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| Format: | Preprint |
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2025
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| Online Access: | https://arxiv.org/abs/2503.02024 |
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| _version_ | 1866909523959087104 |
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| author | Kapanadze, B. Gurchumelia, A. Aller, M. |
| author_facet | Kapanadze, B. Gurchumelia, A. Aller, M. |
| contents | This paper presents the gamma-ray spectral and timing results from the long-term regular observations of Mrk 421 with the Large Area Telescope (LAT) onboard Fermi during 2008 August - 2023 August. We discerned six periods the relatively stronger 0.3-300 GeV activity compared to other time intervals. The baseline brightness level varied on timescales from several months to years during these periods, which was superimposed by shorter-term flares of the different asymmetry associated with various interplay between the light-crossing, particle acceleration and cooling timescales. The source also frequently exhibited two-peak flares, to be triggered by the propagation of forward and reverse shocks after collision between the shells of high-energy plasma, moving with different speeds down the jet. The strongest long-term flaring activity was recorded during 2012 June - 2013 October and 2017 October - 2018 March, when the source was robustly detectable even on intraday timescales. We detected 25 instances of intraday variability and a large number of the flux doubling or halving instances. The source generally showed a lognormal variability in the LAT energy range, explained as an imprinting of the disc nonstationary processes on the jet, proton-initiated hadronic cascades or random fluctuations in the particle acceleration rate. Most of the 0.3-300 GeV spectra were well-fit with a simple power-law model and showed a very broad range of the photon-index from 2.8 down to 1.2, with the mean values of 1.75-1.84 and distribution peaks at 1.73-1.82 during the periods of strong activity. Our spectral study also revealed the features of inverse-Compton upscatter of X-ray photons in the Klein-Nishina regime, relativistic magnetic reconnection, first-order Fermi mechanism within the magnetic field of different confinement efficiencies and stochastic acceleration |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2503_02024 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Long-term Fermi observations of Mrk 421: clues for different non-stationary processes Kapanadze, B. Gurchumelia, A. Aller, M. High Energy Astrophysical Phenomena Astrophysics of Galaxies This paper presents the gamma-ray spectral and timing results from the long-term regular observations of Mrk 421 with the Large Area Telescope (LAT) onboard Fermi during 2008 August - 2023 August. We discerned six periods the relatively stronger 0.3-300 GeV activity compared to other time intervals. The baseline brightness level varied on timescales from several months to years during these periods, which was superimposed by shorter-term flares of the different asymmetry associated with various interplay between the light-crossing, particle acceleration and cooling timescales. The source also frequently exhibited two-peak flares, to be triggered by the propagation of forward and reverse shocks after collision between the shells of high-energy plasma, moving with different speeds down the jet. The strongest long-term flaring activity was recorded during 2012 June - 2013 October and 2017 October - 2018 March, when the source was robustly detectable even on intraday timescales. We detected 25 instances of intraday variability and a large number of the flux doubling or halving instances. The source generally showed a lognormal variability in the LAT energy range, explained as an imprinting of the disc nonstationary processes on the jet, proton-initiated hadronic cascades or random fluctuations in the particle acceleration rate. Most of the 0.3-300 GeV spectra were well-fit with a simple power-law model and showed a very broad range of the photon-index from 2.8 down to 1.2, with the mean values of 1.75-1.84 and distribution peaks at 1.73-1.82 during the periods of strong activity. Our spectral study also revealed the features of inverse-Compton upscatter of X-ray photons in the Klein-Nishina regime, relativistic magnetic reconnection, first-order Fermi mechanism within the magnetic field of different confinement efficiencies and stochastic acceleration |
| title | Long-term Fermi observations of Mrk 421: clues for different non-stationary processes |
| topic | High Energy Astrophysical Phenomena Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2503.02024 |