GRB 090313 X-shooter's first shot at a gamma-ray burst
Author(s)
Date Issued
2010-04-01
Mission(s)
Abstract
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 . 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. Based on observations made with ESO VLT at Paranal Observatory during the commissioning of X-shooter.
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 . 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. Based on observations made with ESO VLT at Paranal Observatory during the commissioning of X-shooter.