We present the spectroscopic and photometric evolution of the nearby (z = 0.059) spectroscopically confirmed type Ic supernova, SN 2010bh, associated with the soft, long-duration gamma-ray burst (X-ray flash) GRB 100316D. Intensive follow-up observations of SN 2010bh were performed at the ESO Very Large Telescope (VLT) using the X-shooter and FORS2 instruments. Owing to the detailed temporal coverage and the extended wavelength range (3000-24800Å), we obtained an unprecedentedly rich spectral sequence among the hypernovae, making SN 2010bh one of the best studied representatives of this SN class. We find that SN 2010bh has a more rapid rise to maximum brightness (8.0 ± 1.0 rest-frame days) and a fainter absolute peak luminosity (L bol ≈ 3 × 10 42 erg s −1 ) than previously observed SN events associated with GRBs. Our estimate of the ejected 56 Ni mass is 0.12 ± 0.02 M ⊙ . From the broad spectral features we measure expansion velocities up to 47,000 km s −1 , higher than those of SNe 1998bw (GRB 980425) and 2006aj (GRB 060218). Helium absorption lines He I λ5876 and He I 1.083 µm, blueshifted by ∼20,000-30,000 km s −1 and ∼28,000-38,000 km s −1 , respectively, may be present in the optical spectra. However, the lack of coverage of the He I 2.058µm line prevents us from confirming such identifications. The nebular spectrum, taken at ∼186 days after the explosion, shows a broad but faint [O I] emission at 6340Å. The light-curve shape and photospheric expansion velocities javík, Iceland

Abstract. We present Ulysses and NEAR data from the detection of the short or intermediate duration (2 s) gamma-ray burst GRB 000301C (2000 March 1.41 UT). The gamma-ray burst (GRB) was localised by the Inter Planetary Network (IPN) and RXTE to an area of ∼50 arcmin 2 . A fading optical counterpart was subsequently discovered with the Nordic Optical Telescope (NOT) about 42 h after the burst. The GRB lies at the border between the long-soft and the short-hard classes of GRBs. If GRB 000301C belongs to the latter class, this would be the first detection of an afterglow to a short-hard burst. We present UBRI photometry from the time of the discovery until 11 days after the burst. We also present JHK photometry obtained with UKIRT on 2000 March 4.5 UT (3.1 days after the burst). Finally, we present spectroscopic observations of the optical afterglow obtained with the ESO VLT Antu telescope 4 and 5 days after the burst. The optical light curve is consistent with being achromatic from 2 to 11 days after the burst and exhibits a break. A broken power-law fit yields a shallow pre-break decay power-law slope of α1 = −0.72 ± 0.06, a break time of t break = 4.39 ± 0.26 days after the burst, and a post-break slope of α2 = −2.29 ± 0.17. These properties of the light curve are best explained by a sideways expanding jet in an ambient medium of constant mean density. In the optical spectrum we find absorption features that are consistent with Fe ii, C iv, C ii, Si ii and Lyα at a redshift of 2.0404 ± 0.0008. We find evidence for a curved shape of the spectral energy distribution of the observed afterglow. It is best fitted with a power-law spectral distribution with index β ∼ −0.7 reddened by an SMC-like extinction law with AV ∼ 0.1 mag. Based on the Lyα absorption line we estimate the H i column density to be log(N(H i)) = 21.2 ± 0.5. This is the first direct indication of a connection between GRB host galaxies and Damped Lyα Absorbers.

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The gamma-ray burst GRB 000210 had the highest γ-ray peak flux of any event localized by BeppoSAX as yet but it did not have a detected optical afterglow, despite prompt and deep searches down to R lim ≈ 23.5. It is therefore one of the events recently classified as dark GRBs, whose origin is still unclear.

Abstract. We present the discovery of the Optical Transient (OT) of the long-duration gamma-ray burst GRB 000926. The optical transient was detected independently with the Nordic Optical Telescope and at Calar Alto 22.2 hours after the burst. At this time the magnitude of the transient was R = 19.36. The transient faded with a decay slope of about 1.7 during the first two days after which the slope increased abruptly (within a few hours) to about 2.4. The light-curve started to flatten off after about a week indicating the presence of an underlying extended object. This object was detected in a deep image obtained one month after the GRB at R = 23.87 ± 0.15 and consists of several compact knots within about 5 arcsec. One of the knots is spatially coincident with the position of the OT and hence most likely belongs to the host galaxy. Higher resolution imaging is needed to resolve whether all the compact knots belong to the host galaxy or to several independent objects. In a separate paper we present a discussion of the optical spectrum of the OT, and its inferred redshift (Møller et al., in prep.).

