SDSS J172102.48+273301.2 (AM CVn) dip after short superoutburst YYYYMMDD(UT) mag observer 20210831.2081 19.372zg (Zwicky Transient Facility Lasair (Masci+ 2019)) 20210903.2167 16.261zr (Zwicky Transient Facility Lasair (Masci+ 2019)) 20210905.2264 16.557zr (Zwicky Transient Facility Lasair (Masci+ 2019)) 20210905.2765 16.267zg (Zwicky Transient Facility Lasair (Masci+ 2019)) 20210907.1802 18.617zg (Zwicky Transient Facility Lasair (Masci+ 2019))