Exploring the epoch of hydrogen reionization using FRBs
  We describe three different methods for exploring the hydrogen reionization
epoch using fast radio bursts (FRBs) and provide arguments for the existence of
FRBs at high redshift (z). The simplest way, observationally, is to determine
the maximum dispersion measure (DM$_{\rm max}$) of FRBs for an ensemble that
includes bursts during the reionization. The DM$_{\rm max}$ provides
information regarding reionization much like the optical depth of the CMB to
Thomson scattering does, and it has the potential to be more accurate than
constraints from Planck, if DM$_{\rm max}$ can be measured to a precision
better than 500 $\mbox{pc cm}^{-3}$. Another method is to measure redshifts of
about 40 FRBs between z of 6-10 with$\sim10\%$ accuracy to obtain the average
electron density in 4 different z-bins with $\sim4\%$ accuracy. These two
methods don't require knowledge of the FRB luminosity function and its possible
redshift evolution. Finally, we show that the reionization history is reflected
in the number of FRBs per unit DM, given a fluence limited survey of FRBs that
includes bursts during the reionization epoch; we show using FIRE simulations
that the contributions to DM from the FRB host galaxy $\&$ CGM during the
reionization era is a small fraction of the observed DM. This third method
requires no redshift information but does require knowledge of the FRB
luminosity function.
