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GCN Circular 22030

Subject
GRB 171020A: Mini-MegaTORTORA upper limits on simultaneous optical emission
Date
2017-10-21T00:31:17Z (7 years ago)
From
Sergey Karpov at SAO RAS <karpov@sao.ru>
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.

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