{
  "body": "Cheng Cheng (CASSACA, NAOC), Liping Xin (NAOC), Jia-Sheng Huang (CASSACA, NAOC) report:\n\nWe observed the field of GRB 261029A (Fermi/GBM, GCN 46071; SVOM, GCN 46072)\nwith the ESO VLT Survey Telescope (VST) equipped with OmegaCAM, under CNTAC\nproposal ID CN2026B-62 (PI: Jia-Sheng Huang) including VST project, ESO\nprogramme 117.2B2A.001. Two 600-s exposures were obtained in the SDSS g and r\nfilters starting at 2026-11-01 01:59:53 UT, i.e. T0 + 72.55 hr, where\nT0 = 2026-10-29 01:27:03.8 UT is the Fermi/GBM trigger time. The observations\nwere carried out at an airmass of 1.96-1.99, and the FWHM of point sources in\nour images is ~0.8 arcsec.\n\nThe optical afterglow AT 2026ahaw (GOTO; GCN 46073; RA, Dec = 00:35:16.32,\n+34:30:00.5, J2000) is detected in our r-band image and marginally in the g\nband. Photometry calibrated using SDSS DR18 Petrosian magnitudes of stars in\nthe same CCD gives:\n\n  Filter    T-T0 (hr)     mag (AB)          Flux (uJy)\n  r         72.63          23.25 +/- 0.09    1.82\n  g         72.82          24.91 +/- 0.21    0.39\n\nThe quoted uncertainties are 1-sigma statistical; an additional systematic\nuncertainty of ~0.05 mag from the zero-point calibration should be added in\nquadrature. The magnitudes are not corrected for Galactic extinction.\n\nWe note that the afterglow is located only about 3 arcsec from the edge of the\nCCD on which it was detected, so the above magnitudes should be considered\npreliminary. Our astrometric solution, derived from Gaia-based astrometry of\nthe same CCD, places the source within 0.2 arcsec of the coordinates given\nabove.\n\nWe thank the ESO Paranal staff and the VST team for the prompt execution of\nthese target-of-opportunity observations.\n",
  "circularId": 46141,
  "format": "text/plain",
  "eventId": "GRB 261029A",
  "createdOn": 1793755481656,
  "subject": "GRB 261029A: VST/OmegaCAM detection of the optical afterglow at 3 days",
  "eventType": [
    "GRB",
    "Afterglow",
    "Optical Transient"
  ],
  "submittedHow": "web",
  "submitter": "Cheng Cheng at CAS South America Center for Astronomy (CASSACA) <chengcheng@nao.cas.cn>"
}