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Goal

We discuss the evolution of CTI and its impact on spectral resolution for X-ray CCDs in different orbital environments.  We specifically prepare models of the energy scale and resolution as a function of the background, CCD type (FI vs. BI), and application of charge injection, considering energies spanning the CCD range.

Outline

  • about the instruments
    • first describe each separately (label CCDIDs)
    • then similarities/differences between ACIS/XIS that impact CTI (just the instruments and operation, no environment yet) in a table and summarize in text
      • initial pre-launch CTI, ACIS BI > XIS BI, XIS FI > ACIS FI
      • Transfer speeds, fast transfer (image-to-framestore) serial transfer not the same
      • Frame time, 3.2s vs 8s
      • Focal plane temperature, -90C vs -120C
      • (plus) (insert additions to this list here)
  • about the orbits and backgrounds
    • steal from Bev's 2008 SPIE paper
    • steal from O'Dell, Markevitch papers on radiation environments
  • about the calibration sources
    • ACIS – Fe55 with Al&Ti (Fe-L), uniform illumination, getting pretty wimpy, only sampled twice per orbit
    • XIS – Fe55 with no targets, no Fe-L, only in corners, getting wimpy, continuously sampled (except SAA)
    • measure Fe55 half-life extremely well
  • Measuring CTI, ACIS vs XIS (methodology)
    • ACIS – fit all grades, only center pixel pulseheight vs ccdy/ccdx (binning/fitting details needed)
    • XIS – fit only good grades, summed pulseheight from top cal source corners
    • process ACIS the same way as XIS for comparison? only use center pixels? CTI metric to be decided (warning)
    • only use Mn K alpha
    • include checker-flag CTI measurement for XIS, SCI-off (Ozawa 2009) (question)
  • CTI evolution, plots of measured CTI vs time
    • for ACIS, apply corrections for temperature and sacrificial charge
    • not done for XIS; temperature is stable, background is integrated over 1 day = 16 orbits
    • decide on time binning (warning)
      • not necessary to be the same for ACIS/XIS, and might be misleading given very different cal source duty cycles
  • compare differences in rate of CTI increase (and shape?)
    • parallel vs serial
    • FI vs BI
    • low vs high orbit
    • with and without CI (for XIS, when possible)
    • (plus) (insert additions to this list here)
  • charge trailing vs time
    • trailing fraction shows how initial ACIS from low energy protons is different from ongoing, higher energy particle damage
    • metric is average lost charge of all events divided by average trailed charge of all events
  • FWHM evolution, plots of measured FWHM vs time
    • ACIS and XIS can pretty much measure this one the same way
    • (G02346, summed pulseheights, fit Gaussians, etc.)
    • discussion related to all the above stuff
    • somewhat more complicated to link to physical causes w/ charge trailing, multi-pixel events
  • relate CTI and FWHM increases
    • depend on BI/FI; are ACIS/XIS different?
  • speculate on CTI/FWHM increase with regard to particle fluence, particle type
    • maybe beyond scope of this paper
  • comparison of a celestial source (question)
    • E0102
      • has been observed extensively over time with ACIS and XIS
      • low energy lines very different from Mn K alpha
      • mostly on ACIS-S3
    • Perseus, other clusters
      • check ACIS time coverage, XIS and ACIS roll angles
      • Fe line centroid changes with kT, location in cluster

Comments from MWB

  • outline quite broad, might want to focus it more
  • (his) primary goal: understand the relationship between spectral resolution, radiation damage, and background
    • frame-to-frame variations in BG lead to variations in trap filling and wobbling of LSF
    • Suzaku especially good since we can already model the BG as a function of orbital position
  • secondary goal: construct a model of the background
    • test this model with a simulated BG (e.g. from Co60 source) in the lab (perhaps follow-up paper)

Paper Drafts

  • v15   2012-03-08   PDF   TeX tarball – Minor fixes/more text
  • v14   2012-03-01   PDF   TeX tarball – Minor fixes/some additional text
  • v13   2012-02-16   PDF   TeX tarball – Minor fixes/changes, not much different from v12
  • v12   2012-02-09   PDF   TeX tarball – Minor fixes/changes, not much different from v11
  • v11   2012-02-02   PDF   TeX tarball – Sections 1-3 most of Eric's comments are acted on, finished thru Section 4.2.2, more text in Section 4.3, added raw frames figure
  • v10   2012-01-26   PDF   TeX tarball – Sections 1-3 comments from Eric, more text in Section 4.
  • v9   2012-1-19   PDF   TeX tarball – more text, Sections 1-3 done?, much more text in Section 4.
  • v8   2012-1-10   PDF   TeX tarball – more text
  • v7   2011-12-20   PDF   TeX tarball – new acis/xis schematics, minor text additions
  • v6   2011-12-06   PDF   TeX tarball – new acis/xis schematics, one new reference, minor text additions
  • v5   2011-11-22   PDF   TeX tarball – new acis/xis schematics, xis cti numbers in table, starting text on calibration sources
  • v4   2011-11-15   PDF   TeX tarball – figures now cmyk, new text in introduction and radiation environments sections
  • v3   2011-11-08   PDF   TeX tarball – updated all figures, added one new figure, minor text changes and additions
  • v2   2011-10-18   PDF   TeX tarball
  • v1   2011-08-19   PDF   TeX tarball






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