Observations of the binary accreting pulsar VELA X-1 with the SIGMA telescope

The high mass binary pulsar Vela X-1 has been observed 15 times by the SIGMA imaging telescope during 1990-1994. The source reached a maximum luminosity in the 30-60 keV range of 8 10(35) erg s(-1) (assuming d = 2 kpc) during a flare lasting 6 hours on June 1(st), 1992. Periodic flux variations with a period of nearly 284 s. have been detected during this flare. By summing all the observations, we have also detected the source with a 30 - 60 keV luminosity of 10(35) erg s(-1). The spectrum recorded during the two states are both well fitted by a power law of index -3.5 between 30 and 60 keV.