A1 Refereed original research article in a scientific journal
Probing the Innermost Regions of AGN Jets and Their Magnetic Fields with RadioAstron. V. Space and Ground Millimeter-VLBI Imaging of OJ 287
Authors: Gómez José L, Traianou Efthalia, Krichbaum Thomas P, Lobanov Andrei P, Fuentes Antonio, Lico Rocco, Zhao Guang-Yao, Bruni Gabriele, Kovalev Yuri Y, Lähteenmäki Anne, Voitsik Petr A, Lisakov Mikhail M, Angelakis Emmanouil, Bach Uwe, Casadio Carolina, Cho Ilje, Dey Lankeswar, Gopakumar Achamveedu, Gurvits Leonid I, Jorstad Svetlana, Kovalev Yuri A, Lister Matthew L, Marscher Alan P, Myserlis Ioannis, Pushkarev Alexander B, Ros Eduardo, Savolainen Tuomas, Tornikoski Merja, Valtonen Mauri J, Zensus Anton
Publisher: IOP Publishing Ltd
Publication year: 2022
Journal: Astrophysical Journal
Journal name in source: ASTROPHYSICAL JOURNAL
Journal acronym: ASTROPHYS J
Article number: ARTN 122
Volume: 924
Issue: 2
Number of pages: 16
ISSN: 0004-637X
DOI: https://doi.org/10.3847/1538-4357/ac3bcc
Web address : https://iopscience.iop.org/article/10.3847/1538-4357/ac3bcc
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/69001195
Preprint address: https://arxiv.org/abs/2111.11200
We present the first polarimetric space very long baseline interferometry (VLBI) observations of OJ 287, observed with RadioAstron at 22 GHz during a perigee session on 2014 April 4 and five near-in-time snapshots, together with contemporaneous ground VLBI observations at 15, 43, and 86 GHz. Ground-space fringes were obtained up to a projected baseline of 3.9 Earth diameters during the perigee session, and at a record 15.1 Earth diameters during the snapshot sessions, allowing us to image the innermost jet at an angular resolution of similar to 50 mu as, the highest ever achieved at 22 GHz for OJ 287. Comparison with ground-based VLBI observations reveals a progressive jet bending with increasing angular resolution that agrees with predictions from a supermassive binary black hole model, although other models cannot be ruled out. Spectral analyses suggest that the VLBI core is dominated by the internal energy of the emitting particles during the onset of a multiwavelength flare, while the parsec-scale jet is consistent with being in equipartition between the particles and magnetic field. Estimated minimum brightness temperatures from the visibility amplitudes show a continued rising trend with projected baseline length up to 10(13) K, reconciled with the inverse-Compton limit through Doppler boosting for a jet closely oriented to the line of sight. The observed electric vector position angle suggests that the innermost jet has a predominantly toroidal magnetic field, which, together with marginal evidence of a gradient in rotation measure across the jet width, indicates that the VLBI core is threaded by a helical magnetic field, in agreement with jet formation models.
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