MOMO V. Effelsberg, Swift and Fermi study of the blazar and supermassive binary black hole candidate OJ 287 in a period of high activity

TL;DR

This study presents multiwavelength observations of the blazar OJ 287 during a high activity period, revealing new states, flares, and correlations that support the binary supermassive black hole model.

Contribution

It combines extensive multiwavelength data to analyze OJ 287's activity, providing new insights into its variability and the nature of its central black hole system.

Findings

Identification of a new UV-optical minimum state in 2021 December.

Observation of a long-lasting UV-optical flare in 2020-2021.

Detection of a bright radio flare in November 2021 potentially linked to gamma-ray activity.

Abstract

We report results from our ongoing project MOMO (Multiwavelength Observations and Modelling of OJ 287). In this latest publication of a sequence, we combine our Swift UVOT--XRT and Effelsberg radio data (2.6-44 GHz) between 2019 and 2022.04 with public SMA data and gamma-ray data from the Fermi satellite. The observational epoch covers OJ 287 in a high state of activity from radio to X-rays. The epoch also covers two major events predicted by the binary supermassive black hole (SMBH) model of OJ 287. Spectral and timing analyses clearly establish: a new UV-optical minimum state in 2021 December at an epoch where the secondary SMBH is predicted to cross the disk surrounding the primary SMBH; an overall low level of gamma-ray activity in comparison to pre-2017 epochs; the presence of a remarkable, long-lasting UV--optical flare event of intermediate amplitude in 2020--2021; a high level of activity in the radio band with multiple flares; and particularly a bright, ongoing radio flare peaking in 2021 November that may be associated with a gamma-ray flare, the strongest in 6 years. Several explanations for the UV--optical minimum state are explored, including the possibility that a secondary SMBH launches a temporary jet, but the observations are best explained by variability associated with the main jet.