The variability of MXB 1730 - 335

The behaviour of the burst source MXB 1730 - 335 during an outburst observed by Ariel V in 1977 April is discussed. Departures from the linear relation between burst interval and energy and the way in which this relation changes with the mean intensity of the source are considered. When the time-averaged source intensity is low, bursts are observed which obey the local E-Δt relation. Many quasi-periodic trains of bursts were seen and in view of this it is likely that the 7.8-min modulation seen with Copernicus in 1973 April was the result of an earlier appearance of MXB 1730 - 335. MXB 1730 - 335 was also present in data obtained by Ariel V in 1975 February. An upper limit to a constant underlying source in 1977 April of 3 x 10-10 erg cm-2s-1 in the 2 to 10 keV band (20 per cent of the time-averaged flux) is set. (author)