Long-term multiband monitoring of blazar 3C 66A: Evidence of the two distinct states with different baseline flux

Author:

Mohana A Krishna1ORCID,Bhattacharya Debbijoy1ORCID,Misra Ranjeev2,Bhattacharyya Subir34ORCID,Bhatt Nilay3ORCID

Affiliation:

1. Manipal Centre for Natural Sciences, Centre of Excellence, Manipal Academy of Higher Education, Manipal 576104, Karnataka, India

2. Inter-University Center for Astronomy and Astrophysics, Pune 411007, Maharashtra, India

3. Astrophysical Sciences Division, Bhabha Atomic Research Centre, Mumbai 400085, Maharashtra, India

4. Homi Bhabha National Institute, Anushaktinagar, Mumbai 400094, Maharashtra, India

Abstract

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 yr Fermi γ-ray light curve of the blazar 3C 66A, where the baseline flux of ∼1.8 × 10−7 ph cm−2 s−1 persisted for three years and then changed over a month time-scale to ∼0.8 × 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 ∼1° or a decrease in the bulk Lorentz factor by ∼25 per cent. We discuss the implication of such a variation occurring on a month time-scale.

Funder

National Aeronautics and Space Administration

National Science Foundation

California Institute of Technology

University of California, Los Angeles

Jet Propulsion Laboratory

Russian Academy of Sciences

Publisher

Oxford University Press (OUP)

Subject

Space and Planetary Science,Astronomy and Astrophysics

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