TITLE: GCN CIRCULAR NUMBER: 38956 SUBJECT: GRB 250101A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations and rebrightening. DATE: 25/01/15 17:13:17 GMT FROM: Giovanni Calapai at Calapai Astronomical Observatory, Massa S. Giorgio, Messina, Italy giovannicalapai@tiscali.it

Giovanni Calapai at Calapai Astronomical Observatory, Massa S. Giorgio, (Messina) Italy Member of: GRB/UAI Gamma Ray Burst Section of Unione Astrofili Italiani.

Report:

We observed the field of GRB 250101A (Swift trigger 1278305, Page et al., GCN 38752) with the 11 inches Schmidt-Cassegrain (Celestron 11) telescope F/D=6,3.

The observations were started at 2025-01-01 18:30 UT (approximately 5.08 hours after burst) stacking a set of unfiltered CCD image. The observations were carried out with clear skies and good visibility conditions.

The OT was detected at the following position:

RA (J2000.0) 02h 28m 16.62s +/- 0,03 Decl. (J2000.0) +19° 11' 37.4" +/- 0,40

Preliminary photometry was obtained using nearby PanSTARRS stars as follows:

Observation Mid-Time T-T0 (hr) Exposure Filter Mag. Err. 2025-01-01 19:12:46 UT 5.79 5x600s CR 19.71 +/-0.13

An optical rebrightening was observed as follows:

Observation Mid-Time T-T0 (hr) Exposure Filter Mag. Err. 2025-01-01 20:31:39 UT 7.11 90x60s CR 19.63 +/-0.09 2025-01-01 22:04:47 UT 8.66 90x60s CR 19.75 +/-0.08

Magnitude was calibrated with the nearby PanSTARRS stars converted using Lupton (2005) equations. No correction for galactic dust extinction was applied.

Our observations are consistent with other already reported Li et al. (GCN 38753), Mohan et al. (GCN 38754), Zhu et al. (GCN 38755); Budnev et al. (GCN 38756), Wu et al. (GCN 38758), Moskvitin and Spiridonova (GCN 38762), Odeh and Guessoum (GCN 38763), Hu et al. (GCN 38764), Moskvitin et al. (GCN 38765), D'Avino and Izzo (GCN 38768), Escudero-Coca et al (GCN 38769), Leonini et al. (GCN 38771), Zhang et al. (GCN 38774), Siegel and Page (GCN 38775), Komesh et al. (GCN 38777), Ghosh et al. (GCN 38779), Moskvitin et al. (GCN 38780), Komesh et al. (GCN 38790), and Bochenek and Perley (GCN 38798), Lapido et al. 2025 (GCN 38810), Anshika Gupta et al. (GCN 38818), M. Ferro et al. (GCN 38831), Jia-Qi Lin et al. (GCN 38837), Pankov et. al. (GCN 38869), Pankov et. al. (GCN 38890), Pankov et. al. (GCN 38926).

The message may be cited.

View this GCN Circular online at https://gcn.nasa.gov/circulars/38956. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...