X-Ray and GeV-γ-Ray Emission Property of TeV Compact Symmetric Object PKS 1413+135 and Implication for Episodic Jet Activity

Abstract

PKS 1413+135, a compact symmetric object (CSO) with a two-sided parsec-scale structure in its miniature radio morphology, is spatially associated with 4FGL J1416.1+1320 and recently detected with MAGIC telescopes. We comprehensively analyze its X-ray and gigaelectronvolt γ-ray observation data to reveal its high-energy radiation physics. It is found that the source is in a low-flux stage before MJD 58500 and experiences violent outbursts after MJD 58500 in the gigaelectronvolt band. The flux at 10 GeV varies by ∼3 orders of magnitude, and the gigaelectronvolt-flux variation is accompanied by clear spectral variation, which is characterized as a soft log-parabola spectrum in the low-flux state and a hard power-law spectrum in the bright flares. The amplitude of the variability of X-rays is lower than that of γ-rays, and no correlation of variability between γ-rays and X-rays is observed. Fitting the broadband spectral energy distribution during a gigaelectronvolt outburst with a multi-zone leptonic model, we show that the gigaelectronvolt γ-rays are attributed to the external Compton process while the X-rays are a hybrid of several components. The predicted teraelectronvolt γ-ray flux during the gigaelectronvolt outburst is consistent with the detection of MAGIC telescopes. These results, together with its CSO radio morphology, imply that PKS 1413+135 has episodic nuclear jet activities. The weak γ-ray emission before MJD 58500 may be from its sub-parsec-/parsec-scale jet component powered by previous activities, and the violent outbursts with short timescale variability after MJD 58500 could be attributed to the recently restarted jet activity.