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.

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