TITLE: GCN CIRCULAR NUMBER: 39425 SUBJECT: GRB 250221A: Optical counterpart detection by LCO. DATE: 25/02/22 15:06:17 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 250221A triggered by Swift (Caputo et al., GCN 39396) in B, r filters of the 1-meter Sinistro telescope at the Las Cumbres Observatory Global Telescope (LCOGT) node located at Cerro Tololo Interamerican Observatory, Chille. 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 February 21, 2025, starting 22.46 hours after the GRB trigger.
We clearly detect the optical transient (OT) reported by GCNs ( Francile et al., GCN 39395; Watson et al., GCN 39397; Melandri et al., GCN 39406; Shilling et al., GCN 39409; Guo et al., GCN 39412; Muenter et al., GCN 39417; Palmerio et al., GCN 39418; Pankov et al., GCN 39422; Pankov et al., GCN 39424) in our B, r band image.
|Date| |UTstart| |t-T0 (hours)| |Exp (sec)| |Filter| |Magnitude| ---------------------------------------------------------------------------------------------------- 2025-02-22 02:02:15.36 22.46 1 x 1200 B B = 21.91 +/- 0.06
2025-02-22 02:10:02.78 22.59 1 x 900 r r = 20.85 +/- 0.06 ----------------------------------------------------------------------------------------------------
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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