High variability in Vela X-1: giant flares and off statesI. Kreykenbohm, J. Wilms, P. Kretschmar, J. M. Torrejón, K. Pottschmidt, M. Hanke, A. Santangelo, C. Ferrigno and R. StaubertA&A, 492 2 (2008) 511-525DOI: https://doi.org/10.1051/0004-6361:200809956
