Predictions for measuring the 21-cm multi-frequency angular power
  spectrum using SKA-Low
  The light-cone (LC) effect causes the mean as well as the statistical
properties of the redshifted 21-cm signal $T_{\rm b}(\hat{\bf n},\nu)$ to
change with frequency $\nu$ (or cosmic time). Consequently, the statistical
homogeneity (ergodicity) of the signal along the line of sight (LoS) direction
is broken. This is a severe problem particularly during the Epoch of
Reionization (EoR) when the mean neutral hydrogen fraction ($\bar{x}_{\rm HI}$)
changes rapidly as the universe evolves. This will also pose complications for
large bandwidth observations. These effects imply that the 3D power spectrum
$P(k)$ fails to quantify the entire second-order statistics of the signal as it
assumes the signal to be ergodic and periodic along the LoS. As a proper
alternative to $P(k)$, we use the multi-frequency angular power spectrum (MAPS)
${\mathcal C}_{\ell}(\nu_1,\nu_2)$ which does not assume the signal to be
ergodic and periodic along the LoS. Here, we study the prospects for measuring
the EoR 21-cm MAPS using future observations with the upcoming SKA-Low.
Ignoring any contribution from the foregrounds, we find that the EoR 21-cm MAPS
can be measured at a confidence level $\ge 5\sigma$ at angular scales $\ell
\sim 1300$ for total observation time $t_{\rm obs} \ge 128\,{\rm hrs}$ across
$\sim 44\,{\rm MHz}$ observational bandwidth. We also quantitatively address
the effects of foregrounds on MAPS detectability forecast by avoiding signal
contained within the foreground wedge in $(k_\perp, k_\parallel)$ plane. These
results are very relevant for the upcoming large bandwidth EoR experiments as
previous predictions were all restricted to individually analyzing the signal
over small frequency (or equivalently redshift) intervals.
