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GCN Circular 35089

Subject
GRB 231117A: GIT optical follow-up
Date
2023-11-18T01:51:44Z (3 months ago)
From
Vishwajeet Swain at IIT Bombay <vishwajeet.s@iitb.ac.in>
Via
Web form
R. Kumar, A. Salgundi, V. Swain, V. Bhalerao (IIT Bombay), G. C. Anupama, S. Barway (IIA), R. Norboo (IAO)

We observed the field of GRB 231117A detected by Swift (S. Laha et al., GCN 35071) with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2023-11-17 13:36:59 UT, i.e., 10.56 hours after the Swift trigger. We obtained the multiple images of 300s each in the r' and g' band. We did not detect any source within the uncertainty radius of Swift-XRT position reported by A.P. Beardmore et al., GCN 35074 upto a limiting magnitude of 22.38 in r' band. We do detect the candidate optical afterglow in our subtracted image at the position reported by Yang et al. (GCN 35083). The photometry values are given below:

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

| JD (mid) | t-t0 (days) | Filter | Exposure (s) | Magnitude (5 sigma) |

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

| 2460266.072780335 | 0.445 | r' | 3 x 300 | 20.80 +/- 0.06 | 
| 2460266.087725621 | 0.460 | r' | 3 x 300 | 21.18 +/- 0.08 | 
| 2460266.098941961 | 0.471 | r' | 3 x 300 | 20.88 +/- 0.07 | 
| 2460266.203419748 | 0.576 | r' | 3 x 300 | 20.84 +/- 0.07 | 
| 2460266.253062681 | 0.625 | g' | 2 x 300 | 20.88 +/- 0.07 |

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

Our data shows slight variability in the source, but no clear decay. The results are comparable to the values reported by B. P. Gompertz et al., GCN 35088; J. C. Rastinejad et al., GCN 35087; Yang et al., GCN 35083; and consistent with the upper limits given by M.Ferro et al., GCN 35086; M. Odeh et al., GCN 35084; J. H. Gillanders et al., GCN 35080; H. Takei., GCN 35076; B. Godson et al., GCN 35073. Based on these measurements, we conclude that this source is unlikely to be the afterglow. 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/.
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