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We present a preliminary analysis of an extensive set of optical observations of the Type Ia SN 2005hk. We show that the evolution of SN 2005hk closely follows that of the peculiar SN 2002cx. SN 2005hk is more luminous than SN 2002cx, while still under-luminous compared to normal Type Ia supernovae. The spectrum at 9 days before maximum is dominated by conspicuous Fe III and Ni III lines, and the Si II 6355 line is also clearly visible. All these features have low velocity (∼ 6000 km/s). The near maximum spectra show lines of Si II, S II, Fe II-III, as well as other intermediate mass and iron group elements. Analysis with the code for synthetic spectra SYNOW indicates that all these spectral lines have similar velocities. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

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]

A γ-ray burst (GRB) has been found with a redshift comparable to the most distant quasars and galaxies: GRB 050904 at z = 6.29 ± 0.01, making it the most distant X-ray source known. The X-ray lightcurve is not a power-law like many afterglows, but is dominated by large amplitude variability from a few minutes to at least half a day. The spectra soften during this time from a power-law with photon index Γ = 1.2 to 1.9. The spectra are well-described by an absorbed power-law with possible evidence of very large intrinsic absorption. There is no evidence for discrete features. This is in spite of the spectrum’s very high signal-to-noise ratio, since GRB 050904 was extraordinarily bright in X-rays. In the first days after the burst, it was by far the brightest known X-ray source at z > 4. In the first minutes after the burst, the X-ray flux was > 10-9 erg cm-2 s-1 in the 0.2–10 keV band, corresponding to an apparent luminosity between 10 5 and 106 times greater than the brightest X-ray quasars at similar distances. More photons were acquired in the first minutes with Swift-XRT than XMM-Newton and Chandra have obtained in ∼ 300 ks of pointed observations of z > 5 AGN. The huge X-ray fluence detected from GRB 050904 is a clear demonstration of concept for efficient X-ray studies of the high-z IGM with new large area, high-resolution X-ray detectors, and shows that GRBs in their early phases are the only backlighting bright enough for X-ray absorption studies of the intervening matter at high redshift. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The attempt to secure conclusive, spectroscopic evidence for the GRB/SN connection has been a central theme in most GRB observing time proposals since the discovery of the very unusual GRB 980425 associated with the peculiar type Ib/c SN 1998bw. GRB 030329 provided this evidence to everybody’s satisfaction. In this contribution we show the results of a spectroscopic campaign of the supernova associated with GRB 030329 carried out at ESOs Very Large Telescope. We also present preliminary results from a photometric and spectroscopic campaign targeting the X-ray Flash of July 23. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]