X-ray Observations of 1ES 1959+650 in its high activity state in 2016-2017 with AstroSat and Swift

TL;DR

This study analyzes multi-frequency data, especially X-ray observations from AstroSat and Swift, of the blazar 1ES 1959+650 during its high activity in 2016-2017, revealing flux-dependent spectral shifts and particle acceleration insights.

Contribution

It provides a detailed X-ray flare characterization and models the spectral energy distributions using a time-dependent leptonic framework, linking flux states to particle acceleration mechanisms.

Findings

X-ray flux correlates with spectral peak shifts.

Synchrotron peak shifts indicate geometric effects like Doppler factor changes.

Model reproduces observed SEDs and X-ray light curves.

Abstract

We present a comprehensive multi-frequency study of the HBL 1ES 1959+650 using data from various facilities during the period 2016-2017, including X-ray data from {\it AstroSat} and {\it Swift} during the historically high X-ray flux state of the source observed until February 2021. The unprecedented quality of X-ray data from high cadence monitoring with the {\it AstroSat} during 2016-2017 enables us to establish a detailed description of X-ray flares in 1ES 1959+650. The synchrotron peak shifts significantly between different flux states, in a manner consistent with a geometric (changing Doppler factor) interpretation. A time-dependent leptonic diffusive-shock-acceleration and radiation transfer model is used to reproduce the spectral energy distributions (SEDs) and X-ray light curves, to provide insight into the particle acceleration during the major activity periods observed in 2016 and 2017. The extensive data of {\it Swift}-XRT from December 2015 to February 2021 (Exp. = 411.3 ks) reveals a positive correlation between flux and peak position.