[vsnet-grb-info 28183] GRB 210619B: GIT optical follow-up and confirmation of jet-break

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  30286
SUBJECT: GRB 210619B: GIT optical follow-up and confirmation of jet-break
DATE:    21/06/21 11:36:42 GMT
FROM:    Harsh Kumar at Indian Inst of Tech,Bombay  <harshkosli13 at gmail.com>

H. Kumar(IITB), U. Stanzin (IAO), V. Bhalerao(IITB), G. C. Anupama(IIA), S.
Barway(IIA) report on behalf of the GIT team:

We observed GRB 210619B detected by Swift-BAT (D'Avanzo et al. GCN #30261)
also see(Lipunov et al. GCN #30259; Zhao et al. GCN #30261; Jelinek et al.
GCN #30263; Kong et al. GCN #30265; Axelsson et al. GCN #30270; Perley et
al. GCN #30271; de Ugarte Postigo et al. GCN #30272; Zheng et al. GCN
#30273; Blazek et al. GCN #30274; Kann et al. GCN #30275; Svinkin et al.
GCN #30276; Xin et al. GCN #30277; Shrestha et al. GCN #30280; Jelinek et
al. GCN #30281), with 0.7m GROWTH-India Telescope (GIT). We obtained multiple
300-sec exposures in the g', r' and i' filters starting at
2021-06-20T18:04:27 UT. We clearly detected the afterglow in our stacked images
at R.A.(J2000)= 21:18:52.39, DEC.(J2000)= +33:51:01.10. The photometric
results follow as:

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

JD (mid) | T_mid - T0(hrs) | Filter | Magnitude (AB) |

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

2459386.26006 | 18.25 | g' | 21.133 +/- 0.07 |

2459386.27823 | 18.69 | r' | 20.184 +/- 0.05 |

2459386.29675 | 19.14 | i' | 20.091 +/- 0.06 |

2459386.33501 | 20.05 | g' | 21.142 +/- 0.07 |

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

Our r' magnitude is significantly fainter as compared to the extrapolation
of power-law from previous observations. We thus confirm jet-break in GRB
210619B, first suggested by Jelinek et al. GCN #30281. The magnitudes are
calibrated against PanSTARRS (Flewelling et al., 2018) and not corrected
for Galactic extinction.

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).