TITLE: GCN CIRCULAR NUMBER: 39930 SUBJECT: GRB 250327B: SVOM/COLIBRÍ (F-GFT) Further Observations DATE: 25/03/29 19:02:34 GMT FROM: Alan Watson at UNAM alan@astro.unam.mx
Jean-Grégoire Ducoin (CPPM), Noémie Globus (UNAM), Camila Angulo (UNAM), Sarah Antier (OCA), Ramandeep Gill (UNAM), Stéphane Basa (LAM), William H. Lee (UNAM), Dalya Akl (AUS), Jean-Luc Atteia (IRAP), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), and Hui Yang (IRAP) report:
We observed the field of SVOM/ECLAIRs GRB 250327B (Bouchet et al. GCN Circ. 39888) with the DDRAGO wide-field imager on the COLIBRÍ telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico.
We obtained 50 minutes of exposure in the i filter from 2025-03-29 03:49 and 11:32 (44.3 and 52.0 hours after the trigger). Our observations were not continuous, but rather were at the start and end of this interval with a long interruption for observations of other sources. We observed through thick clouds.
The data were coadded with the COLIBRI pipeline and analysed in STDWeb/STDPipe (Karpov 2021). The photometric calibration was performed using nearby stars from the Pan-STARRS DR1 catalog and the magnitude is not corrected for Galactic extinction.
At the position of the previously reported optical transient (Moskvitin et al., GCN Circ. 39889; Xin et al., GCN Circ. 39890; O’Neill et al., GCN Circ. 39891; Malesani et al., GCN Circ. 39893; Lian et al., GCN Circ. 39894; Page et al., GCN Circ. 39895; Shrestha et al., GCN Circ. 39896; Perley & Bochenek, GCN Circ. 39902; Kumar et al., GCN Circ. 39904; Dennefeld et al., GCN Circ. 39905; Pankov et al., GCN Circ. 39906; Pérez-Fournon et al., GCN Circ. 39912; Tarasenkov et al., GCN Circ. 39913; Mo et al., GCN Circ. 39914), we detect a source with
i = 22.23 +/- 0.15.
Compared to our previous observation at about 7.65 hours after the trigger, the temporal decay index is about -1.0.
We acknowledge the excellent support of the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and thank the COLIBRÍ and DDRAGO engineering teams.
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