GCN Circular 37731
Subject
GRB 240821A: Host galaxy redshift from VLT/X-shooter
Event
Date
2024-10-07T15:42:50Z (a year ago)
From
Benjamin Schneider at MIT <bschn@mit.edu>
Via
Web form
B. Schneider (MIT), A. Rossi (INAF-OAS), M. Ferro (INAF-OAB), H. Fausey (GWU), A. L. Thakur (INAF-IAPS), A. Martin-Carrillo (UCD), D. B. Malesani (DAWN/NBI and Radboud Univ.), N. R. Tanvir (U. Leicester), A. J. Levan (Radboud Univ. and Warwick Univ.), J. T. Palmerio (CEA), A. Saccardi (GEPI/Obs. de Paris), S. D. Vergani (GEPI/Obs. de Paris) report on behalf of the Stargate collaboration:
We observed the location of the SVOM and Fermi short GRB 240821A (Cangemi et al., GCN 37220; He et al., GCN 37226; Murphy et al., GCN 37232; Dalessi & Meegan, GCN 37239, Quirola-Vasquez et al., GCN 37319) with the X-shooter spectrograph mounted on the ESO VLT UT3 (Melipal) as a follow-up to our previous VLT/X-shooter observation (Saccardi et al., GCN 37369). The observation consisted of two consecutive observations of 4x1200 s each, with mid-times at 03:53:33 UT and 05:18:58 UT on 2024 October 1 (~40.4 days after the trigger). The seeing delivered is significantly better than for our previous observation reported in GCN 37369.
In addition to the emission line at 8120 AA mentioned by Saccardi et al. (GCN 37369), which is clearly detected also in the new spectra, two fainter features are also visible. This allows solving the conundrum from the previous observation, as the three lines nicely match [O II] 3729, H alpha, and [N II] 6584, all at a common redshift z = 0.238.
We acknowledge the expert support from the ESO observing staff at Paranal, in particular Jonathan Smoker and Cedric Ledoux.