hrcf*_ss0.fitsfile. During level 1 processing, the two 1.0 second samples of the total and valid event scalars for a given HRC science frame are summed and output into the
hrcf*_dtf1.fitsfile in column names
VALID_EVT_COUNT. A count of the telemetered events whose time-tags indicate that they occurred during the 2.0 seconds covered by the scalar is also added to the
PROC_EVT_COUNT. As long as the rate is low enough that we are not telemetry saturated the value of
PROC_EVT_COUNTshould be nearly the same as
VALID_EVT_COUNTsince essentially all the valid events can make it into the on-board FIFO and out in telemetry. This appears to be true for the HRC-I; however, it is not the case for the HRC-S.
There is a significant fraction of events on the HRC-S that are counted as valid by the rate scalar that do not get telemetered. This fraction is a configuration dependent. A good data set to view the difference between the HRC-I and HRC-S and the effect of the HRC-S configuration is a sequence of calibration observations of PSR B0540-69 performed in 2000 June to evaluate possible solutions to the HRC timing problem. Table 1 provides a listing of the observations with the relevant configuration changes.
|Detector||ObsID||Antico Veto||Edge-blank||Specmode||Trigger Level|
Figures 1-3 show the total, valid, and telemetered rates for this sequence of observations. The effect of the detector configuration changes can be seen on the rates: the total rate on the HRC-I drops when the trigger level is raised and it drops on the HRC-S when "imaging-mode is selected and the trigger level raised for Timing mode.
|Figure 1: Total event rate for 2000 June 20-21 observations of PSR B0540-69 using the HRC-I and HRC-S under a variety of configurations. Dashed vertical lines separate the individual observations. The configurations for the longer observations are briefly indicated by text in the plot; see table 1 for details of these and the shorter observations.|
|Figure 2: Valid event rate for 2000 June 20-21 observations of PSR B0540-69. Similar to figure 1.|
|Figure 3: Telemetered event rate for 2000 June 20-21 observations of PSR B0540-69. Similar to figure 1.|
Figure 4 shows the ratio of the telemetered event rate to the reported valid event rate. For the HRC-I, the ratio is near 1.0 as expected for the observed rates; the different appearance of the HRC-I default comfiguration is most likely due to the event time-tagging problem. The ratio on the HRC-S is much different from 1.0 without any noticible change in the rates. Selecting HRC-S imaging mode and/or raising the trigger level moves the ratio closer to 1.0.
|Figure 4: Telemetered/valid event rate for 2000 June 20-21 observations of PSR B0540-69. Note that for the HRC-S a significant fraction of the contributors to the valid event rate do not get telemetered.|
Another possible HRC-S configuration change that we can look at is using the edge-blanking function for the selection of the individual MCP segments. Figure 5 shows the telemetered to valid rate ratio for a series of observations of G21.5-0.9 where this was done. We have performed this test three times and the data shown are for the first instance in 1999 September. The data were slightly affected by flaring in the background but the general result that the three MCP segments differ in the ratio is not significantly affected.
|Figure 5: Comparison of the telemetered/valid event rate among the three HRC-S MCP segments from the 1999 September 5 observations of G21.5-0.9 (ObsIDs 147, 151, and 157). The individual segments were selected using edge-blanking regions.|
The difference here would be yet another useful thing to investigate on the flight-spare detector assembly and POC electronics.
Last modified: Fri Dec 7 12:35:11 EST 2001
Dr. Michael Juda
Harvard-Smithsonian Center for Astrophysics
60 Garden Street, Mail Stop 70
Cambridge, MA 02138, USA
Ph.: (617) 495-7062
Fax: (617) 495-7356