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We report optical, near-infrared and X-ray observations of the afterglow of GRB 050814, which was seen to exhibit very red optical colours. By modelling its spectral energy distribution we find that z = 5.3 ± 0.3. We next present a carefully selected sample of 19 Swift GRBs, intended to estimate in an unbiased way the GRB redshift distribution, including the mean redshift (zmean) as well as constraints on the fraction of high-redshift bursts. We find that zmean = 2.7 and that at least 5% of the GRBs originate at z > 5. The redshift distribution of the sample is qualitatively consistent with models where the GRB rate is proportional to the star formation rate in the Universe. The high mean redshift of this GRB sample and the wide redshift range clearly demonstrates the suitability of GRBs as efficient probes of galaxies and the intergalactic medium over a significant fraction of the history of the Universe. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

In recent years, a population of galaxies with huge infrared luminosities and dust masses has been discovered in the submillimetre. Observations suggest that the AGN contribution to the luminosities of these submillimetre-selected galaxies is low; instead their luminosities are thought to be mainly due to strong episodes of star formation following merger events. Our current understanding of GRBs as the endpoints in the life of massive stars suggest that they will be located in such galaxies. We have observed a sample of well-located GRB host galaxies in the submillimetre. Comparing the results with the general submillimetre-selected galaxy population, we find that at low fluxes (S850 ≤ 4 mJy), the two agree well. However, there is a lack of bright GRB hosts in the submillimetre. This finding is reinforced when the results of other groups are included. Possible explanations are discussed. These results help us assess the roles of both GRB host galaxies and submillimetre-selected galaxies in the evolution of the Universe. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

We report on the discovery of the near-IR transient of the long-duration gamma-ray burst GRB 030528 and its underlying host galaxy. The near-IR transient was first observed in JHKs with SofI at the 3.6 m ESO-NTT 16 hrs after the burst and later observations revealed a fading Ks-band afterglow. The afterglow nature was confirmed by Chandra observations which found the source to be a fading X-ray emitter. The lack of an optical afterglow and the early faintness in the near-IR (Ks> 18.5 mag) place GRB 030528 in a parameter space usually populated by dark bursts. We find the host to be an elongated blue galaxy. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

We report on optical and near-infrared follow-up observations of the afterglow of GRB 030226 performed with the telescopes at ESO La Silla and Paranal. Our observations started 0.2 days after the burst when the afterglow was at a magnitude of R ≈ 19. One week later the magnitude of the afterglow had fallen to R=25, and at two weeks after the burst it could no longer be detected (R > 26). VLT blue-band spectra show two absorption line systems at redshifts z = 1.962 ± 0.001 and 1.986 ± 0.001, indicating a metal-rich environment of the burster, and placing the burster very likely at z = 1.986 ± 0.001. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Multiwavelengthp observations of a GRB detected by INTEGRAL (GRB 030227) revealed a dim optical afterglow (OA) that would not have been detected by many previous searches due to its faintess (R∼ 23). This OA was seen to decline following a power law decay with index α = -0.95 ± 0.16. The spectral index β of the OA yields -1.32 ± 0.15, with the intrinsec absorption consistent with zero. These values may be explained by a relativistic expansion of a fireball in an homogeneous medium. We also find evidence for inverse Compton scattering in X-rays. A possible break is detected at ∼ 1.5 days. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

We summarize our ongoing program of sub-millimeter observations of gamma-ray bursts (GRBs) using the Sub-millimetre Common-User Bolometer Array (SCUBA) on the James Clerk Maxwell Telescope (JCMT). Sub-millimeter observations of the early afterglows are of interest because this is where the emission peaks in some bursts in the days to weeks following the burst. Of increasing interest is to look for underlying quiescent sub-millimeter sources that may be dusty star-forming host galaxies. [ABSTRACT FROM AUTHOR]

We briefly summarize the results from our ongoing program of submillimeter observations of GRB counterparts using the SCUBA instrument on the James Clerk Maxwell Telescope (JCMT). Full details have already been published elsewhere [1,2]. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]