MOMO VI: Multifrequency radio variability of the blazar OJ 287 from 2015-2022, absence of predicted 2021 precursor-flare activity, and a new binary interpretation of the 2016/2017 outburst

TL;DR

This study presents detailed multi-frequency radio and gamma-ray observations of blazar OJ 287 from 2015 to 2022, revealing flux variability, absence of predicted precursor flares, and proposing a new binary black hole interpretation for the 2016/2017 outburst.

Contribution

It provides the first dense radio monitoring of OJ 287 across multiple frequencies over several years, challenging existing binary SMBH models with new observational insights.

Findings

Deep radio and optical-UV flux fades occur every 1-2 years.

The predicted precursor flare was not observed.

The 2016/2017 outburst is explained by a binary scenario without a highly precessing secondary SMBH.

Abstract

Based on our dedicated Swift monitoring program, MOMO, OJ 287 is one of the best-monitored blazars in the X-ray--UV--optical regime. Here, we report results from our accompanying, dense, multi-frequency (1.4--44 GHz) radio monitoring of OJ 287 between 2015 and 2022 covering a broad range of activity states. Fermi gamma-ray observations are added. We characterize the radio flux and spectral variability in detail, including DCF and other variability analyses, and discuss its connection with the multiwavelength emission. Deep fades of radio and optical--UV fluxes are found to occur every 1--2 years. Further, it is shown that a precursor flare of thermal bremsstrahlung predicted by one of the binary supermassive black hole (SMBH) models of OJ 287 was absent. We then focus on the nature of the extraordinary, nonthermal 2016/2017 outburst that we initially discovered with Swift. We interpret it as the latest of the famous optical double-peaked outbursts of OJ 287, favoring binary scenarios that do not require a highly precessing secondary SMBH.