Detection of Short Fading Episodes in Two Dwarf Novae from VSNET Observations

From the observations reported to VSNET, we detected short fading episodes in two dwarf novae, RX And (orbital period 5.0 hr) and SU UMa (orbital period 1.8 hr). The episodes in RX And can be naturally explained as the response to a short-term reduction of the mass-transfer rate. A qualitative comparison with VY Scl-type fadings is also discussed. In SU UMa, the same explanation is expected to be more difficult to apply. The viable, but still poorly understood, possibilities include the temporary reduction of quiescent disk viscosity and the temporary reduction of mass-transfer rate. If the latter possibility is confirmed, we probably need a different mechanism from that of VY Scl-type stars.