TITLE: GCN CIRCULAR NUMBER: 40174 SUBJECT: GRB 250419A: VLT/X-shooter spectroscopic redshift z = 0.845 DATE: 25/04/19 09:56:04 GMT FROM: Aishwarya L Thakur at INAF-IAPS, Rome aishth@outlook.com
A. L. Thakur (INAF-IAPS), M. Garnichey (LUX-Paris Obs.), G. Corcoran (UCD), A. J. Levan (Radboud), D. B. Malesani (DAWN/NBI and Radboud), A. Martin-Carrillo (UCD), G. Pugliese (API-UvA), A. Saccardi (CEA/Irfu), S. D. Vergani (LUX-Paris Obs.) report on behalf of the Stargate collaboration:
We observed the optical counterpart (Lopez et al., GCN 40169; Xin et al., GCN 40170; Zheng et al., GCN 40171; Kumar et al., GCN 40172) of the SVOM/ECLAIRs GRB 250419A (Wang et al., GCN 40168) using the ESO/VLT UT3 (Melipal) equipped with the X-shooter spectrograph. Observations started on 2025 April 19 at 07:10:59 UT (4.69 hr after the burst). Our spectra cover the wavelength range 3000-21000 AA and consist of 4 exposures of 600 s each. Seeing conditions were very poor at ~3".
In a preliminary reduction of the spectra, we clearly detect a continuum over the entire wavelength range. From the detection of multiple absorption features, including Fe II, Mg II, Mg I, Ca II and Ca I we infer a redshift of z = 0.845.
We note that no object is visible in the Legacy Survey at the coordinates of the optical transient (López et al., GCN 40169; Xin et al., GCN 40170), down to a magnitude r ~ 24. This is consistent with the lack of emission lines in our spectrum.
We acknowledge the prompt response and excellent support of the ESO observing staff in Paranal, particularly from Martina Baratella. This analysis was carried out with the help of the zHunter tool (https://doi.org/10.5281/zenodo.15189495).
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