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1. Blazar spectral variability as explained by a twisted inhomogeneous jet

Author

M. S. Butuzova, C. Espinosa, O. Vince, K. Kuratov, Sergey S. Savchenko, Joseph Moody, A. Di Paola, Boyko Mihov, Ivan S. Troitsky, L. V. Larionova, José L. Gómez, T. S. Grishina, Mark Gurwell, Sol N. Molina, Brian Skiff, V. Bozhilov, G. V. Baida, D. A. Morozova, A. A. Mokrushina, Katsura Matsumoto, Sofia O. Kurtanidze, G. A. Borman, A. Strigachev, C. S. Lin, J. Echevarría, S. V. Nazarov, Raul Michel, G. Rodriguez-Coira, Alan P. Marscher, M. I. Carnerero, C. M. Raiteri, Joni Tammi, N. V. Efimova, Omar M. Kurtanidze, F. Pinna, Iain A. Steele, B. Jordan, B. McBreen, Kozo Sadakane, Paul S. Smith, C. Protasio, Manasvita Joshi, J. M. Ohlert, F. J. Redondo-Lorenzo, Clemens Thum, Elena G. Larionova, T. A. Polakis, L. Slavcheva-Mihova, Carolina Casadio, Anne Lähteenmäki, D. N. Okhmat, M. Villata, Helen Jermak, Erika Benítez, E. N. Kopatskaya, Arkady A. Arkharov, N. Rizzi, J. A. Acosta-Pulido, A. A. Vasilyev, Michael P. Malmrose, M. Minev, N. Castro-Segura, M. G. Nikolashvili, P. Calcidese, Manash R. Samal, Sh. A. Ehgamberdiev, Merja Tornikoski, C. Lázaro, Filippo D'Ammando, W. Boschin, T. Pursimo, D. Carosati, Rumen Bachev, A. C. Sadun, Goran Damljanović, Evgeni Semkov, D. O. Mirzaqulov, Evgeni Ovcharov, Yu. V. Troitskaya, Svetlana G. Jorstad, David Hiriart, A. Giunta, Antonio Fuentes, Ivan Agudo, Valeri M. Larionov, and Wen Ping Chen

Subjects
ACTIVE GALACTIC NUCLEI, Brightness, Active galactic nucleus, PARTICLE-ACCELERATION, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Relativistic beaming, Astrophysical jet, 0103 physical sciences, HELICAL JETS, PHOTOMETRY, OUTBURST, Blazar, 010303 astronomy & astrophysics, QC, QB, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Multidisciplinary, ta115, ta114, 010308 nuclear & particles physics, EXTRAGALACTIC RADIO-SOURCES, COMPARISON STARS, Quasar, Astrophysics - Astrophysics of Galaxies, Galaxy, CTA-102, QUASARS, WEBT CAMPAIGN, Astrophysics of Galaxies (astro-ph.GA), RELATIVISTIC JETS, Astrophysics - High Energy Astrophysical Phenomena
Abstract

Blazar emission is dominated by non-thermal radiation from a relativistic jet pointing toward us, therefore undergoing Doppler beaming. This is responsible for flux enhancement and contraction of the variability time scales, so that most blazars appear as luminous sources characterized by noticeable and fast flux changes at all frequencies. The mechanisms producing their unpredictable variability are debated and include injection, acceleration and cooling of particles, with possible intervention of shock waves or turbulence. Changes in the viewing angle of the emitting knots or jet regions have also been suggested to explain flaring events or specific properties such as intraday variability, quasi-periodicities, or the delay of radio flux variations relative to optical changes. However, such a geometric interpretation has not been universally accepted because alternative explanations based on changes of physical conditions can also work in many cases. Here we report the results of optical-to-radio monitoring of the blazar CTA 102 by the Whole Earth Blazar Telescope Collaboration and show that the observed long-term flux and spectral variability is best explained by an inhomogeneous, curved jet that undergoes orientation changes. We propose that magnetohydrodynamic instabilities or rotation of a twisted jet cause different jet regions to change their orientation and hence their relative Doppler factors. In particular, the recent extreme optical outburst (six magnitudes) occurred when the corresponding jet emitting region acquired a minimum viewing angle., Comment: 31 pages, 11 figures. This is the accepted version (before Nature editing) of the paper published by Nature, online version at http://dx.doi.org/10.1038/nature24623, Nature 2017/12/04/online

