Probing the Innermost Regions of AGN Jets and Their Magnetic Fields with RadioAstron. III. Blazar S5 0716+71 at Microarcsecond Resolution

Abstract

We present RadioAstron Space VLBI imaging observations of the BL Lac object S5 0716+71 made on 2015 January 3-4 at a frequency of 22 GHz (wavelength λ = 1.3 cm). The observations were made in the framework of the AGN Polarization Key Science Program. The source was detected on projected space-ground baselines up to 70,833 km (5.6 Earth diameters) for both parallel-hand and cross-hand interferometric visibilities. We have used these detections to obtain a full-polarimetric image of the blazar at an unprecedented angular resolution of 24 μas, the highest for this source to date. This enabled us to estimate the size of the radio core to be 2.2 × 1013 K for the blazar core. This implies that the inverse-Compton limit must be violated in the rest frame of the source, even for the largest Doppler factor δ ∼ 25 reported for 0716+714. © 2020. The American Astronomical Society. All rights reserved. ; We thank the anonymous referee for useful comments which helped to improve the manuscript. The authors are grateful to Uwe Bach for providing measurements of the absolute EVPA orientation obtained at Effelsberg. E.V.K. acknowledges support from the Italian Space Agency under contract ASIINAF 2015-023-R.O. J.L.G. and A.F. were supported by the Spanish Ministry of Economy and Competitiveness grants AYA2013-40825-P and AYA2016-80889-P. Y.Y.K. was supported by the government of the Russian Federation (agreement 05.Y09.21.0018) and the Alexander von Humboldt Foundation. G.B. acknowledges financial support under the INTEGRAL ASI-INAF agreement 2013-025.R01. The RadioAstron project is led by the Astro Space Center of the Lebedev Physical Institute of the Russian Academy of Sciences and the Lavochkin Scientific and Production Association under a contract with the State Space Corporation ROSCOSMOS, in collaboration with partner organizations in Russia and other countries. Results of optical positioning measurements of the Spektr-R spacecraft by the global MASTER Robotic Net (Lipunov et al. 2010), ISON collaboration, and Kourovka observatory were used for spacecraft orbit determination in addition to mission facilities. This research has made use of data from the MOJAVE database that is maintained by the MOJAVE team (Lister et al. 2018). This study makes use of 43 GHz VLBA data from the VLBA-BU Blazar Monitoring Program (VLBA-BU-BLAZAR), funded by NASA through the Fermi Guest Investigator grants, the most recent 80NSSC17K0649. The VLBA is an instrument of the Long Baseline Observatory. The Long Baseline Observatory is a facility of the National Science Foundation operated by Associated Universities, Inc. This publication makes use of data obtained at the Metsähovi Radio Observatory, operated by the Aalto University. This work is partly based on observations carried out using the 100 m telescope of the MPIfR (MaxPlanck-Institute for Radio Astronomy) at Effelsberg, the Noto telescope operated by INAF—Istituto di Radioastronomia and the 32 m radio telescope operated by Torun Centre for Astronomy of Nicolaus Copernicus University in Torun (Poland) and supported by the Polish Ministry of Science and Higher Education SpUB grant. The European VLBI Network is a joint facility of independent European, African, Asian, and North American radio astronomy institutes. Scientific results from data presented in this publication are derived from the following global VLBI project code: GL041. Facilities: RadioAstron Space Radio Telescope (Spektr-R), VLBA, Green Bank 100 m radio telescope, Sheshan 25 m radio telescope (Shangai), EVN, Effelsberg 100 m radio telescope, Noto 32 m radio telescope. Software: AIPS (Greisen 2003), Difmap (Pearson et al. 1994), ROOT framework (Antcheva et al. 2009). ; Peer reviewed