A Potential Cyclotron Resonant Scattering Feature in the ULX Pulsar NGC
  300 ULX1 seen by NuSTAR and XMM-Newton
  Based on phase-resolved broadband spectroscopy using $XMM$-$Newton$ and
$NuSTAR$, we report on a potential cyclotron resonant scattering feature at $E
\sim 13$ keV in the pulsed spectrum of the recently discoverd ULX pulsar NGC
300 ULX1. If this interpretation is correct, the implied magnetic field of the
central neutron star is $B \sim 10^{12}$ G (assuming scattering off electrons),
similar to that estimated from the observed spin-up of the star, and also
similar to known Galactic X-ray pulsars. We discuss the implications of this
result for the connection between NGC 300 ULX1 and the other known ULX pulsars,
particularly in light of the recent discovery of a likely proton Cyclotron line
in another ULX, M51 ULX-8.
