Repeating flaring activity of the blazar AO 0235+164

• Published in: Astronomy and astrophysics (Berlin) Vol. 682; p. A100
• Main Authors: Escudero Pedrosa, J., Agudo, I., Tramacere, A., Marscher, A. P., Jorstad, S., Weaver, Z. R., Casadio, C., Thum, C., Myserlis, I., Fuentes, A., Traianou, E., Kim, J.-Y., Kramer, J., López-Coto, R., D’Ammando, F., Bernardos, M., Bonnoli, G., Blinov, D. A., Borman, G. A., Grishina, T. S., Hagen-Thorn, V. A., Kopatskaya, E. N., Larionova, E. G., Larionov, V. M., Larionova, L. V., Morozova, D. A., Savchenko, S. S., Troitskiy, I. S., Troitskaya, Y. V., Vasilyev, A. A.
• Format: Journal Article
• Language: English
• Published: Heidelberg EDP Sciences 01.02.2024
• Subjects: Blazars; Broadband; Correlation analysis; Emission; Flares; Kinematics; Mathematical models; Parameters; Polarimetry; Red shift; Spectral energy distribution; Statistical correlation; Very long base interferometry; X ray spectra
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361/202346885

Context. Blazar AO 0235+164 , located at a redshift of z  = 0.94, has undergone several sharp multi-spectral-range flaring episodes over recent decades. In particular, the episodes that peaked in 2008 and 2015, which were subject to extensive multi-wavelength coverage, exhibited an interesting behavior. Aims. We study the actual origin of these two observed flares by constraining the properties of the observed photo-polarimetric variability as well as of the broadband spectral energy distribution and the observed time-evolution behavior of the source. We use ultra-high-resolution total-flux and polarimetric very-long-baseline interferometry (VLBI) imaging. Methods. The analysis of VLBI images allowed us to constrain kinematic and geometrical parameters of the 7 mm jet. We used the discrete correlation function to compute the statistical correlation and the delays between emission at different spectral ranges. The multi-epoch modeling of the spectral energy distributions allowed us to propose specific models of the emission; in particular, with the aim to model the unusual spectral features observed in this source in the X-ray region of the spectrum during strong multi spectral-range flares. Results. We find that these X-ray spectral features can be explained by an emission component originating in a separate particle distribution than the one responsible for the two standard blazar bumps. This is in agreement with the results of our correlation analysis, where we did not find a strong correlation between the X-ray and the remaining spectral ranges. We find that both external Compton-dominated and synchrotron self-Compton-dominated models are able to explain the observed spectral energy distributions. However, the synchrotron self-Compton models are strongly favored by the delays and geometrical parameters inferred from the observations.