Blazar OJ 287 after First VHE Activity: Tracking the Reemergence of the HBL-like Component in 2020

Abstract

Abstract We report the reemergence of a new broadband emission through a detailed and systematic study of the multiwavelength spectral and temporal behavior of OJ 287 after its first-ever reported very high energy activity in 2017 to date, which includes the second-highest X-ray flux of the source. The source shows high optical to X-ray flux variations, accompanied mainly by strong spectral changes. The optical to X-ray flux variations are correlated and simultaneous except for two durations when they are anticorrelated. The flux variations, however, are anticorrelated with the X-ray spectral state while correlated with optical–UV (ultraviolet). Weekly binned Fermi-LAT data around the duration of the highest X-ray activity show a few detections with a log-parabola model but none with a power law, yet the extracted LAT spectral energy distribution of the high-activity duration for both the models is similar and shows a hardening above 1 GeV. Further, near-infrared data indicate strong spectral change, resembling a thermal component. Overall, the combined optical to gamma-ray broadband spectrum establishes the observed variations to a new high-energy-peaked broadband emission component, similar to the one seen during the highest reported X-ray flux state of the source in 2017. The observed activities indicate some peculiar features that seem to be characteristic of this emission component, while its appearance a few years around the claimed ∼12 yr optical outbursts strongly indicates a connection between the two.