GX Cas superoutburst YYYYMMDD(UT) mag observer 20171215.7667 <140 (Jose Ripero) 20171215.824 <147 (Gary Poyner) 20171216.612 131 (Hiroyuki Maehara) 20171216.7417 132 (Eddy Muyllaert) 20171216.7639 <140 (Jose Ripero) 20171217.533 131 (Hiroyuki Maehara)