  The spectra of several X-ray binary pulsars display a clear soft excess,
which in most cases can be described with a blackbody model, above the main
power-law component. While in the high-luminosity sources it is usually
characterized by low temperature (kT < 0.5 keV) and large emission radius (R >
100 km), in the two persistent and low-luminosity pulsars 4U 0352+309 and RX
J0146.9+6121 this component has a high temperature (kT > 1 keV) and a smaller
radius (R < 0.5 km), consistent with the estimated size of the neutron-star
polar cap. Here we report on the timing and spectral analysis of RX
J1037.5-5647, another low-luminosity persistent Be binary pulsar, based on the
first XMM-Newton observation of this source. We have found a best-fit period P
= 853.4(+/-0.2) s, that implies an average pulsar spin-up dP/dt ~ -2E-8 s/s in
the latest decade. The estimated source luminosity is Lx ~ 10^34 erg/s, a value
comparable to that of the other persistent Be binary pulsars and about one
order of magnitude lower than in most of the previous measurements. The source
spectrum can be described with a power law plus blackbody model, with kTbb =
1.26(+0.16/-0.09) keV and Rbb = 128(+13/-21) m, suggesting a polar-cap origin
of this component. These results strengthen the hypothesis that, in addition to
low luminosities and long periods, this class of sources is characterized also
by common spectral properties
