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Many X-ray accreting pulsars have a soft excess below 10 keV. This featurehas been detected also in faint sources and at low luminosity levels,suggesting that it is an ubiquitous phenomenon. In the case of the highluminosity pulsars (Lx > 10^36 erg/s), the fit of this component with thermalemission models usually provides low temperatures (kT < 0.5 keV) and largeemission regions (R > a few hundred km); for this reason, it is referred to asa `soft' excess. On the other hand, we recently found that in persistent,low-luminosity (Lx ~ 10^34 erg/s) and long-period (P > 100 s) Be accretingpulsars the observed excess can be modeled with a rather hot (kT > 1 keV)blackbody component of small area (R < 0.5 km), which can be interpreted asemission from the NS polar caps. In this paper we present the results of arecent XMM-Newton observation of the Galactic Be pulsar RX J0440.9+4431, whichis a poorly studied member of this class of sources. We have found a best-fitperiod P = 204.96(+/-0.02) s, which implies an average pulsar spin-down duringthe last 13 years, with dP/dt ~ 6x10^(-9) s/s. The estimated source luminosityis Lx ~ 8x10^(34) erg/s: this value is higher by a factor < 10 compared tothose obtained in the first source observations, but almost two orders ofmagnitude lower than those measured during a few outbursts detected in thelatest years. The source spectrum can be described with a power law plusblackbody model, with kTbb = 1.34(+/-0.04) keV and Rbb = 273(+/-16) m,suggesting a polar-cap origin of this component. Our results support theclassification of RX J0440.9+4431 as a persistent Be/NS pulsar, and confirmthat the hot blackbody spectral component is a common property of this class ofsources.

XMM-Newton observation of the persistent Be/NS X-ray binary pulsar RX J0440.9+4431