHardy et al.), we showed that the X-ray and infrared (IR) variability from 3C273 was highly correlated in 1997, with the IR flux leading the X-rays by ∼0.75 ± 0.25 d. The strong correlation, and lag, supports the synchrotron self-Compton (SSC) model, where the seed photons are synchrotron photons from the jet itself. The previous correlation was based on one moderately well-sampled flare and another poorly sampled flare, so the possibility of chance correlated variability exists. Here, we report on further X-ray and IR observations of 3C273 which confirm the behaviour seen in Paper I. During a 2-week period of observations, we see a flare of amplitude ∼25 per cent, lasting for ∼5 d, showing a high correlation between IR and X-ray variations, with the X-rays lagging by ∼1.45 ± 0.15 d. These observations were not scheduled at any special time, implying that the same mechanism – almost certainly SSC – dominates the X-ray emission on most occasions and that the structure of the emission region is similar in most small flares.

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Urry, C. Megan0000-0002-0745-9792
Additional Information:© 2007 The Authors. Journal compilation © 2007 RAS. Accepted 2006 December 18. Received 2006 December 18; in original form 2006 September 17. We thank the management and operational staff of both RXTE and UKIRT for their cooperation in scheduling and carrying out these observations. IM thanks PPARC for support by grant GRK21931 and by the award of a Senior Fellowship. The Boston University effort was supported in part by the National Science Foundation through grants AST-0098579 and AST-0406865 and by NASA through grants NAG5-11811 and NAG5-13074.
Funding AgencyGrant Number
Particle Physics and Astronomy Research Council (PPARC)GRK21931
Subject Keywords:galaxies : active; quasars : individual : 3C273; X-rays : galaxies
Issue or Number:4
Record Number:CaltechAUTHORS:20091116-083339451
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:16709
Deposited By: Tony Diaz
Deposited On:25 Nov 2009 20:03
Last Modified:03 Oct 2019 01:15

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