TITLE: GCN CIRCULAR NUMBER: 40499 SUBJECT: GRB 250520A: COLIBRÍ optical upper limit DATE: 25/05/20 10:34:25 GMT FROM: Rosa L. Becerra at Tor Vergata, Roma rosa.becerra@roma2.infn.it
Margarita Pereyra (UNAM), Stéphane Basa (UAR Pytheas), Jean-Luc Atteia (IRAP), Rosa L. Becerra (U Roma), William H. Lee (UNAM), Alan M. Watson (UNAM), Fredd Alvarez (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Sarah Antier (OCA), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM):
We imaged the field of the GRB 250520A detected by Swift/BAT (Eyles-Ferris et al., GCN Circ. 40491), SVOM/GRM (SVOM/GRM team, GCN Circ. 40495) and AstroSat/CZTI (Tembhurnikar et al., GCN Circ. 40497) using the DDRAGO wide-field imager on the COLIBRÍ telescope. We observed from 2025-05-20 06:42 to 06:45 UTC (from 4.0 to 4.1 hours after the trigger) and obtained 3 minutes of exposure in the i filter.
The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction.
In the stacked image, we do not detect any new source at the XRT enhanced position (Goad et al., GCN Circ. 40494) down to the following 3-sigma limit:
i > 21.3
This upper limit is consistent with the non-detection reported by GOTO (Kumar et al., GCN Circ. 40493) and DDOTI (Becerra et al., GCN Circ. 40498).
Further observations and analysis are ongoing.
We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams.
COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico.
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