XRT Stray Light Study 2017 -- Phase 3 (after 27-May-2017).

Link to the 2014 summary page.
Link to the 2015 phase 1 summary.
Link to the 2015 phase 2 summary.
Link to the 2016 (phase 2) summary.
Link to the 2017 phase 2 (before 3rd rupture).

(26 June, 2017 by Aki Takeda)
(11 Sept, 2017 added results of later measurements.)
(22 Sept, 2017 added section of image correction.)

0. Motivation.

On 27-May-2017, around 11UT, a saturation of G-band images was observed (reported by DV [xrt_co:31950]). This strongly suggests another rupture of the XRT pre-filter. The flare patrol images (taken with Ti-poly) also show the increase of stray light component (see images below). The new rupture seems to have occurred during the period XRT paused observation due to SAA passage and S/C night (i.e., no observation between the two images below).

1. Purposes of the project 2017, phase 3.

Since 27-May-2017, XRT's stray light status has entered a new stage, so we call it "phase 3". (Note that we were in phase 2 since the 2nd pre-filter rupture event on 14-Jun-2015).

2. Summary of Results.

3. Measurements 2017 (phase 3) at a glance.

ID No. date & time (UT) XOB purposes (link: obtained plots & images) memo
5 13-Jun-2017, 17:31:30 1B98 light curve, Ti-poly (1.0s), and Al-mesh(2.83s) at DC. prev. bakeout + 6 days. Ti-poly > 2500 DN.
G-band monitor images saturated.
6 14-Jun-2017, 18:07:00 1B99 light curve, Al-poly (4.0s), Thin-Be (11.3s) at DC prev. bakeout + 7 days.
G-band monitor images saturated.
Sunset during thin-Be stray light exposure.
7 15-Jun-2017, 18:42:30 1B9A light curve, med-Al (32.0s) at DC prev. bakeout + 8 days.
G-band monitor images saturated.
Sunset during stray light exposure.
8 16-Jun-2017, 17:39:30 1B9B light curve, med-Be (22.6s) at DC prev. bakeout + 9 days.
G-band monitor images saturated.
Sunset during stray light exposure.
9 18-Jun-2017, 17:12:00 1B9E light curve, Ti-poly (500ms), Al-mesh (2.83s) at DC prev. bakeout + 11 days.
Monitor imgs to 384x384 no binning.
10 19-Jun-2017, 17:47:30 1B9F light curve, Al-poly (4.0s), Thin-Be (11.3s) at DC prev. bakeout + 12 days.
Monitor imgs to 384x384 no binning.
Sunset during thin-Be stray light exposure.
11 25-Jul-2017, 17:45:30 1BAC light curve, Al-mesh(1.4s) and Al-poly(2.0s) at E-limb, prev. bakeout + 7 days.
Monitor imgs to Al-mesh 384x384 full-res.
12 26-Jul-2017, 18:21:00 1BAC light curve, Al-mesh(1.4s) and Al-poly(2.0s) at N-limb, prev. bakeout + 8 days.
Monitor imgs to Al-mesh 384x384 full-res.
13 27-Jul-2017, 17:18:00 1BAC light curve, Al-mesh(1.4s) and Al-poly(2.0s) at W-limb, prev. bakeout + 9 days.
Monitor imgs to Al-mesh 384x384 full-res.
Al_poly has abnormal intensity.
14 28-Jul-2017, 17:53:00 1BAC light curve, Al-mesh(1.4s) and Al-poly(2.0s) at S-limb, prev. bakeout + 10 days.
Monitor imgs to Al-mesh 384x384 full-res.
15 8-Aug-2017, 17:51:30 1BAE light curve, Al-mesh(1.4s) and Ti-poly(500ms) at DC, prev. bakeout + 1 days.
Monitor imgs to Al-mesh 384x384 full-res.
No NGT event, but X-ray well absorbed.
16 9-Aug-2017, 18:27:30 1BAF light curve, Al-poly(2.8s) and Thin-Be(11.3s) at DC, prev. bakeout + 2 days.
Monitor imgs to Al-mesh 384x384 full-res.
No NGT event, but X-ray well absorbed.

4. Stray light images 2017, at a glance.

Tp 20150718 (1.4s)
- phase 2 - [bo +1d]
Tp 20170509 (1.0s)
- phase 2 - [bo +14d]
Tp 20170613 (1.0s)
- phase 3 - [bo +6d]
Tp 20170618 (500ms)
- phase 3 - [bo +11d]
Tp 20170808 (500ms)
- phase 3 - [bo +1d]

After PREP comparison
20170618 v.s. 20170509
(bo+11d v.s. bo+14d)
20170808 v.s. 20150718
(bo+1d v.s. bo+1d)
Am 20150718 (1.0s)
- phase 2 -
Am 20170509 (2.9s)
- phase 2 -
Am 20170613 (2.9s)
- phase 3 -
Am 20170618 (2.9s)
- phase 3 -
Am 20170808 (1.4s)
- phase 3 -

After PREP comparison

20170808 v.s. 20150718
(bo+1d v.s. bo+1d)

Am 20170725 (1.4s)
- E-limb (ph3) -
Am 20170726 (1.4s)
- N-limb (ph3) -
Am 20170727 (1.4s)
- W-limb (ph3) -
Am 20170728 (1.4s)
- S-limb (ph3) -

Ap 20160511 (4.1s)
- phase 2 - [bo+9d]
Ap 20170510 (4.1s)
- phase 2 - [bo+15d]
Ap 20170614 (4.1s)
- phase 3 - [bo+7d]
Ap 20170619 (4.1s)
- phase 3 - [bd+12d]
Ap 20170809 (2.8s)
- phase 3 - [bd+2d]

After PREP comparison

20170619 v.s. 20160511
(bo+12d v.s. bo+9d)

Ap 20170725 (2.0s)
- E-limb (ph3) -
Ap 20170726 (2.0s)
- N-limb (ph3) -
Ap 20170727 (2.0s)
- W-limb (ph3) -
Ap 20170728 (2.0s)
- S-limb (ph3) -

tnBe 20160511 (5.8s)
- phase 2 -
tnBe 20170510 (11s)
- phase 2 -
tnBe 20170614 (11s)
- phase 3 -
tnBe 20170619 (11s)
- phase 3 -
tnBe 20170809 (11s)
- phase 3 -
med-Be,20170512(32s)
- phase 2 -
med-Be,20170616(23s)
- phase 3 -
med-Al,20170511(32s)
- phase 2 -
med-Al,20170615(32s)
- phase 3 -

5. Image correction.

[Click image to enlarge]
Before subtracting stray light img. After subtracting stray light img. Intensity profile, image(*,512)
[Click image to enlarge]
Before subtracting stray light img. After subtracting stray light img. Intensity profile, image(*,512)

6. G-band images analysis.

G-band VLS=open and close images have nearly equal intensity in the phase 3. Although sunspots (AR12662 and 12663) are barely seen by subtraction, but their intensity contrast is worse than that of contamination spots.

(click image to enlarge)

Comparison with the Phase 2 (Jan-2016).

(click image to enlarge)