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THE ASTRONOMER Electronic Circular No 2713      2011 Feb 18 19.45UT
Ed:Guy M Hurst, 16,Westminster Close, Kempshott Rise,  Basingstoke,
Hants, RG22 4PP,England.Telephone/FAX(01256)471074Int:+441256471074
INTERNET: GUY@TAHQ.DEMON.CO.UK      Backup: gmh@wdcc1.bnsc.rl.ac.uk
WORLD WIDE WEB                         http://www.theastronomer.org
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OT 110215
Ivan Sergey of Belarus notified us of a flare object recorded in the 
field of EN Cep. Subsequently GCN Circular 11739 has provided further 
information by Sergey and D. Denisenko of Moscow:

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):

   RA 00:26:40  DEC +83:24:10 (2000)

Within 90 seconds the optical transient brightened from below the 
detection limit of magnitude 17 and reached the maximum brightness of 
12.7 CR (unfiltered with the red zero point) at 17:47 UT 
(JD=2455608.242). Subsequently it faded to 15.0 CR in the course of 13 
minutes, then more slowly to 16.0 CR within the next 22 minutes, but 
suddenly re-brightened again to 14.1 CR at 18:30 UT, after which 
gradually faded to ~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 catalogues, nor present on 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.  Colour-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. Colour-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. favour the extragalactic nature of the 
source.  The huge amplitude of the optical flare of over 7 magnitudes is 
unprecedented for the flares of UV Ceti stars.

On a later GCN Circular 11750, Antonio Deugarte at IAA-CSIC and 
colleagues report:
We have re-observed the field of this optical transient using NOTCam at 
the 2.5m NOT telescope at Roque de los Muchachos Observatory (La Palma, 
Spain). We obtained J and K-band imaging on 17 Feb between 20:10 and 
21:56 UT with a seeing of 0.6".
The 4 sources described in our previous circular are detected with 
consistent magnitudes, showing no clear variability in any of them 
between the 2 epochs. We note that source 3 is extended, the rest being 
unresolved. We do not detect anything at the position of the UVOT source 
(Chester et al., GCNC 11746) down to a 3-sigma limit of J ~ 21.5.

Guy M Hurst