Title: Understanding the physics behind variability in blazars

Speaker: Dr. Sunil Chandra, Center for Space Research, North West University, South Africa

Abstract: Blazars, a subclass of Active Galactic Nuclei (AGNs) supposedly seen along the axis of the jet of relativistic plasma emanated from very close to the central engine, an accreting supermassive blackhole (SMBH), make a unique sample to understand a variety of physics occurring in the exotic environment. The formation of gigantic jets, the greater degree of collimation, the role and morphology of magnetic field close to SMBH and at the base of jet etc are a few open questions which are being tackled using observables from this subclass. The acceleration of particles to ultra-relativistic energies within a short span of time, as indicated from the rapid flux and polarization variations during flares is among the least understood phenomenon about relativistic jets. The observational and theoretical limitations forces us to have poor constraints on this, leading to multiple alternatives to explain same observed event, e.g.,diffusive shock accelerations (Fermi type-I and II), reconnections, or even geometry based models etc.

Our group, including a list of theoretical and observational experts from India and abroad, is conducting combined efforts to utilize almost simultaneous and rich multi-wavelength data for a sample of blazars to understand the particle accelerations during flares from relativistic jets. We have been conducting multi-wavelength campaigns using AstroSat, NuSTAR, Swift, SALT, HESS and FACT to monitor a sample whenever we notice flux enhancements in MeV-GeV band (100 MeV - 300 GeV) by Fermi -LAT telescope. In this seminar I plan to summarize the part of work done by us over last couple of years.