GCN Circular 15220

E. Gorbovskoy, V. Lipunov, D.Denisenko, V.Kornilov, A.Belinski, N.Tyurina, 
D.Kuvshinov, N.Shatskiy, P.Balanutsa, A.Kuznetsov, V.V.Chazov, 
A.Sankovich,  D.Zimnukhov
Sternberg Astronomical Institute, Moscow State University

A. Tlatov, A.V. Parhomenko, D. Dormidontov, V.Sennik
Kislovodsk Solar Station of the Pulkovo Observatory

V.Yurkov, Yu.Sergienko, D.Varda, E.Sinyakov
Blagoveschensk Educational State University, Blagoveschensk

K.Ivanov, S.Yazev, N.M.Budnev, O.Gres, O.Chuvalaev, V.A.Poleshchuk
Irkutsk State University

V.Krushinski, I.Zalozhnih,  A. Popov
Ural Federal University, Kourovka

Hugo Levato and Carlos Saffe
Instituto de Ciencias Astronomicas, de la Tierra y del Espacio (ICATE)

Claudio Mallamaci, Carlos Lopez and Federico Podest
Observatorio Astronomico Felix Aguilar (OAFA)

MASTER II  robotic telescope (MASTER-Net: http://observ.pereplet.ru)
located in Kislovodsk was pointed to the  GRB130907A 18 sec  after notice
time and 43 sec after GRB time at 2013-09-07  21:42:00 UT in two
polarizations. The observations were performed at low elevation (zenith 
angle 84 deg)and under the changing transparency conditions. The OT (Page et. al. 
GCN15183
Not found
 
 
) appears on the 4th image in the series and is visible on four 
consecutive  images (20, 30, 40 and 50 sec exposures) in both tubes with 
the signal-to-noise ratio from 3 to 6. Starting with T0+5 min, the image 
quality was further deteriorating with the OT visible only on the sum of 
two pairs of synchronous images.

Our photometry results are presented in Table 1.

Table 1.
-------
Start date and time     exptime   T_start-T_trig   T_mid-T_trig  P| mag.   err_P      P- mag    err_P-    P| + P-    err. (P| + P-)
-----------------------+--------+----------------+--------------+--------+---------+----------+---------+----------+---------------
2013-09-07 21:42:00.31    10        47               52           <10.5      ---       <10.5      ---      <11.0        ---
2013-09-07 21:42:22.79    10        69               74           <10.5      ---       <10.5      ---      <11.0        ---
2013-09-07 21:42:43.59    20        91               101          <11.0      ---       <11.0      ---      <11.5        ---
2013-09-07 21:43:16.66    20        123              133           12.2      0.2        13.0      0.3       12.5        0.2
2013-09-07 21:43:47.44    30        154              169           13.3      0.4        13.6      0.6       13.5        0.4
2013-09-07 21:44:29.95    40        197              217           13.7      0.5        13.7      0.6       13.9        0.5
2013-09-07 21:45:21.88    50        249              274           13.7      0.5        14.4      0.8       14.0        0.6
2013-09-07 21:46:23.87    60+80     311              387          <13.8      ---       <13.7      ---       13.9        0.6

*) All time intervals in seconds.  P| and P- is an unfiltered magnitude 
with RA and DEC orientated polaroid correspondingly.
The sign '<'  before magnitude means the value is upper limit.


The light curve and movie available here 
http://master.sai.msu.ru/static/GRB/GRB130907A/grb130907A.html

The epoch of our observations completely covers Swift BAT weak, soft peak 
from T+210 sec to T+240 sec (Cummings et. al. GCN15202
Not found
 
 
).

Our first automatic and not so exact (due to difficult observing 
conditions) estimation of the  OT magnitude, given in the previous 
telegram (Gorbovskoy et. al GCN15184
Not found
 
 
),  belongs to  epoch of the 5th 
exposure with t_mid=217 sec. after the trigger. This fact isn't clear from 
the telegram  text that could mislead some researchers.
We apologize for this inaccuracy.

The message may be cited.