**
Charge Transfer In-efficiencies (CTIs) of ACIS CCDs are graudually changing with time, and it is essential to know
how the degradation progresses. Since CTI are strongly depending on focal temperature, to see the degradation, it is better
to remove the temperature dependency of CTI observations.
MIT/ACIS team suggested that there is a (close to) linear relation between a focal plane temperature and CTI, and
the CTI temperature dependency can be easily corrected (MIT ACIS Memo #204). Related memos and detail analysis can be
found at ACIS CTI @-120C page maintained by Catherine E. Grant at MIT.
**

The following three plots show time trends of monthly averaged CTI of imaging CCDs, spectral CCDS, and backside illuminated CCDs
computed using *Mn K _{α}* line. CTIs are averaged over four quadrants of each CCD.
The CTI values used here are corrected for temperature dependency and detrended (see How CTI are computed?),
except those for the backside illuminated CCDs. The latters are temeprature dependency corrected, but not detrended.

Imaging CCDs | Spectral CCDs |
---|---|

Back Side CCDs | |

The following table lists links to individual CCD/Quad CTI trend plots computed using * Mn K_{α}* line.
Each page shows five different CTI trend plots. From the top to the bottom, they are:

- Un-corrected cases with an integration time > 2000 sec
- The focal temperature ≤ -119.7 C cases with an integration time > 2000 sec
- The focal temperature ≤ -119.7 C with an integration time > 7000 sec
- Newly computed temperature dependency corrected cases with an integration time > 2000 sec
- MIT/ACIS temperature dependency corrected cases with an integration time > 2000 sec

The third case is the * cleanest estimation*, but we lose many data points, especially after year 2012.
The fourth/fifth cases keep all data points, but they may introduce errors from temperature corrections.
Two trending lines are fitted on each plot. The dividing point are slightly different from that of the combined data.
For the imaging and the spectral CCDs, the division point is year 2011 and year 2009 for the backsdie CCDs.

CTI data are far more scattered after year 2012 and extreme data points are dropped before fitting the trending lines. These scatters were introduced because less and less time, the focal tempearture stays at or around 119.7C and fractuates widely.

CCD0 | CCD1 | CCD2 | CCD3 | CCD4 | CCD5 | CCD6 | CCD7 | CCD8 | CCD9 |
---|---|---|---|---|---|---|---|---|---|

Quad0 | Quad0 | Quad0 | Quad0 | Quad0 | Quad0 | Quad0 | Quad0 | Quad0 | Quad0 |

Quad1 | Quad1 | Quad1 | Quad1 | Quad1 | Quad1 | Quad1 | Quad1 | Quad1 | Quad1 |

Quad2 | Quad2 | Quad2 | Quad2 | Quad2 | Quad2 | Quad2 | Quad2 | Quad2 | Quad2 |

Quad3 | Quad3 | Quad3 | Quad3 | Quad3 | Quad3 | Quad3 | Quad3 | Quad3 | Quad3 |

The following table shows the links to individual CCD/Quad plots similar to above, but the data are detrended by dtracning drop amp effect.
See *How CTI are computed?* section for details. Backside Illuminated CCDs 5 and 7 are not detrended and
not included.

CCD0 | CCD1 | CCD2 | CCD3 | CCD4 | CCD5 | CCD6 | CCD7 | CCD8 | CCD9 |
---|---|---|---|---|---|---|---|---|---|

Quad0 | Quad0 | Quad0 | Quad0 | Quad0 | Quad0 | Quad0 | Quad0 | Quad0 | Quad0 |

Quad1 | Quad1 | Quad1 | Quad1 | Quad1 | Quad1 | Quad1 | Quad1 | Quad1 | Quad1 |

Quad2 | Quad2 | Quad2 | Quad2 | Quad2 | Quad2 | Quad2 | Quad2 | Quad2 | Quad2 |

Quad3 | Quad3 | Quad3 | Quad3 | Quad3 | Quad3 | Quad3 | Quad3 | Quad3 | Quad3 |

Although they are not clean as CTI computed from *Mn K _{α}* line, we also computed CTI based on

Line | CCD0 | CCD1 | CCD2 | CCD3 | CCD4 | CCD5 | CCD6 | CCD7 | CCD8 | CCD9 | |
---|---|---|---|---|---|---|---|---|---|---|---|

Al K alpha | Quad0 | Quad0 | Quad0 | Quad0 | Quad0 | Quad0 | Quad0 | Quad0 | Quad0 | Quad0 | |

Quad1 | Quad1 | Quad1 | Quad1 | Quad1 | Quad1 | Quad1 | Quad1 | Quad1 | Quad1 | ||

Quad2 | Quad2 | Quad2 | Quad2 | Quad2 | Quad2 | Quad2 | Quad2 | Quad2 | Quad2 | ||

