Rapid X-ray Variability in Mkn 421 during a Multiwavelength Campaign
Creators: name: Markowitz, Alex G.
name: Nalewajko, Krzysztof
name: Bhatta, Gopal
name: Dewangan, Gulab C.
name: Chandra, Sunil
name: Dorner, Daniela
name: Schleicher, Bernd
name: Pajdosz-Smierciak, Urszula
name: Stawarz, Lukasz
name: Zola, Staszek
name: Ostrowski, Michal
name: Carosati, Daniele
name: Krishnan, Saikruba
name: Bachev, Rumen
name: Benitez, Erika
name: Gazeas, Kosmas
name: Hiriart, David
name: Hu, Shao-Ming
name: Larionov, Valeri
name: Marchini, Alessandro
name: Matsumoto, Katsura
name: Nikiforova, A. A.
name: Pursimo, Tapio
name: Raiteri, Claudia M.
name: Reichart, Daniel E.
name: Rodriguez, Diego
name: Semkov, Evgeni
name: Strigachev, Anton
name: Sugiura, Yuki
name: Villata, Massimo
name: Webb, James R.
name: Arbet-Engels, Axel
name: Baack, Dominik
name: Balbo, Matteo
name: Biland, Adrian
name: Bretz, Thomas
name: Buss, Jens
name: Eisenberger, Laura
name: Elsaesser, Dominik
name: Hildebrand, Dorothee
name: Iotov, Roman
name: Kalenski, Adelina
name: Mannheim, Karl
name: Mitchell, Alison
name: Neise, Dominik
name: Noethe, Maximilian
name: Paravac, Aleksander
name: Rhode, Wolfgang
name: Sliusar, Vitalii
name: Walter, Roland
Publisher: name: arXiv
Year: 2022
Subjects: subject: High Energy Astrophysical Phenomena (astro-ph.HE)
subject: Astrophysics of Galaxies (astro-ph.GA)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: The study of short-term variability properties in AGN jets has the potential to shed light on their particle acceleration and emission mechanisms. We report results from a four-day coordinated multi-wavelength campaign on the highly-peaked blazar (HBL) Mkn 421 in 2019 January. We obtained X-ray data from AstroSAT, BVRI photometry with the Whole Earth Blazar Telescope (WEBT), and TeV data from FACT to explore short-term multi-wavelength variability in this HBL. The X-ray continuum is rapidly variable on time-scales of tens of ks. Fractional variability amplitude increases with energy across the synchrotron hump, consistent with previous studies; we interpret this observation in the context of a model with multiple cells whose emission spectra contain cutoffs that follow a power-law distribution. We also performed time-averaged and time-resolved (time-scales of 6 ks) spectral fits; a broken power-law model fits all spectra well; time-resolved spectral fitting reveals the usual hardening when brightening behaviour. Intra-X-ray cross correlations yield evidence for the 0.6-0.8 keV band to likely lead the other bands by an average of 4.6 +- 2.6 ks, but only during the first half of the observation. The source displayed minimal night-to-night variability at all wavebands thus precluding significant interband correlations during our campaign. The broadband SED is modeled well with a standard one-zone leptonic model, yielding jet parameters consistent with those obtained from previous SEDs of this source.
description: This article has been accepted for publication in The Monthly Notices of the Royal Astronomical Society (2022), and is published in Volume 513, Issue 2, pp.1662-1679. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. 19 pages; 12 figures