Multiple black hole system in 4C31.61 (2201+315)

¹ Institut d’Astrophysique, UPMC Univ. Paris 06, CNRS, UMR 7095, 98 bis Bd Arago, 75014 Paris, France
e-mail: roland@iap.fr
² Laboratoire d’Astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, Allée Geoffroy Saint-Hilaire, 33615 Pessac, France
³ SYRTE, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, LNE, France

Received: 29 November 2018
Accepted: 11 December 2019

Abstract

Modeling trajectories of radio components ejected by the nucleus of 4C31.61 (2201+315) and observed by very long baseline interferometry (VLBI) in the frame of the MOJAVE survey suggests that they are ejected from three different origins that possibly host three different supermassive black holes. These origins correspond to three stationary components, one of which one is the VLBI core. Most of the mass of the nucleus is associated with a supermassive binary black hole system whose separation is ≈0.3 milliarc second, that is, a distance of ≈1.3 parsec and the mass ratio is ≈2. In contrast, the mass ratio with respect to the third black hole is ≈1/100. The three origins lie within 0.6 milliarc second, or a distance of ≈2.6 parsec. Based in this structure of the nucleus, we explain the variations observed in the astrometric coordinate time series obtained from VLBI geodetic surveys. This study shows that it is possible to exploit large MOJAVE-like VLBI databases to propose more insights into the structure of the extragalactic radio sources that are targeted by VLBI in geodetic and astrometry programs.