[vsnet-grb-info 26653] GRB 201020B: GROWTH-India Telescope optical observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  28753
SUBJECT: GRB 201020B: GROWTH-India Telescope optical observations
DATE:    20/10/22 20:37:16 GMT
FROM:    Harsh Kumar at Indian Inst of Tech,Bombay  <harshkosli13 at gmail.com>

H. Kumar(IITB), K. Sharma(IITB), J. Stanzin(IAO), V. Bhalerao(IITB), G. C.
Anupama(IIA), S. Barway(IIA), report on behalf of the GROWTH-India
collaboration:


We followed-up GRB 201020B reported by Fermi GBM Team (GCN #28702, also
see: V. Lipunov et. al., GCN #28718; D. Xu et. al., GCN #28719) with 0.7m
GROWTH-India telescope. We obtained 300-sec exposures in the SDSS r’ filter
starting at 2020-10-21T14:53:24.42 UT (~ 21.4 hrs after the burst detection
by Fermi-GBM). We clearly detected uncataloged sources at a position
consistent with V. Lipunov et. al., GCN #28718; D. Xu et. al., GCN #28719.

Here are the photometric results from GIT observations:-

------------------------------------------------------------------

 JD (mid) | T_mid-T0(hrs) | Filter | Mag |

------------------------------------------------------------------

2459144.12392 | 21.45 | r | 19.36 +/- 0.07

2459144.12752 | 21.53 | r | 19.49 +/- 0.08

2459144.13110 | 21.62 | r | 19.37 +/- 0.07

2459144.27999 | 25.15 | r | 19.64 +/- 0.02

2459144.30582 | 25.77 | r | 19.79 +/- 0.02

2459144.35140 | 26.86 | r | 19.83 +/- 0.03

2459144.39582 | 27.91 | r | 19.83 +/- 0.03

2459144.42656 | 28.67 | r | 19.89 +/- 0.02

-----------------------------------------------------------------

Combining our photometric results with r band measurements of D. Xu et.
al., GCN #28719, we conclude that the source is fading with a power-law
index of 1.65 +/- 0.21. The magnitudes are calibrated against PanSTARRs PS1
data release, (Flewelling et al., 2018) and not corrected for galactic
extinction. Extrapolating backwards to the epoch of MASTER observations (t0
+ 3.2 min), the expected r magnitude is approximately 8.6, significantly
higher than the measured clear band magnitude of 13.7. This may be
indicative of a break in the afterglow. Further observations are strongly
encouraged.

The GROWTH India Telescope (GIT) is a 70-cm telescope with a 0.7 degree
field of view, set up by the Indian Institute of Astrophysics and the
Indian Institute of Technology Bombay with support from the Indo-US Science
and Technology Forum (IUSSTF) and the Science and Engineering Research
Board (SERB) of the Department of Science and Technology (DST), Government
of India (https://sites.google.com/view/growthindia/). It is located at the
Indian Astronomical Observatory (Hanle), operated by the Indian Institute
of Astrophysics (IIA).