Detection of a second jet within the nuclear core of Mrk 501
Year: 2026
Type: article
Abstract: ABSTRACT The blazar Mrk 501 still poses challenging questions for astrophysics, primarily because of the different orientations observed at pc- and kpc-scales. A much-debated issue is whether its core harbours a supermassive binary black hole (SMBBH). We remodel and reanalyse 83 data sets observed with the Very Long Baseline Array (2011-09-24–2023-07-24) at 43 GHz and compare them with earlier results for 15 and 8 GHz. In addition to the previously known parsec-scale jet in the core of Mrk 501, we detect a second nuclear jet (Jet 2), which appears to start off on the counterjet side and loop anticlockwise around the primary core. The image on 2022 June 24 indicates Jet 2 being lensed into a partial Einstein ring. The entire jet system (Jet 1 + Jet 2) at 43 GHz appears significantly displaced in a clockwise direction relative to the 15 GHz jet, and periodic transverse motion on a time-scale of about 7 yr is revealed. The total flux density light curve at 43 GHz also shows modulations with a similar period (7.4 yr). A shorter period of about 121 d is found in the 43 GHz flux density light curve of the core, albeit with less certainty. This shorter period is supported by the quasi-periodic appearance of Jet 2. We explore several physical scenarios and find that an SMBBH with a 7-yr orbital plane precessional period and a 121-d orbital period can reasonably explain our observational results. Assuming equal masses, we estimate the SMBBH to have its two components separated by 27–128 Schwarzschild radii and each having a mass of $10^{8}$–$10^{9}$ ${\rm M}_\odot$.
Institutions: Max Planck Institute for Radio Astronomy, Radboud University Nijmegen, University of Aveiro, Center for Excellence in Basic Sciences, TU Wien, P.N. Lebedev Physical Institute of the Russian Academy of Sciences, Moscow Institute of Physics and Technology, Konkoly Observatory, HUN-REN Research Centre for Astronomy and Earth Sciences, Ruhr University Bochum, National Radio Astronomy Observatory, Consejo Superior de Investigaciones Científicas, Universidad de La Laguna, Instituto de Astrofísica de Canarias, Max Planck Institute for Physics, University of Mississippi
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $3,046
Funders: National Science Foundation, National Aeronautics and Space Administration, Alexander von Humboldt-Stiftung, Indian National Science Academy, National Radio Astronomy Observatory, Radboud Universiteit, Austrian Science Fund, Nurses Organization of Veterans Affairs, Horizon 2020 Framework Programme, European Regional Development Fund, Nuclear Fuel Cycle and Supply Chain, U.S. Naval Observatory
OpenAlex ID: W7141151447