Multiple flares during the April-June 2020 outburst of the blazar OJ 287

ATel #13785; S. Komossa (MPIfR), D. Grupe (Morehead State University)
on 5 Jun 2020; 23:23 UT
Credential Certification: St. Komossa (stefanie.komossa@gmx.de)

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We report detection of OJ 287 in a prolonged phase of X-ray, UV and optical activity, with multiple flare events observed with the Neil Gehrels Swift observatory. The blazar OJ287, one of the best candidates to date of hosting a binary supermassive black hole (e.g. Laine et al. 2020), is undergoing a bright outburst at optical, UV, X-ray and radio wavelengths (ATel #13637, #13658, #13702). After an initial decline (ATel #13677) and re-rise (ATel #13755) in the optical, we saw it reaching a second maximum in the UV and optical band around 2020 May 23 (UVW2), followed by a rapid decline of ~one magnitude, which has now stalled. On 2020 June 4, we measured UVOT magnitudes in the VEGA system of UVW2: 14.01+-0.04 (13.81), UVM2: 13.98+/-0.04 (13.74), UVW1: 13.95+/-0.04 (13.78), U: 14.30+/-0.04 (14.17), B: 15.21+/-0.04 (15.10), V: 14.83+/-0.04 (14.75), where values in brackets are corrected for Galactic extinction. After two previous peaks, the X-rays are on the rise again, and are currently at a countrate of ~0.35 cts/s, compared to ~1 cts/s at peak. The X-ray spectrum follows a "softer when brighter" pattern, also seen at other epochs including the 2016-2017 outburst (ATel #10043, #9709, #9629, #9632, #10051; Komossa et al. 2017) with the X-ray photon index Gamma now varying between 2.9 and 2.2. It is well possible, that the April--June 2020 outburst continues with multiple subflares. However, OJ 287 will soon reach (or has already reached) its sun-constraint with most space-based missions. Ground-based observations continue to be of importance to follow the outburst evolution as long as OJ 287 can be observed despite its proximity to the sun. The results obtained here are part of our multi-year, multi-frequency monitoring of OJ 287 since 2015 (Komossa et al. 2017, 2020). It is our great pleasure to thank the Swift team for carrying out our observations.