  We present results of a search for late-time radio emission and Fast Radio
Bursts (FRBs) from a sample of type-I superluminous supernovae (SLSNe-I). We
used the Karl G. Jansky Very Large Array to observe ten SLSN-I more than 5
years old at a frequency of 3 GHz. We searched fast-sampled visibilities for
FRBs and used the same data to perform a deep imaging search for late-time
radio emission expected in models of magnetar-powered supernovae. No FRBs were
found. One SLSN-I, PTF10hgi, is detected in deep imaging, corresponding to a
luminosity of $1.2\times10^{28}$ erg s$^{-1}$. This luminosity, considered with
the recent 6 GHz detection of PTF10hgi in Eftekhari et al (2019), supports the
interpretation that it is powered by a young, fast-spinning ($\sim$ ms spin
period) magnetar with $\sim$ 15 Msun of partially ionized ejecta. Broadly, our
observations are most consistent with SLSNe-I being powered by neutron stars
with fast spin periods, although most require more free-free absorption than is
inferred for PTF10hgi. We predict that radio observations at higher frequencies
or in the near future will detect these systems and begin constraining
properties of the young pulsars and their birth environments.
