2025ApJS..280...32A -
Astrophys. J., Suppl. Ser., 280, 32 (2025/September-0)
From Equipartition to Curvature: The Spectral Evolution of 4FGL Blazars.
ANJUM M.S., HOU S.-J., CHEN L., LI Z. and GU M.
Abstract (from CDS):
We investigate the evolution of spectral energy distribution (SED) and underlying electron energy distribution (EED) by modeling the nearly simultaneous broadband spectra of selected bright 4FGL blazars, in the context of a combined cooling and stochastic acceleration scenario. We find that a one-zone leptonic model with log-parabolic EED can successfully fit the GeV-TeV emission of blazars. The synchrotron frequency νs of blazars mainly evolves due to the variation of electron peak energy γ3p. BL Lac (BL Lacs) objects show a negative trend in the νs-νsLs SED plane, known as the blazar sequence, that does not seem to be an artifact of Doppler boosting, but is driven by the equipartition constraints. A positive correlation is found between the derived magnetic field B and electron density ne, whereas ne and γ3p negatively relate, as expected in an equipartition scenario. The flat-spectrum radio quasars (FSRQs) deviate significantly from such a scenario, indicating their jet parameters should vary independently. The synchrotron peak frequency νs and its spectral curvature bs negatively correlate for all blazars, confirming the stochastic particle acceleration in blazar jets. However, blazars do not show the signature of hard-sphere acceleration, indicating that magnetic turbulence in the jets might be soft and physical conditions might be near steady state, consistent with equipartition. Furthermore, for BL Lacs, the SED curvature bs and the EED curvature r nearly meet the theoretical relationship of r = 5bs, whereas the FSRQs show a large deviation due to a poor constraint on bs due to the presence of a thermal component.
Abstract Copyright:
© 2025. The Author(s). Published by the American Astronomical Society.
Journal keyword(s):
Blazars - Active galactic nuclei - BL Lacertae objects
Simbad objects:
102
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