XRT Stray Light Study 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 page.
Link to the 2017 phase 3 page (after 27-May-2017).

(20 May, 2017 by Aki Takeda)
(13 Oct, 2017: After PREP plots corrected using MSU_XRT_PREP.)

1. Purposes of the stray light measurement in 2017.

Judging from the intensity level of G-band images and FLD images (Ti-poly 8x8), we expect no further increase in stray light level since the end of last eclipse season (Aug-2015). The 2017 measurements are to confirm this with real data taken during eclipses.

2. Summary of Results.

3. Measurements 2017 at a glance.

ID No. date & time (UT) XOB purposes (link: obtained plots & images) memo
1 09-May-2017, 18:11:30 1B83 light curve, Ti-poly (1s) and Al-mesh (2.83s) at DC. prev. bakeout + 14 days.
2 10-May-2017, 18:47:00 1B84 light curve, Al-poly (4s), Thin-Be (11.3s) at DC prev. bakeout + 15 days.
3 11-May-2017, 17:41:30 1B85 light curve, med-Al (32s) at DC prev. bakeout + 16 days.
4 12-May-2017, 18:17:00 1B86 light curve, med-Be (22s) at DC prev. bakeout + 17 days.

[NOTE] X-ray light curves in 2017 measurement are low contrast(X-ray vs G-band) due to the lack of ARs in the monitoring area.

4. Stray light images 2017, at a glance.

Note: exposure times are different from 2015 measurements.
The Ti-poly "After PREP comparison" plot shows that the stray light intensity in 2017/05/09 is ~9 % larger than that of 2015/07/18. Considering the difference of the time past since their previous bakeout (+14 days for 2016 while +1 day for 2015), this increase can be explained by the increased contamination thickness (variable component cleared by every CCD bakeout and slightly increased persistent layer).

Ti-poly, 20150718(1.4s) Ti-poly, 20170509(1.0s) After PREP comparison Ti-poly, 20160510(1.0s)

The Al-mesh "After PREP comparison" plot shows that the stray light intensity on 2017/05/09 is 10% smaller than that of 2015/07/18, in spite of the time difference since the previous CCD bakeout (+14 and +2 days, respectively). This suggests that the Al_mesh stray light intensities are affected by other factors than CCD contamination thickness.

Al-mesh, 20150718(1.0s)
Al-mesh, 20170509(2.8s)
After PREP comparison Al-mesh, 20160510(2.8s)

In plots below exposure difference is not corrected yet.

Al-poly,20150620(0.8s) Al-poly,20175010(4.1s)

thin-Be,20150620(5.8s) thin-Be,20170510(11s)

med-Be,20150508(32s) med-Be,20160513(23s)

med-Al,20150509(23s) med-Al,20170511(32s)