TITLE: GCN CIRCULAR NUMBER: 39383 SUBJECT: GRB 250219A: NOT optical observations DATE: 25/02/20 08:48:49 GMT FROM: Daniele B. Malesani at IMAPP / Radboud University d.malesani@astro.ru.nl

S. Y. Fu (NAOC), J. T. Palmerio (CEA/Irfu), D. B. Malesani (DAWN/NBI and Radboud Univ.), L. Cotter (UCD), D. Xu (NAOC), B. Schneider (LAM), B. N. Hauptmann (NOT and DTU Space), A. M. Kadela (NOT and NBI), report on behalf of a larger collaboration:

We observed the optical afterglow candidate (Xin et al., GCN 39380; Magnani et al., GCN 39382; see also Kennea et al., GCN 39379) of the SVOM/ECLAIRs GRB 250219A (Daigne et al., GCN 39376). Observations were carried out using the ALFOSC instrument mounted on the Nordic Optical Telescope (NOT). We obtained 3 x 300 s Sloan r-band frames at a median time of 10.16 hr post-burst and 5 x 200 s Sloan z-band frames at a median time of 10.46 hr post-burst.

In the stacked r-band image, the afterglow is weakly detected, at coordinates

R.A. (J2000) = 11:33:29.18 Dec. (J2000) = +22:42:21.85

with an uncertainty of ~0.3 arcsec, which is consistent with the SVOM/VT counterpart position (Xin et al, GCN 39380). The source had r ~ 23.6 +/- 0.3 mag (AB), calibrated against nearby objects from the Pan-STARRS catalog. The decay between the NOT and the SVOM/VT epochs (see also Magnani et al., GCN 39382) confirms the source is the afterglow of the burst.

The source is not detected in the stacked z-band image, down to a limiting magnitude of z ~ 22.2 mag (AB), again calibrated against Pan-STARRS.

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