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Date submitted: 14-Dec-1997
12/14/97 LWA ORBIT VARIATION OF DARK SIGNAL IN DECEMBER 1997 The purpose of this test was to verify that the SXT dark signal variation with time past sunrise (FMS = first minute of sun) still has the properties reported in show_pix/calibration/FMS_DARSIGNAL_CHANGE show_pix/calibration/Orbit_Dark_Variation_1991 show_pix/calibration/Orbital_Dark_Variation show_pix/calibration/Orbit_Dark_Changes show_pix/calibration/orbit_dark_variation The data, acquired between (first, last) = ' 2-DEC-97 00:24:51', '12-DEC-97 16:22:53' All images are AlMg darkframes with DPE=2 or DPE=27. The data acquired between (first, last) = ' 5-DEC-97 18:13:42', ' 5-DEC-97 19:12:24' happened to be acquired in an orbit without any UV flood, providing a useful control sample. These are indicated in the figures with triangles and asterisks. ****They have had 10.5 added to their value for convenience in plotting.**** The physical effect causing the strong decrease in dark current is charge released from traps over a period of time after "charging" by the UV flood. The smaller variation, indicated by the diamonds, may be caused by thermal effect(?). The turn-up at sunset was noted in earlier studies. The two upper plots demonstrate that the effect is stronger in the moderately radiation damaged region. However, the old correction curve is adequate for adjusting these data. The underestimate of the central dark signal if the correction is based upon the whole CCD is less than 2 percent.. The correction formula given in Orbital_Dark_Variation is normalized to the dark current signal at FMS=30. Finally, it is important to note that only the dark current changes. The read noise must be subtracted off before the correction curve is applied.