TITLE: GCN CIRCULAR NUMBER: 41305 SUBJECT: GRB 250808A: VLT X-shooter candidate counterpart DATE: 25/08/09 21:27:38 GMT FROM: luca.izzo@inaf.it

A. Levan (Radboud U.), D. B. Malesani (DAWN/NBI and Radboud Univ.), I. F. Giudice (INAF/OACn), L. Izzo (INAF/OACn & DARK/NBI), A. L. Thakur (INAF-IAPS), N. R. Tanvir (U. Leicester), G. Corcoran (UCD), A. de Ugarte Postigo (LAM), A. Martin-Carrillo (UCD), A. Saccardi (CEA/Irfu), M. De Pasquale (U. Messina), D. Hartmann (Clemson U.) report on behalf of the Stargate collaboration:

We observed the field of SVOM/ECLAIRs GRB 250808A (Adrien et al., GCN 41297) using ESO VLT UT3 (Melipal) equipped with the X-shooter instrument, starting at 9 August 08:56 UT, approximately 14.5 hr after the burst trigger. A sequence of 1x120s (r band) and 5x60s (z band) images was obtained with the acquisition camera. Comparison to z-band images obtained with the Legacy Survey shows a new source within the Swift/XRT localisation region (Evans et al., GCN 41300) at coordinates:

RA(J2000) = 04:14:12.39 Dec(J2000) = -22:49:23.5

The source has an approximate magnitude of z ~ 21.8 mag (AB). We suggest this is the optical counterpart of GRB 250808A. We notice that this source is also detected in the r-band acquisition image.

We also note the presence of a very faint (r = 24.28 mag, z = 23.73 mag) catalogued object in the Legacy Survey DR10 just below the afterglow position. We propose this source to be the host galaxy of GRB 250808A.

We acknowledge excellent support from the ESO observing staff in Paranal, in particular Cecilia Bustos, Rodrigo Palominos, and Rob van Holstein.

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