TITLE: GCN CIRCULAR NUMBER: 36813 SUBJECT: GRB 240619A: Host galaxy redshift from VLT/X-shooter DATE: 24/07/03 15:58:09 GMT FROM: Laura Cotter laura.cotter@ucdconnect.ie

L. Cotter (UCD), B. Schneider (MIT), D. Xu (NAOC), J. T. Palmerio (GEPI, Obs. de Paris), D. B. Malesani (DAWN/NBI and Radboud Univ.), A. de Ugarte Postigo (CNRS, OCA, LAM), G. Pugliese (Amsterdam), B. P. Gompertz (Birmingham), A. Martin-Carrillo (UCD), A. Rossi (INAF), D. Hartmann (Clemson Univ.), T. Aishwarya (INAF), N. R. Tanvir (Leicester), A. J. Levan (Radboud) report on behalf of the Stargate collaboration:

We observed the location (Gompertz et al., GCN 36715; Capalbi et al., GCN 36721; Mo et al., GCN 36739; Rhodes et al., GCN 36744) of the Fermi GRB 240619A (Fermi GBM team, GCN 36694; Preis et al., GCN 36695; Dalessi et al., GCN 36717) using the X-shooter spectrograph mounted on the ESO VLT UT3 (Melipal). The observation was performed on 2024 July 02 (13.8 days after the GRB). It consisted of 4 exposures of 600 s each and covered the wavelength range 3000-21000 AA.

The target is faintly detected in the r-band acquisition image, with an AB magnitude r ~ 22.8 (calibration is difficult due to paucity of calibrators in the field). This is significantly brighter than the archival object visible in the Pan-STARRS and Legacy surveys, first noticed by Gompertz et al. (GCN 36715), and likely includes a transient contribution.

In a preliminary reduction, we detect several strong emission lines that we identify as H-alpha, H-beta, H-gamma, the [O II] doublet, [O III] 4959, [O III] 5007, and [Ne III] 3869 at a common redshift of z = 0.3965, which is lower than the photometric value reported in the PS1-STRM catalog (Beck et al. 2020) for galaxy PSO J162.3946+17.2828. We therefore propose this to be the redshift of the GRB.

The Legacy survey images also show a second, fainter object about 1.7" west of the optical afterglow position. This was also included in the slit, and we measure for it z = 1.338 from detection of [O II] and H-alpha. Given the larger offset, we consider this galaxy to be unrelated to the GRB.

We acknowledge expert support from the ESO staff in Paranal, in particular Matias Jones and Thomas Szeifert.

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