ACIS - HETG Energy Comparisons, Sept.'99

9/20/99

In order to help assess the present order separation ability of the ACIS-S chips, gains have been applied to the ACIS-S chips to put the ACIS/HETG energy ratio near 1.0 - see the plot:

• HR1099, OBSID 62538, Day 258, E_ACIS / E_HETG <-- CCD gains adjusted
  Note that the top panel (MEG-minus) and bottom panel (HEG-plus) are the arms of the HETG "X" closest to the framestore area and seem to be a bit better behaved.
• Gain factors for S0,...,S5 used above = 1.54, 1.11, 1.18, 1.00, 1.11, 1.18 .

W A R N I N G !!! The conclusions regarding gain changes given below are confounded by the change in ACIS temperature which took place between the two observations - in particular, S1 and S3 changes may be due to temperature and FI changes may be larger than measured. Catherine Grant notes (9/21/99):

For the front side CCDs, cooling from -100 (Capella) to -110 (HR 1099)
should *raise* the gain. (i.e. HR1099/Capella change in ACIS E > 1)
So the decrease you are measuring [here] is smaller than the actual
change.

For the back side CCDs, cooling from -100 to -110 should *lower* the
gain (i.e. HR1099/Capella change in ACIS E < 1) [as is seen below.]

The plots linked below show the ratio of the ACIS pulse height derived energy (ENERGY in Level 1 file) to the HETG dispersion derived energy (from HAK analysis using corrected Sky corrdinates.) Events are selected to be in the standard grade set (02346), within +/- 1mm of the dispersion axis, and in the energy range 0.4 to 10.0 keV.

• Capella, OBSID 1235, Day 240, E_ACIS / E_HETG
  
  
• HR1099, OBSID 62538, Day 258, E_ACIS / E_HETG

The four panels in each plot show the results along the four HETG diffraction arms, from top to bottom: MEG minus side, MEG plus side, HEG minus side, HEG plus side. The ACIS-S chips corresponding to specific energy regions in these plots are given here:

MEG-minus: [___S0___] 0.48 keV [___S1___] 0.85 keV [___S2___] 4.3 keV [___S3___]

MEG-plus :      [___S5___]  0.60 keV [___S4___] 1.40 keV [___S3___]

HEG-minus: [___S0___] 0.95 keV [___S1___] 1.70 keV [___S2___] 8.5 keV [___S3___]

HEG-plus :     [___S5___] 1.20 keV [___S4___] 2.8 keV [___S3___]

Evolution of the chips during the 18 days between observations is visible, in particular in the HEG-minus panel the S0 chip at low energy has dropped from E_acis/E_grating = 85% to more like 50% and is falling out of the large order selection range between the dashed lines.

Changes can be measured by looking at specific lines in the spectrum. The following plots show the events detected at the location of the plus and minus orders of a line as well as a histogram of the ACIS reported ENERGY.

• Capella line plots .ps
• HR1099 line plots .ps

The values for the HR1099 observation are summarized here along with the change in ACIS Energy = E_HR1099 / E_Capella in the right most column. The results are ordered by chip and energy. Note that S1 and S3 do show slight gain decreaes as well.

 -------------------------------------- HR1099 OBSID 62538 Values ----------------------     HR1099/Capella
Chip/Spec  Wavelength   Energy          X-location   Y-location   Num Events  Ave ACIS E    Change in ACIS E

S0  HEGm   15.014 A,   0.8258 keV :      -2689.32      247.246          53     0.55               0.71

S1  MEGm   18.970 A,   0.6536 keV :      -1700.03     -139.232         869     0.639184           0.9495
S1  MEGm   17.054 A,   0.7270 keV :      -1529.52     -125.251         475     0.661813           0.9817
S1  MEGm   15.014 A,   0.8258 keV :      -1345.68     -110.025         392     0.781081           0.9919
S1  HEGm   12.135 A,   1.0217 keV :      -2173.32      200.379         630     0.913342           0.8055
S1  HEGm    9.170 A,   1.3520 keV :      -1642.27      151.525         137      1.35915           0.9883
S1  HEGm    8.421 A,   1.4724 keV :      -1508.19      139.326         237      1.44189           0.9697

S2  MEGm   12.135 A,   1.0217 keV :      -1087.46     -88.5363        1767     0.843989           0.8958
S2  MEGm    9.170 A,   1.3520 keV :      -821.713     -66.6620         688      1.07627           0.8896
S2  MEGm    8.421 A,   1.4724 keV :      -754.396     -61.1106         828      1.20395           0.9197
S2  MEGm    6.652 A,   1.8638 keV :      -595.995     -48.1116         534      1.53105           0.9202
S2  HEGm    6.652 A,   1.8638 keV :      -1191.04      110.439         146      1.52215           0.9224

S3  MEGp    8.421 A,   1.4724 keV :       754.495      63.4541         507      1.48701           0.9750
S3  MEGp    6.652 A,   1.8638 keV :       596.090      50.4038         825      1.80116           0.9817

S4  MEGp   18.970 A,   0.6536 keV :       1699.94      141.466         271     0.568405           0.8506
S4  MEGp   17.054 A,   0.7270 keV :       1529.25      127.582         194     0.631310           0.9874
S4  MEGp   15.014 A,   0.8258 keV :       1345.63      112.320         254     0.666961           0.8930
S4  MEGp   12.135 A,   1.0217 keV :       1087.59      90.9339        1646     0.803869           0.8760
S4  MEGp    9.170 A,   1.3520 keV :       821.770      69.0222         650      1.12219           0.9223
S4  HEGp    9.170 A,   1.3520 keV :       1642.13     -149.095         144      1.28942           1.0133
S4  HEGp    8.421 A,   1.4724 keV :       1508.49     -136.615         222      1.33134           0.9252
S4  HEGp    6.652 A,   1.8638 keV :       1191.21     -107.626         147      1.63451           1.0348

S5  HEGp   15.014 A,   0.8258 keV :       2689.48     -244.834          57     0.70               0.89
S5  HEGp   12.135 A,   1.0217 keV :       2173.73     -197.623         408     0.922946           0.8789

Please send any comments to Dan Dewey at dd@space.mit.edu.