Grazing Eclipsing Dwarf Nova CW Monocerotis: Dwarf Nova-Type Outburst in a Possible Intermediate Polar?

We observed the 2002 October-November outburst of the dwarf nova CW Mon. Theoutburst showed a clear signature of a premaximum halt, and a more rapiddecline after reaching the outburst maximum. On two separate occasions, duringthe premaximum stage and near the outburst maximum, shallow eclipses wererecorded. This finding confirms the previously suggested possibility of thegrazing eclipsing nature of this system. The separate occurrence of theeclipses and the premaximum halt can be understood as a result of a combinationof two-step ignition of an outburst and the inside-out propagation of theheating wave. We detected a coherent short-period (0.02549 d) signal on twosubsequent nights around the optical maximum. This signal was likely presentduring the maximum phase of the 2000 January outburst. We interpret this signalas a signature of the intermediate polar (IP) type pulses. The rather strangeoutburst properties, strong and hard X-ray emission, and the low luminosity ofthe outburst maximum might be understood as consequences of the supposed IPnature. The ratio between the suggested spin period and the orbital period,however, is rather unusual for a system having an orbital period of ~0.176 d.Comment: 11 pages, 11 figures, to appear in PAS