• Short-timescale variability of the blazar Mrk 421 from AstroSat and simultaneous multi-wavelength observations

• Fulltext

https://www.ias.ac.in/article/fulltext/joaa/042/0080

• Keywords

Active Galactic Nuclei (AGN); blazar; variability; Mrk 421; multiwavelength.

• Abstract

We study the multi-wavelength variability of the blazar Mrk 421 at minutes to days timescales using simultaneous data at c-rays from Fermi, 0.7–20 keV energies from AstroSat, and optical and near infrared (NIR) wavelengths from ground based observatories. We compute the shortest variability timescalesat all of the above wave bands and find its value to be $\sim$1.1 ks at the hard X-ray energies and increasingly longer at soft X-rays, optical and NIR wavelengths as well as at the GeV energies. We estimate the value ofthe magnetic field to be 0.5 Gauss and the maximum Lorentz factor of the emitting electrons $\sim 1.6 \times 10^5$ assuming that synchrotron radiation cooling drives the shortest variability timescale. Blazars vary at a largerange of timescales often from minutes to years. These results, as obtained here from the very short end of the range of variability timescales of blazars, are a confirmation of the leptonic scenario and in particular the synchrotron origin of the X-ray emission from Mrk 421 by relativistic electrons of Lorentz factor as high as $10^5$. This particular mode of confirmation has been possible using minutes to days timescale variability data obtained from AstroSat and simultaneous multi-wavelength observations.

• Author Affiliations

1. Department of Physics, Presidency University, 86/1 College Street, Kolkata 700 073, India.
2. Visva-Bharati University, Santiniketan, Bolpur 731 235, India.
3. Astronomy and Astrophysics Division, Physical Research Laboratory, Navrangapura, Ahmedabad 380 009, India.
4. Department of Physics, Indian Institute of Technology, Gandhinagar 382 355, India.
5. Astronomical Institute, St. Petersburg State University, Universitetskij Prospekt 28, Petrodvorets, St. Petersburg, Russia 198504.
6. Pulkovo Observatory, St. Petersburg, Russia.

• Journal of Astrophysics and Astronomy

Volume 43, 2022
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