Multi-frequency Variability Study of Ton 599 during the High Activity of 2017

Abstract

Abstract In this work, I have presented a multi-frequency variability and correlation study of the blazar Ton 599, which was observed for the first time in the flaring state at the end of 2017. Data from Fermi-LAT, Swift-XRT/UVOT, Steward observatory, and Owens Valley Radio Observatory(OVRO) (15 GHz) are used and it is found that the source is more variable in γ-rays and optical/UV than in X-rays and radio. Large variations in degree of polarization and position angle are observed during the flaring period. Maximum flux during the γ-ray flare is found to be 12.63 × 10−7 at MJD 58057.5 from the 1 day bin light curve, which is the highest flux ever achieved by this source. It is further found that all the peaks of the flare are very symmetric, which suggests the cooling time of electrons is much smaller than the light-crossing time. Using 1 day as a fast variability time, the size of the γ-ray emission region is estimated as 1.88 × 1016 cm. Two 42 GeV of photons are detected during the flare, which puts a constraint on the location of the emission region, and it is found that the γ-ray emitting blob is located at the outer edge or outside the broad-line region. The trend of increasing fractional variability toward higher energies is also seen. Strong correlations were seen between γ-ray, optical/UV, X-ray, and radio (15 GHz) emission. A small time lag between γ-rays and the optical/UV suggests their emission to be co-spatial, while the lag of 27 days between γ-rays and OVRO (15 GHz) suggests two different emission zones separated by a distance of ∼5 pc.