[vsnet-grb-info 5418] GRB 071112C: Optical and NIR data observed with KANATA

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  7094
SUBJECT: GRB 071112C: Optical and NIR data observed with KANATA
DATE:    07/11/15 15:13:07 GMT
FROM:    Makoto Uemura at Hiroshima U  <uemuram at hiroshima-u.ac.jp>

M. Uemura, M. Sasada, A. Arai, and T. Uehara (Hiroshima Univ.), 
report on behalf of the KANATA GRB team:

  We finished a full reduction of our optical-NIR images
of the field of GRB061112C taken with TRISPEC/KANATA.  
A part of preliminary results was reported in GCN Circ. 7062.  
Obtained magnitudes are below: 

# Time after burst V-mag  err.
#     (sec)
# mid start   end 
  324   309   339  17.69  0.14
  377   362   392  17.89  0.19
  430   415   445  17.93  0.20
  483   468   498  18.02  0.22
  538   523   553  18.15  0.27
  590   575   605  18.64  0.53
  643   628   658  18.41  0.39
  699   684   714  18.30  0.33
  752   737   767  18.37  0.36
  970   835  1105  18.72  0.36
 1271  1136  1406  19.53  0.11
 1571  1436  1706  19.59  0.39
 1873  1738  2008  19.62  0.53
 2173  2038  2308  19.61  0.13
 3079  2340  3818  20.66  0.53
 4583  3844  5322  19.80  0.34
#
# Time after burst J-mag  err.
#     (sec)
# mid start   end 
  367   309   425  15.93  0.27
  527   469   585  16.37  0.52
  688   630   746  16.67  0.28
  969   835  1103  17.07  0.42
 1269  1136  1402  17.34  0.46
 1570  1436  1704  17.19  0.18
 1871  1738  2004  17.47  0.41
 2172  2038  2306  17.50  0.45
 3078  2340  3816  17.97  0.35
 4581  3844  5318 >17.67
#
# Time after burst Ks-mag err.
#     (sec)
# mid start   end 
  541   309   773  15.00  0.37
 1201   835  1567  15.91  0.50
 1959  1593  2325  16.58  0.45
 2728  2353  3103  16.70  1.01
 4222  3130  5314 >16.77

Comparison star: 
V-band: GSC2.3 02:36:41.48 +28:20:53.5 V=14.43
J-band: 2MASS  02:36:41.46 +28:20:53.4 J=13.238
K-band: 2MASS  02:36:41.46 +28:20:53.4 K=12.792

  Using our data, we calculated decay indices, alpha :
    alpha_V  = 0.96 +/- 0.09
    alpha_J  = 0.82 +/- 0.06
    alpha_Ks = 1.01 +/- 0.09
No prominent color change was seen during our observations. 

  After correcting the interstellar extinction in our galaxy 
(Schlegel, et al. 1998), we calculated the spectral energy index, 
beta = 0.65 +/- 0.03 between V and Ks-band region.  
This beta is in agreement with the beta in X-rays 
(GAMMA_X=1.7, beta_X=0.7, in Stratta et al. GCN Report 104.1), 
while the optical emission is possibly affected by the 
reddening effect in the host galaxy of the GRB.  

  As reported in Stratta et al. GCN Report 104.1, 
there is an X-ray flare around 600-700 sec after the burst, 
whose amplitude is about factor 4 on the decay trend.  
We found that no correlated flux variation was found in our 
V-, J-, and Ks-band data.  The upper limit of the amplitude 
is 0.4 mag in V-band.