Simultaneous BeppoSAX and RXTE observations of the X-ray burst sources GX 3+1 and Ser X-1 T. Oosterbroek, D. Barret, M. Guainazzi and E. C. Ford A&A, 366 1 (2001) 138-145 Published online: 15 January 2001 DOI: 10.1051/0004-6361:20000028