Fast Luminous Blue Transients in the Reionization Era and Beyond
  To determine the epoch of reionization precisely and to reveal the property
of inhomogeneous reionization are some of the most important topics of modern
cosmology. Existing methods to investigate reionization which use cosmic
microwave background, Ly$\alpha$ emitters, quasars, or gamma ray bursts, have
difficulties in terms of accuracy or event rate. We propose that recently
discovered fast luminous blue transients (FLBTs) have a potential as a novel
probe of reionization. We study the detectability of FLBTs at the epoch of
reionization with upcoming WFIRST Wide-Field Instruments (WFI), using a star
formation rate derived from galaxy observations and an event rate of FLBTs
proportional to the star formation rate. We find that if FLBTs occur at a rate
of 1\% of the core-collapse supernova rate, 2 (0.3) FLBTs per year per deg$^2$
at $z>6$ ($z>8$) can be detected by a survey with a limiting magnitude of 26.5
mag in the near-infrared band and a cadence of 10 days. We conclude that the
WFIRST supernova deep survey can detect $\sim20$ FLBTs at the epoch of
reionization in the near future.
