New constraints on Lyman-{\alpha} opacity with a sample of 62 quasars at
  z > 5.7
  We present measurements of the mean and scatter of the IGM Lyman-{\alpha}
opacity at 4.9 < z < 6.1 along the lines of sight of 62 quasars at z > 5.7, the
largest sample assembled at these redshifts to date by a factor of two. The
sample size enables us to sample cosmic variance at these redshifts more
robustly than ever before. The spectra used here were obtained by the SDSS,
DES-VHS and SHELLQs collaborations, drawn from the ESI and X-Shooter archives,
reused from previous studies or observed specifically for this work. We measure
the effective optical depth of Lyman-{\alpha} in bins of 10, 30, 50 and 70 cMpc
h-1, construct cumulative distribution functions under two treatments of upper
limits on flux and explore an empirical analytic fit to residual Lyman-{\alpha}
transmission. We verify the consistency of our results with those of previous
studies via bootstrap re-sampling and confirm the existence of tails towards
high values in the opacity distributions, which may persist down to z = 5.2.
Comparing our results with predictions from cosmological simulations, we find
further strong evidence against models that include a spatially uniform
ionizing background and temperature-density relation. We also compare to IGM
models that include either a fluctuating UVB dominated by rare quasars or
temperature fluctuations due to patchy reionization. Although both models
produce better agreement with the observations, neither fully captures the
observed scatter in IGM opacity. Our sample of 62 z > 5.7 quasar spectra opens
many avenues for future study of the reionisation epoch.
