Hydrogen-poor superluminous stellar explosions. by Quimby, R, Kulkarni, SR, Kasliwal, M, Gal-Yam, A, Arcavi, I, Sullivan, M, Nugent, P, Thomas, R, Howell, D, Nakar, E, Bildsten, L, Theissen, C, Law, N, Dekany, R, Rahmer, G, Hale, D, Smith, R, Ofek, E, Zolkower, J, Velur, V, Walters, R, Henning, J, Bui, K, McKenna, D, Poznanski, D