Name: Ritaban Chatterjee
Affiliation: Presidency University
Conference ID : ASI2022_463
Title : Locating the Gamma-Ray Emission Region in the Jets Using Simultaneous GeV/Optical Flares of Blazars
Authors : Ritaban Chatterjee (Department of Physics, Presidency University, Kolkata, India); Saugata Barat (Anton Pannekoek Institute for Astronomy, University of Amsterdam, the Netherlands); Kaustav Mitra (Department of Astronomy, Yale University, New Haven, USA)
Abstract Type: Poster
Abstract Category : Extragalactic Astronomy
Abstract : Whether GeV emission in the jets of blazars is produced at 0.1-1 pc from the central super-massive black hole (SMBH) or farther down the jet is not known. However, it is an important quantity in the process of constraining the relevant emission mechanisms and physical parameters of the jet, as well as in our understanding of its interaction with the interstellar and intergalactic medium. Modeling of the broadband spectral energy distribution of blazars have often indicated that the GeV emission originates within the broad line region (BLR), i.e., less than a pc from the SMBH. However, in several blazars TeV emission has been detected during GeV outbursts, which is only possible if the emission region is outside the BLR because otherwise TeV photons would not be able to escape due to the photon-photon interaction at the BLR. Furthermore, simultaneous multi-wavelength observations of blazars along with monitoring of their pc-scale jet using very long baseline interferometry (VLBI) at GHz frequencies have revealed that the gamma-rays may be produced near the "VLBI core," which is located tens of pc down the jet from the SMBH. In this talk, I shall present a method to overcome the above ambiguity and identify the location of the GeV emission. We study simultaneous months-timescale optical and GeV outbursts in approximately ten blazars using their archival light curves spanning eight years. The relative properties of the multi-wavelength outbursts depend on a number of parameters including the location of the emission region. By comparing the properties of the observed flares with that from a theoretical model we have developed, we constrain their location to be farther down the jet from the BLR at a few to ten pc from the central SMBH.