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   71035
   Characteristics of the accretion flow at very low accretion rate is
   poorly understood yet. It is often considered that advection dominated
   accretion flow (ADAF) is realized as indicated by the observation of
   black hole transients in quiescence. However, low level X-ray emission
   from neutron star transients in quiescence seems to contradict to the
   idea of ADAF. We propose an observation of SAX J1808.4-3658, which is
   the only accretion-powered millisecond pulsar (P=2.49 msec).
   Observation of the pulsation in quiescence enables us to probe the
   accretion flow at very low accretion rate.
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