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
The on-sky position of GRB 160625B (Dirirsa et al., GCN Circ. 19580) has
been observed by Mini-MegaTORTORA nine-channel wide-field monitoring system
with high temporal resolution (http://mmt.favor2.info) before, during and
just after the LAT trigger time (T0 = 2016-06-25 22:43:24).
Mini-MegaTORTORA reacted to Fermi GBM trigger 488587220 and started
observing its error box at 2016-06-25 22:41:07, 52 seconds after GBM
trigger and 136 seconds before LAT trigger. Due to large size of error box,
the observations have been performed in "widefield+deep" regime, with
channels simultaneously covering ~30x30 deg field of view with 30 s
exposures in white light to achieve deepest detection limit. The system
acquired 20 frames in such regime, covering time interval from T0-136 to
The system detected a bright optical flash on a frame coincident with LAT
trigger time (T0-15.9 - T0+14.1 s) at position reported by Troja et al.
(GCN Circ. 19588), with a magnitude of about V=8.8 mag. Next frame
displayed a slight rebrightening of about 0.1 mag, and then the light curve
followed nearly smooth power-law decay with slope of about -1.6, down to
V=12.2 at last acquired frame. The images acquired prior to LAT trigger do
not display any object at that position down to about V=13.5 mag.
The system also reacted to second GBM trigger 488587880 with slightly
different coordinates, and due to large field of view again covered the
position of a transient, acquiring 20 more frames from T0+1691 to T0+2264
s. No object is seen in these frames down to about V=13.5 mag.
Snapshots of a frames from first follow-up (20 arcmin fields around the
transient) is available at
Further analysis and calibration of the data is ongoing.
Mini-MegaTORTORA belongs to Kazan Federal University and is located at
Special Astrophysical Observatory near Russian 6-m telescope.