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GCN Circular 36191

Subject
GRB 240419B: optical afterglow from the NOT
Date
2024-04-20T06:40:47Z (3 months ago)
From
Daniele B. Malesani at IMAPP / Radboud University <d.malesani@astro.ru.nl>
Via
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Daniele B. Malesani (DAWN/NBI and Radboud Univ.) and David Jones (NOT) report on behalf of a larger collaboration.

We observed the field of GRB 240419B (Dichiara et al., GCN 36180) with the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations were carried out straddling the morning twilight, at airmass ~2, and the seeing was about 1.7".

An object consistent with the X-ray localization error circle (Osborne et al., GCN 36186) is detected in our images. Its coordinates are (J2000):

RA = 21:43:35.289
Dec = +04:14:05.30

Calibrating against nearby point-like sources from the Pan-STARRS catalog, we measure the following AB magnitudes:

r = 22.01 +- 0.10  (Apr 20.214 UT, or 0.698 days after the trigger);
z = 20.81 +- 0.19  (Apr 20.222 UT, or 0.701 days after the trigger).

This object is not visible in the Legacy Survey images, which are deeper than ours, and we thus conclude that it is the optical afterglow of GRB 240419B. We note however the presence of a fainter (r ~ 23.2), distinct source visible in the Legacy Survey, approximately 2.5" to the west of the afterglow. Given the relatively large offset, the relation of this object with the GRB is unclear.
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