Abstract Details

Name: Krishna Mohana A
Affiliation: Manipal Centre for Natural Sciences, Centre of Excellence, Manipal Academy of Higher Education, Manipal
Conference ID: ASI2021_335
Title : A long-term study of 3C 66A and PKS 0208-512: an exhibition of baseline activity change and decade long stay at very low-state
Authors and Co-Authors : Krishna Mohana A (Manipal Centre for Natural Sciences, Centre of Excellence, Manipal Academy of Higher Education, Manipal-576104, Karnataka, India), Debbijoy Bhattacharya (Manipal Centre for Natural Sciences, Centre of Excellence, Manipal Academy of Higher Education, Manipal-576104, Karnataka, India), Ranjeev Misra ( Inter University Centre for Astronomy and Astrophysics, Pune, India), Subir Bhattacharyya (Bhabha Atomic Research Centre, Mumbai - 400085, India ), Nilay Bhatt (Bhabha Atomic Research Centre, Mumbai - 400085, India )
Abstract Type : Poster
Abstract Category : Extragalactic Astronomy
Abstract : Blazars are known to exhibit variations of different time scales across the waveband. We report a presence of two long-term activity states with a factor of two difference in average ɣ-ray flux from the 11 yr of ɣ-ray lightcurve of 3C 66A with transition timescale of the month. The first activity state was for ~3 yr, followed by a change in the baseline activity during 2011 May, which further continued for the next 8 yr. Also, a similar change in baseline flux was noticed in the optical band. From the construction and modeling of broad-band SEDs during the different activity states of 3C 66A, we found a decrease in the Doppler beaming factor could explain the observed reduction in the average flux. We speculate either a bending jet scenario with an increase in the jet inclination angle by ~1° or slowing down of the jet by ~25% during the later state. From the Fermi-LAT ɣ-ray lightcurve, we noticed that the activity of another source PKS 0208-512 reduced significantly during the first 10 yr of Fermi operation (2008-2018) compared to its average flux as observed by its predecessor EGRET during its first five years of observation (1991-1995). During the last two years, the source activity has increased noticeably, reaching the high gamma-ray flux level observed during EGRET time. We have observed this source through AstroSat during low and very high activity states. The results of multi-band study of 3C 66A and PKS 0208-512 during their different activity states will also be presented here.