TITLE: GCN CIRCULAR NUMBER: 39091 SUBJECT: GRB 250129A: Skynet optical observations DATE: 25/01/29 23:18:26 GMT FROM: dschlekat@unc.edu Donovan Schlekat, Dylan Dutton, Daniel Reichart, Joshua Haislip, and Vladimir Kouprianov report on behalf of the Skynet Robotic Telescope Network at the University of North Carolina at Chapel Hill. We observed the field of GRB 250129A with two of Skynet's PROMPT telescopes located at the Cerro Tololo Inter-American Observatory. The observation began at 05:12:20 UT on January 29 2025, roughly 27 minutes after the Swift-BAT trigger (Beardmore et al., GCN 39066). Observations were performed in the B, V, R, and I bands. Exposure lengths were calculated using our automated exposure length scaling model. We detect the optical afterglow consistent with the coordinates reported by other facilities (Francile et al., GCN 39065; Beardmore et al., GCN 39066; Schneider et al., GCN 39071; Belkin et al., GCN 39072; Izzo et al., GCN 39073; Izzo & Malesani, GCN 39074; Ghosh et al., GCN 39077; Schneider et al., GCN 39078; Brivio et al., GCN 39079; Siegel et al., GCN 39085; Zheng et al., GCN 39090). The coordinates are: R.A. (J2000): 13:14:42.39 Dec. (J2000): 05:01:50.22 We detect the object in the B, V, R, and I band. The initial detection photometry for each band is reported below. Additional Skynet observations are ongoing. Tmid - T0 (s)| Telescope | Filter | Exposure (s) | Mag | Mag Error ------------------------------------------------------------------ 1674.49 | PROMPT-5 | B | 59 | 17.525 | 0.051 1678.99 | PROMPT-6 | V | 34 | 16.902 | 0.054 1711.99 | PROMPT-6 | R | 22 | 16.628 | 0.057 1938.49 | PROMPT-6 | I | 19 | 16.111 | 0.095 Our images have been calibrated using stars from the APASS catalog. Magnitudes were not corrected for dust extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/39091. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...