The Observed and Expected Orbital Modulation of TeV γ-Rays from PSR 1957+20 de Jager, C. O. ; Brink, C. ; Raubenheimer, B. C. ; Nel, H. I. ; North, A. R. ; Meintjes, P. J. ; Visser, B. Abstract Publication: 23rd International Cosmic Ray Conference (ICRC23), Volume 1 Pub Date: 1993 Bibcode: 1993ICRC....1..467D