Claudia M. Raiteri, a researcher at the INAF-Osservatorio Astronomico di Torino in Italy, has recently reviewed the variability of blazars across the electromagnetic spectrum. Blazars are a type of active galactic nucleus (AGN) with their jets pointing directly towards us, making them ideal for studying the physics and structure of extragalactic jets. These jets are powerful cosmic particle accelerators and are believed to be one of the sources of high-energy neutrinos detected by the IceCube Observatory.
Blazars exhibit variability in their brightness, spectrum, and polarization across different wavelengths, ranging from years down to minutes. This variability can be attributed to both intrinsic and extrinsic mechanisms. Intrinsic mechanisms include shock waves, magnetic reconnection, and turbulence within the jet, which can accelerate particles and lead to variations in the observed emission. Extrinsic mechanisms, on the other hand, involve changes in the Doppler beaming of the jet’s nonthermal radiation due to jet precession, rotation, or twisting.
The observed variability in blazars puts strong constraints on the size of the emitting regions, suggesting a multizone structure within the jet. Twisting jets have been proposed to explain long-term multiwavelength variability, supported by radio observations of bent or helical jets and results from relativistic magnetohydrodynamics simulations. Additionally, the detection of (quasi)periodic behavior in blazar variability has been attributed to various phenomena, such as orbital motion in black hole binary systems, jet precession, kink instabilities within the jet, or perturbations in the accretion disc. In some cases, gravitational microlensing has been suggested as an explanation for blazar behavior.
Polarization observations provide valuable information about the structure and behavior of the magnetic field in the emission zones of blazars. Both the degree and angle of polarization can show strong and fast variability, sometimes correlated with flux variations. However, interpreting the flux, spectral, and polarization variability within a consistent picture remains a challenge for current models of blazar variability.
This research was published in the journal “The Astronomy and Astrophysics Review,” providing a comprehensive overview of the current understanding of blazar variability and its implications for the study of extragalactic jets and high-energy astrophysical processes. While the direct practical applications for the energy sector may be limited, understanding the fundamental physics of these extreme environments can contribute to broader advancements in astrophysics and high-energy particle research.
This article is based on research available at arXiv.