TITLE:   GCN CIRCULAR
NUMBER:  21954
SUBJECT: GRB 171001A: IRSF Observation
DATE:    17/10/02 01:07:51 GMT
FROM:    Katsuhiro L. Murata at Nagoya U  <murata@u.phys.nagoya-u.ac.jp>

R. Itoh (Tokyo Tech), K. L. Murata (Tokyo Tech), K. Morihana (Nagoya U.)
and T. Nagayama (Kagoshima U)

We observed the field of GRB 171001A (Lien et al., GCNCircular #21946) with
the near-infrared (J, H, Ks) simultaneous imaging camera SIRIUS attached to
1.4 m telescope IRSF (InfraRed Survey Facility) in Sutherland observatory,
South Africa.

The observations started on 2017-10-01 19:16:51 UT. We detected the
afterglow within the enhanced XRT error circle (Evans et al., GCN Circular
#21952) in J band. The measured magnitudes (Vega magnitude system) were
listed as below.

T0+[min]    MID-UT      T-EXP[sec]        J                 H
Ks
-------------------------------------------------------------------------------------------------
~48         19: 31              1270            17.0+-1.1      >16.3
>16.0
-------------------------------------------------------------------------------------------------
T0+ : Elapsed time after the burst
T-EXP: Total Exposure time

Given magnitudes were calibrated against 2MASS point sources in this field.

This observation was carried out by IRSF and OISTER collaboration.