GCN Circular 21210
Subject
GRB 170531B: Zeiss-1000/CrAO optical observations
Date
2017-06-07T21:38:36Z (8 years ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>
E. Mazaeva (IKI), A. Pozanenko (IKI), D. Chestnov (ISON), A. Novichonok
(ISON), V. Agletdinov (KIAM), I. Nikolenko (CrAO), A. Volnova (IKI),
report on behalf of larger GRB follow-up collaboration:
We report refined analysis of Zeiss-1000/CrAO observations. Results
reported below supersede GCN cir. 21174.
We observed the field of the GRB 170531B (Evans et al., GCN 21171) with
Zeiss-1000/Koshka (CrAO) telescope between May 31 (UT) 22:32:32 and
June 01 (UT) 00:58:11. We took several unfiltered images with
exposure of 180 s. The afterglow (Lipunov et al. GCN 21173;
Pozanenko et al. GCN 21174) is clearly visible in each image in first
initial images, and detected later in combined images. The finding chart
of the combined image can be found at
http://grb.rssi.ru/GRB170531B/GRB170531B_Koshka_170531_sources.png
The coordinates of the afterglow (source A in the finding chart) are
(J2000) 19:07:32.10 -16:25:06.0 with uncertainty of 0.5 arcsec in both
coordinates. The coordinates are consistent with the position reported
by de Ugarte Postigo et al., GCN 21177, Tyurina et al., GCN 21179,
and Siegel et al., GCN 21188.
Preliminary photometry of the afterglow can be found in the light curve at
http://grb.rssi.ru/GRB170531B/GRB170531B_light_curve_v2.png
The photometry is based on nearby USNO-B1.0 stars, calibrated against to
R2 magnitudes
USNO-B.1_id R2
0736-0718845 16.77
0735-0729622 16.96
0735-0729439 16.59
0735-0729327 17.22
Due to presence of sources in near vicinity to the afterglow the
photometry of wide FOV telescopes might be affected by the sources. In
particular our photometry reported in GCN 21189 is apparently biased by
the two sources C and D (see the finding chart). We report coordinates
and brightness of the nearby sources.
Source coordinates(J2000) AG distance filter mag. err.
C 19:07:32.34 -16:25:09.1 4.6" CR 20.46 0.04
D 19:07:31.83 -16:25:05.6 3.9" CR 20.47 0.04