MGAB-V258 possible superoutburst YYYYMMDD(UT) mag observer 20210823.4701 19.445zg (Zwicky Transient Facility Lasair (Masci+ 2019)) 20210825.4670 20.335zr (Zwicky Transient Facility Lasair (Masci+ 2019)) 20210827.4496 20.419zg (Zwicky Transient Facility Lasair (Masci+ 2019)) 20210827.4498 20.419zg (Zwicky Transient Facility Lasair (Masci+ 2019)) 20210902.4561 17.734zg (Zwicky Transient Facility Lasair (Masci+ 2019)) 20210902.4838 17.537zr (Zwicky Transient Facility Lasair (Masci+ 2019)) 20210904.4502 17.657zg (Zwicky Transient Facility Lasair (Masci+ 2019)) 20210904.4504 17.657zg (Zwicky Transient Facility Lasair (Masci+ 2019))