We have tended Event Histogram mode in order to characterize the ACIS response. Two distinctive data are tended. One is data where ACIS is exposed to an external source, and the other is data where ACIS is seeing a background.

When HRC-S is located at the focal point (sim position:+250.1 mm: -100800 - -98400 motor steps), ACIS is exposed to the external source. When this happens, ACIS observes Al K alpha, Mn K alpha, and Ti K alpha lines. Whenever this happens, we collected histogram mode data, and fit a Gaussian profile to each peak, and find out a peak position, a peak width, and a count rate. The peak portion is recoded in ADU (bin position), the peak width is FWHM and in ADU, the count rate is counts/sec (each histogram file typically contains 1650 frames or 5,348 sec).

There are also two different data sets in this histogram mode. One was obtained from CCD row positions 21-221, and the other are the row positions 801-1001. Since charges travel more in the latter, the peaks are more spread compared to the former cases.

When HRC-I is located at the focal point (sim position:+127.0 mm: -51700 - -49300 motor steps), ACIS is seeing a background. Since there are not enough counts per observation, and there are not many HRC-I observations, we did not create trend plots, but we created a composite background plot for each CCD, Node, and CCD row. The bin size for the background is 40 ADU so that there are 100 bins in the plot, and count rate is counts/second.

The following table contains:
1. CCD Name and row sampled
2. Trends of Peak Positions in ADU against Time (DOT). Three peaks (Mn, Al, and Ti) are plotted separately. Each point is from one histogram observation (~5,340 sec observation). No error is estimated.
3. Trends of Peak Widths (FWHM) in ADU against Time (DOT).
4. Trends of Peak Counts in Counts/sec against Time (DOT).
5. Trends of Background Count Rates in Counts/sec against Time (DOT). Counts are taken for each histogram observation, and each bin size is 500 (ADU). There are 8 separate plots.
6. Composite Background Plots. A bin size is 40 ADU and there are 100 bins in the plots.

Note: For the background, we used the entire range, instead of 201-401 or 801-1001.

Reference:
http://asc.harvard.edu/cal/Acis/Cal_prods/bkgrnd/current/background.html
Using C handra Level 0 Event Histogram Files to Characterize the High-Energy Particle Background (PS file)
Biller, B., Plucinsky, P., Edgar, R. 01/22/02

Fitting Results