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Search for "memory" effects as a potential cause of background events
Motivation : the "track" found by Dave Lumb (e-mail Nov. 24, 2000) All pattern 0 events

Was found to be the sum of "pieces of track" in consecutive frames :

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Question : can there be pattern 0 events delayed after a cosmic-ray hit ?

EPIC Cal.Ops. Meeting - ESA/HQ Feb.7-8, 2001

Philippe Ferrando CEA/SAp


Strategy
· Use observation in closed position with high EMDH threshold · Use pattern 31 events as cosmic-ray position indicators · Look for correlation between pattern 0 and pattern 31 events in consecutive frames

Data
· · · · · Observation in orbit 39 (99711101, exposure 9) 53 ks of data CCD 1 and CCD 2 with EMDH threshold at 32767 (instead of 4095) CCD 1 analysed About 1 million events, 800,000 pattern 31

EPIC Cal.Ops. Meeting - ESA/HQ Feb.7-8, 2001

Philippe Ferrando CEA/SAp


Selection cuts - on energy only
Pattern 0 spectrum Pattern 31 spectrum

Only events with E1 > 1000 ADU kept 9629 events, out of 155,321 total for 20,238 frames

Events with E1+E2 > 4000 ADU kept (751 85 4 evts) N.B. : 96 % of pattern 31 events are above the nominal EMDH high threshold

EPIC Cal.Ops. Meeting - ESA/HQ Feb.7-8, 2001

Philippe Ferrando CEA/SAp


Pattern 31 distribution in the same frame

· Clustering of events within a few pixels, showing that in a large number of cases there are more than 1 pattern 31 event per cosmicray track · Otherwise, at large distances, the distribution is consistent with homogeneous hits on the chip

EPIC Cal.Ops. Meeting - ESA/HQ Feb.7-8, 2001

Philippe Ferrando CEA/SAp


Pattern 0 versus pattern 31 in same frame

· No correlation at all between pattern 0 and pattern 31 positions · Fully consistent with homogeneous distribution of events

EPIC Cal.Ops. Meeting - ESA/HQ Feb.7-8, 2001

Philippe Ferrando CEA/SAp


Pattern 0 versus pattern 31 in consecutive frames

· No correlation at all between pattern 0 and pattern 31 positions · Fully consistent with homogeneous distribution of events

EPIC Cal.Ops. Meeting - ESA/HQ Feb.7-8, 2001

Philippe Ferrando CEA/SAp


Conclusions

There is no evidence for any memory effect from one frame to the next one...

EPIC Cal.Ops. Meeting - ESA/HQ Feb.7-8, 2001

Philippe Ferrando CEA/SAp