It is thought that the first generations of massive stars in the Universe were an important, and quite possibly dominant 1 , source of the ultra-violet radiation that reionized the hydrogen gas in the intergalactic medium (IGM); a state in which it has remained to the present day. Measurements of cosmic microwave background anisotropies suggest that this phase-change largely took place 2 in the redshift range z=10.8 ±1.4, while observations of quasars and Lyman-α galaxies have shown that the process was essentially completed 3,4,5 by z≈6. However, the detailed history of reionization, and characteristics of the stars and proto-galaxies that drove it, remain unknown. Further progress in understanding requires direct observations of the sources of ultra-violet radiation in the era of reionization, and mapping the evolution of the neutral hydrogen (H I) fraction through time. The detection of galaxies at such redshifts is highly challenging, due to their intrinsic faintness and high luminosity distance, whilst bright quasars appear to be rare It has long been recognised that GRBs have the potential to be powerful probes of the early universe. Known to be the end product of rare massive stars 11 , GRBs and their afterglows can briefly outshine any other source in the universe, and would be theoretically detectable to z ~ 20 and beyond 12,13 . Their association with individual stars means that they serve as a signpost of star formation, even if their host galaxies are too 5 faint to detect directly. Equally important, precise determination of the hydrogen Lyman-α absorption profile can provide a measure of the neutral fraction of the IGM at the location of the burst 9,10,14,15 . With multiple GRBs at z > 7, and hence lines of sight through the IGM, we could thus trace the process of reionization from its early stages.However, until now the highest redshift GRBs (at z = 6. Ground-based optical observations in the r, i and z filters starting within a few minutes of the burst revealed no counterpart at these wavelengths (see Supplementary Information (SI)).The United Kingdom Infrared Telescope (UKIRT) in Hawaii responded to an automated request, and began observations in the K-band 21 minutes post burst. These images ( Figure 1) revealed a point source at the reported X-ray position, which we concluded was likely to be the afterglow of the GRB. We also initiated further nearinfrared (NIR) observations using the Gemini-North 8-m telescope, which started 75 min after the burst, and showed that the counterpart was only visible in filters redder than about 1.2 µm. In this range the afterglow was relatively bright and exhibited a shallow spectral slope F ν ∝ ν -0.26 , in contrast to the deep limit on any flux in the Y filter (0.97-1.07 µm). Later observations from Chile using the MPI/ESO 2.2m telescope, Gemini South and the Very Large Telescope (VLT) confirmed this finding. The nondetection in the Y-band implies a power-law spectral slope between Y and J steeper than. This is impossible for dust at any redshift, and is a tex...

Abstract. We present BV RcIc broad-band flux spectra for the host galaxies of GRB 970508, GRB 980613, GRB 980703, GRB 990123 and GRB 991208 obtained with the 6-m telescope of SAO RAS. The comparison of the broad-band flux spectra of these host galaxies with the template spectral energy distributions (SEDs) of local starburst galaxies of different morphological types shows that the BV RcIc of the hosts are best fitted by the spectral properties of template SEDs of starburst galaxies and that there is a significant internal extinction in these host galaxies. We derived the absolute magnitudes of the GRB host galaxies making use of SEDs for the starburst galaxies. To create theoretical templates we performed the population synthesis modeling of the continuum spectral energy distribution of the host galaxies of GRB 970508 and GRB 980703 using different extinction laws (Cardelli et al. 1989 andCalzetti et al. 2000) and assuming burst and exponential scenarios of star formation. The comparison of BV RcIc broad-band flux spectra with the local starburst galaxies templates and theoretical templates as well as direct estimates (using Balmer emission lines) of the internal extinction shows that it is likely to be of great importance to take into account effects of the internal extinction in the host galaxies. From the energy distribution in the spectrum of the host galaxy of GRB 991208 and from the intensity of their spectral lines (with allowance for the effects of internal extinction) it follows that this is a GRB galaxy with the highest massive star-formation rate of all known GRB galaxies -up to hundreds of solar masses per year. The reduced luminosity of these dusty galaxies (e.g. for the host of GRB 970508 AV ∼ 2 mag, for the host of GRB 980703 AV ∼ 0.6 mag and for the host of GRB 991208 AV ∼ 2 mag) could explain the observational fact (it results independently from our BV RcIc photometry and from calculated spectral distribution for the subset of galaxies having been observed with the 6-m telescope): none of the observed GRB host galaxies with known distances is brighter than the local galaxies with the luminosity L * (where L * is the "knee" of the local luminosity function).

Abstract. We report on deep UBVRI-imaging of the field of the 17.3 Myr radiopulsar PSR B0950+08 obtained with the ESO/VLT/FORS1. Firm detection of the candidate pulsar optical counterpart in the BVRI bands with the magnitudes B = 27.06 ± 0.35, V = 27.05 ± 0.15, R c = 26.49 ± 0.10 and I c = 26.20 ± 0.17 enabled us to study, for the first time, the broadband spectrum of the object. The derived ∼0. 24 offset of the object from the radiopulsar position is insignificant within the 0. 21 uncertainties of our astrometry and ∼0. 75 seeing value during the observations. The positional coincidence and unusual colors of the candidate ensure us that we likely detect the optical emission from PSR B0950+08. The optical-near-UV spectrum of the pulsar has a negative slope and can be fitted by a power law F ν ∝ ν −α with α = 0.65 ± 0.40, suggesting nonthermal emission. Within errors the optical flux is consistent with the power law fit of the ROSAT spectrum from the X-ray counterpart. We analyze our results together with the available multiwavelength data on other isolated pulsars of different ages detected in the optical range and find a significant correlation between their optical and 2-10 keV X-ray luminosities. This implies an origin of the nonthermal emission in both spectral domains. These objects show a significantly non-monotonic evolution of the efficiency of the optical-X-ray photon production from the pulsar spindown power, with a pronounced minimum at the beginning of the middle-age epoch and comparably high efficiencies of younger and older pulsars. This suggests different sensitivities of the photon production processes to the Goldreich-Julian current in magnetospheres of different age pulsars.

We present photometry and spectroscopy of the Type IIP supernova (SN IIP) 2009bw in UGC 2890 from a few days after the outburst to 241 d. The light curve of SN 2009bw during the photospheric phase is similar to that of normal SNe IIP but with a brighter peak and plateau ( mag,  mag). The luminosity drop from the photospheric to the nebular phase is one of the fastest ever observed, ∼2.2 mag in about 13 d. The radioactive tail of the bolometric light curve indicates that the amount of ejected 56Ni is ≈0.022 M⊙. The photospheric spectra reveal high‐velocity lines of Hα and Hβ until about 105 d after the shock breakout, suggesting a possible early interaction between the SN ejecta and pre‐existent circumstellar material, and the presence of CNO elements. By modelling the bolometric light curve, ejecta expansion velocity and photospheric temperature, we estimate a total ejected mass of ∼8–12 M⊙, a kinetic energy of ∼0.3 foe and an initial radius of ∼3.6–7 × 1013 cm.