Rapid X-ray variability in Mkn 421 during a multiwavelength campaign
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.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- June 2022
- DOI:
- 10.1093/mnras/stac917
- arXiv:
- arXiv:2206.03874
- Bibcode:
- 2022MNRAS.513.1662M
- Keywords:
-
- acceleration of particles;
- black hole physics;
- galaxies: active;
- BL Lacertae objects: Mkn 421;
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 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