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Title:
Simultaneous X-ray and infrared variability in the quasar 3C273 - II. Confirmation of the correlation and X-ray lag
Authors:
McHardy, Ian; Lawson, Anthony; Newsam, Andrew; Marscher, Alan P.; Sokolov, Andrei S.; Urry, C. Megan; Wehrle, Ann E.
Affiliation:
AA(School of Physics and Astronomy, University of Southampton SO17 1BJ), AB(School of Physics and Astronomy, University of Southampton SO17 1BJ), AC(School of Physics and Astronomy, University of Southampton SO17 1BJ; Liverpool John Moores University, Astrophysics Research Institute, Birkenhead CH41 1LD), AD(Institute for Astrophysical Research, 725 Commonwealth Avenue, Boston University, Boston, MA 02215, USA), AE(Institute for Astrophysical Research, 725 Commonwealth Avenue, Boston University, Boston, MA 02215, USA), AF(Department of Physics, Yale University, PO Box 208121, New Haven, CT 06520-8121, USA), AG(IPAC, Jet Propoulsion Laboratory and California Institute of Technology, Pasadena, CA 91125, USA)
Publication:
Monthly Notices of the Royal Astronomical Society, Volume 375, Issue 4, pp. 1521-1527. (MNRAS Homepage)
Publication Date:
03/2007
Origin:
MNRAS
MNRAS Keywords:
galaxies: active , quasars: individual: 3C273 , X-rays: galaxies
Abstract Copyright:
(c) 2007 The Authors. Journal compilation © 2007 RAS
DOI:
10.1111/j.1365-2966.2006.11420.x
Bibliographic Code:
2007MNRAS.375.1521M

Abstract

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 ~25per 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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