The flaring activity of blazar AO 0235+164 in 2021

¹ Instituto de Astrofísica de Andalucía, CSIC, Glorieta de la Astronomía s/n, 18080 Granada, Spain
² Institute for Astrophysical Research, Boston University, 725 Commonwealth Avenue, Boston, MA 02215, United States
³ Department of Astronomy, University of Geneva, ch. d’Ecogia 16, 1290 Versoix, Switzerland
⁴ Department of Physics, University of Crete, 71003 Heraklion, Greece
⁵ Institute of Astrophysics, Foundation for Research and Technology – Hellas, Voutes, 70013 Heraklion, Greece
⁶ Institut de Radioastronomie Millimétrique, Avenida Divina Pastora 7, Local 20, 18012 Granada, Spain
⁷ INAF – Istituto di Radioastronomia, Via Gobetti 101, 40129 Bologna, Italy
⁸ INAF Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Merate (LC), Italy
⁹ Saint Petersburg State University, 7/9 Universitetskaya nab., St. Petersburg 199034, Russia
¹⁰ Center for Astrophysics – Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA

Received: 25 February 2024
Accepted: 15 May 2024

Abstract

Context. The blazar AO 0235+164, located at redshift z = 0.94, has displayed interesting and repeating flaring activity in the past, with recent episodes in 2008 and 2015. In 2020, the source brightened again, starting a new flaring episode that peaked in 2021.

Aims. We study the origin and properties of the 2021 flare in relation to previous studies and the historical behavior of the source, in particular the 2008 and 2015 flaring episodes.

Methods.We analyzed the multiwavelength photo-polarimetric evolution of the source. From Very Long Baseline Array images, we derived the kinematic parameters of new components associated with the 2021 flare. We used this information to constrain a model for the spectral energy distribution of the emission during the flaring period. We propose an analytical geometric model to test whether the observed wobbling of the jet is consistent with precession.

Results. We report the appearance of two new components that are ejected in a different direction than previously, confirming the wobbling of the jet. We find that the direction of ejection is consistent with that of a precessing jet. Our derived period agrees with the values commonly found in the literature. Modeling of the spectral energy distribution further confirms that the differences between flares can be attributed to geometrical effects.