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Image name: MAR_99_Filter_Failure.png (click image to enlarge)
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Date submitted: 03-Aug-2001
MARCH 1999 ENTRANCE FILTER FAILURE EVENT L. Acton, 3-Aug-2001 The figure demonstrates that the March 1999 entrance filter failure took place during a Yohkoh/SXT data gap. The above curve is the signal in a strip across the bottom of long-exposure AlMg FFIs. The exposures for these images was DPE=19 for QR and DPE=25 for HR. The area summed, after QR images were rebinned to HR, was [1:510,0:50]. The data points with diamonds are from the HR images, showing that there was no HR/QR bias in these data. The images were prepped with /dc_orbit_correct but without leak correction. There is an obvious bifurcation of the straylight signal in these x-ray images both before and after the entrance filter event. The few parameters I've checked, i.e., FMS, pointing, cannot accout for this effect. The lower curve is made from the signal in all useful NB straylight monitor images. It clearly shows the entrance filter failure, too. Because of the paucity of data at this time it is impossible to determine the exact time of filter failure. For SXT data analysis purposes a failure time of 12-Mar-1999 02:00 is a satisfactory time to enter into yo_dates. This time is indicated on the figure by the dotted lines. Until better information is available we should asign a complete sector of 1/12 (0.083) as having opened up at the time of this event for data analysis purposes.