Abstract Details

Name: Ashwani Pandey
Affiliation: ARIES Nainital
Conference ID: ASI2020_419
Title : Multiwavelength Studies of TeV Blazars
Authors and Co-Authors : Ashwani Pandey
Abstract Type : Oral
Abstract Category : Thesis
Abstract : Blazars, comprising BL Lacertae objects (BL Lacs) and flat-spectrum radio quasars (FSRQs), are the active galactic nuclei (AGNs) with strong relativistic jets pointing towards the direction of the observer. Their double-humped spectral energy distributions (SEDs) extend from radio to very high energy γ−rays. TeV (Tera- electron Volt) blazars, those significantly observed at TeV energies, are mostly the high-frequency peaked BL Lac objects (HBLs), that is, the first hump of their SED peaks at optical to X-ray energy bands. In the first part of the thesis, we have examined 46 hard X-ray light curves (LCs) of all (11) the TeV HBLs that have been observed with the NuSTAR satellite for intraday flux and spectral variability. We detected strong intraday variability (IDV) in the LCs of six TeV HBLs. Using discrete autocorrelation function (ACF) we found evidence for variability timescales ranging from 2.5 to 57.4 ks in the twelve LCs of four TeV HBLs. For these four TeV HBLs, we have constrained the values of magnetic field strength (B), electron Lorentz factor (γ) and the emitting region size (R) using their minimum variability timescales. The second part of the thesis consists of the results of optical (BV RI) variability study of five TeV HBLs performed during 2016−2018. We have examined 61 optical LCs of five TeV HBLs for IDV using two latest statistical tests: the power-enhanced F-test and the ANOVA test. We found evidence of significant IDV with very small variability amplitudes only in six LCs. We generated the optical SEDs of TeV blazars and fitted them with a single power-law to examine the variations in their optical spectral indices during our monitoring period.