Rapid variability of Markarian 421 during extreme flaring as seen through the eyes of XMM-Newton

Gokus A, Wilms J, Kadler M, Dorner D, Nowak MA, Kreikenbohm A, Leiter K, Bretz T, Schleicher B, Markowitz AG, Pottschmidt K, Mannheim K, Kreykenbohm I, Langejahn M, McBride F, Beuchert T, Dauser T, Kreter M, Abhir J, Baack D, Balbo M, Biland A, Brand K, Buss J, Eisenberger L, Elsaesser D, Günther P, Hildebrand D, Linhoff M, Paravac A, Rhode W, Sliusar V, Hasan S, Walter R (2024)

Publication Type: Journal article

Publication year: 2024


Book Volume: 529

Pages Range: 1450-1462

Journal Issue: 2

DOI: 10.1093/mnras/stae643


By studying the variability of blazars across the electromagnetic spectrum, it is possible to resolve the underlying processes responsible for rapid flux increases, so-called flares. We report on an extremely bright X-ray flare in the high-peaked BL Lacertae object Markarian 421 (Mrk 421) that occurred simultaneously with enhanced γ-ray activity detected at very high energies by First G-APD Cherenkov Telescope on 2019 June 9. We triggered an observation with XMM-Newton, which observed the source quasi-continuously for 25 h. We find that the source was in the brightest state ever observed using XMM-Newton, reaching a flux of 2.8 × 10-9 over an energy range of 0.3-10 keV. We perform a spectral and timing analysis to reveal the mechanisms of particle acceleration and to search for the shortest source-intrinsic time-scales. Mrk 421 exhibits the typical harder-when-brighter behaviour throughout the observation and shows a clock-wise hysteresis pattern, which indicates that the cooling dominates over the acceleration process. While the X-ray emission in different sub-bands is highly correlated, we can exclude large time lags as the computed z-transformed discrete correlation functions are consistent with a zero lag. We find rapid variability on time-scales of 1 ks for the 0.3-10 keV band and down to 300 s in the hard X-ray band (4-10 keV). Taking these time-scales into account, we discuss different models to explain the observed X-ray flare, and find that a plasmoid-dominated magnetic reconnection process is able to describe our observation best.

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Gokus, A., Wilms, J., Kadler, M., Dorner, D., Nowak, M.A., Kreikenbohm, A.,... Walter, R. (2024). Rapid variability of Markarian 421 during extreme flaring as seen through the eyes of XMM-Newton. Monthly Notices of the Royal Astronomical Society, 529(2), 1450-1462. https://doi.org/10.1093/mnras/stae643


Gokus, A., et al. "Rapid variability of Markarian 421 during extreme flaring as seen through the eyes of XMM-Newton." Monthly Notices of the Royal Astronomical Society 529.2 (2024): 1450-1462.

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