Abstract Details
| Name: Susmita Das Affiliation: Presidency University, Kolkata Conference ID: ASI2025_247 Title : X-Ray Spectral Evolution and Fourier Time Lags in Two HSP Blazars Authors and Co-Authors : Susmita Das and Ritaban Chatterjee Abstract Type : Oral Abstract Category : High Energy Phenomena, Fundamental Physics and Astronomy Abstract : We study X-ray (0.7-20 keV) spectra and light curves of two high synchrotron peaked (HSP) blazars, Mrk 421 and 1ES 1959+650, using simultaneous observations by the SXT and LAXPC instruments onboard AstroSat during 2016-19. We carry out time-resolved spectroscopy to study hours-timescale spectral variation, and find correlation between the variability of the best-fit spectral parameters. Cross-correlation analysis shows the hard and soft X-ray variability are strongly correlated with positive, negative or zero time lag at different epochs. We compute the cross-spectrum between the light curves in order to study the variation of the time lag as a function of Fourier frequency. We find hard-to-soft or soft-to-hard transitions in time lags with increasing Fourier frequency. For HSP blazars, the X-ray emission is dominated by synchrotron radiation by the highest energy electrons, and the energy dependent acceleration and cooling timescale may explain the time lags. We compare our results with a theoretical time dependent multi-zone model of non-thermal emission from blazars. We find that high-energy particles, having a simple power-law energy distribution injected by a shock front moving down the emission region, emitting synchrotron and inverse-Compton radiation in the presence of a turbulent magnetic field can give rise to the above spectral and temporal variability properties. However, partial mismatch in certain spectral properties suggest additional features in the energy distribution of injected particles or emission mechanisms. |