TITLE:   GCN CIRCULAR
NUMBER:  37821
SUBJECT: GRB 241018A: NOT optical observations
DATE:    24/10/19 00:51:25 GMT
FROM:    Daniele B. Malesani at IMAPP / Radboud University <d.malesani@astro.ru.nl>

Daniele B. Malesani (DAWN/NBI and Radboud Univ.), Antonio de Ugarte Postigo (OCA/LAM - CNRS), Ny Avo Rakotondrainibe (LAM), and Alba Casasbuenas Corral, report on behalf of a larger collaboration:

We observed the field of the SVOM GRB 241018A (Atteia et al., GCN 37812; Maggi et al., GCN 37814; Qiu et al., GCN 37814) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC imager. Given the proximity of the bright Moon and the large foreground extinction affecting this field, observations were carried out in the z band filter only, and consisted of 12x200 s exposures, at a mean epoch of 2024 Oct 18.988 UT (10.28 hr after the SVOM trigger).

Following inspection of a preliminary stack of the data, a faint source is marginally detected at a position consistent with the VT optical afterglow candidate (Qiu et al., GCN 37814). We measure a preliminary magnitude z = 22.1 +- 0.3 AB, calibrated against nearby Pan-STARRS objects.

The fading of the source, as well as the association with Swift XRT source #1 (Evans, GCN 37817), further confirm the identification of the VT object as the optical afterglow of GRB 241018A.

We thank the SVOM team, in particular Liping Xin on behalf of VT commissioning team, for providing improved coordinates of the VT source.