Abstract Details
| Name: Anwesh Majumder Affiliation: Presidency University, Kolkata Conference ID: ASI2019_110 Title : Physical Inference from γ-ray, X-ray and Optical/IR Time Variability of a Large Sample of Fermi Blazars Authors and Co-Authors : Anwesh Majumder, Kaustav Mitra, Ritaban Chatterjee, CD Bailyn, CM Urry, Prantik Nandi Abstract Type : Oral Abstract Category : Extragalactic Astronomy Abstract : Blazars are a class of active galactic nuclei with a bright relativistic jet pointed within few degrees of our line of sight. We present cross-correlation studies of γ-ray (0.1-300 GeV), X-ray (0.2-10 keV) and optical (R-band) variability of a sample of ∼15 blazars during 2008-2016 using publicly available light curves from the Fermi-LAT, Swift-XRT, and Yale-SMARTS blazar monitoring program, respectively. We stack the discrete cross-correlation functions of the blazars so that spurious peaks in individual sources average out while the consistent features of the population become more prominent in the final result. We find that, on average, the variability at multiple bands are strongly correlated with time lag consistent with zero in both flat spectrum radio quasars (FSRQ) and BL Lac objects (BLL). However, in some individual BLLs the γ-ray/optical correlation is weak or absent while in two FSRQs the γ-ray/optical time delay is much longer (> 50 days). We develop a model of non-thermal emission from blazar jets including synchrotron radiation by relativistic electrons and inverse-Compton scattering of synchrotron photons as well as photons external to the jets, e.g. from the broad line region and dusty torus by the same electrons. By comparing the model results with that from the actual data we find that the model light curves and the strength and time delay of inter-band cross-correlation are consistent with an emission region of size ∼0.1 pc within the broad line region for FSRQs. We rule out large changes of magnetic field (> 0.5 Gauss) across the emission region or very small values of magnetic field (< 0.2 Gauss). |