Particle acceleration signatures in the time-dependent one-zone synchrotron self-Compton model of blazar flares

¹ LUX, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, 92190 Meudon, France
² Centre for Space Research, North-West University, Potchefstroom 2520, South Africa

^★ Corresponding authors: This email address is being protected from spambots. You need JavaScript enabled to view it. ; This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 17 February 2025
Accepted: 22 January 2026

Abstract

Context. The study of multiwavelength flux and spectral variations during rapid flares from blazars provides strong constraints on the physical parameters of the compact emission regions responsible for these still poorly understood events. Although a full description of the continuous and transient emission from blazars seems to require more sophisticated scenarios, standard leptonic one-zone models are a promising first step toward understanding their underlying physical acceleration and emission processes, when concentrating on the variable emission during rapid flare events.

Aims. Different scenarios of particle acceleration and loss mechanisms can be approximately described within the simple one-zone framework, enabling a systematic study of their impact on the observable properties of multiwavelength flare light curves. Our goal is to identify characteristic signatures in these light curve profiles that permit one to discriminate between the main physical processes situated inside the relativistic jet and commonly invoked to explain blazar flares. The present study exclusively focuses on modeling flares from BL Lac type objects, which can be described within the synchrotron self-Compton (SSC) emission scenario.

Methods. Combinations of several commonly employed mechanisms to describe the gain and loss of energetic particles in one-zone models during flaring events are studied in a systematic way: particle injection; diffusive shock and stochastic acceleration and reacceleration; particle escape; adiabatic losses; radiative losses through synchrotron and inverse-Compton radiation. The current study is limited to the case of “hard-sphere” scattering. For each scenario, the resulting multiwavelength light curves are characterized by the shape and timescales of the rising and falling parts of the flare, as well as their asymmetry or lack thereof.

Results. A large variety of light curve shapes arises from the different scenarios under study. Characteristic signatures, in particular energy-dependent time delays and differences in the shapes of the rising part of the flare, should allow the distinction to be made between different injection and acceleration scenarios, given the availability of sufficiently high-quality multiwavelength data sets. This is illustrated with a simplified application to a flare event from the blazar Mrk 421.