  We conducted a deep XMM$\unicode{x2013}$Newton observing campaign on the
23.5-s radio pulsar PSR J0250+5854 in order to better understand the connection
between long-period, radio-emitting neutron stars and their
high-energy-emitting counterparts. No X-ray emission was detected resulting in
an upper limit in the bolometric luminosity of PSR J0250+5854 of $<$10$^{31}$
erg s$^{-1}$ for an assumed blackbody with a temperature of 85 eV, typical of
an X-ray Dim Isolated Neutron Star (XDINS). We compared the upper limit in the
bolometric luminosity of PSR J0250+5854 with the known population of XDINSs and
found that the upper limit is lower than the bolometric luminosity of all but
one XDINS. We also compared PSR J0250+5854 with SGR 0418+5729, the magnetar
with low dipole magnetic field strength, where the upper limit suggests that if
PSR J0250+5854 has a thermal hot spot like SGR 0418+5729, it would have a
blackbody temperature of $<$200 eV, compared to 320 eV of the magnetar.

High Energy Astrophysical Phenomena