{
  "eventId": "GRB 250424A",
  "circularId": 40229,
  "body": "S. de Wet (DTU), P.J. Groot (Radboud/UCT/SAAO) and P.M. Vreeswijk (Radboud) report on behalf of the BlackGEM consortium:\n\nThe BlackGEM Unit Telescope 4 (BG4) located at ESO La Silla, Chile, responded automatically to the Swift trigger on GRB 250424A (Cenko et al., GCN 40224) and obtained a repeating series of 60 s exposures in the q,u,g,r,i,z bands. The first exposure started 264 s after the trigger time at 06:56:53 UT on 2025 April 24. A total of 26 exposures were obtained. \n\nWe detect the optical afterglow with the following AB magnitudes:\n\nq = 18.30 +/- 0.03 at 06:57:24 UT\nu = 19.33 +/- 0.18 at 06:58:47 UT\ng = 18.98 +/- 0.05 at 07:01:32 UT\nr = 18.58 +/- 0.04 at 07:04:17 UT\ni = 18.26 +/- 0.04 at 07:07:02 UT\nz = 18.22 +/- 0.10 at 07:09:46 UT\n\nBlackGEM is an array of wide-field telescopes designed, built and operated by a consortium consisting of Radboud University, the Netherlands Research School for Astronomy NOVA, KU Leuven, the University of Manchester, Tel Aviv University, the Weizmann Institute, the Hebrew University of Jerusalem, the University of Potsdam, Texas Tech University, the University of California at Davis, the Danish Technical University and the Armagh Observatory and Planetarium.",
  "submitter": "Simon de Wet at University of Cape Town <simdewet@gmail.com>",
  "createdOn": 1745487809546,
  "subject": "GRB 250424A: BlackGEM optical afterglow detection",
  "submittedHow": "web",
  "bibcode": "2025GCN.40229....1D",
  "format": "text/plain"
}