TITLE: GCN CIRCULAR NUMBER: 40322 SUBJECT: GRB 250502A: Early optical counterpart detection by LCO. DATE: 25/05/02 12:52:02 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 250502A triggered by the SVOM/ECLAIRs(Wang et al., GCN 40313) in the V, r filter of the 0.4 m SCICAM QHY600 at the Las Cumbres Observatory Global Telescope (LCOGT) node located at Haleakala Observatory, Hawai. The 0.4 m SCICAM QHY600 is equipped with 9576 x 6388 pixel CCD (FOV: 1.9 x 1.2 degrees, scale: 0.74 arcsec/pixel) but we only used the FOV of 30 x 30 arcmin for our observation.
Observations began on May 02, 2025, starting 2.00 hours after the GRB trigger.
We clearly detect the optical transient (OT) reported by GCNs (Rakotondrainibe et al., GCN 40315; An et al., GCN 40319, Li et al., GCN 40320) in our V, r band image.
------------------------------------------------------------------------------------------------------ |Date| |JD start| |t-T0 (hours)| |Exp (sec)| |Filter| |Magnitude| ------------------------------------------------------------------------------------------------------ 2025-05-02 2460797.94930 2.00 1 x 600 V V = 19.08 +/- 0.04 2025-05-02 2460797.95500 2.15 1 x 600 r r = 19.02 +/- 0.04 ------------------------------------------------------------------------------------------------------
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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