XRT Calibration Meeting 2021.

(Aki Takeda, 27 January 2021, online via zoom)


Topics from MSU
  1. Results of the stray light measurements of 2020 eclipse season. (AT)
  2. Status of the XRT irradiance study :
    --- XRT effective area modification for stray light contamination. (AT)
  3. Status of the CCD contamination layer thickness DB. (KY)
  4. Status of the XRT coalignment DB. (KY)



1. Stray light measurements in 2020.

This is a digest version of the following page:
http://solar.physics.montana.edu/takeda/xrt_sl2020/xrt20_sl.html

1.1 Measurements 2020 at a glance.

ID No. date & time (UT) XOB purposes (link: obtained plots & images) memo
1 7-May-2020, 18:37:30 1C81 light crv., Al-mesh (1.4s) and Al-poly (2.0s) at DC. previous bakeout + 14 day.
2 8-May-2020, 18:54:30 1C82 light crv., thin_Be (11.3s) at DC. prev. b.o. + 15 day.
3 13-May-2020, 18:22:00 1C83 light crv., Al-mesh (1.4s) and Al-poly (2.0s) at DC. prev. b.o. + 0 day. Many lost frames.
4 14-May-2020, 19:08:00 1C84 light crv., thin_Be (11.3s) at DC. prev. b.o. + 1 day.
5 12-Jul-2020, 01:16:30 1C88 light crv., Al-mesh (1.4s) and Al-poly (2.0s) on AR. prev. b.o. + 21 days.

1.2 Summary of Results.

1.3 Sample images

Al-mesh, 20200507(1.4s)
[bd+14d]
pnt.(-18.5, 7.4)
Al-mesh, 20200513(1.4s)
[bd+0d]
pnt.(-17.6, 12.5)
Al-mesh, 20180712(1.4s)
[bd+2d]
pnt.(-22.1,19.8)
After PREP comparison 1
comparison with 2018
After PREP comparison 2
before/after bakeout
Al-poly, 20200507(2.0s)
[bd+14d]
pnt.(-18.5, 7.4)
Al-poly, 20200513(2.0s)
[bd+0d],
pnt.(-17.6, 12.5)
Al-poly, 20180712(2.0s)
[bd+2d],
pnt.(-22.2,19.8)
After PREP comparison 1
comparison with 2018
After PREP comparison 2
before/after bakeout

- Other pointings

Al-poly, 20200712(2.0s)
[bd+21d]
pnt.(881.0, 73.5)


1.4 Additional analysis of G-band monitor (VLS=Open/Close) images.

"Attempt to determine the pre-filter opening ratio."

Intensity profiles of G-band VLS=close full-Sun images for the phase 1 to 4. Intensity is normalized to (DN/sec/full-res pix).

XRT elementsPre-filters G-band lens & filters

[Observed intensity of the G-band Sun] =
I_sun * [aperture of G-band system] * [G-band system's transmission] * [transmission of FW G-band filter]

[Observed stray light intensity] =
I_sun * [aperture of X-ray system] * [pre-filter opening ratio] * [transmission of FW G-band filter]

- Phase 0 (2011/04/18 & 2012/04/30)

- Phase 1 (2013/05/11)

- Phase 2 (2015/06/22)

Using the ratio of disk-integrated G-band and stray-light images, the pre-filter open ratio for each phase was calculated as follows.

  • - open_ratio(@phase1) = 0.00162 (~0.1%)
  • - open_ratio(@phase2) = 0.0325 (~3.3%)
  • - open_ratio(@phase3) = 0.0747 (~7.5%)
  • - open_ratio(@phase4) = 0.0993 (~9.9%)
  • Estimation of pre-filter open ratio

    2. Status of XRT full-Sun irradiance study.

    This is the science topic I have tackled for these years, but it requires to estimate the effect of the stray light contamination on XRT's effective area function.

    This study was partly contributed by Suman Panda, through our summer project, Jun-Sep 2020. http://solar.physics.montana.edu/takeda/REUproj2020/index.html

    2.1 Derivation of soft X-ray irradiance using XRT full-Sun images

    IMPORTANT NOTE: Since 2012 May, XRT started to suffer the visible stray light contamination caused by a series of failures (appearance of small openings) on the XRT pre-filter. The XRT irradiance derived with this method is affected by the stray light in the following two ways:

    (1) Subtraction of stray light image from each X-ray images.
    (2) Modify XRT response functions (through effective area function modification) so that they reflect the contamination of the stray light.

    2.2 XRT irradiance (5-60A), filter ratio Te and EM

    We initially tried to determine the pre-filter opening ratio by comparing the XRT irradiance with other instruments, like GOES/XRS and TIMED/SEE. Suman contributed to prepare the daily averaged data set from GOES-15/XRS (1-8A) and TIMED/SEE (1-10A and 1-60A).
    However, this method did not work: it turned out that the irradiances from different instruments are not similar enough to correct the deviation of XRT irradiance curve from that supposed to be without pre-filter failure. Later we figured out other method using G-band images to determine the pre-filter opening ratios.

    Despite our current best effort of correction, the above plots have serious problems, which need to be further corrected.

  • - significant difference in Te in two solar minimums(cycle 23 & 24).
  • - significant difference in EM in two solar minimums(cycle 23 & 24).
  • These results indicate that there is still a missing piece of puzzle to fully (quantitatively) correct the visible stray light contamination included in our X-ray images.

    3 & 4. status of CCD contamination DB & co-alignment DB.

    see Keiji's presentation file.