The discovery of quiescent X-ray emission from SAX J1808.4-3658, the   transient 2.5ms pulsar
  We report on a 20 ks BeppoSAX observation of the transient 2.5 ms X-ray pulsar SAX J1808.4-3658 in its quiescent state. A source at a level of ~ 3 x 10^-3 c/s was detected with the BeppoSAX/MECS at a position consistent with that of SAX J1808.4-3658. The inferred 0.5-10 keV luminosity was to that measured from other quiescent low mass X-ray transients hosting an old neutron star. This result is discussed in the light of the propeller and radio pulsar shock emission models for the quiescent emission of these systems. 
L. Stella, S. Campana, S. Mereghetti, D. Ricci and G.L. Israel