Abstract Details
| Name: Anwesh Majumder Affiliation: Presidency University Conference ID: ASI2018_1588 Title : Gamma-Ray/X-Ray/Optical Time Variability of Fermi Blazars Authors and Co-Authors : 1. Anwesh Majumder; Affiliation: Presidency University, Kolkata 2. Ritaban Chatterjee; Affiliation: Presidency University, Kolkata 3. Kaustav Mitra; Affiliation: Presidency University, Kolkata 4. Prantik Nandi; Affiliation: Presidency University, Kolkata(Currently at S.N. Bose National Centre for Basic Sciences) Abstract Type : Poster Abstract Category : Extragalactic astronomy Abstract : Blazars are a class of active galactic nuclei (AGN) with a prominent relativistic jet pointing within a few degrees of our line of sight. Due to relativistic beaming, apparent jet emission is amplified by a factor of 10-10,000. Hence, the spectral energy distribution (SED) of blazars is dominated by the emission from the jet. Blazar SED has two major components, e.g., a peak at infrared-optical wavebands believed to be due to synchrotron radiation by the relativistic electrons present in the jet, and another at X-ray-gamma-ray energies possibly due to inverse-Compton (IC) scattering of photons —— produced in or outside the jet ——- by the same electrons. In the above scenario, optical synchrotron emission may be produced by electrons of Lorentz factor ~10^4, assuming a magnetic field of ~few Gauss. Emission at ~1 GeV may be produced by electrons at similar energies by up-scatterng infrared photons from the dusty torus. X-rays, on the other hand, may be produced by very high-energy (Lorentz factor ~10^6) electrons through synchrotron radiation or by electrons of lower energy (Lorentz factor ~10^2) through IC processes. Therefore, it is imperative to study the cross-correlation between the variability at optical-X-ray-gamma-ray wave bands in a large sample of blazars and compare with predictions of the above model. Large Area Telescope (LAT) onboard Fermi Gamma-Ray Space Telescope has been observing the gamma-ray sky since its launch in 2008 and have detected ~2000 blazars. Supporting multi-wavelength campaigns have followed Fermi-detected blazars at a range of wavebands all over the electromagnetic spectrum. Therefore, it is now possible to determine the nature of the above cross-correlation for a large sample of blazars. In this work, we collect optical-X-ray-gamma-ray light curves of 30 blazars from the public databases of Fermi, Swift, and Yale-SMARTS blazar monitoring project, and study their cross-correlation. Due to the transient nature of blazars, multi-band cross-correlation for one source is often not representative of the average nature of the entire population. Therefore, we stack the cross-correlation function of multiple blazars such that the spurious peaks average out while the consistent peaks become more significant in the final result. In order to interpret the results obtained from the above cross-correlation study, we have constructed a numerical model of non-thermal emission from blazar jets, which includes emission from a distribution of electrons undergoing energy loss due to synchrotron radiation, IC process, and adiabatic expansion due to the conical geometry of the jet. We generate many simulated light curves at multiple wavelengths from our model and study the nature of their average cross-correlation. We compare our numerical results with those from observed data to provide constraints on the parameters related to the geometry and emission mechanism of blazar jets. |