GCN Circular 38487
Subject
GRB 241209A: VLT/X-shooter spectroscopy
Event
Date
2024-12-09T11:09:41Z (a year ago)
From
Andrea Saccardi at CEA/Irfu <andrea.saccardi@cea.fr>
Via
Web form
A. Saccardi (CEA/Irfu), S. D. Vergani (GEPI/Obs. de Paris), J. T. Palmerio (CEA/Irfu), D. B. Malesani (DAWN/NBI and Radboud Univ.), N. Habeeb (Leicester), A. de Ugarte Postigo (OCA and LAM) report on behalf of the Stargate collaboration:
We performed ESO VLT/X-shooter spectroscopic observations of the VLT/FORS2 candidate counterpart (de Ugarte Postigo et al., GCN 38484) of GRB 241209A (Fermi GBM team, GCN 38474; Parsotan et al., GCN 38476). Our spectra cover the wavelength range 3000-25000 AA, and consist of 4 exposures of 600 s each. The observation mid-time was 2024 Dec 9.302 UT (1.66 hr after the GRB).
From a preliminary reduction of the spectra, we do not detect any continuum. Emission lines are detected in the visible and near-infrared arms, which we identify as Halpha, [OIII] 5007 AA and the [OII] 3726, 3729 AA doublet at a common redshift of z = 1.490. No absorption lines are identified due to the faintness of the source (de Ugarte Postigo et al., GCN 38484) and the low S/N of the spectra.
We notice that the recently released UVOT-enhanced X-ray position (Evans et al., GCN 38486) encompasses both this object and the brighter galaxy mentioned by de Ugarte Postigo et al. (GCN 38484), making it unclear which one, if any, is the GRB counterpart. The brighter galaxy has of course a smaller chance association probability.
We encourage further photometric observation to detect the variability of any of these two sources.
We acknowledge the excellent support from the ESO staff in Paranal, in particular Jonathan Smoker.