# What does less than one count from an x-ray detector mean? (Swift BAT detector)

I'm reading a paper about a recent x-ray burst from a suspected magnetar (A. Dai et al 2016) where they show a light curve of a burst that lasted about 10ms. (Their figure 1). The value of count rate for the peak of the burst from the graph is $6\text{ counts/s}$ over a timespan of less than $0.01s$. This corresponds to about $6*0.01=0.06 \text{ counts}$ for that time period. What does this mean? Is it not counts of photons? What is 0.06 photons? Is there a step in the data analysis I'm missing? (Fig. 1 Swift/BAT mask-weighted light curves in different energy bands)

• An average rate in counts per second hardly needs to be integral! – Carl Witthoft Oct 3 '16 at 12:38
• @CarlWitthoft I don't follow, how do you mean? – zeitoon Oct 13 '16 at 19:52
• Try it: take 100 random integer samples and calculate the mean value. Odds are it'll be a non-integer value. – Carl Witthoft Oct 13 '16 at 19:53
• Oh yes, I understand that, but my problem with 0.06 counts isn't that it's non-integer but that it's less than 1. If less than a single photon was detected in some 2ms time bin what was actually detected? Rob's answer below helped me answer that. When you said "integral" I thought "sum over total time span" rather than "integer" – zeitoon Oct 13 '16 at 19:55