We present the detection of [O iii] emission lines from the galaxies responsible for two high‐redshift z > 1.75 damped Lyman‐α (DLA) absorption lines. We find two sources of [O iii] emission corresponding to the z= 1.92 DLA absorber towards the quasar Q 2206−1958, and we also detect [O iii] emission from the galaxy responsible for the z= 3.10 DLA absorber towards the quasar 2233.9+1381. These are the first detections of rest‐frame optical emission lines from high‐redshift DLA galaxies. Unlike the Lyα line, the [O iii] line provides a measure of the systemic velocity of the galaxy. We compare the [O iii] redshifts with the velocity profile of the low‐ionization metal lines in these two absorbers, with the goal of distinguishing between the model of Prochaska and Wolfe of DLA absorbers as large rapidly rotating cold thick discs, and the standard hierarchical cold dark matter model of structure formation, in which DLAs arise in protogalactic fragments. We find some discrepancies with the predictions of the former model. Furthermore, the image of the DLA galaxy towards Q 2206−1958 shows a complex disturbed morphology, which is more in accord with the hierarchical picture. We use the properties of the rest‐frame optical emission lines to further explore the question posed by Møller et al.: are high‐redshift DLA galaxies Lyman‐break galaxies (LBGs) selected by gas cross‐section? The measured velocity dispersions of the DLA galaxies are in agreement with this picture, while the data on the [O iii] luminosities and the velocity differences between the Lyα and [O iii] lines are inconclusive, as there are insufficient LBG measurements overlapping in luminosity. Finally, we estimate the star formation rates in these two DLA galaxies, using a variety of diagnostics, and include a discussion of the extent to which the [O iii] line is useful for this purpose.

We report optical and near-infrared follow-up observations of GRB 011121 collected predominantly at ESO telescopes in Chile. We discover a break in the afterglow light curve after 1.3 days, which implies an initial jet opening angle of about 9 . The jet origin of this break is supported by the fact that the spectral energy distribution is achromatic during the first 4 days. During later phases, GRB 011121 shows significant excess emission above the flux predicted by a power law, which we interpret as additional light from an underlying supernova. In particular, the spectral energy distribution of the optical transient approximately 2 weeks after the burst is clearly not of power-law type but can be presented by a blackbody with a temperature of $6000 K. The deduced parameters for the decay slope and the spectral index favor a wind scenario, i.e., an outflow into a circumburst environment shaped by the stellar wind of a massive gamma-ray burst (GRB) progenitor. Because of its low redshift of z ¼ 0:36, GRB 011121 has been the best example for the GRB-supernova connection until GRB 030329 and provides compelling evidence for a circumburster wind region expected to exist if the progenitor was a massive star.

We report the identification of the optical afterglow of GRB 980613 in R-and I-band images obtained between 16 and 48 hours after the gamma-ray burst. Early near-infrared (NIR) H and K ′ observations are also reported. The afterglow was optically faint (R ≈ 23) at discovery but did not exhibit an unusually -3rapid decay (power-law decay slope α < 1.8 at 2σ). The optical/NIR spectral index (β RH < 1.1) was consistent with the optical-to-X-ray spectral index (β RX ≈ 0.6), indicating a maximal reddening of the afterglow of ≈ 0.45 mag in R. Hence the dimness of the optical afterglow was mainly due to the fairly flat spectral shape rather than internal reddening in the host galaxy. We also present late-time HST/STIS images of the field in which GRB 980613 occurred, obtained 799 days after the burst. These images show that GRB 980613 was located close to a very compact, blue V = 26.1 object inside a complex region consisting of star-forming knots and/or interacting galaxy fragments. Therefore, GRB 980613 constitutes a strong case for the association of cosmological gamma-ray bursts with star-forming regions.