I have compiled the light curve of this unusual large-amplitude optical transient using online data from ASAS-SN and ATLAS surveys available as of 09:20 UT on 2021 Nov. 29. It is posted at http://scan.sai.msu.ru/~denis/J0302+1917-LC-Nov2021.gif

Note 20+16 upper limits from two different ASAS-SN units on Nov. 25.27-25.29 UT and 25.78-25.80 UT. Not a usual observing cadence by this instrument. Looks like ASAS-SN was also covering the IceCube neutrino event, and just missed the optical transient by a magnitude or so!

References

MASTER: ATel #15067 (Zhirkov, Kechin, Lipunov et al.) ASAS-SN: Kochanek et al., 2017 ATLAS: Tonry et al., 2018 R. Fidrich: vsnet-alert 26468

Note: MASTER-OAFA observation time was given in ATel #15067 as "5 hours later" (after MASTER-Tavrida detection, that is). I have used MJD=59545.034 for the MASTER-OAFA point with 13.4m. Time error box (+/-30 min, or 0.02 d) is smaller than the symbol size on the plot.

Another note: 20.8 mag. star 2" to the west-north-west of the transient is not related to the variable itself. It has a proper motion detectable between SDSS and Pan-STARRS epochs, and at the DSS plates is was located to the south of the OT position. Most likely it is a red dwarf closer to the Sun than the MASTER OT.

Finally, the progenitor has quite a blue color in SDSS: u=22.17 g=21.95 r=21.93 i=22.19 z=22.41

Denis Denisenko