TITLE: GCN CIRCULAR NUMBER: 36576 SUBJECT: GRB 240529A: GROWTH-India optical follow-up DATE: 24/05/30 17:30:52 GMT FROM: vishwajeet.s@iitb.ac.in

T. Mohan, V. Swain, A. Salgundi, R. Kumar, V. Bhalerao (IITB), G.C. Anupama, S. Barway (IIA) and K. Angail (IAO) report on behalf of the GIT team:

We observed the field of GRB 240529A detected by Swift (Eyles-Ferris et al., GCN 36556) with 0.7m GROWTH-India Telescope (GIT). We started the observation at 2024-05-29 19:54:44 UT, i.e., 16.93 hours after the Swift trigger. We obtained multiple exposures of 400 seconds in the r', g' and i' filters. In our stacked images, we clearly detected the afterglow at the coordinates reported by Swift/UVOT Detection (Shilling et al., GCN 36562). The photometry results follow as:

--------------------------------------------------------------------------------- | JD (mid) | t-t0 (days) | Filter | Total Exposure (s) | Magnitude (AB) | | ----------------- | ----------- |------- | ------------------ | -------------- | | 2460460.425332341 | 0.801 | g' | 7x400 | 20.43 +/- 0.09 | | 2460460.349607928 | 0.725 | r' | 8x400 | 19.14 +/- 0.05 | | 2460460.386415344 | 0.762 | i' | 7x400 | 18.46 +/- 0.08 |

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The measurement is calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction.

Based on the publicly avialable photometry (Fu et al., GCN Circ. 36561; Postigo et al., GCN Circ. 36574; Adami et al., GCN Circ. 36575) and our measurements, we find that the source in r'-filter is fading as a power-law with flux proportional to (t−t0)^−alpha where t0 is Swift/BAT triggered time and calculated alpha = 1.12 +/- 0.01.

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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