CCD dark calibration using CCD bakeout

20-Dec-2017 : prepared by Aki Takeda
16-Jan-2018 : added images and plots.
7-Feb-2020 : added readings of v-slope.

Motivation

Check CCD performance after 10 years of on-orbit operation. The previous on-orbit calibration was performed in 2008.
The goal of the coming calibration:

Operation sequence

Note:

  1. Exposure time for dark images does not correctly appear in the EXPTIME tag in FITS headers. You should use the EXCCDEX tag instead.

Data Analysis

What you need to know for data analysis: XRT CCD basics.

Variation of CCD temperature

(click plot to enlarge)

Obtained images

Full_res Cetner 512x512 Short (Seqn. 2 of XOB#1BAD)
Full_res Cetner 512x512 Long (Seqn. 2 of XOB#1BAD)
Full_res Cetner 512x512 Normal (Seqn. 61 of XOB#1BAD)

Full-CCD readout Short (Seqn. 24 of XOB#1BAD) --- all size rebined to 512x512.
Full-CCD readout Long (Seqn. 24 of XOB#1BAD) --- all size rebined to 512x512.

Cal_image 2716x2112 Dark (Seqn. 47 of XOB#1BAD)
Cal_image 2716x2112 Normal (Seqn. 47 of XOB#1BAD)

Typical pattern (click image to enlarge)

5-AUG-2017 09:15:01
full-CCD 1024x1024(pix),
1.04800(sec), 20.1868(C)
5-AUG-2017 12:09:17
full-CCD 2048x2048(pix),
1.04800(sec), 30.6163(C)
5-AUG-2017 11:02:04
center ful-res 512x512(pix),
1.04800(sec), 31.1968(C)

CCD count variations

CCD count v.s. Time (×: 1.0sec data, ◊: 32.0sec data)
CCD count v.s. CCD Temp.
CCD normalized count v.s. CCD Temp. --- 32sec data are not suitable for analysis due to partial saturation.
Dark electrons v.s. CCD Temp.
Dark electrons v.s. CCD Temp. --- use only area (512x185) lower than the blob.

Comparison with 2007 (7/23-24) bakeout data

(click image to enlarge)
plots 24-JUL-2007 07:04:27
cal-mode image 2176x2112(pix)
1.04800(sec), 30.0359(C)
23-JUL-2007 13:05:13
center full-res 512x512(pix),
1.04800(sec), 31.1968(C)
vertical intensity slopes
(from a calibration image)
[2017 conterpart]

DN/sec v.s. CCD temperature
(from 512x512 image set)
[2017 conterpart]

Comparison of Dark electrons v.s. CCD temperature.
(click image to enlarge)

Comparison of vertical slope of calibration images.


(click image to enlarge)
- blue line : 21 pix around x=512
- white line : 21 pix around x=1024

Calculation of dark current produced during charge transfer (8 sec):
date CCD temp. exp time x pos.a: DN @ y=0b: DN @ y=2050 (a-b)/8
2017/08/05 30(C)0.059(sec) 512 100 3050 368.8 (DN/sec)
2007/07/24 30(C)1.048(sec) 512 300 1900 200.0 (DN/sec)

Results

Below are written before Kano-san's comments.