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GCN Circular 31227

Subject
GRB 211211A: HCT and GIT optical follow up observations
Date
2021-12-13T11:11:53Z (2 years ago)
From
Harsh Kumar at Indian Inst of Tech,Bombay <harshkosli13@gmail.com>
H. Kumar(IITB), V. Bhalerao(IITB), Rahul Gupta(ARIES), Rigzin Norbu (IAO),
G. C. Anupama(IIA), D. K. Sahu (IIA), S. Barway(IIA), A. Dutta (IIA), B.
Kumar (ARIES), Dimple (ARIES), S.B. Pandey (ARIES), Kuntal Mishra (ARIES)
report on behalf of the HCT and GIT team:

We observed GRB 211211A detected by Fermi GBM (GCN #31201) and Swift-BAT
(A. D'Ai et al., GCN #31202); optical counterpart first reported by W Zheng
and A V. Filippenko, (GCN #31203) with 2.0m Himalayan Chandra Telescope
(HCT) and 0.7m GROWTH-India Telescope (GIT). We obtained a 900-sec exposure
in the Bessell R filter using HCT and multiple 300-sec r' band exposures
with GIT. We obtained the following photometric results:-

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

 JD (mid) | T_mid-T0(hrs) | Exposure | Filter | Magnitude | Tel |

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

 2459560.50469 | 10.94 | 900 sec | Bessell R | 20.30 +/- 0.13 | HCT |

 2459561.47439 | 34.21 | 1500 sec | r' | > 21.19 | GIT |

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

Our results from HCT are similar to R band magnitudes reported in N. Ito
et. al, (GCN #31217) which suggests that there was no significant decay in
the early hours ( <~11 hrs). GIT r' band observations at ~34 hrs did not
detect the afterglow, with a limiting magnitude of 21.19 - confirming the
fading of the afterglow at late times reported by R. Strausbaugh et. al.,
(GCN #31214).

The magnitudes were calibrated by querying the SDSS catalog (Alam+, 2015).
We converted magnitudes to the R band using Lupton (2005) equations for HCT
calibration.


HCT observations were carried out under the ToO program HCT-2021-C3-P02. We
thank HCT and GIT observers, staff for undertaking the observations.

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 (IIA) and the
Indian Institute of Technology Bombay (IITB) with funding from DST-SERB and
IUSSTF. It is located at the Indian Astronomical Observatory (Hanle),
operated by IIA. We acknowledge funding by the IITB alumni batch of 1994,
which partially supports operations of the telescope. Telescope technical
details are available at https://sites.google.com/view/growthindia/.
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