Letter to the Editor

Linear polarization in the nucleus of M87 at 7 mm and 1.3 cm

¹ INAF Istituto di Radioastronomia, Via P. Gobetti 101, Bologna 40129, Italy
e-mail: evgeniya.kravchenko@inaf.it
² Astro Space Center, Lebedev Physical Institute, Profsouznaya 84/32, Moscow 117997, Russia
³ Mizusawa VLBI Observatory, National Astronomical Observatory of Japan, 2-12 Hoshigaoka, Mizusawa, Oshu, Iwate 023-0861, Japan
⁴ Department of Astronomical Science, The Graduate University for Advanced Studies (SOKENDAI), 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
⁵ Department of Astronomy, Caltech, Pasadena, CA 91125, USA
⁶ Jet Propulsion Laboratory, Pasadena, CA 91109, USA
⁷ Institute of Astronomy and Astrophysics, Academia Sinica, PO Box 23-141 Taipei 10617, Taiwan
⁸ Department of Physics and Astronomy, Seoul National University, Gwanak-gu, Seoul 08826, Republic of Korea
⁹ National Radio Astronomy Observatory, Socorro, NM 87801, USA
¹⁰ National Institute of Technology, Hachinohe College, 16-1 Uwanotai, Tamonoki, Hachinohe City, Aomori Prefecture 039-1192, Japan

Received: 13 December 2019
Accepted: 24 April 2020

Abstract

We report on high angular resolution polarimetric observations of the nearby radio galaxy M87 using the Very Long Baseline Array at 24 GHz (λ = 1.3 cm) and 43 GHz (λ = 7 mm) in 2017–2018. New images of the linear polarization substructure in the nuclear region are presented, characterized by a two-component pattern of polarized intensity and smooth rotation of the polarization plane around the 43 GHz core. From a comparison with an analogous dataset from 2007, we find that this global polarization pattern remains stable on a time interval of 11 yr, while showing smaller month-scale variability. We discuss the possible Faraday rotation toward the M87 nucleus at centimeter to millimeter wavelengths. These results can be interpreted in a scenario where the observed polarimetric pattern is associated with the magnetic structure in the confining magnetohydrodynamic wind, which also serves as the source of the observed Faraday rotation.