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Several SU UMa-type dwarf novae, in particular, WZ Sge-type stars tend toexhibit rebrightenings after superoutbursts. The rebrightening phenomenon isproblematic for the disk instability theory of dwarf novae since it requires alarge amount of remnant matter in the disk even after superoutbursts. Here, wereport our optical and infrared observations during the first-ever outburst ofa new dwarf nova, SDSS J102146.44+234926.3. During the outburst, we detectedsuperhumps with a period of 0.056281 +/- 0.000015 d, which is typical forsuperhump periods in WZ Sge stars. In conjunction with the appearance of along-lived rebrightening, we conclude that the object is a new member of WZ Sgestars. Our observations, furthermore, revealed infrared behaviors for the firsttime in the rebrightening phase of WZ Sge stars. We discovered prominentinfrared superhumps. We calculate the color temperature of the infraredsuperhump source to be 4600-6400 K. These temperatures are too low to beexplained with a fully-ionized disk appearing during dwarf nova outbursts. Wealso found a Ks-band excess over the hot disk component. These unprecedentedinfrared activities provide evidence for the presence of mass reservoir at theoutermost part of the accretion disk. We propose that a moderately highmass-accretion rate at this infrared active region leads to the long-livedrebrightening observed in SDSS J102146.44+234926.3.

Discovery of a WZ Sge-Type Dwarf Nova, SDSS J102146.44+234926.3: Unprecedented Infrared Activity during a Rebrightening Phase