NSV 4618 superoutburst YYYYMMDD(UT) mag observer 20200416.4461 <138c (Yutaka Maeda) 20200417.2090 16.308zg (Zwicky Transient Facility Lasair (Masci+ 2019)) 20200420.600 136 (Rod Stubbings) and NSV 4618 200424.537 132 Stu.RASNZ superoutburst