GCN Circular 11739
I. Sergey (Molodechno, Belarus), D. Denisenko (IKI, Moscow) report: During the routine monitoring of EN Cep field with the 200-mm f/5 reflector and CCD the bright optical flash was detected starting on 2011 Feb. 15.741 UT at the approximate coordinates (J2000.0): 00:26:40 +83:24:10 Within 90 seconds the optical transient has brightened from below detection limit (<17.0) and reached the maximum brightness of 12.7 CR (unfiltered with the Red zero point) at 17:47 UT (JD=2455608.242). After that it faded downto 15.0 CR in the course of 13 minutes, then more slowly to 16.0 CR within the next 22 minutes, but suddenly rebrightened again to 14.1 CR at 18:30 UT, after which gradually faded downto ~17 mag during the next hour. Lightcurve: http://hea.iki.rssi.ru/~denis/J002641+832409-LC-Sergei.png Image: http://hea.iki.rssi.ru/~denis/J002641+832409-OT110215-Sergei.png No star or other object down to limiting B~21 and R~20 is present in USNO-A2.0 or USNO-B1.0 catalogs, as well as at the Palomar POSS-II B, R, POSS-I O, R and Quick-V plates. However, a faint object is marginally visible on the IR plate of 1996 Sep. 18. Color-combined (BRIR) DSS image of the 8'x8' field with the position of the transient marked is available here: http://hea.iki.rssi.ru/~denis/J002641+832409-BRIR-8x8.jpg We note that the position of OT fits very well (within 5") the 2MASS object 2MASS J00264184+8324093 with the following infrared magnitudes: J=16.46+/-0.15, H=15.80+/-0.18, K=15.22+/-0.16. Color-combined (JHK) chart: http://hea.iki.rssi.ru/~denis/J002641+832409-JHK-8x8.jpg Large J-K index (1.22+/-0.24) and small galactic extinction E(B-V)=0.161 mag according to Schlegel et al. favor the extragalactic nature of the source. Huge amplitude of the optical flare (over 7 magnitudes in CR) is unprecedented for the flares of UV Ceti stars.// Follow-up spectroscopic and photometric observations of this optical transient are strongly encouraged. This message can be cited.