Multi-wavelength activity of the BL Lac Blazar OJ 287 After its First VHE Activity: Spectro-temporal Evolution and Remergence of the HBL like Component

We report the reemergence of a new broadband emission through a detailed and systematic study of the multi-wavelength spectral and temporal behavior of OJ 287 after its first VHE activity in 2017 to date, which includes the second-highest X-ray flux of the source. The source shows strong 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 anti-correlated. The flux variations, however, are anti-correlated with spectral state for X-rays but correlated for optical-UV (ultraviolet). Weekly binned {\it 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 LAT spectral energy distributions (SEDs) for high activity duration is similar for both the models and show a hardening above 1 GeV. Near-infrared (NIR) data indicate strong spectral change while joint Swift and NuSTAR spectrum indicate a thermal component of $\rm 3\times 10^4$~K. Overall, the observed spectral features establish the observed variations to a new high-energy-peaked (HBL) broadband non-thermal emission component, similar to the one seen during the highest 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 \(\sim 12\)-year optical outbursts strongly indicate a connection between the two.