Rapid X-ray variability in Mkn 421 during a multiwavelength campaign
A. Markowitz, Krzysztof Nalewajko, Gopal Bhatta, G. C. Dewangan, S. Chandra, D. Dorner, Bernd Schleicher, Urszula Pajdosz-Śmierciak, Ł. Stawarz, S. Zoła, M. Ostrowski, D. Carosati, Saikruba Krishnan, R. Bachev, E. Benítez, K. Gazeas, D. Hiriart, Shaoming Hu, V. M. Larionov, Alessandro Marchini, Katsura Matsumoto, A. A. Nikiforova, T. Pursimo, C. M. Raiteri, D. Reichart, Diego Rodríguez, E. Semkov, A. Strigachev, Yuki Sugiura, M. Villata, J. R. Webb, Axel Arbet-Engels, Dominik Baack, Matteo Balbo, A. Biland, T. Bretz, Jens Buß, Laura Eisenberger, D. Elsäesser, D. Hildebrand, Roman Iotov, Adelina Kalenski, K. Mannheim, Alison Mitchell, Dominik Neise, Maximilian Noethe, Aleksander Paravac, W. Rhode, Vitalii Sliusar, R. Walter
Abstract
ABSTRACT 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 4-d coordinated multiwavelength 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 First G-APD Cherenkov Telescope to explore short-term multiwavelength 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 broad-band SED is modelled well with a standard one-zone leptonic model, yielding jet parameters consistent with those obtained from previous SEDs of this source.