Speaker
Axel Arbet-Engels
(Max Planck Institute for Physics)
Description
Thanks to its brightness and proximity, the BL Lac type object Mrk 421 is an ideal target to probe blazar jet physics. We present a detailed characterisation and theoretical interpretation of the broadband emission of Mrk 421, focusing on the multi-band flux correlations. The analysis makes use of an extensive multi-wavelength campaign organised in 2017, during which the correlation patterns show some disparity and complex behaviours. Four multi-hour NuSTAR observations were organised simultaneously to those from MAGIC, which allow us to obtain a precise measurement of the high energy turnover of the two spectral bumps. A detailed investigation of the very-high-energy (VHE; >100 GeV) versus X-ray flux correlation is performed, by binning the data into several sub-energy bands. A positively correlated variability is observed at a significance level above 5 sigma, but the correlation changes substantially across the various bands probed. Furthermore, during the simultaneous MAGIC and NuSTAR observations, a variation of the inverse Compton component up to a factor 3 is detected, without a corresponding variability in the synchrotron regime, what is usually referred to as an "orphan gamma-ray activity". During the campaign, we also detected an intriguing bright flare at VHE without a substantial flux increase in the X-rays. Within a leptonic scenario, this behaviour is best explained by the appearance of a second population of highly-energetic electrons spanning a narrow range of energies. Finally, our intra-band correlation study reveals an anti-correlation between the UV/optical and X-ray bands at a significance level above 3 sigma. This behaviour suggests changes in the acceleration and cooling efficiencies of the electrons.
Summary
Based on arXiv:2106.05516
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Primary author
Axel Arbet-Engels
(Max Planck Institute for Physics)
Co-authors
Dr
David Paneque
(Max Planck Institut for Physics)
Mrs
Lea Heckmann
(Max Planck Institut for Physics)
