are highly likely to be separated by one orbital period. Measurement of such “recurrence times” was done by folding the dates of significant detections on a range of trial periods, and selecting the period that produced the minimum scatter in phase. This is similar to taking the mean separation of outbursts, but includes multiple data-points for each outburst, and accounts for the fact that we do not know the date of outburst-maximum very well, due to sparse sampling. The uncertainty is calculated by multiplying the minimum standard deviation in phase by the best period. We term this method “simple timing analysis” (STA). Given the small number of points available (typically 4-20), STA results are a “best estimate" only.

In other cases (e.g. AX J 0051.6-7311, see Figure \[fig:172amp\]) the long-term lightcurve contains many detections of the pulsar on dates that do not form an obvious periodic sequence. The explanations include X-ray emission that is genuinely aperiodic, as well as missed outbursts which could hide an underlying periodic pattern. These cases were analyzed with both PDM and STA and the most likely periods or recurrence times reported, in order to provide a guide for other observers.

Finally a few systems (e.g. 