| Name: | Krishna Mohana A |
| Affiliation: | Manipal Centre for Natural Sciences, Manipal Academy of Higher Education |
| Conference ID : | ASI2022_286 |
| Title : | Long-term multi-band monitoring of blazar 3C 66A: Evidence of the two distinct states with different baseline flux |
| 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: | Oral |
| Abstract Category : | Extragalactic Astronomy |
| Abstract : | Blazar variability can be described as flaring activities on a wide range of time-scales over a baseline flux level. It is important to detect and distinguish baseline flux changes from long-term flare variations, since the former may reflect state transitions caused by a secular change in bulk properties such as the bulk Lorentz factor or the viewing angle. We report such a transition observed in the 11 year Fermi $\gamma$-ray lightcurve of the blazar 3C 66A, where the baseline flux of $\sim 1.8\times 10^{-7}$ ph cm$^{-2}$ s$^{-1}$ persisted for three years and then changed over a month timescale to $\sim 0.8\times 10^{-7}$ ph cm$^{-2}$ s$^{-1}$ and remained in that level for the next eight years. Moreover, there is evidence for a similar shift in baseline flux in the optical band. Broad-band spectral energy distribution modelling for the two activity states reveals that the baseline flux change is consistent with an overall decrease in the Doppler factor, which in turn implies an increase in the jet inclination angle by $\sim 1^\circ$ or a decrease in the bulk Lorentz factor by $\sim 25$\%. We discuss the implication of such a variation occurring on a month time-scale. The results of this recently published work will be presented here. |