Multi-Messenger and Multi-Timescale Variability in Blazars

Dear Colleagues,

Our knowledge of blazars—and active galactic nuclei, in general—has tremendously enriched thanks to the outpouring of observations from several ground- and space-bound telescopes operating in a wide range of electromagnetic spectral bandwidths. Similarly, the contemporaneous advancement in computers and computer science—e.g., machine learning—has significantly added to the large-scale simulations of the accretion disk around the supermassive black hole and parsec-scale relativistic jets. In spite of these successes, the details of the key blazar issues, e.g., the nature of the central engine, ejection of the relativistic jets, and emission of TeV emission still elude us. In such a context, blazar variability, with all its richness and complexity, continues to provide one of the most promising tools to probe the aforementioned issues.

The purpose of this issue is to gather, in one volume, papers from leading researchers on the topics of Blazar variability on all timescales across the entire electromagnetic spectrum in addition to other mediums, such as particles and gravitational waves. Although there have been no gravitational waves reportedly detected as of yet, the theoretical calculation of expectations has been done.  This issue welcomes theoretical papers, as well as observational and analytical studies of blazar multi-media variability. Work in these various fields is published in a variety of journals such as ApJ, Physics Review, PSAP, and Galaxies and other leading journals separately.  We feel a Special Issue containing papers covering all aspects of Blazar variability in one place would be extremely valuable to the community.

References:

1. Bhatta, G.; et al. The 72-h WEBT microvariability observation of blazar S5 0716 + 714 in 2009. Astrophys. 2013, 558, A92.
2. Bhatta, G.; Pánis, R.; Stuchlík, Z. et al. Deterministic Aspect of the γ-Ray Variability in Blazars, J. 2020, 905, 160
3. Blandford, R.; Meier, D.; Readhead, A. et al. Relativistic Jets from Active Galactic Nuclei, Rev. Astron. Astrophys. 2018, 57, 467-509
4. Böttcher, M., Progress in Multi-wavelength and Multi-Messenger Observations of Blazars and Theoretical Challenges. Galaxies 2019, 7, 20.
5. Hayashida, M.; et al. Rapid Variability of Blazar 3C 279 during Flaring States in 2013-2014 with Joint Fermi-LAT, NuSTAR, Swift, and Ground-Based Multiwavelength Observations. J. 2015, 807, 79.
6. Kim, J. Y.; et al. Event Horizon Telescope imaging of the archetypal blazar 3C279 at an extreme 20 microarcsecond resolution, Astrophys. 2020, 640, A69.
7. Marscher, A. Variability of Blazars and Blazar Models over 38 Years. Galaxies 2016, 4, 37.
8. Rieger, F., Gamma-Ray Astrophysics in the Time Domain. Galaxies 2019, 7, 28.
9. Oikonomou, F.; Murase, K.; Padovani, P.; Resconi, E.; Mészáros, P. High-energy neutrino flux from individual blazar flares. Notices Royal Astron. Soc. 2019, 489, 4347.
10. Webb, J.R. Multi-Frequency Blazar Micro-Variability as a Tool to Investigate Relativistic Jets. Galaxies 2016, 4, 15.

Prof. James R. Webb
Prof. Gopal Bhatta
Guest Editors

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• blazar variability
• multifrequency variability
• relativistic jets
• particles from blazars
• blazar gravitational wave emission