AstroSat observation of the HBL 1ES 1959+650 during its October 2017 flaring

TL;DR

This study analyzes the X-ray flaring activity of the blazar 1ES 1959+650 during October 2017 using AstroSat, revealing spectral evolution, correlations with time delays, and estimating particle acceleration and emission region parameters.

Contribution

It provides the first detailed spectral and temporal analysis of 1ES 1959+650's X-ray flares during this period, modeling particle acceleration timescales and emission region size.

Findings

X-ray flux and particle density anti-correlate with spectral index.

A time delay of approximately 60 ks enhances the correlation between density and index.

Estimated particle acceleration timescale is around 1.97×10^5 seconds.

Abstract

We present the results of the X-ray flaring activity of 1ES 1959+650 during October 25-26, 2017 using AstroSat observations. The source was variable in the X-ray. We investigated the evolution of the X-ray spectral properties of the source by dividing the total observation period ($\sim 130$ ksecs) into time segments of 5 ksecs, and fitting the SXT and LAXPC spectra for each segment. Synchrotron emission of a broken power-law particle density model provided a better fit than the log-parabola one. The X-ray flux and the normalised particle density at an energy less than the break one, were found to anti-correlate with the index before the break. However, a stronger correlation between the density and index was obtained when a delay of $\sim 60$ ksec was introduced. The amplitude of the normalised particle density variation $|\Delta n_\gamma/n_\gamma| \sim 0.1$ was found to be less than that of the index $\Delta \Gamma \sim 0.5$. We model the amplitudes and the time delay in a scenario where the particle acceleration time-scale varies on a time-scale comparable to itself. In this framework, the rest frame acceleration time-scale is estimated to be $\sim 1.97\times10^{5}$ secs and the emission region size to be $\sim 6.73\times 10^{15}$ cms.