Open AccessSimultaneous X‐ray and infrared variability in the quasar 3C273 – II. Confirmation of the correlation and X‐ray lag
Author(s) -
McHardy Ian,
Lawson Anthony,
Newsam Andrew,
Marscher Alan P.,
Sokolov Andrei S.,
Urry C. Megan,
Wehrle Ann E.
Publication year - 2007
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2006.11420.x
Subject(s) - physics , astrophysics , quasar , photon , synchrotron , flare , compton scattering , infrared , blazar , rosat , x ray , electron , astronomy , flux (metallurgy) , scattering , amplitude , gamma ray , galaxy , optics , nuclear physics , materials science , metallurgy
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.