  The radiations from the first luminous sources drive the fluctuations in the
21-cm signal at Cosmic Dawn (CD) via two dominant astrophysical processes i.e.
the Ly$\alpha$ coupling and X-ray heating, making this signal highly
non-Gaussian. The impact of these processes on the 21-cm signal and its
non-Gaussianity vary depending on the properties of these first sources of
light. In this work, we consider different CD scenarios by varying two major
source parameters i.e. the minimum halo mass $M_{\rm h,\, min}$ and X-ray
photon production efficiency $f_{\rm X}$ in a 1D radiative transfer code
GRIZZLY. We study the impact of variation in these source parameters on the
large scale ($k_1 = 0.16 {\, \rm Mpc}^{-1}$) 21-cm bispectrum for all possible
unique triangles in the Fourier domain. Our detailed and comparative analysis
of the power spectrum and bispectrum shows that the shape, sign and magnitude
of the bispectrum combinedly provide the best measure of the signal
fluctuations and its non-Gaussianity compared to the power spectrum. We also
conclude that it is important to study the sequence of sign changes along with
the variations in the shape and magnitude of the bispectrum throughout the CD
history to arrive at a robust conclusion about the dominant IGM processes at
different cosmic times. We further observe that among all the possible unique
$k$-triangles, the large-scale non-Gaussianity in signal is best probed by the
small $k$-triangles in the squeezed limit and by triangles of similar shapes.
This opens up the possibility of constraining the source parameters during the
CD using the 21-cm bispectrum.
