The X-shooter sample of GRB afterglows

2026-04-16T00:00:00Z

Thanks to their exceptional brightness GRB afterglows can be used as powerful extragalactic background sources. They behave like distant lighthouses capable of unveiling the properties of the universe at different redshifts. The afterglow spectrum reveals the signatures of the gas associated with the GRB host, but also with the IGM and with other galaxies present along the GRB line of sight. Many physical properties of the gas (temperature, density, metallicity,...) can be derived from the analysis of the absorption lines, mainly for GRBs at z>2. The metallicity and abundance measurements can be used to constrain the chemical enrichment of the Universe. Differently from QSOs that probe random lines of sight through the foreground galaxies, GRBs mostly probes the gas associated with the star forming regions of their host galaxy.
Since 2009, we are carrying out a legacy programme with the VLT/X-Shooter spectrograph to collect a large complete homogeneous sample of GRB afterglows (PI : J. Fynbo).
We published about 15 papers on individual spectra and we now have more than 60 spectra, making our sample by far the largest of this kind. It is now time to use the sample to study different aspects of the GRB host galaxy ISM and the GRB line of sight, producing a series of sample papers.
The observation are obtained in target of opportunity mode and data analysis of the whole sample is particularly complex as each spectrum has different characteristics (very different signal-to-noise, different GRB redshift, different properties of the probed ISM and line of sight...) and due to the large X-shooter spectral range.
The goal of this workshop is to bring together the members of the legacy to to work on the sample papers and to discuss about the different aspects involved on each sample paper (specific data reduction, common tools and methods for the data analysis, issues, ...).
Some specific topics :
– spectra normalization
– absorption line fitting tools
– absorption line fitting methods
– ISM metallicity and dust
– comparison between emission and absorption properties of the GRB host galaxies - fine structure lines and gas cloud distances
– the Ly-alpha systems
– molecules
– staking analysis
– IGM probed through GRB afterglows
– foreground systems along the GRB lines of sight

Centre de Conférences Jules Janssen

The X-shooter sample of GRB afterglows