Hinode/XRT stray light correction 2015

XRT Stray Light Study 2015 -- Phase 2 (after 14-June-2015).

Link to the 2014 summary page.
Link to the 2015 phase 1 summary.
Link to the 2016 summary.

(22 June, 2015 by Aki Takeda)
(27 July, 2015 revised.)
(3 August, 2015, non-DC correction added.)

0. Motivation.

On 14-June-2015, around 12UT, there was another jump-up of the stray light intensity, probably caused by the rupture of another sector of pre-filter. G-band intensity monitor at SAO

1. Purposes of the project 2015, phase 2.

measure the current level of the stray light of Ti-poly and C-poly.
also measure other thin filters (Al-mesh, Al-poly, and thin-Be) if they are affected by the stray light increase of this time.
collect 2015 light curves of the XRT eclipses.

2. Summary of Results.

Ti-poly stray light intensities after 14-Jun-2015 are more than 10 times larger than those before.
C-poly stray light intensities after 14-Jun-2015 are ~8 times larger than before.
The slight stray light patern detected in Al-mesh filter, but its intensity is not significant.
The stray light component in Al-poly and thin-Be is negligible.
For Ti-poly images:
- Solar-disk component --> NE-SW diagonal band. with CCD contamination spots seen as while dots (like G-band images).
- The peak intensity of stray light composnent reaches to 2500 DN (threshold of reliable photometry) at 1.4 sec exposure. --> max exposure time for Ti-poly is ~1 sec for photometry.
For C-poly images:
- Solar-disk component --> NE-SW diagonal band.
- The bright-arc paterns still seen.
Flare monitor image : the flare trigger is currently working (for M-class flares) but may be hard for smaller ones. (Ti-poly --> Al-poly?)

3. Measurements 2015 (phase 2) at a glance.

ID No.	date & time (UT)	XOB	purposes (link: obtained plots & images)	memo
12	18-Jun-2015, 17:51:30	1A92	light curve, T-poly(1.4s) and Al-mesh(1s) at DC.	prev. bakeout + 16 days.
13	20-Jun-2015, 17:23:00	1A97	light curve, Al-poly (1s), Thin-Be (5.6s) at DC	prev. bakeout + 18 days.
14	20-Jun-2015, 19:03:30	1A98	light curve, Ti-poly (2s), C-poly (2s) at DC	prev. bakeout + 18 days.
15	30-Jun-2015, 18:23:30	1AA3	light curve, Ti-poly (1.4s), C-poly (2s) at DC	* Data lost *
16	1-Jul-2015, 17:25:00	1AA4	light curve, Ti-poly (1.4s), Al-mesh (1s) at W-limb	prev. bakeout + 1 day.
17	2-Jul-2015, 17:22:30	1AA5	light curve, Ti-poly (1.4s), Al-mesh (1s) at S-pole	prev. bakeout + 2 days.
18	3-Jul-2015, 18:36:30	1AA6	light curve, Ti-poly (1.4s), C-poly (2s) at N-pole	prev. bakeout + 3 days.
19	3-Jul-2015, 23:32:00	1AA7	light curve, Ti-poly (1.4s), C-poly (2s) at E-limb	prev. bakeout + 3 days.
20	18-Jul-2015, 16:05:00	1AB4	light curve, Ti-poly (1.4s), Al-mesh (1s) at DC	prev. bakeout + 1 day.
21	19-Jul-2015, 18:19:00	1AB4	light curve, Ti-poly (1.4s), Al-mesh (1s) at DC	prev. bakeout + 2 days.
22	11-Aug-2015, 17:18:30	1ABF	light curve, C-poly (2s) at DC	*** Data partialy lost. (+6days)
23	16-Aug-2015, 18:40:00	1ABF	light curve, C-poly (2s) at DC	not enough X-ray extinction.

4. Stray light images 2015, at a glance.

Ti-poly, 20150518 DC	Ti-poly, 20150618 DC	Ti-poly, 20150620 DC	Ti-poly, 20150718 DC	Ti-poly, 20150719 DC

difference image [2015/06/18]-[2015/07/18]
difference image [2015/07/19]-[2015/07/18]

C-poly, 20150518 DC	C-poly, 20150620 DC	C-poly, 20150811 DC

Al-mesh, 20150509 DC	Al-mesh, 20150618 DC	Al-mesh, 20150718 DC	Al-mesh, 20150719 DC

Al-poly, 20150507 DC	Al-poly, 20150620 DC

thin-Be, 20150507 DC	thin-Be, 20150620 DC

Ti-poly, 20150701 WL	Ti-poly, 20150702 SP	Ti-poly, 20150703 NP	Ti-poly, 20150703 EL

Al-mesh, 20150701 WL	Al-mesh, 20150702 SP	C-poly, 20150703 NP	C-poly, 20150703 EL

5. Correction of the images.

5.1 Ti-poly composite images (at DC pointing)

2015/06/18: correction is imperfect because of strong scattered light due to M3.0 flare from the AR12371.

2015/06/18, Before corr.	After correction

2015/06/20: stray light image taken with 2sec was too long to be used for quantitative treatment (center portion exceeds 2500 DN). So the stray light image from other date (with proper exposure) should be used for correction.
Three problems in the corrected image:

Edges of the diagonal bands not removed.
Stripes(specific to Ti-poly filter) not removed well.
Dark spots due to dust contmination on CCD --- can be removed by additionally applying XRT_SPOTCOR after subtracting the stray light image.
Bright spots due to dust contmination on stray light images. --- most of them can be corrected by XRT_SPOTCOR, but enhanced if you use a shifted stray light image (see 7/18 correction).

2015/06/20, Before corr.	Corr. by 6/18 stray light img.	Corr. by 7/18 stray light img.

2015/07/18 and 2015/07/19: Stray light image taken soon after CCD bakeout, with right exposure (1.4.sec). Synoptic images taken right before (assure same pointing). In the corrected image, stripes gone, while diagonal band edges still seen. Spots were removed by XRT_SPOTCOR.

2015/07/18, Before corr.	After correction
		1024x1024 image movie [Before, SL-img & After] some more attempt to get better correction.

2015/07/19, Before corr.	After correction	Corr. with 7/18 stray-light img.

5.2 Ti-poly composite images (at non-DC pointings)

The edges of diagonal band are hard to correct, even with the stray light image taken within 10 minutes.

2015/07/01, Before corr.	After corr.

2015/07/02, Before corr.	After corr.

2015/07/03, Before corr.	After corr.

2015/07/03, Before corr.	After corr.

5.3 C-poly composite images (at DC pointing)

2015/08/16, Before corr.	Corr. with 8/11 stray-light img.

5.4 Al-mesh composite images (at DC pointing)

No noticable changes.

2015/07/18, Before corr.	After corr.

6. Light curves 2015, collection.

moved to the phase 1 page.