XRT response function modification
----- due to stray light and filter contamination

(Aki Takeda, 19 March 2021, initial version. )
(Aki Takeda, 6 October 2021, modified for the 2nd XRT calibration meeting 2021.)


0. Introduction

Review of the status as of the previous meeting

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.

    1. New attempts

    Considering the contamination on Focal Plane Analysis Filters(FPAFs)

    Applying the similar corrections as those performed in Narukage et al.(2011), in which the temperature around the FPAFs and the frequency of the filter use are key factors.

    [Note about XRT's THERMAL phases defined by Narukage et al (2011)] (not stray light phase)


    Fig. 7 from Narukage etal 2011 Fig.37 from Narukage etal (2011) $SSW data readings
    Monthly frequency
    yearly frequency plot with more filters
    Monthly exposure time

    Te and EM with FPAF contamination

    --- First Attempt ---
    We assume that the additional contamination layer was built during the period the FPAF temperature was low (roughly < 10C) after the OP hearter kept turned OFF in the late November, 2009. First, we assumed the similar growing curve as the CCD contamination.
    extracted CCD growth curve
    assumed growth curve for X-ray filters
    max filter contam. factor :
    2.0(Alms) & 4.0(Tpol)    		 2.0(Alms) & 5.0(Tpol) 2.0(Alms) & 7.0(Tpol)
    max filter contam. factor :
    1.5(Alms) & 3.0(Tpol)    		 1.5(Alms) & 3.5(Tpol) 1.5(Alms) & 4.0(Tpol) 1.5(Alms) & 5.0(Tpol)

    --- Second Attempt ---
    Assuming that the contamination grows only during the eclipse season from 2010 to 2017 (when the FPAF temperature less than 5C).
    - factor relative to the last value of curent DB : type 1    type 2
    - converted to the thickness of the contamination layer : type 1    type 2

    type 1 (teem_*_ofrac_fctm3_ series) type 2 (teem_*_ofrac_fctm4_ series)

    other try and errors

    derived irradiance

    type 1 (fctm3 series) type 2 (fctm4 series)
    multi-plot (irrad, Te & EM) multi-plot (irrad, Te & EM)

    2. Follow-up analysis by K. Reeves

    XRT_lightleak_calibration (29-Sep-2021)

    3. If we have time for it ...

    Report of the 2021 stray light analysis
    Extended study using the corrected response functions

    4. Follow-up of the 6-Oct meeting

    Variation of the full-Sun signals with different filters (7-Oct-2021)
    * Al_mesh, Ti_poly and Al_poly plots were made from the current irradiance study.
    * Thin_Be signals were measured by my 2021 REU student, Stefanie Davis.
    * Al_poly data points (2008-2015) can be increased by additional work.
    * Al_mesh singals are prone to attenuate by the contamination.

    Al_mesh Ti_poly
    Al_poly Thin_Be


    5. New filter contam. functions

    --- Third Attempt ---
    The stray light correction turned out to shift the temperature too high and EM too low. But the opening factors are very small until the phase 2, so its effect to effective area function might be smaller. In this attempt, prefilter open fraction was set to the half value of those obtained from GET_PF_OPENFRAC.PRO.


    try'n error plot Te 1      EM 1      fctm factor 5_1      fctm in Å 5_1

    try'n error plot Te 2      EM 2

    try'n error plot Te 3      EM 3

    try'n error plot Te 4      EM 4

    try'n error plot Te 5      EM 5      fctm factor 5_5

    --- 4th Attempt ---
    It turned out that the reduced pre-filter open fraction tried in the above causes unnatural EM curve in the phase 3 and 4: EM in 2017 becomes lower than that of 2019-2020(solar min.). We thus bring a little back the open fraction values. 
     
1: ofrac(i)=0
2: ofrac(i)=work*0.50
3: ofrac(i)=work*0.65
4: ofrac(i)=work*0.80
else: ofrac(i)=work*1.0
    Te 6_1      EM 6_1      fctm factor 6_1 

     
1: ofrac(i)=0
2: ofrac(i)=work*0.50
3: ofrac(i)=work*0.60
4: ofrac(i)=work*0.70
else: ofrac(i)=work*1.0
    Te 6_2      EM 6_2      fctm factor 6_2

    Te 6_3      EM 6_3      fctm factor 6_3

    Te 6_4      EM 6_4      fctm factor 6_4

    Te 6_5      EM 6_5      fctm factor 6_5

    Te 6_6      EM 6_6      fctm factor 6_6

    Te 6_7      EM 6_7      fctm factor 6_7