No Persistent Pulsations in Aquila X‐1 As It Fades into Quiescence

We searched for coherent X-ray pulsations from Aql X-1 in a series of RXTEobservations taken shortly after a recent outburst. During the course of theseobservations, Aql X-1 passes through an apparent ``propeller'' phase as itsluminosity fades to its quiescent value. No pulsations were detected, and weplace upper limits (ranging from 0.52% to 9.0%) on the fractional RMS amplitudeof any periodic signal contained in the various data sets searched. This resulthas implications for the geometry of the system, if the quiescent luminosity isdue to continued low-level accretion. Alternatively, our result supports theidea that the quiescent luminosity may be due to thermal emission.Comment: 27 pages, 1 figure; ApJ, accepte