  The origin of ultra-high-energy cosmic rays (UHECRs) remains elusive.
Gamma-ray bursts (GRBs) are among the best candidates able to meet the
stringent energy requirements needed for particle acceleration to such high
energies. If UHECRs were accelerated by the central engine of GRB 221009A, it
might be possible to detect secondary photons and neutrinos as the UHECRs
travel from the source to the Earth. Here we attempt to interpret some of the
early publicly available data connected to this burst. If the reported early
GeV-TeV detection was produced by secondary emission from UHECRs it probably
indicates that UHECRs reached energies $> 10^{21}$ eV and that GRB 221009A
exploded inside a magnetic void with intergalactic magnetic field (IGMF)
strength $B \leq 3 \times 10^{-16}$ G. In order to understand the entire energy
deposition mechanism, we propose to search existing and future Fermi-LAT data
for secondary emission arriving over larger spatial scales and longer
time-scales. This strategy might help clarify the origin of UHECRs, constrain
the intergalactic magnetic field (IGMF) strength along this line of sight and
start to quantify the fraction of magnetic voids around GRBs.
