Rotation, pulsations and outbursts in the Be star v Cygni (HD 202904)

nu Cyg is a Be star that shows variations at all timescales. We monitored its spectrum for several years from 1998 to 2004 and, in particular, during a spectroscopic multisite campaign in 2000. In this paper we present and analyse the data. We observed several outbursts including an intense one in 2000. Moreover, we found several periods of short-term variations, including two frequencies at 2.95 and 2.6 c d(-1), which are well reproduced by models of non radial pulsations with a retrograde mode with l = 3 and m = 3 and a zonal mode with l = 3 or 4 and m = 0, respectively. The stellar rotation is probably also identified at f similar to 1.5 c d(-1), which is coherent with the rotation frequency deduced from our determination of stellar parameters. The peak-to-peak amplitude of variations also seems to vary in time, maybe due to a beating effect between close frequencies, but the resolution in time of our data does not allow us to separate such close frequencies. Finally, a longer timescale variation may be present, with a period around 11 years, which could be associated with a binary companion.