  High-energy neutrino flares are interesting prospective counterparts to
photon flares, as their detection would guarantee the presence of accelerated
hadrons within a source, provide precious information about cosmic-ray
acceleration and interactions, and thus impact the subsequent modeling of
non-thermal emissions in explosive transients. In these sources, photomeson
production can be efficient, producing a large amount of secondary particles,
such as charged pions and muons, that decay and produce high-energy neutrinos.
Before their decay, secondary particles can experience energy losses and
acceleration, which can impact high-energy neutrino spectra and thus affect
their detectability. In this work, we focus on the impact of secondary
acceleration. We consider a one zone model, characterized mainly by a
variability timescale $t_{\rm var}$, a luminosity $L_{\rm bol}$, a bulk Lorentz
factor $\Gamma$. The mean magnetic field $B$ is deduced from these parameters.
The photon field is modeled by a broken power-law. This generic model allows to
evaluate systematically the maximum energy of high-energy neutrinos in the
parameter space of explosive transients, and shows that it could be strongly
affected by secondary acceleration for a large number of source categories. In
order to determine the impact of secondary acceleration on the high-energy
neutrino spectrum and in particular on its peak energy and flux, we complement
these estimates by several case studies. We show that secondary acceleration
can increase the maximum neutrino flux, and produce a secondary peak at the
maximum energy in the case of efficient acceleration. Secondary acceleration
could therefore enhance the detectability of very-high-energy neutrinos, that
will be the target of next generation neutrino detectors such as KM3NeT,
IceCube-Gen2, POEMMA or GRAND.
