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Abstract We report the study of a huge optical intraday flare on 2021 November 12 at 2 a.m. UT in the blazar OJ 287. In the binary black hole model, it is associated with an impact of the secondary black hole on the accretion disk of the primary. Our multifrequency observing campaign was set up to search for such a signature of the impact based on a prediction made 8 yr earlier. The firstI-band results of the flare have already been reported by Kishore et al. (2024). Here we combine these data with our monitoring in theR-band. There is a big change in theR–Ispectral index by 1.0 ± 0.1 between the normal background and the flare, suggesting a new component of radiation. The polarization variation during the rise of the flare suggests the same. The limits on the source size place it most reasonably in the jet of the secondary BH. We then ask why we have not seen this phenomenon before. We show that OJ 287 was never before observed with sufficient sensitivity on the night when the flare should have happened according to the binary model. We also study the probability that this flare is just an oversized example of intraday variability using the Krakow data set of intense monitoring between 2015 and 2023. We find that the occurrence of a flare of this size and rapidity is unlikely. In machine-readable Tables 1 and 2, we give the full orbit-linked historical light curve of OJ 287 as well as the dense monitoring sample of Krakow.
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This content will become publicly available on February 1, 2026
The polarisation behaviour of OJ 287 viewed through radio, millimetre, and optical observations between 2015 and 2017
OJ 287 is a bright blazar with century-long observations, and one of the strongest candidates to host a supermassive black hole binary. Its polarisation behaviour between 2015 and 2017 (MJD 57300–58000) contains several interesting events that we re-contextualise in this study. We collected optical photometric and polarimetric data from several telescopes and obtained high-cadence light curves from this period. In the radio band, we collected millimetre-wavelength polarisation data from the AMAPOLA programme. We combined them with existing multi-frequency polarimetric radio results and the results of very long-baseline interferometry imaging with the Global mm-VLBI Array at 86 GHz. In December 2015, an optical flare was seen according to the general relativistic binary black hole model. We suggest that the overall activity near the accretion disk and the jet base during this time may be connected to the onset of a new moving component, K, seen in the jet in March 2017. With the additional optical data, we find a fast polarisation angle rotation of ∼210° coinciding with the December 2015 flare, hinting at a possible link between these events. Based on the 86 GHz images, we calculated a new speed of 0.12 mas/yr for K, which places it inside the core at the time of the 2015 flare. This speed also supports the scenario in which the passage of K through the quasi-stationary feature S1 could have been the trigger for the very high-energy gamma-ray flare of OJ 287 seen in February 2017. With the millimetre-polarisation data, we establish that these bands follow the centimetre-band data but show a difference during the time when K passes through S1. This indicates that the millimetre bands trace substructures of the jet that are still unresolved in the centimetre bands.
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- Award ID(s):
- 2108622
- PAR ID:
- 10598647
- Publisher / Repository:
- EDP Sciences
- Date Published:
- Journal Name:
- Astronomy & Astrophysics
- Volume:
- 694
- ISSN:
- 0004-6361
- Page Range / eLocation ID:
- A206
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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