GCN Circular 40921
Subject
GRB 250702F: Skynet Optical Observations
Event
Date
2025-07-03T16:24:13Z (14 days ago)
From
Dylan Dutton at UNC Chapel Hill <ddutton59@gmail.com>
Via
Web form
Dylan Dutton, Daniel Reichart, Joshua Haislip, Vladimir Kouprianov, Staszek Zola, Tyler Linder, and Jonathan Keohane report on behalf of the Skynet Robotic Telescope Network at the University of North Carolina at Chapel Hill.
We observed the field of GRB 250702F detected by Swift (Siegel, GCN 40894) with one of Skynet's PROMPT telescopes located at the Astronomical Observatory of the Jagiellonian University, two of Skynet's PROMPT telescopes located at the Cerro Tololo Inter-American Observatory, and a 0.4m telescope located at Hampden-Sydney College. Observations began roughly 2.5 minutes post trigger and continued for 8 hours.
We detect the optical afterglow (Siegel, GCN 40894; Jelinek, GCN 40895; Kumar GCN 40896; Lipunov GCN 40899; Martin-Carrillo GCN 40900; Talamantes GCN 40907; Becerra GCN 40911; Brivio GCN 40913; An GCN 40916) in the B, V, R, I, and r bands. We report the initial detection photometry below.
Inspection of the first 2.5 hours of photometry indicates a fading from ~15.5 mag (two minutes post-trigger) to ~18 mag (two-hours post-trigger) in R band. The light curve appears to plateau for the remaining 30 minutes. Analysis of the additional 5.5 hours of photometry is ongoing.
Exposure lengths were calculated using our automated exposure length scaling model.
Tmid - T0 (s) | Telescope | Filter | Exposure (s) | Mag | Mag Error
------------------------------------------------------------------------
153 | PROMPT-OAUJ | V | 2 | 15.454 | 0.101
168 | PROMPT-OAUJ | R | 2 | 15.447 | 0.118
Our images have been calibrated using stars from the APASS catalog. Magnitudes were not corrected for dust extinction.