TITLE:   GCN CIRCULAR
NUMBER:  29937
SUBJECT: GRB 210504A: NOT optical afterglow detection
DATE:    21/05/05 00:15:45 GMT
FROM:    Daniel Perley at Liverpool JMU  <d.a.perley@ljmu.ac.uk>

K. E. Heintz (Univ. of Iceland and DAWN/NBI), D. A. Perley (LJMU), D. B. 
Malesani (DTU Space), and A. A. Djupvik (NOT) report on behalf of a 
larger collaboration:

We observed the location of the optical and X-ray afterglow of GRB 
210504A (Beardmore et al., GCN 29929; Breeveld & Beardmore, GCN 29933) 
using the Nordic Optical Telescope (NOT) equipped with the ALFOSC
camera.  We obtained 3x300 s frames in the Sloan r-band filter, followed 
by 5x200s frames in the z-band filter.  Observations were carried out on 
2021-05-04 UT between 23:10 and 23:35 (9.3 hours after the BAT trigger 
time given by Lien et al. (GCN 29930).

The optical afterglow is detected in the combined images.  We report a 
refined position (J2000) of:

RA:   14:49:34.04
Dec: -30:32:02.6

No source is visible at this location in Pan-STARRS reference imaging.

The r-band magnitude of the afterglow at the time of the observation is 
measured to be 20.95 +/- 0.05.









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