Sensitivity for 21cm Bispectrum from Epoch of Reionization
  The 21cm line brightness temperature brings rich information about Epoch of
Reionizaton (EoR) and high-$z$ universe (Cosmic Dawn and Dark Age). While the
power spectrum is a useful tool to investigate the EoR signal statistically,
higher-order statistics such as bispectrum are also valuable because the EoR
signal is expected to be highly non-Gaussian. In this paper, we develop a
formalism to calculate the bispectrum contributed from the thermal noise taking
array configularion of telescopes into account, by extending a formalism for
the power spectrum \cite{2006ApJ...653..815M}. We apply our formalism to the
ongoing and future telescopes such as expanded Murchison Widefield Array (MWA),
LOw Frequency ARray (LOFAR) and Square Kilometre Array (SKA). We find that
expanded MWA does not have enough sensitivity to detect the bispectrum signal.
On the other hand, LOFAR has better sensitivity and will be able to detect the
peaks of the bispectrum as a function of redshift at large scales with comoving
wavenumber $k \lesssim 0.03 {\rm Mpc}^{-1}$. The SKA has enough sensitivity to
detect the bispectrum for much smaller scales $k \lesssim 0.3 {\rm Mpc}^{-1}$
and redshift $z \lesssim 20$
