Re-visiting XRT calibration for the better irradiance study

20-Dec-2025 : initial version

1. Background

XRT temperature analysis must include three kinds of correction:
  1. contanimation layer accumulated on CCD.
    ⇒ corection (2006 to present) included in the current official xrt_teem.pro
  2. contanimation layer accumulated on FPAFs (Focal Plane analysis filters) i.e., X-ray and G-band filters.
    ⇒ corection included until Feb-2007 in the current official xrt_teem.pro.
  3. stray light containation due to pre-filter failure (after May-2012).
    ⇒ not considered at all in the current official xrt_teem.pro.
Problem: when the stray light correction applied, Te and EM at 2 solar minima (2008 and 2020) do not match.

XRT filter-ratio Te and EM obtained from solar spectrum calculated using Chianti ver.9.0.1 with coronal abundance (by Feldman 1992).

Default correction (a + b).
(Stray light intensity was subtracted from images).
Default correction + (c)
Effective area functions modified due to Stray light contam.

XRT filter-ratio Te and EM obtained from Al_poly/Al_mesh filters, using the solar spectrum calculated with Chianti ver.11.0.2 assuming the coronal abundance (Chianti 2021).

Default correction (a + b).
(Stray light intensity was subtracted from images).
Default correction + (c)
Effective area functions modified due to Stray light contam.

XRT filter-ratio Te and EM using thin_Be/Al_poly filters.
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2. Method

  1. Start from the same image pairs from the full-Sun integrated study.
  2. Calculate Te and EM with XRT_TEEM modified for synoptic images.
  3. Refine image arrays (remove bad Te images : more images need to be eliminated than full-Sun integrated pairs).
  4. Calculate 2D soft X-ray irradiance for 5-60A wavelength range.
  5. Mask out the area > 1.1 Rs and calculate values for comparison with full-Sun integrated case.

3. Programs

(in idlpro/xrt/irrad10/)

4. Results







(click image to enlarge)


composite Te image is created with logTe_threshold at 6.45 (2.82MK).
  • Te_composite = Te_amap where log_Te < 6.45
  • Te_composite = Te_aptb where log_Te >= 6.45
comosite EM is created by replacing the same pixels as Te_composite.
  • EM_composite = EM_amap at pixels where log_Te < 6.45
  • EM_composite = EM_aptb at pixels where log_Te >= 6.45
composite irradiance image is calculated using Te_composite and EM_composite images.

Total irradiance calculated for 2024/09/12 04:19 UT (in W/m^2 in log sccale):
-2.74 (Apol/Alms), -3.02 (tnBe/Apol) & -2.83 (composite)