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
    • (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
  • only use Mn K alpha
  • include checker-flag CTI measurement for XIS, SCI-off (Ozawa 2009)

• 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
    • 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)
  • (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
  • 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

• v22   2012-09-19   PDF   TeX tarball – Figures switched to Gehrels fits with error bars. Updated text to match. Added cal source comparison figure (not final?).
• v21   2012-08-01   PDF   TeX tarball – Version sent to Mark. Finished? up temperature section, many minor edits.
• v20   2012-07-18   PDF   TeX tarball – Incorporates comments from Bev and Eric. New figure 3, XIS spectra, referenced in Section 3.1. Some words on quantitative sacrificial charge in Section 4.3. Figure 11 now shows uncorrected too. Minor edits.
• v19   2012-05-22   PDF – Comments by Bev (Preview.app annotations)
• v19   2012-05-22   PDF – Comments by EDM (Preview.app annotations)
• v19   2012-05-22   PDF   TeX tarball – Section 4.3 mostly done, starting on Section 4.4
• v18   2012-05-15   PDF   TeX tarball – Some of Bev's comments addressed, more work in section 4.3
• v17   2012-05-08   PDF   TeX tarball – Addresses Eric's comments, XIS COR is now COR2, other minor fixes
• v16   2012-05-01   PDF – Comments by EDM (Preview.app annotations)
• v16   2012-03-22   PDF   TeX tarball – Minor fixes/more text
• 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