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A parsec-scale wobbling jet in the high-synchrotron peaked blazar PG 1553+113

AuthorsLico, R.; Liu, J.; Giroletti, M.; Orienti, M.; Gómez Fernández, J. L. ; Piner, B. G.; MacDonald, N. R.; D'Ammando, F.; Fuentes, A.
KeywordsGalaxies: active
BL Lacertae objects: individual: PG 1553+113
Galaxies: jets
Galaxies: magnetic fields
Issue Date2020
PublisherEDP Sciences
CitationAstronomy and Astrophysics - Les Ulis 634: A87 (2020)
AbstractContext. The detection of quasi-periodic variability in active galactic nuclei in general, and in blazars in particular, is key to our understanding of the origin and nature of these objects as well as their cosmological evolution. PG 1553+113 is the first blazar showing an approximately two-year quasi-periodic pattern in its gamma-ray light curve, which is also revealed at optical frequencies.Aims. Such quasi-periodicity might have a geometrical origin, possibly related to the precessing nature of the jet, or could be intrinsic to the source and related to pulsational accretion flow instabilities. In this work we investigate and characterise the high-resolution radio emission properties of PG 1553+113 on parsec scales in order to differentiate between these different physical scenarios.Methods. We monitored the source with the very long baseline array (VLBA) at 15, 24, and 43 GHz during an entire cycle of gamma-ray activity in the period 2015-2017, with a cadence of about 2 months, both in total and polarised intensity. We constrained the jet position angle across the different observing epochs by investigating the total intensity ridge lines.Results. We find a core-dominated source with a limb-brightened jet structure extending for similar to 1.5 mas in the northeast direction whose position angle varies in time in the range similar to 40 degrees-60 degrees. No clear periodic pattern can be recognized in the VLBA light curves during 2015-2017 or in the 15 GHz Owens Valley Radio Observatory light curve during the period 2008-2018. The core region polarisation percentage varies in the range similar to 1-4%, and the polarisation angle varies from being roughly parallel to roughly transverse to the jet axis. We estimate a rotation measure value in the core region of similar to-1.00.4x10(4) rad m(-2). The brightness temperature (T-B) is found to decrease as the frequency increases with an intrinsic value of similar to 1.5x10(10) K and the estimated Doppler factor is similar to 1.4.Conclusions. Although the jet wobbling motion indicates that geometrical effects can produce an enhanced emission through the Doppler boosting modulation, additional mechanisms are required in order to account for the quasi-periodic variability patterns observed in gamma rays. The intrinsic T-B value indicates that the total energy in the core region is dominated by the magnetic field.© R. Lico et al. 2020
Description© R. Lico et al. 2020 Licence Creative Commons Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Open Access funding provided by Max Planck Society.
Publisher version (URL)http://dx.doi.org/10.1051/0004-6361/201936564
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