TITLE: GCN CIRCULAR NUMBER: 22030 SUBJECT: GRB 171020A: Mini-MegaTORTORA upper limits on simultaneous optical emission DATE: 17/10/21 00:31:17 GMT FROM: Sergey Karpov at SAO RAS S.Karpov, G.Beskin (SAO RAS and Kazan Federal University, Russia), S.Bondar, E.Ivanov, E.Katkova, N.Orekhova, A.Perkov (OJS RPC PSI, Russia), A.Biryukov (SAI MSU and Kazan Federal University, Russia), V.Sasyuk (Kazan Federal University, Russia) Mini-MegaTORTORA nine-channel wide-field monitoring system with high temporal resolution has been observing the Swift field of view before, during and after the time of Swift BAT trigger corresponding to GRB171020A (Page et al, GCN 22028). The whole burst localization region has been covered since 2017-10-20 23:00:07.90 UT (T0-422 s) and until 2017-10-20 23:10:17.68 UT (T0+187 s, thus including the whole gamma-ray activity interval) with temporal resolution of 0.1 s in white light. Dedicated real-time transient detection pipeline did not detect any events longer than 0.3 s and brighter than approximately V=10.5 mag during this interval. Visual inspection of co-added images with 10 s effective exposure (summation of 100 consecutive frames each) has not revealed any variable source down to V=12.0 mag during that interval. Also, the multi-regime follow-up (when all channels except for the one containing the trigger are repointed towards it and observe it with various exposures with and without photometric and polarimetric filters installed) has been initiated at 2017-10-20 23:08:12.0 UT (T0+61.25 s). The inspection of 10 s exposure frames acquired in white light between 2017-10-20 23:08:12.0 UT (T0+61.25 s) and 2017-10-20 23:09:43 UT (T0+152.25 s) did not reveal any source brighter than V=13.5 mag at the position of the burst. Mini-MegaTORTORA belongs to Kazan Federal University and is located at Special Astrophysical Observatory near Russian 6-m telescope. The message may be cited.