Title:	A comprehensive study of the 2019–2020 flare of OJ 287 using AstroSat, Swift and NuSTAR
Authors:	Prince, Raj Raman, Gayathri Khatoon, Rukaiya Agarwal, Aditi Varun Gupta, Nayantara Czerny, Bożena Majumdar, Pratik
Keywords:	galaxies: active galaxies: jets galaxies: nuclei quasars: individual OJ 287 X-rays
Issue Date:	10-Sep-2021
Publisher:	Oxford University Press on behalf of the Royal Astronomical Society
Citation:	Monthly Notices of Royal Astronomical Society, 2021, Vol. 508, p315
Abstract:	OJ 287 is a well-studied binary black hole (BBH) system, which occasionally exhibits bright X-ray and optical flares. Here we present a detailed spectral study of its second brightest X-ray flare observed during 2019–2020 using archival Swift and Nuclear Spectroscopic Telescope Array (NuSTAR) observations along with Target of Opportunity observations from AstroSat. The entire flaring period is divided into three states, defined as low, intermediate and high states. The variation of the hardness ratio with 0.3–10.0 keV integrated flux suggests a ‘softer-when-brighter’ behaviour, as also previously reported based on flux-index variations. Simultaneous high-state X-ray spectra obtained using Swift, NuSTAR and AstroSat are very steep with a power-law index >2. A significant spectral change is observed in the spectrum obtained with the Soft X-ray Telescope (SXT) and Large Area X-ray Proportional Counter (LAXPC) onboard AstroSat, which is consistent with the spectrum from NuSTARand from the X-ray Telescope (XRT) onboard Swift. Together, optical–ultraviolet and X-ray spectra during the high-flux state suggest the emergence of a new high BL Lacertae component. We have modelled the synchrotron peak with the publicly available code called gamera for low-, intermediate- and high-flux states. Our modelling suggests the need for a high magnetic field to explain the high state under leptonic scenarios. An increase in the magnetic field value inside the jet could be linked to an increase in the accretion rate, as expected in the BH–disc impact scenario. The colour–magnitude diagram reveals a ‘bluer-when-brighter’ spectral energy distribution chromatism during the flaring period. Different chromatism or no chromatism on various occasions suggests a complex origin of optical emission, which is believed to be produced by disc impact or through synchrotron emission in the jet.
Description:	Restricted Access. An open-access version is available at arXiv.org (one of the alternative locations)
URI:	http://hdl.handle.net/2289/7914
ISSN:	0035-8711 1365-2966 (Online)
Alternative Location:	https://ui.adsabs.harvard.edu/abs/2021MNRAS.508..315P/abstract https://arxiv.org/abs/2105.03937 https://doi.org/10.1093/mnras/stab2545 https://inspirehep.net/literature/1862720
Copyright:	2022 The Author(s)
Appears in Collections:	Research Papers (A&A)

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