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GCN Circular 34984

Subject
GRB231111A: GIT confirmation of the optical afterglow
Date
2023-11-11T17:31:04Z (6 months ago)
From
Anirudh Salgundi <salgundi.anirudh@gmail.com>
Via
Web form
R. Kumar, A. Salgundi, V. Swain, V. Bhalerao (IIT Bombay), S. Barway, G. C. Anupama (IIA), K. Angail (IAO)

We observed the field of GRB 231111A detected by Swift (Melandri et al., GCN 34981Not found
 
 
) with 0.7m GROWTH-India Telescope (GIT). We started the observation at 14:30:41 UT on 2023-11-11, i.e., 14.46 minutes after the Swift trigger. We obtained multiple frames in the g' and r' bands, and have a clear detection at the position reported by Swift/XRT (Melandri et al., GCN 34981Not found
 
 
). The details of the photometry are given in the below table:

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JD (mid) | t-t0 (minutes) | Filter | Exposure (s) | Magnitude (AB) |

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2460260.105395619 | 14.46  | r' | 200 | 17.88 +/- 0.05 |
2460260.108019142 | 18.23  | g' | 200 | 18.35 +/- 0.04 |
2460260.110584214 | 21.92  | r' | 200 | 18.24 +/- 0.04 |
2460260.113222184 | 25.72  | g' | 200 | 18.64 +/- 0.04 |
2460260.204636255 | 157.36 | r' | 300 | 19.52 +/- 0.07 |
2460260.208421405 | 162.81 | g' | 300 | 19.99 +/- 0.07 |

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Based on our photometry, we find that the source is consistently fading with power-law decay rate of 0.69 +/- 0.04 in both g' and r' band. Our results are consistent with magnitudes and decay rate obtained by Nanshan/HMT (Jiang et al. GCN 34982Not found
 
 
). The magnitudes are calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction.

The GROWTH India Telescope (GIT; Kumar et al. 2022) 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 the operations of the telescope. Telescope technical details are available at https://sites.google.com/view/growthindia/.