Models for the Spectral Energy Distributions and Variability of Blazars

TL;DR

This review summarizes recent theoretical models for blazar emission, comparing leptonic and lepto-hadronic approaches, and discusses recent observational data, including VHE gamma-ray detections, to understand blazar spectral energy distributions and variability.

Contribution

It provides a comprehensive overview of both stationary and time-dependent blazar models, highlighting recent developments and their implications for interpreting observational data.

Findings

Both leptonic and lepto-hadronic models can fit the SEDs of various blazars.

Recent VHE gamma-ray detections challenge traditional blazar classifications.

Time-dependent models offer new insights into blazar variability and emission mechanisms.

Abstract

In this review, recent progress in theoretical models for blazar emission will be summarized. The salient features of both leptonic and lepto-hadronic approaches to modeling blazar spectral energy distributions will be reviewed. I will present sample modeling results of spectral energy distributions (SEDs) of different types of blazars along the blazar sequence, including Fermi high-energy gamma-ray data, using both types of models. Special emphasis will be placed on the implications of the recent very-high-energy (VHE) gamma-ray detections of non-traditional VHE gamma-ray blazars, including intermediate and low-frequency-peaked BL Lac objects and even flat-spectrum radio quasars. Due to the featureless optical spectra of BL Lac objects, the redshifts of several BL Lacs remain unknown. I will briefly discuss possible constraints on their redshift using spectral modeling of their SED including Fermi + ground-based VHE gamma-ray data. It will be shown that in some cases, spectral modeling with time-independent single-zone models alone is not sufficient to constrain models, as both leptonic and lepto-hadronic models are able to provide acceptable fits to the overall SED. Subsequently, recent developments of time-dependent and inhomogeneous blazar models will be discussed, including detailed numerical simulations as well as a semi-analytical approach to the time-dependent radiation signatures of shock-in-jet models.