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   72111
   We propose a 200ks ASCA observation of the low-luminosity AGN NGC4258
   which we plan to make simultaneous with RXTE observations. This object
   has become the test-bed of the so-called `Strong ADAF Principle' which
   states that an accretion disk will always be an Advection Dominated
   Accretion Flow (ADAF) if the mass accretion rate is below a critical
   value. Our joint ASCA/RXTE data will allow us to search for a broad
   iron line in the X-ray spectrum of NGC4258. The detection of any such
   line will point to the presence of a cold, radiatively efficient
   accretion disk rather than a hot advective flow and provide a firm
   counter-example to the Strong ADAF Principle. This is of fundamental
   importance to our understanding of accretion disk physics.
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