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Blazar Variability at High Temporal Resolution Across the Electromagnetic Spectrum

Presentation #129.02D in the session AGN and Quasars II.

Published onJun 29, 2022
Blazar Variability at High Temporal Resolution Across the Electromagnetic Spectrum

Amongst active galactic nuclei (AGN), the subclass of blazars exhibits the most dramatic variability on different timescales. I analyze the variable nonthermal emission of γ-ray bright blazars from radio to γ-ray wavelengths, with special emphasis on the shortest variability timescales. I study the jet kinematics of a sample of 38 AGN based on roughly monthly monitoring with the Very Long Baseline Array at 43 GHz over 10 years. The sample consists of flat-spectrum radio quasars (FSRQs), BL Lac objects (BLs), and radio galaxies (RGs). I have determined the apparent speeds of 425 moving features in the jets and identified 96 quasi-stationary features downstream of the presumably stationary mm-wave cores of the jets. I show that acceleration of moving knots is connected with their passage across quasi-stationary features. From the properties of the knots, I derive physical parameters of the jets, such as the bulk Lorentz factor, viewing and opening angles, and Doppler factor of variability. These parameters are applied to high time-resolution photometric and polarimetric observations of three sources as a case study for each blazar subtype: the FSRQ 3C 454.3, BL Lacertae, and the RG 3C 120. The variability timescales studied range from days at radio wavelengths to hours at γ-ray, X-ray, and optical wavelengths, and to minutes in data from the Transiting Exoplanet Survey Satellite (TESS). For each source, I investigate the size of emission regions, based on the minimum and average timescale of variability, as well as properties of the magnetic field. I determine the relative location of these regions at different wavelengths, along with likely emission mechanisms. I discuss the future of such studies with high temporal resolution afforded by new facilities such as PLATO, the Legacy Survey of Space and Time, the Cherenkov Telescope Array, and the Event Horizon Telescope. This research was supported in part by NSF grant AST-1615796, NASA grants 80NSSC17K0649, 80NSSC20K1567, and 80NSSC20K1566 (Fermi), 80NSSC20K0080 (NuSTAR), 80NSSC19K1731 (TESS), NRAO Student Observing Support Program, Massachusetts Space grant 316080, and Boston University Hariri Institute Research Incubation Award 2019-03-007.

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