The high-redshift gamma-ray burst GRB140515A
  High-redshift gamma-ray bursts have several advantages for the study of the
distant universe, providing unique information about the structure and
properties of the galaxies in which they exploded. Spectroscopic identification
with large ground-based telescopes has improved our knowledge of the class of
such distant events. We present the multi-wavelength analysis of the high-$z$
Swift gamma-ray burst GRB140515A ($z = 6.327$). The best estimate of the
neutral hydrogen fraction of the intergalactic medium (IGM) towards the burst
is $x_{HI} \leq 0.002$. The spectral absorption lines detected for this event
are the weakest lines ever observed in gamma-ray burst afterglows, suggesting
that GRB140515A exploded in a very low density environment. Its circum-burst
medium is characterised by an average extinction (A$_{\rm V} \sim 0.1$) that
seems to be typical of $z \ge 6$ events. The observed multi-band light curves
are explained either with a very flat injected spectrum ($p = 1.7$) or with a
multi-component emission ($p = 2.1$). In the second case a long-lasting central
engine activity is needed in order to explain the late time X-ray emission. The
possible origin of GRB140515A from a Pop III (or from a Pop II stars with local
environment enriched by Pop III) massive star is unlikely.
