The blazar OJ 287 in a long-lasting low-state with small-amplitude rapid flares superposed

ATel #16071; S. Komossa (MPIfR), D. Grupe (NKU), A. Kraus (MPIfR), MOMO team
on 2 Jun 2023; 13:38 UT
Credential Certification: St. Komossa (stefanie.komossa@gmx.de)

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We report new Swift observations of the blazar and binary black hole candidate OJ 287 that show the source in a long-lasting UV-optical low-state, also seen in the radio, X-rays, and gamma-rays. OJ 287 has been monitored densely by us since 2015 in the course of the project MOMO (Multi-wavelength Observations and Modelling of OJ 287; Komossa et al. 2021, ApJ 923, 51) with the goal of exploring jet-disc physics and testing the different binary black hole scenarios suggested for this blazar. We have recently falsified the binary model that required a massive primary black hole of mass >10^10 M_sun and strong orbital precession (e.g., Valtonen et al. 2021, Galaxies 10, 1) because the measured primary black hole mass is a factor 100 lower (of order 10^8 M_sun) and the measured limit on the accretion disk luminosity is a factor ~100 lower than required by that model (Komossa et al. 2023a, MNRAS 522, L84). Further, that model predicted the latest bright outburst of OJ 287 in October 2022 (Valtonen et al. 2022, arXiv:2209.08360). However, our dense Swift coverage of that epoch showed that no such outburst materialized. Instead, OJ 287 was found in an UV-optical low-state in 2022 October and thereafter (Komossa et al. 2023b, ApJ 944, 177).

Here, we report the persistence of that low-state until the end of May 2023. Right now, and during the last few months, OJ 287 has been at low emission levels in all observed bands including the radio, optical, UV, X-rays and gamma-rays. In addition, in the optical and UV multiple, rapid, small-amplitude flares are superposed on the low-state with amplitudes that reach up to one magnitude. With Swift UVOT, on 2023 May 29, we measured the following magnitudes in the VEGA system: V: 15.99+/-0.07 (15.91), B: 16.46+/-0.05 (16.35), U: 15.73+/-0.05 (15.60), UVW1: 15.71+/-0.06 (15.54), UVM2: 15.74+/-0.06 (15.50), and UVW2: 15.90+/-0.05 (15.70), with reddening-corrected values in brackets. The lowest optical magnitude was measured on 2023 March 29 at V = 16.68+/-0.09 (16.48) mag. The (0.3-10 keV) X-rays are at a level of 0.125+/-0.012 cts/s (or an observed, absorption-corrected flux of 4.2 x 10^-12 erg/cm^2/s/Hz using a power law index Gamma_x = 2.12). With Fermi, OJ 287 has been rarely detected in recent months, with an upper limit on the (0.1-100 GeV) photon flux of < 4.6 x 10^-8 ph/cm2/s on 2023 May 29 (Kocevski et al. 2021, ATel #15110).

The new optical-UV observations also re-confirm that no outburst occurred since 2022 October, and that emission levels remain low also now. The latest of the bright double-peaked optical outbursts of OJ 287 was observed in 2016-2017 (Komossa et al. 2023b, ApJ), and we expect the next one in the time frame 2026-2028, given the occurrence of the previous big outbursts every 11.5 +- 1 years.

Data reported here have been obtained in the course of the dedicated multi-year, multi-frequency monitoring project MOMO (Komossa et al. 2017 - 2023, and e.g., ATel #8411, #15764). We would like to thank the Swift team for carrying out the observations we proposed.