Probing the environment of high-z quasars using the proximity effect in
  projected quasar pairs
  We have used spectra of 181 projected quasar pairs at separations $\le 1.5$
arcmins from the Sloan Digital Sky-Survey Data Release 12 in the redshift range
of 2.5 to 3.5 to probe the proximity regions of the foreground quasars. We
study the proximity effect both in the longitudinal as well as in the
transverse directions, by carrying out a comparison of the \lya absorption
lines originating from the vicinity of quasars to those originating from the
general inter-galactic medium at the same redshift. We found an enhancement in
the transmitted flux within 4 Mpc to the quasar in the longitudinal direction.
However, the trend is found to be reversed in the transverse direction. In the
longitudinal direction, we derived an excess overdensity profile showing an
excess up to $r\leq 5$ Mpc after correcting for the quasar's ionization, taking
into account the effect of low spectral resolution. This excess overdensity
profile matches with the average overdensity profile in the transverse
direction without applying any correction for the effect of the quasar's
ionization. Among various possible interpretations, we found that the
anisotropic obscuration of the quasar's ionization seems to be the most
probable explanation. This is also supported by the fact that all of our
foreground quasars happen to be Type-I AGNs. Finally, we constrain the average
quasar's illumination along the transverse direction as compared to that along
the longitudinal direction to be $\leq$27\% (3$\sigma$ confidence level).
