Paper Outline

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

• 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