Comparison of Paradigms

This webpage is to compare the results of applying the "aimpoint" and "CCD-specific" energy to PH conversions to ECS data. The aimpoint conversion paradigm consists of two conversions, one for I3, and one for S3. The I3 conversion would be used for all CCDs if the aimpoint is on I3, and the S3 conversion would be used for all CCDs if the aimpoint is on S3. The CCD_specific conversion consists of a conversion for each CCD, applied with a 2D/1D window block for each CCD (I0 would have a window with the I0 conversion, I1 would have a window with the I1 conversion,etc).

The following figures show four conversions over plotted on the ECS data from 0.0 to 1.25 keV for each of the ten CCDs. The four conversions are:

• The current conversion (purple-pink)
• The CCD specific conversion (blue)
• The I3 conversion (red)
• The S3 conversion (green)

In this analysis, the energy vs PHA_read out (PHA_RO) space was divided into 4 regions. The figure below shows this for an energy of 810 eV. The data are I3 data from an ECS observation, OBSID 59579.

The vertical line represents the minimum energy desired by the user (810eV in this example). This energy has been converted into an ACIS PH using an I3 specific conversion in this example. This value is then used in the ACIS PB as the "lowerEventAmplitude". Data to the left of the line are LESS than the desired energy, data to the right of this line are GREATER than or equal to the desired energy.

The horizontal line is the ADU used for the lowerEventAmplitude. This divides the data into those telemetered (ABOVE the line) and those not telemetered (BELOW) the line.

Using these two lines, the data set can be divided into 4 regions:

• Data below energy requested and telemetered (can lead to extra data that the observer can filter out)
• Data below energy requested and NOT telemetered (as desired)
• Data above or equal to energy requested and telemetered (as desired)
• Data above or equal to energy requested and NOT telemetered (lost data)

Using ECS data from OBSIDs 59579 and 59576, I stepped over a range of energies from 300 eV to 1000 eV in 50 eV steps and calculated the PH that corresponded to the energy for the I3, S3, and CCD-specific conversions. I then computed the percentages of events telemetered and non-telemetered which were below the desired energy. This was repeated for the percentage of events telemetered and non-telemetered above the desired energy. I then computed the difference between the CCD specific conversion and the I3 conversion and the difference between CCD specific conversion and the S3 conversion. The figures below show the difference in percentages for these 4 regions. There are 4 lines drawn on each figure:

• Black: The difference in percent of events telemetered if using CCD specific conversions versus ACIS-I aimpoint (the I3 conversions).
• Green: The difference in percent of events telemetered if using CCD specific conversions versus ACIS-S aimpoint (the S3 conversions).
• Red:The difference in percent of events not telemetered if using CCD specific conversions versus ACIS-I aimpoint (the I3 conversions).
• Blue:The difference in percent of events not telemetered if using CCD specific conversions versus ACIS-S aimpoint (the S3 conversions).

In some cases, the red and black lines may not appear. This is due to similar values with the blue and green lines and they are over plotted.

Raw Data

Discussion

The goal of this analysis is to understand the effect of the different conversions on the number of desired events which are telemetered and not-telemetered and the number of undesired events which are telemetered and not-telemetered.

We want to have fewer events BELOW the specified energy telemetered with more events ABOVE the specified energy telemetered.

Looking at the specific conversions:
Compare the S3 conversion to the CCD-specific conversion for the FI CCDs

• from 150 - 600 eV, negligible change in telemetered events above the desired energy (less than 0.6%)
  
• from 150 - 600 eV, significant reduction in telemetered events below the desired energy (ACIS-S conversion accepts up to 20% fewer events)
  
• from 600 to 1250 eV, significant reduction in telemetered events above the desired energy (ACIS-S conversion accepts up to 37% fewer for S0,12-15% fewer for I0-I3)
  
• from 600 to 1250 eV, significant reduction in telemetered events below the desired energy (ACIS-S conversion accepts up to 70% fewer events)
  

Compare the I3 conversion to the CCD-specific conversion for S3

• from 150 - 600 eV, NO change in telemetered events above the desired energy
  
• from 150 - 600 eV, significant increase in telemetered events below the desired energy (ACIS-I conversion accepts up to 70% more events)
  
• from 600 - 1250 eV, NO change in telemetered events above the desired energy
  
• from 600 - 1250 eV, significant increase in telemetered events below the desired energy (ACIS-I conversion accepts up to 25% more events)
  

The results argue for the use of the aimpoint conversions since the vast majority of lower energy thresholds specified by G0s are between 100 and 600eV (97.489%)

With the proper instructions, the USINT scientists could advise the GOs how to achieve the desired energies with lower energy thresholds above 600eV. Since we have had only a handful (33 total) of such observations over the course of the mission, it seems feasible that these could be handled on a case by case basis.

DATA

Algorithm used

Variable names and descriptions adu_r=PHA value for CCD specific conversion
adu_i=PHA value for I3 conversion
adu_s=PHA value for S3 conversion
adu_c=PHA value for current conversion
bet=events below energy, telemetered
ben=events below energy, not telemetered
aet=events above energy, telemetered
aen=events above energy, not telemetered

1. Read in the conversions for each CCD.
2. Read in the event files for the I and S arrays
3. for each CCD
   select the appropriate event file
   1. select only the events from that CCD
   2. select only events between 0-1250 ev
   3. sort the energy, reset the energy and pha arrays to the sorted values
   4. clean the CCD 5 file for anomalous events
   5. determine how many events are below(and equal) and above this energy
   6. for each 50 ev from 300-1000 eV
      calculate the CCD specific PHA (adu_r)
      1. for the values below the energy, determine how many events are >= the ADU (bet)
      2. for the values below the energy, determine how many events are < ADU (ben)
      3. for the values above the energy, determine how many events are >= the ADU(aet)
      4. for the values above the energy, determine how many events are < ADU (aen)
      5. divide the below energy values (ben and bet) by the total number of events below the energy. Confirm the total is 1.0
      6. divide the above energy values (aen and aet) by the total number of events above the energy to 1250eV. Confirm the total is 1.0
      7. store percentages
      8. REPEAT for I3 conversions to get (adu_i)
      9. REPEAT for S3 conversions to get (adu_s)
      10. REPEAT for current conversion to get (adu_c)
   7. plot the CCD specific - ACIS-I values and ACIS-S values for bet and ben
   8. plot the CCD specific - ACIS-I values and ACIS-S values for aet and aen
   9. plot the CCD specific AIMPOINT minus Current values for be/ae
4. store percentages in a text file