Count rates

These count rates were measured by the UVOT Safety Circuit as the super-high countrates discussed don't make it through to the DPU's data products. Counts above a rate of 200 000 count/s are discarded before entering the DPU and can make images appear to have a darker top half.

Count rates in each filter (showing effect of Earth background)

filters
This plot shows all the recorded count rates for each filter. The data come from the safety circuit RateOp from 2005 day 200 to 2006-02-20. The clear rise in count rates to the left shows the effect of the bright Earth (sometimes the Earth limb is dark so there is no rise).


V filter

V


B filter

B


U filter

B


UVW1 filter

B


UVW2 filter

B


UVM2 filter

B


Grism1 UV

Grism1 UV


Grism2 Vis

Grism2 V


White filter

White


Record breaker

The highest count rate ever was 513822 count/s (359676 count in 0.7s) seen at about 14:41 in this plot angles
originally here on msslje. This was a bump in count rate seen in the V filter (a slow flash). The count rate went from 30 000 to a huge 500 000 count/s for about a minute.

Opinion

The count rate is seen many times to rise above the 200 000 count/s "maximum allowed" because of scattered light from the bright Earth limb and from the mysterious bright spikes and bumps in count rate. The bright spikes can sometimes cause unexplained safety circuit trips. The ramp up to the left of the graphs is caused by the Earth light and the high single points are caused by bright flashes lasting 0.5s or bright bumps lasting 50s. A few may be due to data aretfacts (bad quality data received on the ground).

The detector and (Data Capture Interface) DCI start losing events above 200 000 count/s. The DPU starts discarding frames above 50 000 to 100 000 count/s depending on observing mode. Any images taken with a real count rate above 50 000 count/s and certainly above 200 000 count/s may be misleading as events are discarded without warning. This must happen often in the grisms and the white filter.