Abstract Details
| Name: Agniva Roychowdhury Affiliation: Presidency University, Kolkata Conference ID: ASI2018_1685 Title : Study of multi-band X-Ray Time Variability of Mrk 421 using ASTROSAT Authors and Co-Authors : Ritaban Chatterjee, Department of Physics, Presidency University, 86/1 College Street, Kolkata 700073. Sunil Chandra, Centre for Space Research, North-West University, Potchefstroom, 2520, South Africa. Atreyee Sinha, AstroParticule et Cosmologie, Universite Paris Diderot, CNRS/IN2P3, Paris 75013. Gulab C.Dewangan, Inter University Center for Astronomy and Astrophysics, Pune - 411 007, India. Abstract Type : Contributed Talk Abstract Category : Extragalactic astronomy Abstract : We analyze a 100 ks Astrosat observation of the blazar Markarian 421. We calculate the broad-band X-ray power spectral density (PSD) using light curves from SXT and LAXPC onboard Astrosat, and archival data from Swift. We find that the X-ray PSD is best fit by a bending power-law model with a break at ~days timescale. In the past, similar break in the X-ray PSD have been found in Galactic X-ray binaries and Seyfert galaxies, where the observed X-ray emission is dominated by those from the accretion disk or corona. This implies the break timescale to be linked with accretion dynamics. However, Mrk 421 is a BL Lac object. Hence, the disk emission is weak and X-rays are mostly from the jet. Our corresponding result of a break in the PSD hence implies a signature of accretion disk dynamics in the jet. This is one of the most direct evidences of an accretion-disk jet connection. We find that the variability of soft and hard X-rays observed by SXT and LAXPC, respectively, are very well-correlated. Presence of correlation implies that the same electron populations are giving rise to emission in both bands. Inter-band time delays arise due to mixed contributions of various timescales like the radiation cooling timescales, light crossing timescale of emission region, or timescale related to acceleration or injection of particles. The cooling and acceleration timescales increase and decrease respectively with the energy of the relativistic electrons. The sign of the lag hence depends on the timescale that is dominating. If the cooling timescale is significantly higher than the acceleration timescale, we see a soft lag, i.e., variation of hard X-rays leading those at the softer energies. When the acceleration timescale is comparable to the cooling timescale of the highest energy particles, hard lags may be seen, i.e. similar changes taking place earlier at lower and later at higher energies. This is just one of the several explanations behind such correlation and lag. The possible contributions due to other timescales, the variation of the PSD break timescale with photon energy and their implications are also discussed. |