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Context. Theory suggests that about 10% of Swift-detected gamma-ray bursts (GRBs) will originate at redshifts, z, greater than 5 yet a number of high redshift candidates may be left unconfirmed due to the lack of measured redshifts.

Context. GRB afterglow spectra are sensitive probes of interstellar matter along the line-of-sight in their host galaxies, as well as in intervening galaxies. The rapid fading of GRBs makes it very difficult to obtain spectra of sufficient resolution and S/N to allow for these kinds of studies.

Context. The collapsar model predicts that the progenitors of Gamma-ray Bursts (GRBs) are metal poor in Fe group elements. The existence of low metallicity stellar populations could manifest itself in the characteristics of the GRB site immediate environment in the host galaxy.

Context. The first magnetic fields in O- and B-type stars that do not belong to the Bp-star class, have been discovered. The cyclic UV wind-line variability, which has been observed in a significant fraction of early-type stars, is likely to be related to such magnetic fields.

Context.We present high resolution VLT UVES and low resolution FORS optical spectroscopy of supernova 2006aj and its host galaxy, associated with the nearby ($z = 0.03342$) gamma-ray burst GRB 060218. This host galaxy is a unique case, as it is one of the few nearby GRB host galaxies known, and it is only the second time high resolution spectra have been taken of a nearby GRB host galaxy (after GRB 980425).

Context.Before the launch of the Swiftsatellite, the majority of the gamma-ray burst (GRB) afterglows for which Lyαwas redshifted into the observable spectrum showed evidence for a damped Lyαabsorber. This small sample indicated that GRBs explode either in galaxies, or regions within them, having high neutral hydrogen column densities.

Aims.We present early optical spectroscopy of the afterglow of the gamma-ray burst GRB 060206 with the aim of determining the metallicity of the GRB absorber and the physical conditions in the circumburst medium. We also discuss how GRBs may be important complementary probes of cosmic chemical evolution.

?Casis a B2 IV star with $v\sin i = 17$km s-1. Time-resolved circular spectropolarimetric observations of ?Casobtained in 2001 and 2002 with the Musicos échelle spectropolarimeter at the 2 m Télescope Bernard Lyot (TBL) show a sinusoidally varying longitudinal magnetic field with a strength between 10 G and -46 G for the averaged line-of-sight component, corresponding to $B_{\rm pol}=335^{+120}_{-65}$G. The period corresponds very accurately with the 5.37045 day period as derived from stellar wind variations observed in the ultraviolet. The epoch of the positive maximum field corresponds in phase with the maximum emission in the UV wind lines. This gives compelling evidence for a magnetic rotator model for this star, with an unambiguous rotation period of 5.37 days. We searched for periodicity in line-profile variations (lpv), radial velocity and minimum intensity curves in the ~400 optical spectra. We found a non-radial pulsation mode with $l=2 \pm 1$at the frequency $f=0.64$c d-1. From this periodicity and from stellar parameters derived from model fits, we propose to classify ?Casas a Slowly Pulsating B (SPB) star. This is the third detection of a magnetic field in an early B-type pulsating star and the first one in a SPB star.

Context. The collapsar model predicts that the progenitors of Gamma-ray Bursts (GRBs) are metal poor in Fe?group elements. The existence of low metallicity stellar populations could manifest itself in the characteristics of the GRB site immediate environment in the host galaxy. Aims. We analyse the strong emission lines from the sub-luminous host galaxy of GRB?980425, which showed the first connection with a supernova explosion (SN?1998bw). The host is of sufficient size to allow detailed resolved spectroscopy of individual Hii?regions and to search for regions with peculiar properties close to the the GRB?site.Methods. Using integral field spectroscopy with VIMOS we study most of the high surface brightness part of the host including the Hii?region where the supernova and GRB?occurred.Results. The star formation rate, reddening, equivalent width and stellar mass in the GRB?region is similar to other Hii?regions in the host. Extreme values arise in the only region that shows emission lines from Wolf-Rayet stars, a region that is located 800?pc in projection from the GRB?site. Strong emission line diagnostics of all Hii?regions imply oxygen abundances between?0.3 and 0.8?solar with the lowest values arising in the?WR and GRB?regions. Including uncertainties from the metallicity diagnostics, all metallicities are similar to within?3?. We demonstrate that there is a good agreement between the luminosity weighted and mass weighted specific star formation rates (SSFR) in individual young Hii regions. While the global average of the SSFR is similar to high redshift GRB?hosts, there are significant variations between individual resolved Hii?regions. Comparing the measured emission line ratios of low redshift?GRB hosts to theoretical models and observations of field galaxies, we find that GRBs are present in different environment metallicities while the regions of their origin are consistently very young. Similar line ratios of GRB hosts compared with those of the WR region can arise in spatially unresolved galaxies with bright Hii?regions close to the GRB?location.

Aims. We present optical photometry and spectroscopy of the afterglow and host galaxy of gamma-ray burst GRB?040924. This GRB had a rather short duration of T90~2.4?s, and a well sampled optical afterglow light curve. We aim to use this dataset to find further evidence that this burst is consistent with a massive star core-collapse progenitor. Methods. We combine the afterglow data reported here with those from the literature and compare the host properties with survey data.Results. We find that the global behaviour of the optical afterglow is well fit by a broken power-law, with a break at ~0.03?days. We determine the redshift z = 0.858 ? 0.001 from the detected emission lines in our spectrum. Using the spectrum and photometry we derive global properties of the host, showing it to have similar properties to other long GRB hosts. We detect the [Ne?III] emission line in the spectrum, and compare the fluxes of this line of a sample of 15?long GRB host galaxies with survey data, showing the long GRB hosts to be comparable to local metal-poor emission line galaxies in their [Ne?III] emission. We fit the supernova bump accompanying this burst, and find that it is similar to other long GRB supernova bumps, but fainter.Conclusions. All properties of GRB?040924 (the associated supernova, the spectrum and SED of host and afterglow) are consistent with an origin in the core-collapse of a massive star.

We perform a detailed study of the gamma-ray burst GRB 091127/SN 2009nz host galaxy at z= 0.490 using the VLT/X-shooter spectrograph in slit and integral-field unit (IFU) mode. From the analysis of the optical and X-ray afterglow data obtained from ground-based telescopes and Swift-XRT, we confirm the presence of a bump associated with SN 2009nz and find evidence of a possible jet break in the afterglow lightcurve. The X-shooter afterglow spectra reveal several emission lines from the underlying host, from which we derive its integrated properties. These properties agree with those of previously studied GRB-SN hosts and, more generally, with those of the long GRB host population. We use the Hubble Space Telescope and ground-based images of the host to determine its stellar mass (M⋆). Our results extend to lower M⋆values the M-Z plot derived for the sample of long GRB hosts at 0.3 < z< 1.0 adding new information to probe the faint end of the M-Z relation and the shift of the LGRB host M-Z relation from that found from emission-line galaxy surveys. Thanks to the IFU spectroscopy, we can build the two-dimensional (2D) velocity, velocity dispersion, and star formation rate (SFR) maps. They show that the host galaxy has perturbed rotation kinematics with evidence of a SFR enhancement consistent with the afterglow position.

Aims.The aim of this paper is to study the environment and intervening absorbers of the gamma-ray burst GRB 090926A through analyzing optical spectra of its afterglow.