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

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 1999) we showed that the X-ray and IR variability from 3C273 was highly correlated in 1997, with the IR flux leading the X-rays by ~0.75 +/- 0.25 days. The strong correlation, and lag, supports the Synchrotron Self-Compton (SSC) model, where the seed photons are synchroton 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%, lasting for ~5 days, showing a high correlation between IR and X-ray variations, with the X-rays lagging by ~1.45+/- 0.15 days. 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.

arXiv comment7 pages in total, including 5 figures. Accepted for publication in Monthly Notices of the Royal Astronomical Society

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• Multi-color optical monitoring of the quasar 3C 273 from 2005 to 2016
• X-Ray Variability of AGN and Relationship to Galactic Black Hole Binary Systems
• Exploring the nature of broadband variability in the FSRQ 3C 273
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• Short Timescale AGN X-ray Variability with EXOSAT: Black hole mass and Normalised Variability Amplitude
• Multifractality Signatures in Quasars Time Series. I. 3C 273
• Multiwavelength Analysis of the Variability of the Blazar 3C 273
• SDSSJ14584479+3720215: A Benchmark JHK Blazar Light Curve from the 2MASS Calibration Scans