We report on observations of the unusual neutron-star binary system FIRST J102347.6+003841 ( catalog FIRST~J102347.6+003841 ) carried out using the XMM-Newton satellite .
This system consists of a radio millisecond pulsar in an 0.198 -day orbit with a \sim 0.2 M _ { \sun } Roche-lobe-filling companion , and appears to have had an accretion disk in 2001 .
We observe a hard power-law spectrum ( \Gamma = 1.26 ( 4 ) ) with a possible thermal component , and orbital variability in X-ray flux and possibly hardness of the X-rays .
We also detect probable pulsations at the pulsar period ( single-trial significance \sim 4.5 \sigma from an 11 ( 2 ) \% modulation ) , which would make this the first system in which both orbital and rotational X-ray pulsations are detected .
We interpret the emission as a combination of X-rays from the pulsar itself and from a shock where material overflowing the companion meets the pulsar wind .
The similarity of this X-ray emission to that seen from other millisecond pulsar binary systems , in particular PSR J0024-7204w ( catalog 47~Tuc~W ) ( PSR J0024 - 7204W ) and PSR J1740-5340 ( catalog PSR~J1740 $ - $ 5340 ) , suggests that they may also undergo disk episodes similar to that seen in J1023 in 2001 .