Periodic Modulation of the X-ray Flux from Four Galactic X-ray sources White, N. E. ; Huckle, H. E. ; Mason, K. O. ; Charles, P. A. ; Pollard, G. ; Culhane, J. L. ; Sanford, P. W. Abstract Publication: Bulletin of the American Astronomical Society Pub Date: June 1976 Bibcode: 1976BAAS....8Q.441W