Multi-frequency variability study of Ton 599 during high activity of 2017

Abstract

In this work, I have presented a multi-frequency variability and correlation study of the blazar Ton 599, which was observed first time in flaring state at the end of 2017. Data from \textit{Fermi}-LAT, Swift-XRT/UVOT, Steward Observatory, and OVRO (15 GHz) is used, and it is found that the source is more variable in $γ$-ray and optical/UV than X-ray and radio. Large variations in the degree of polarization (DoP) and position angle (PA) is noticed during the flaring period. Maximum flux during $γ$-ray flare is found to be 12.63$\times$10$^{-7}$ at MJD 58057.5 from the 1-day bin light curve (LC), which is the maximum flux ever achieved by this source. It is further found that all the peaks of flare are very symmetric, which suggests the cooling time of electrons is much smaller than light crossing time. Using 1-day as a fast variability time, the size of the $γ$-ray emission region is estimated as 1.88$\times$10$^{16}$ 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 (BLR). A trend of increasing fractional variability towards 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 $γ$-ray and optical/UV suggest their emission to be co-spatial while lag of 27 days between $γ$-ray and OVRO (15 GHz) suggest two different emission zone separated by a distance of $\sim$ 5 pc.