Abstract
We study the multi-wavelength variability of the blazar Mrk 421 at minutes to days timescales using simultaneous data at \(\gamma \)-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 timescales at 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 of the 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 large range 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.
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Acknowledgements
We thank the anonymous referee for comments and suggestions that made the manuscript more comprehensive. RC thanks Presidency University for support under the Faculty Research and Professional Development (FRPDF) Grant, ISRO for support under the AstroSat archival data utilization program, and IUCAA for their hospitality and usage of their facilities during his stay at different times as part of the university associateship program. RC received support from the UGC start-up grant. RC acknowledges financial support from BRNS through a project grant (sanction no: 57/14/10/2019-BRNS) and thanks the project coordinator Pratik Majumdar for support regarding the BRNS project. This work has made use of data from the AstroSat mission of the ISRO, archived at the Indian Space Science Data Centre (ISSDC). This work has been performed utilizing the calibration databases and auxiliary analysis tools developed, maintained and distributed by AstroSat-SXT and AstroSat-LAXPC teams with members from various institutions in India and abroad and the SXT and LAXPC Payload Operation Center (POC) at the TIFR, Mumbai for the pipeline reduction. We are also thankful to the AstroSat Science Support Cell hosted by IUCAA and TIFR for providing the necessary data analysis software. The work has made use of software, and/or web tools obtained from NASA’s High Energy Astrophysics Science Archive Research Center (HEASARC), a service of the Goddard Space Flight Center and the Smithsonian Astrophysical Observatory.
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This article is part of the Special Issue on “AstroSat: Five Years in Orbit”.
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Chatterjee, R., Das, S., Khasnovis, A. et al. Short-timescale variability of the blazar Mrk 421 from AstroSat and simultaneous multi-wavelength observations. J Astrophys Astron 42, 80 (2021). https://doi.org/10.1007/s12036-021-09709-3
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DOI: https://doi.org/10.1007/s12036-021-09709-3