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

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.