MASTER OT J055845.55+391533.4 superoutburst The 2021 Jan.-Feb. and 2018 Apr. superoutbursts showed a dip and a long rebrightening. YYYYMMDD(UT) mag observer 20210828.8465 <142c (Yutaka Maeda) 20210829.8457 <146c (Yutaka Maeda) 20210830.8308 <162c (Yutaka Maeda) 20210831.8157 <156c (Yutaka Maeda) 20210909.7884 146:cG (Yutaka Maeda) 20210911.1820 14.20cG (Masao Funada)