http://arxiv.org/abs/2105.03937
OJ 287 is a well-studied binary black hole system that 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. Various X-ray instruments were used to capture this historic moment. Their data is analyzed and modeled along with optical and UV data. Based on Swift-XRT and UVOT observations, the entire period is divided into three states, defined as a low, intermediate, and high state. The results of our analysis suggest a “softer-when-brighter” behavior. We proposed a Target of Opportunity (ToO) observation using AstroSat to compliment this study along with the Swift-XRT, XMM-Newton, and NuSTAR observations. Simultaneous X-ray spectra observed by various instruments during high states are very steep and agree with each other within the errorbar. A significant spectral change is observed in the optical-UV and X-ray spectrum during the high flux state, suggesting the emergence of a new HBL component. A significant shift of two orders of magnitude in the synchrotron peak is observed as the source evolves from low flux to high flux state. The emergence of a new HBL component could be associated with the increase in accretion rate post-BH-disk impact, and eventually, it could trigger the flare produced in the jet. The color-magnitude diagram reveals a “bluer-when-brighter” chromatism during the flaring period. Different chromatism or no chromatism at 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.
R. Prince, G. Raman, R. Khatoon, et. al.
Tue, 11 May 21
85/93
Comments: 14 pages, 13 figures, 3 tables, submitted to MNRAS. Comments/suggestions are welcome
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