Published
2017

2. Blazar spectral variability as explained by a twisted inhomogeneous jet.

Author

Raiteri CM, Villata M, Acosta-Pulido JA, Agudo I, Arkharov AA, Bachev R, Baida GV, Benítez E, Borman GA, Boschin W, Bozhilov V, Butuzova MS, Calcidese P, Carnerero MI, Carosati D, Casadio C, Castro-Segura N, Chen WP, Damljanovic G, D'Ammando F, Di Paola A, Echevarría J, Efimova NV, Ehgamberdiev SA, Espinosa C, Fuentes A, Giunta A, Gómez JL, Grishina TS, Gurwell MA, Hiriart D, Jermak H, Jordan B, Jorstad SG, Joshi M, Kopatskaya EN, Kuratov K, Kurtanidze OM, Kurtanidze SO, Lähteenmäki A, Larionov VM, Larionova EG, Larionova LV, Lázaro C, Lin CS, Malmrose MP, Marscher AP, Matsumoto K, McBreen B, Michel R, Mihov B, Minev M, Mirzaqulov DO, Mokrushina AA, Molina SN, Moody JW, Morozova DA, Nazarov SV, Nikolashvili MG, Ohlert JM, Okhmat DN, Ovcharov E, Pinna F, Polakis TA, Protasio C, Pursimo T, Redondo-Lorenzo FJ, Rizzi N, Rodriguez-Coira G, Sadakane K, Sadun AC, Samal MR, Savchenko SS, Semkov E, Skiff BA, Slavcheva-Mihova L, Smith PS, Steele IA, Strigachev A, Tammi J, Thum C, Tornikoski M, Troitskaya YV, Troitsky IS, Vasilyev AA, and Vince O

Abstract

Blazars are active galactic nuclei, which are powerful sources of radiation whose central engine is located in the core of the host galaxy. Blazar emission is dominated by non-thermal radiation from a jet that moves relativistically towards us, and therefore undergoes Doppler beaming. This beaming causes flux enhancement and contraction of the variability timescales, so that most blazars appear as luminous sources characterized by noticeable and fast changes in brightness at all frequencies. The mechanism that produces this unpredictable variability is under debate, but proposed mechanisms include injection, acceleration and cooling of particles, with possible intervention of shock waves or turbulence. Changes in the viewing angle of the observed emitting knots or jet regions have also been suggested as an explanation of flaring events and can also explain specific properties of blazar emission, such as intra-day variability, quasi-periodicity and the delay of radio flux variations relative to optical changes. Such a geometric interpretation, however, is not universally accepted because alternative explanations based on changes in physical conditions-such as the size and speed of the emitting zone, the magnetic field, the number of emitting particles and their energy distribution-can explain snapshots of the spectral behaviour of blazars in many cases. Here we report the results of optical-to-radio-wavelength monitoring of the blazar CTA 102 and show that the observed long-term trends of the flux and spectral variability are best explained by an inhomogeneous, curved jet that undergoes changes in orientation over time. We propose that magnetohydrodynamic instabilities or rotation of the twisted jet cause different jet regions to change their orientation and hence their relative Doppler factors. In particular, the extreme optical outburst of 2016-2017 (brightness increase of six magnitudes) occurred when the corresponding emitting region had a small viewing angle. The agreement between observations and theoretical predictions can be seen as further validation of the relativistic beaming theory.

Published
2017
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