  Strongly-magnetized ($B\geq10^{12}$ G) accreting neutron stars (NSs) are
prime targets for studying the launching of jets by objects with a solid
surface; while classical jet-launching models predict that such NSs cannot
launch jets, recent observations and models argue otherwise. Transient Be/X-ray
binaries (BeXRBs) are critical laboratories for probing this poorly-explored
parameter space for jet formation. Here, we present the coordinated monitoring
campaigns of three BeXRBs across four outbursts: giant outbursts of SAX
2103.5+4545, 1A 0535+262, and GRO J1008-57, as well as a Type-I outburst of the
latter. We obtain radio detections of 1A 0535+262 during ten out of twenty
observations, while the other targets remained undetected at typical limits of
$20$-$50$ $\mu$Jy. The radio luminosity of 1A 0535+262 positively correlates
with its evolving X-ray luminosity, and inhabits a region of the $L_X$-$L_R$
plane continuing the correlation observed previously for the BeXRB Swift
J0243.6+6124. We measure a BeXRB $L_X$-$L_R$ coupling index of $\beta = 0.86
\pm 0.06$ ($L_R \propto L_X^\beta$), similar to the indices measured in NS and
black hole low-mass X-ray binaries. Strikingly, the coupling's $L_R$
normalisation is $\sim 275$ and $\sim 6.2\times10^3$ times lower than in those
two comparison samples, respectively. We conclude that jet emission likely
dominates during the main peak of giant outbursts, but is only detectable for
close-by or super-Eddington systems at current radio sensitivities. We discuss
these results in the broader context of X-ray binary radio studies, concluding
that our results suggest how supergiant X-ray binaries may host a currently
unidentified additional radio emission mechanism.

High Energy Astrophysical Phenomena