MOMO detection of the blazar OJ 287 in a deep optical-UV-radio low-state
ATel #16659; S. Komossa (MPIfR), D. Grupe (NKU), A. Kraus (MPIfR)
on 16 Jun 2024; 21:48 UT
Credential Certification: St. Komossa (stefanie.komossa@gmx.de)
Subjects: Radio, Optical, Ultra-Violet, X-ray, AGN, Blazar
We report on the Neil Gehrels Swift observatory and Effelsberg telescope detection of the blazar OJ 287 in a very deep low-state. Observations were obtained in the course of the longterm MOMO (multiwavelength observations and modelling of OJ 287) program. The blazar OJ 287 is a binary SMBH candidate with a (primary) mass of 10^8 M_sun (Komossa et al. 2023a, MNRAS). The system exhibits bright, double-peaked outbursts, the last one observed in 2016--2017 (Komossa et al. 2023b, ApJ). In addition it shows occasional deep multi-wavelength low-states. Here, we report the deepest  of these since the beginning of the MOMO project in 2015.
With Swift, we last observed OJ 287 on 2024 June 13. The following low-state magnitudes were measured with the UVOT: V=16.65+/-0.11 (16.57), B=17.13+/-0.08 (17.02), U=16.38+/-0.07 (16.23), W1=16.01+/-0.06 (15.84), M2=16.44+/-0.07 (16.20), and W2=16.53+/-0.06(16.33), where values in brackets are corrected for Galactic extinction. This is a factor of 29 lower in V than the brightest state of OJ 287
(observed in October 2016; ATel #9629; Komossa et al. 2020), and a factor of 5.6 lower in V than the highest value measured earlier this year in April. OJ 287 has shown a systematic decline since then into this low-state. In the X-ray band, OJ 287 has only shown mild variability in 2024 and remainsat low emission levels. On June 13, we measured a (0.3-10 keV) countrate of 0.114+/-0.009 Â counts/s, or an absorption-corrected flux of f= 4.41+/-0.46 10^-10 erg/s/cm^2 using Galactic absorption and using the measured powerlaw photon index of Gamma_x= 1.76+/-0.18.
In the radio bands, we last observed OJ 287 on 2024 June 2 with the Effelsberg 100m telescope at frequencies between 2.95 and 24.75 GHz, and find that the flux densities are very low in the radio regime as well, have been decreasing, and may decrease further depending on frequency. Flux densities of 3.00+/-0.02 Jy (2.95 GHz), 4.66+/-0.12 Jy (10.45 GHz), and 4.66+/-0.17 Jy (24.75 GHz) were measured on June 2.
We would like to thank the Swift team for carrying out the observations we proposed.