TITLE:   GCN CIRCULAR
NUMBER:  20966
SUBJECT: DOAO 1m telescope V, R, I observation of GRB 170317A
DATE:    17/04/01 02:04:01 GMT
FROM:    Changsu Choi at Seoul Nat U  <changsu@astro.snu.ac.kr>

Changsu Choi(CEOU/SNU), Tae-Woo Kim(DOAO/NYSC), Myungshin Im(CEOU/SNU),  on
behalf of a larger collaboration

We observed the field of GRB 170317A (LaPorte et al., GCN  20885) with 1m
telescope of Deokheung Optical Astronomy Observatory (DOAO) in Korea,
starting from 2017/3/17 10:41:47 to 11:59:41.5 UT which is 0.042 days to
0.093 days after BAT trigger. .

We obtained V, R, I images and clearly detected afterglow on the stacked
images (LaPorte et al., GCN 20885; Mazaeva et al., GCN20886; Xin et al.,
GCN 20888; Mao  et al., GCN 20889; Kuroda et al., GCN20899).

The photometric calibration is based on in APASS catalog in the observed
field. No galactic extinction correction is applied.

Date            UT start         t-T0       Filter     Exp.      Mag
Err.

                            (mid, days)           (s)


2017-03-17 10:41:47        0.042     I           180*3    18.86     0.10

2017-03-17 10:51:01        0.049     R          300*3    19.66     0.07

2017-03-17 11:06:18        0.057     I           300*5    20.29     0.26

2017-03-17 11:31:41        0.079     V          300*3    20.38     0.15

2017-03-17 11:46:59        0.086     R          300*2    19.98     0.15
2017-03-17 11:57:10        0.093     V          300*2    20.77     0.23