TITLE: GCN CIRCULAR NUMBER: 35406 SUBJECT: GRB 231210B: new optical transient detected with the Greenhill Observatory University of Tasmania within the BAT-Swift enhanced position DATE: 23/12/20 12:59:48 GMT FROM: Karelle Siellez at University of Tasmania <karelle.siellez@utas.edu.au> K. Siellez, B. Emptage, K. Hill, J.-P. Beaulieu (Institute of Astrophysics in Paris / UTas), A. Cole, T. Plunkett report: a new optical transient for the GRB 231210B observed with the Harlingten 50cm Telescope starting on 2023-12-11 17:14:35 UT in Sloan r' and g' filters. We detect an optical transient at the position RA (J2000) = 06h 23m 05.924s, Dec (J2000) = -48d 19' 11.65", which is not included in the Swift XRT position (Page et al., GCN 35314), but is within the BAT enhanced ground-calculated position (Sakamoto et al., GCN 35322). It has a different position than the optical afterglows already published (GCN 35316, GCN 35323). The observations leading to the measurements of the magnitude were made as followed: Date Time Filter Exposure (sec) -------------------------|-----------|----------------------------------- 2023-12-11 17:14:35.536 r 180 2023-12-11 17:17:44.365 r 180 2023-12-11 17:20:53.192 r 180 2023-12-11 17:24:02:021 r 180 2023-12-11 17:27:10.853 r 180 On 2023-12-11 we stacked 5 pictures of 180s exposure time for a total of 900s exposure time, with r' filter. We obtain a magnitude of 19.2 +/- 0.1 in r'. Date Time Filter Exposure (sec) -------------------------|-----------|----------------------------------- 2023-12-12 11:49:41.012 g' 180 2023-12-12 11:52:49.835 g' 180 2023-12-12 11:55:58.661 g' 180 2023-12-12 11:59:07.480 g' 180 2023-12-12 12:05:25.121 g' 180 On 2023-12-12 we stacked 5 pictures of 180s exposure time for a total of 900s exposure time, with g' filter. We obtain a magnitude of 20.3 +/- 0.1 in g'. On 2023-12-17 we stacked 5 pictures of 180s exposure time for a total of 900s exposure time, with r' filter. We obtain a magnitude of 20.1 +/- 0.1 in r'. More data were taken on the days in between and will be released soon. We encourage the follow up of this optical transient in all wavelengths. We acknowledge the traditional custodians of the land upon which we built our telescope: the Palawa / Pakana and Gadigal people. The team wants to thank Caisey Harlingten for his donation and support, the late Dr. John Greenhill who created and pushed forward the development of this optical observatory, as well as Dr. Tony Sprent and Dr. Keith Bolton, who keep supporting and developing the telescopes. View this GCN Circular online at https://gcn.nasa.gov/circulars/35406. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...