Photometric observations of an SUUMa-type dwarf nova, VW coronae borealis, during outbursts

We report on photometric observations of an SU UMa-type dwarf nova, VW CrB, during two superoutbursts in 2001 and 2003 and a normal outburst in 2003. Superhumps with a period of 0.07287(1) d were observed during the 2003 superoutburst. The change rate of the superhump period was positive. During a normal outburst, there is some hint of modulation up to a 0.2-mag amplitude. However, no periodicity was found. The recurrence cycles of the normal outburst and the superoutburst, and the distance were estimated to be greater than or equal to 50 d, 270 similar to 500 d, and 690(-170)(+230) pc, respectively. These recurrence cycles are the usual values for an SU UMa-type dwarf nova having this superhump period. The superhump period of VW CrB was the longest among those of SU UMa stars with positive derivatives of the superhump period. The coverage of our observations was, however, not sufficient, and the variation of the P-SH change rate of VW CrB is still unknown. A superhump regrowth and a brightening were seen near the end of the plateau phase. Measuring the deviation of the start timings of the brightening and the superhump regrowth (> 2 days in VW CrB) will be a key to reveal the mechanism of these phenomena.