GRB 090313: X-shooter's first shot at a gamma-ray burst

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Context. X-shooter is the first second-generation instrument to become operative at the ESO Very Large Telescope (VLT). It is a broad-band medium-resolution spectrograph designed with gamma-ray burst (GRB) afterglow spectroscopy as one of its main science drivers.

Aims. During the first commissioning night on sky with the instrument fully assembled, X-shooter observed the afterglow of GRB¿090313 as a demonstration of the instrument's capabilities.

Methods. GRB¿090313 was observed almost two days after the burst onset, when the object had already faded to R ~ 21.6. Furthermore, the 90% illuminated Moon was just 30 degrees away from the field. In spite of the adverse conditions, we obtained a spectrum that, for the first time in GRB research, simultaneously covers the range from 5700 to 23¿000 Å.

Results. The spectrum shows multiple absorption features at a redshift of 3.3736, which we identify as the redshift of the GRB. These features are composed of 3 components with different ionisation levels and velocities. Some of the features have never been observed before in a GRB at such a high redshift. Furthermore, we detect two intervening systems at redshifts of 1.8005 and 1.9597.

Conclusions. These results demonstrate the potential of X-shooter in the GRB field, because it was capable of observing a GRB down to a magnitude limit that would include 72% of long GRB afterglows 2 h after the burst onset. Coupled with the rapid response mode available at VLT, allowing reaction times of just a few minutes, X-shooter constitutes an significant leap forward on medium resolution spectroscopic studies of GRBs, their host galaxies and intervening systems, probing the early history of the Universe.

Original languageEnglish
JournalAstronomy & Astrophysics
Pages (from-to)A42
Number of pages7
Publication statusPublished - 22 Apr 2010

ID: 32961352