Multi-wavelength temporal and spectral variability of the blazar OJ 287 during and after the December 2015 flare: a major accretion disc contribution

Abstract

We present a multi-wavelength spectral and temporal analysis of the blazar OJ 287 during its recent activity between December 2015 -- May 2016, showing strong variability in the near-infrared (NIR) to X-ray energies with detection at $\gamma$-ray energies as well. Most of the optical flux variations exhibit strong changes in polarization angle and degree. All the inter-band time lags are consistent with simultaneous emissions. Interestingly, on days with excellent data coverage in the NIR--UV bands, the spectral energy distributions (SEDs) show signatures of bumps in the visible--UV bands, never seen before in this source. The optical bump can be explained as accretion-disk emission associated with the primary black hole of mass $\sim 1.8\times 10^{10}{\mathrm{M}}_{\odot }$ while the little bump feature in the optical-UV appears consistent with line emission. Further, the broadband SEDs extracted during the first flare and during a quiescent period during this span show very different $\gamma$-ray spectra compared to previously observed flare or quiescent spectra. The probable thermal bump in the visible seems to have been clearly present since May 2013, as found by examining all available NIR-optical observations, and favors the binary super-massive black hole model. The simultaneous multi-wavelength variability and relatively weak $\gamma$-ray emission that shows a shift in the SED peak is consistent with $\gamma$-ray emission originating from inverse Compton scattering of photons from the line emission that apparently contributes to the little blue bump.

24 pages, 6 figures, 2 tables, MNRAS in press

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• Multiwavelength variability power spectrum analysis of the blazars 3C 279 and PKS 1510-089 on multiple timescales
• Strong Soft X-ray Excess in 2015 XMM-Newton Observation of BL--Lac OJ~287
• Multi-wavelength Analysis and Modeling of OJ 287 During 2017-2020
• A Multi-wavelength View of OJ 287 Activity in 2015-2017: Implications of Spectral Changes on Central-engine Models and MeV-GeV Emission Mechanism
• Long Term Multi-band Near Infra-Red Variability of the Blazar OJ 287 during 2007--2021
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• Quasi-simultaneous Optical Flux and Polarization Variability of the Binary Super Massive Black Hole Blazar OJ 287 from 2015 to 2023: Detection of an Anticorrelation in Flux and Polarization Variability
• Spectral States of OJ 287 blazar from Multi-wavelength Observations with $AstroSat$
• A hadronic emission model for black hole-disc impacts in the blazar OJ 287
• Correlation between optical and $\gamma$-ray flux variations in BL Lacs
• Blazar OJ 287 After First VHE Activity: Tracking the Re-emergence of the HBL like Component in 2020
• Broadband study of BL Lac during flare of 2020: Spectral evolution and emergence of HBL component
• Multi-wavelength temporal variability of the blazar PKS 1510-089
• A comprehensive study of 2019-2020 flare of OJ 287 using AstroSat, Swift, and NuSTAR
• The blazar OJ 287 jet from parsec- to kiloparsec-scales
• X-ray Flux and Spectral Variability of the Blazar OJ 287 with Suzaku
• Temporal and Spectral Variability of OJ 287 before the April--June 2020 Outburst
• On the Spectral Changes of OJ 287: The Lowest X-ray state Spectrum -- extended at Optical-UV and Hard at X-rays
• The First VHE Activity of OJ 287 and the Extragalactic Background Light
• Simultaneous Optical to X-ray Spectra of OJ 287: Insights into X-ray spectral changes and particle spectra