SIMBAD references

We present the results of the X-ray flaring activity of 1ES 1959+650 during 2017 October 25-26 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 (∼130 ks) into time segments of 5 ks, and fitting the Soft X-ray focusing Telescope and Large Area X-ray Proportional Counter 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 normalized particle density at an energy less than the break one were found to anticorrelate with the index before the break. However, a stronger correlation between the density and index was obtained when a delay of ∼60 ks was introduced. The amplitude of the normalized particle density variation |Δn_γ/n_γ| ∼ 0.1 was found to be less than that of the index ΔΓ ∼ 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 ∼1.97 x 10⁵ s and the emission region size to be ∼6.73 x 10¹⁵ cm.