  The upcoming radio interferometer Square Kilometre Array is expected to
directly detect the redshifted 21-cm signal from the Cosmic Dawn for the first
time. In this era temperature fluctuations from X-ray heating of the neutral
intergalactic medium can impact this signal dramatically. Previously, in (Ross
et al, 2017), we presented the first large-volume, 244 $h^{-1}$Mpc = 349 Mpc a
side, fully numerical radiative transfer simulations of X-ray heating. This
work is a follow-up where we now also consider QSO-like sources in addition to
high mass X-ray binaries. Images of the two cases are clearly distinguishable
at SKA1-LOW resolution and have RMS fluctuations above the expected noise. The
inclusion of QSOs leads to a dramatic increase in non-Gaussianity of the
signal, as measured by the skewness and kurtosis of the 21-cm signal. We
conclude that this increased non-Gaussianity is a promising signature of early
QSOs.
