Detection of a deep low-state of the blazar OJ 287 in the radio, optical, and UV band in the course of the MOMO program

ATel #15764; S. Komossa (MPIfR), D. Grupe (NKU), A. Kraus (MPIfR), A. G. Gonzalez (Saint Mary's Univ.), L. C. Gallo (Saint Mary's Univ.), M. Berton (ESO-Chile)
on 18 Nov 2022; 15:47 UT
Credential Certification: St. Komossa (stefanie.komossa@gmx.de)

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We have been monitoring the blazar and binary SMBH candidate OJ 287 since 2015 in the radio to X-ray band. Here, we report the detection of a deep low-state of OJ 287 in the UV-optical band with the Neil Gehrels Swift observatory, and in the 2.6-44 GHz band with the Effelsberg 100m radio telescope.

During our latest observation of OJ 287 on 2022 November 17, we measured with the Swift UVOT the following VEGA magnitudes: UVW2: 16.22+/-0.06 (16.02), UVM2: 16.06+/-0.07 (15.82), UVW1: 15.98+/-0.07 (15.81), U: 15.81+/-0.05 (15.68), B: 16.63+/-0.06 (16.52), and V: 16.10+/-0.08 (16.02), where numbers in bracket correspond to the magnitudes corrected for Galactic extinction. In the UV, the low-state is one of the deepest we have detected with Swift since 2005. A comparably deep UV low-state was seen during the deep fade of 2017 October--December (Komossa et al. 2021) where we measured a minimum magnitude of 16.15+/-0.05 (15.95) in the UVW2 band.

The X-rays do not follow the deep fade, but have remained relatively constant and at a low level throughout 2022 October-November. On November 17, we obtained a Swift XRT count rate of 0.16 +/-0.01 cts/s. This pattern matches our previous finding of the lack of significant X-ray variability during the UV-optical deep fade in 2017 (Komossa et al. 2021). We measured an X-ray photon index of Gamma_x = 1.97+/-0.23 in the 0.3-10 keV band, assuming a single power law model with Galactic absorption.

In the radio band, we measured flux densities of 4.24+/-0.12 Jy (at 36.25 GHz) and 4.46+/-0.01 Jy (at 4.85 GHz) during our last observation with the Effelsberg telescope on 2022 November 5. These show that OJ 287 is in a deep low-state in the radio regime as well, and that the and radio flare reported earlier in 2021--2022 (Komossa et al. 2022) has ended.

Data reported here have been obtained in the course of our dedicated multi-year, multi-frequency monitoring project MOMO (Multi-wavelength Observations and Modelling of OJ 287; Komossa et al. 2017 -- 2022, and e.g., ATel #8411, #9629, #10043, #12086, #13785, #15145). We would like to thank the Swift team for carrying out the observations we proposed. We would also like to acknowledge the use of the "Build an XRT Product" page at the University of Leicester (https://www.swift.ac.uk/user_objects/).