M. Weidinger

On the Lyalpha emission from gamma-ray burst host galaxies: Evidence for low metallicities

We report on the results of a search for Ly emission from the host galaxy of the z= 2:140 GRB 011211 and other galaxies in its surrounding field. We detect Ly emission from the host as well as from six other galaxies in the field. The restframe equivalent width of the Ly line from the GRB 011211 host is about 21 A. This is the fifth detection of Ly emission out of five possible detections from GRB host galaxies, strongly indicating that GRB hosts, at least at high redshifts, are Ly emitters. This is intriguing as only 25% of the Lyman-Break selected galaxies at similar redshifts have Ly emission lines with restframe equivalent width larger than 20 A. Possible explanations are i) a preference for GRB progenitors to be metal-poor as expected in the collapsar model, ii) an optical afterglow selection bias against dusty hosts, and iii) a higher fraction of Ly emitters at the faint end of the luminosity function for high- z galaxies. Of these, the current evidence seems to favour i).

The line-of-sight towards GRB 030429 at z = 2.66: Probing the matter at stellar, galactic and intergalactic scales

We report the discovery of the optical afterglow (OA) of the long-duration gamma-ray burst GRB 030429, and present a comprehensive optical/near-infrared dataset used to probe the matter at different distance scales, i.e. in the burst environment, in the host galaxy and in an intervening absorber. A break in the afterglow light curve is seen approximately 1 day from the onset of the burst. The light curve displays a significant deviation from a simple broken power-law with a bright 1.5 mag bump with a duration of 2-3 days. The optical/near-infrared spectral energy distribution is best fit with a power-law with index beta = -0.36 ± 0.12 reddened by an SMC-like extinction law with (a modest) AV = 0.34 ± 0.04. In addition, we present deep spectroscopic observations obtained with the Very Large Telescope. The redshift measured via metal absorption lines in the OA is z = 2.658 ± 0.004. Based on the damped Lyalpha absorption line in the OA spectrum we measure the H I column density to be log N(H I) = 21.6 ± 0.2. This confirms the trend that GRBs tend to be located behind very large H I column densities. The resulting dust-to-gas ratio is consistent with that found in the SMC, indicating a low metallicity and/or a low dust-to-metal ratio in the burst environment. We find that a neighbouring galaxy, at a separation of only 1.2 arcsec, has z = 0.841 ± 0.001, ruling it out as the host of GRB 030429. The small impact parameter of this nearby galaxy, which is responsible for Mg II absorption in the OA spectrum, is in contrast to previous identifications of most QSO absorption-selected galaxy counterparts. Finally, we demonstrate that the OA was not affected by strong gravitational lensing via the nearby galaxy.

On the afterglow of the x-ray flash of 2003 July 23: photometric evidence for an off-axis gamma-ray burst with an associated supernova?

We present optical and near-infrared follow-up observations of the X-ray flash (XRF) of 2003 July 23. Our observations in the R band cover the temporal range from 4.2 hr to 64 days after the high-energy event. We also present the results of multicolor imaging extending to the K band on three epochs. The light curve of the R-band afterglow the first week after the burst is similar to the light curve for long-duration gamma-ray bursts (GRBs), i.e., a broken power law with a late time slope of � � 2: 0( F� / t � � ). Furthermore, the spectral energy distribution (SED) has a power-law (F� / � � � ) shape with slope � � 1:0. However, the decay slope at t < 1d ay is shallow, consistent with zero. This is in qualitative agreement with the prediction that XRFs are off-axis classical GRBs. After the first week there is a strong bump in the light curve, which peaks at around 16 days. The SED after the peak becomes significantly redder. We discuss the possible interpretations of this bump and conclude that an underlying supernova is the most likely explanation since no other model appears consistent with the evolution of the SED. Finally, we present deep spectroscopy of the burst both in the afterglow and in the bump

The extended lyman-α emission surrounding the z=3.04 radio-quiet QSO1205-30 : Primordial infalling gas illuminated by the quasar?

We present spectroscopic observations obtained with the FORS1 instrument on the ESO VLT under good seeing conditions of the radio-quiet

Optical Photometry of GRB 021004: The First Month*

z_{\rm em}=3.04

Deep Ly alpha imaging of two z=2.04 GRB host galaxy fields

quasar Q1205-30 and its associated extended Ly α emission. The extended Ly α emission was originally found in a deep narrow band image targeting a

The lyman-α glow of gas falling into the dark matter halo of a z = 3 galaxy

z_{\rm abs} \approx z_{\rm em}

The afterglow and the host galaxy of GRB 011211

Lyman-limit system in the spectrum of the QSO. Using spectral point-spread function fitting to subtract the QSO spectrum, we clearly detect the extended Ly α emission as well as two foreground galaxies at small impact parameters (

Small-scale variations in the radiating surface of the GRB 011211 jet

2.12\,\pm\, 0.04

Tracing large-scale structure at high redshift with Lyman-α emitters: the effect of peculiar velocities

and