TITLE:   GCN CIRCULAR
NUMBER:  37081
SUBJECT: EP240804a (GRB 240804B): NOT optical observations
DATE:    24/08/06 19:49:32 GMT
FROM:    Daniele B. Malesani at IMAPP / Radboud University <d.malesani@astro.ru.nl>

D. B. Malesani (DAWN/NBI and Radboud Univ.), J. P. U. Fynbo (DAWN/NBI), J. Verwohlt (DARK/NBI), K. Valeckas (DAWN/NBI), T. Bach Johannessen (Aarhus Univ.), J. K. Mogensen (Aarhus Univ.), D. Xu (NAOC), S. Grund (NOT) report on behalf of a larger collaboration:

We observed the optical counterpart (An et al., GCN 37035; Poidevin et al., GCN 37038; Bochenek et al., GCN 37039; Li et al., GCN 37044) of the X-ray transient EP240804a (Wang et al., GCN 37034), identified with GRB 240804B (Frederiks et al., GCN 37071). using the Nordic Optical Telescope equipped with the ALFOSC imager. A set of three 300-s r-band observations were carried out at large airmass (average 2.75), with mid time Aug 6.081 UT (28.34 hr after the EP trigger).

The optical counterpart is well detected in the stack of our data, for which we measure r = 21.72 +- 0.08 (AB), calibrated against nearby stars from the SkyMapper catalog.