Detection of X-ray pulsations from the Be/X-ray transient A 0535+26 duringa disc loss phase of the primary

Using the RossiXTE experiment, we detect weak Xray emission from the recurr ent Be/X-ray transient A 0535+26 at a time when the optical counterpart V72 5 Tau displayed Her in absorption, indicating the absence of a circumstella r disc. The X-ray radiation is strongly modulated at the 103.5-s pulse peri od of the neutron star, confirming that it originates from A 0535+26. The s ource is weaker than in previous quiescence detections by two orders of mag nitude and should be in the centrifugal inhibition regime. We show that the X-ray luminosity cannot be due to accretion on to the magnetosphere of the neutron star. Therefore this detection represents a new state of the accre ting pulsar. We speculate that the X-ray emission can be due to some matter leaking through the magnetospheric barrier or thermal radiation from the n eutron star surface due to crustal heating. The observed luminosity is prob ably compatible with recent predictions of thermal radiation from X-ray tra nsients in quiescence. The detection of the X-ray source in the inhibition regime implies a reduced density in the outflow from the Be companion durin g its disc-less phase.