Deceptively cold dust in the massive starburst galaxy GN20 at z~4 by Cortzen, I, Magdis, GE, Valentino, F, Daddi, E, Liu, D, Rigopoulou, D, Sargent, M, Riechers, D, Cormier, D, Hodge, JA, Walter, F, Elbaz, D, Béthermin, M, Greve, TR, Kokorev, V, Toft, S