PKS 1424+240: yet another masquerading BL Lac object as a possible
  IceCube neutrino source
  We show that the blazar PKS 1424+240, which has been recently associated by
IceCube with a neutrino excess at the $3.3\,\sigma$ level together with three
other sources, is similar to the first plausible non-stellar neutrino source,
TXS 0506+056, in being also a masquerading BL Lac object, i.e., intrinsically a
flat-spectrum radio quasar with hidden broad lines and a standard accretion
disk. We point out that these two sources share other properties, including
spectral energy distribution, high powers, parsec scale properties, and
possibly radio morphology. We speculate that the relatively rare combination of
proton-loaded jets, possibly typical of high-excitation sources, and efficient
particle acceleration processes, related to their relatively high synchrotron
peak frequencies, might favour neutrino production in these two sources. GB6
J1542+6129, which has also recently appeared twice in a list of IceCube
associations, seems also to belong to this rare blazar sub-class, which
includes at most ~ 20 Fermi-4LAC blazars.
