The evolution of the spectral energy distribution during flares constrains models of particle acceleration in blazar jets. The archetypical blazar BL Lacertae provided a unique opportunity to study spectral variations during an extended strong flaring episode from 2020 to 2021. During its brightest γ-ray state, the observed flux (0.1–300 GeV) reached up to 2.15×10−5phcm−2s−1 ⁠, with sub-hour-scale variability. The synchrotron hump extended into the X-ray regime showing a minute-scale flare with an associated peak shift of inverse-Compton hump in γ-rays. In shock acceleration models, a high Doppler factor value >100 is required to explain the observed rapid variability, change of state, and γ-ray peak shift. Assuming particle acceleration in minijets produced by magnetic reconnection during flares, on the other hand, alleviates the constraint on required bulk Doppler factor. In such jet-in-jet models, observed spectral shift to higher energies (towards TeV regime) and simultaneous rapid variability arises from the accidental alignment of a magnetic plasmoid with the direction of the line of sight. We infer a magnetic field of ∼0.6 G in a reconnection region located at the edge of broad-line region (∼0.02 pc). The scenario is further supported by lognormal flux distribution arising from merging of plasmoids in reconnection region.

Flaring activity from magnetic reconnection in BL Lacertae

B Banerjee;M Branchesi
2023-01-01

Abstract

The evolution of the spectral energy distribution during flares constrains models of particle acceleration in blazar jets. The archetypical blazar BL Lacertae provided a unique opportunity to study spectral variations during an extended strong flaring episode from 2020 to 2021. During its brightest γ-ray state, the observed flux (0.1–300 GeV) reached up to 2.15×10−5phcm−2s−1 ⁠, with sub-hour-scale variability. The synchrotron hump extended into the X-ray regime showing a minute-scale flare with an associated peak shift of inverse-Compton hump in γ-rays. In shock acceleration models, a high Doppler factor value >100 is required to explain the observed rapid variability, change of state, and γ-ray peak shift. Assuming particle acceleration in minijets produced by magnetic reconnection during flares, on the other hand, alleviates the constraint on required bulk Doppler factor. In such jet-in-jet models, observed spectral shift to higher energies (towards TeV regime) and simultaneous rapid variability arises from the accidental alignment of a magnetic plasmoid with the direction of the line of sight. We infer a magnetic field of ∼0.6 G in a reconnection region located at the edge of broad-line region (∼0.02 pc). The scenario is further supported by lognormal flux distribution arising from merging of plasmoids in reconnection region.
2023
magnetic reconnection, radiation mechanisms: non-thermal, BL Lacertae objects: individual: BL Lac, galaxies: jets, gamma-rays: galaxies, X-rays: galaxies
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/20.500.12571/29064
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