Temporal and spectral study of PKS 0208-512 during 2019-20 flare

Abstract

We present the temporal and spectral study of blazar PKS 0208-512, using recent flaring activity from November 2019 to March 2020, as detected by Fermi-LAT, Swift-XRT/UVOT observatories. The source was in a low γ-ray flux state for a decade and started flaring in November 2019, which continues until March 2020. During the activity state, 2-days binned γ-ray lightcurve shows multiple-peaks indicating sub-flares. To understand the possible physical mechanisms behind flux enhancement, a detailed temporal and spectral study has been carried out by dividing the activity into several flux-states. Timing analysis of lightcurves suggests that peaks of sub-flares have rise and decay time in days-order with flux-doubling time ∼ 2-days. The 2-days binned γ-ray lightcurve shows double-lognormal flux distribution. The broadband spectral energy distribution for three selected flux states can be well fitted under synchrotron, synchrotron-self-Compton (SSC) and external-Compton (EC) emission mechanisms. We obtained the physical parameters of the source and their confidence intervals through χ 2 -statistics. Our spectral study suggests that during quiescent-state, gamma-ray spectrum can be well explained by considering the EC-scattering of IR-photons from the dusty-torus. However, gamma-ray spectra corresponding to flares demand additional target photons from broad-line-region (BLR) along with the IR. These suggest that during flares, the emission-region is close to the edge of BLR, while for quiescent-state the emission-region is away from the BLR. The best-fit results suggest that, marginal increase in the magnetic-field can result in the flux enhancement. This is possibly associated with the efficiency of particle acceleration during flaring-states as compared to quiescent-state.

Multiband light curves from eccentric accreting supermassive black hole binaries

“…In addition to γ-ray data, there exists X-ray, optical, and infrared data for PKS 0208-512, and they have been analyzed in a number of contexts (see e.g. Chatterjee et al 2013;Khatoon et al 2021). It has been suggested that the disk emission is observable when the jet activity is low (Chatterjee et al 2013).…”

“…For example, it has recently been noted that PKS 0208-512 has had an increase in γ-ray activity beginning around 2019 (see e.g. Khatoon et al 2021), and the trend in flare amplitudes suggests a lump-like (e.g. 5-orbit) period.…”