Erratic profiles of type II bursts of very low fluence from the Rapid Burster

During ∼17 hr of EXOSAT observations of the Rapid Burster in 1985 September about 541 type II bursts were observed which lasted less than ∼30 s. These bursts have an approximately time-invariant profile, showing successive peaks (ringing) in the decay portion of the burst. However, most of the ∼20 bursts at the extreme low end of the fluence distribution have different profiles. In these low-fluence bursts the valleys between the peaks (in the ringing) are deeper than in bursts of higher fluence though the location of the peaks, in comparison with the time-invariant profile, remains approximately the same. For the bursts with the lowest fluences the profile can become erratic, showing a series of flares.