Spectral States of OJ 287 blazar from Multi-wavelength Observations with $AstroSat$

Abstract

We present {\it AstroSat} soft X-ray, near-UV (NUV), and far-UV (FUV) observations of a blazar, OJ~287, carried out in 2017, 2018, and 2020. The simultaneous observations with NuSTAR in 2017 provide a broad-band look encompassing NUV, FUV, soft and hard X-rays. Captured in three different broadband spectral states in three observations, the X-ray spectrum is found to be the hardest during 2018, while the high-energy-end of the simultaneous optical-FUV spectrum shows a steepening that is modeled with a broken power-law spectrum. The spectral energy distribution (SED) in 2017 shows a relatively flatter optical-FUV and soft X-ray spectra, implying an additional emission component. The 2020 optical-FUV spectrum is harder than in 2017 and 2018, with an extremely soft X-ray spectrum and a hardening above $\sim$1 GeV, similar to the SEDs of High-energy-peaked BL Lac objects (HBL), thereby establishing that this additional emission component has HBL-like properties. The {\it AstroSat} multi-wavelength observations trace the spectral evolution from the end-phase of the HBL component in 2017 to its disappearance in 2018 followed by its revival in 2020. A single zone leptonic model reproduces the 2018 broadband spectrum while the 2017 and 2020 SEDs require an additional HBL-like emitting zone. The spectral evolution of the high-energy-end of the optical-UV spectrum, revealed by the FUV observations in 2017 and 2018, strongly suggests that X-ray spectral changes in the normal broadband spectral state of OJ~287 are primarily due to the evolution of the optical-UV synchrotron spectrum.

13 pages, 5 Figures, 3 Tables, MNRAS (in press)

References in corpus (16)

• HI4PI: A full-sky HI survey based on EBHIS and GASS
• Rapid Variability of Blazar 3C 279 during Flaring States in 2013-2014 with Joint Fermi-LAT, NuSTAR, Swift, and Ground-Based Multi-wavelength Observations
• Spitzer Observations of the Predicted Eddington Flare from Blazar OJ 287
• Multi-wavelength temporal and spectral variability of the blazar OJ 287 during and after the December 2015 flare: a major accretion disc contribution
• Multiband optical variability of the blazar OJ 287 during its outbursts in 2015 -- 2016
• Explaining temporal variations in the jet position angle of the blazar OJ 287 using its binary black hole central engine model
• X-ray spectral components of the blazar and binary black hole candidate OJ 287 (2005-2020)
• Is OJ 287 a Single Supermassive Black Hole?
• 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
• A possible tidal disruption event candidate in the black hole binary system of OJ 287
• A hadronic emission model for black hole-disc impacts in the blazar OJ 287
• Curvit: An open-source Python package to generate light curves from UVIT data
• A comprehensive study of 2019-2020 flare of OJ 287 using AstroSat, Swift, and NuSTAR
• Supermassive binary black holes and the case of OJ 287

Cited by in corpus (8)

• MOMO VI: Multifrequency radio variability of the blazar OJ 287 from 2015-2022, absence of predicted 2021 precursor-flare activity, and a new binary interpretation of the 2016/2017 outburst
• Long Term Multi-band Near Infra-Red Variability of the Blazar OJ 287 during 2007--2021
• The microvariability and wavelength dependence of polarization degree/angle of BL Lacertae in the outburst 2020 to 2021
• X-ray Flux and Spectral Variability of the Blazar OJ 287 with Suzaku
• Exploration of the origin of 2020 X-ray outburst in OJ 287
• 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