TITLE: GCN CIRCULAR NUMBER: 40039 SUBJECT: GRB 250403A: Optical counterpart detection by LCO. DATE: 25/04/04 08:44:09 GMT FROM: ankur ghosh at CAPP, University of Johannesburg ghosh.ankur1994@gmail.com
Ankur Ghosh, Soebur Razzaque (CAPP, University of Johannesburg), Alexander Moskvitin, Yulia Sotnikova (SAO RAS), Naveen Dukiya (ARIES), Rahul Gupta (NASA GSFC) on behalf of a larger collaboration.
We observed the field of the GRB 250403A triggered by Fermi (Fermi GBM team, GCN 40025) in the V, r filter of the 1-meter Sinistro telescope at the Las Cumbres Observatory Global Telescope (LCOGT) node located at Teide Observatory, Tenerife, Canary Islands, Spain. The 1-m Sinistro telescope is equipped with a 4K x 4K CCD (FOV: 26 x 26 arcmin, scale: 0.39 arcsec/pixel).
Observations began on March 29, 2025, starting 1.49 hours after the GRB trigger.
We clearly detect the optical transient (OT) reported by GCNs (Julakanti et al. 2025, GCN 40026, Starling et al., GCN 40028; Wu et al., GCN 40029; Du et al., GCN 40031; Li et al., GCN 40032, Julakanti et al. 2025, GCN 40034) in our r band image.
------------------------------------------------------------------------------------------------- |Date| |UTstart| |t-T0 (hours)| |Exp (sec)| |Filter| |Magnitude| -------------------------------------------------------------------------------------------------- 2025-04-04 00:11:21.696 8.93 1 x 900 r r = 20.83 +/- 0.07 --------------------------------------------------------------------------------------------------
The field was calibrated against nearby APASS stars, with magnitudes converted using Lupton (2005) equations, and has not been corrected for Galactic extinction.
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