  Magnetars are a special kind of neutron stars. There may also be accreting
magnetars. From the studies of isolated magnetars, it is known that a neutron
star with a strong dipole field only is not a magnetar. Super-slow X-ray
pulsars may just be accreting high magnetic field neutron stars. The
ultra-luminous X-ray pulsar NuSTAR J095551+6940.8 may be an accreting magnetar.
It may be an accreting low magnetic field magnetar with multipole field of
10^14 G and dipole field of 10^12 G. This point of view is consistent with the
study of isolated magnetars. An ultra-luminous X-ray pulsar phase in the binary
evolution may result in massive millisecond pulsars.