Quad3 | Quad3 | Quad3 | Quad3 | Quad3 | Quad3 | Quad3 | Quad3 | Quad3 | Quad3 | ||

Line | CCD0 | CCD1 | CCD2 | CCD3 | CCD4 | CCD5 | CCD6 | CCD7 | CCD8 | CCD9 | |

Ti K alpha | Quad0 | Quad0 | Quad0 | Quad0 | Quad0 | Quad0 | Quad0 | Quad0 | Quad0 | Quad0 | |

Quad1 | Quad1 | Quad1 | Quad1 | Quad1 | Quad1 | Quad1 | Quad1 | Quad1 | Quad1 | ||

Quad2 | Quad2 | Quad2 | Quad2 | Quad2 | Quad2 | Quad2 | Quad2 | Quad2 | Quad2 | ||

Quad3 | Quad3 | Quad3 | Quad3 | Quad3 | Quad3 | Quad3 | Quad3 | Quad3 | Quad3 |

Line | CCD0 | CCD1 | CCD2 | CCD3 | CCD4 | CCD5 | CCD6 | CCD7 | CCD8 | CCD9 | |
---|---|---|---|---|---|---|---|---|---|---|---|

Al K alpha | Quad0 | Quad0 | Quad0 | Quad0 | Quad0 | Quad0 | Quad0 | Quad0 | Quad0 | Quad0 | |

Quad1 | Quad1 | Quad1 | Quad1 | Quad1 | Quad1 | Quad1 | Quad1 | Quad1 | Quad1 | ||

Quad2 | Quad2 | Quad2 | Quad2 | Quad2 | Quad2 | Quad2 | Quad2 | Quad2 | Quad2 | ||

Quad3 | Quad3 | Quad3 | Quad3 | Quad3 | Quad3 | Quad3 | Quad3 | Quad3 | Quad3 | ||

Line | CCD0 | CCD1 | CCD2 | CCD3 | CCD4 | CCD5 | CCD6 | CCD7 | CCD8 | CCD9 | |

Ti K alpha | Quad0 | Quad0 | Quad0 | Quad0 | Quad0 | Quad0 | Quad0 | Quad0 | Quad0 | Quad0 | |

Quad1 | Quad1 | Quad1 | Quad1 | Quad1 | Quad1 | Quad1 | Quad1 | Quad1 | Quad1 | ||

Quad2 | Quad2 | Quad2 | Quad2 | Quad2 | Quad2 | Quad2 | Quad2 | Quad2 | Quad2 | ||

Quad3 | Quad3 | Quad3 | Quad3 | Quad3 | Quad3 | Quad3 | Quad3 | Quad3 | Quad3 |

The following links show CTI change rate per year of each quadrant and those of averaged cases are listed.

- Fitting Results: Int Time > 2000 sec
- Fitting Results: Int Time > 2000 sec & Temp <= -119.7 C
- Fitting Results: Int Time > 7000 sec & Temp <= -119.7C
- Fitting Results: Int Time > 2000 sec, MIT/ACIS Temp Factor Correction
- Fitting Results: Int Time > 2000 sec, Updated Temp Factor Correction

- Fitting Results: Int Time > 2000 sec
- Fitting Results: Int Time > 2000 sec & Temp <= -119.7 C
- Fitting Results: Int Time > 7000 sec & Temp <= -119.7C
- Fitting Results: Int Time > 2000 sec, MIT/ACIS Temp Factor Correction
- Fitting Results: Int Time > 2000 sec, Updated Temp Factor Correction

Al K alpha | CCD 0 | CCD 1 | CCD 2 | CCD 3 | CCD 4 | CCD 5 | CCD 6 | CCD 7 | CCD 8 | CCD 9 |
---|---|---|---|---|---|---|---|---|---|---|

Mn K alpha | CCD 0 | CCD 1 | CCD 2 | CCD 3 | CCD 4 | CCD 5 | CCD 6 | CCD 7 | CCD 8 | CCD 9 |

Ti K alpha | CCD 0 | CCD 1 | CCD 2 | CCD 3 | CCD 4 | CCD 5 | CCD 6 | CCD 7 | CCD 8 | CCD 9 |

CTIs are computed in the following steps:

- ACIS evt1 data file for CTI observation is extracted from Database
- Find the time span of the observation and extract the focal temperature data for that duration.
- Compute an average focal tempearture of that observation.
- If the integration time is more than 600 sec, compute CTI using MTA CTI computing tool.
- The extracted data are listed in ASCII data. The columns are:
- start time
- quad 0 CTI
- quad 1 CTI
- quad 2 CTI
- quad 3 CTI
- obsid
- end time
- averaged focal plane temperature
- standard deviation of the temperatre
- minimum temperatre of the period
- maximum temperatre of the period
- start time in sec from 1998.1.1
- end time in sec from 1998.1.1

- If the averged focal plane temperature is colder than or equal to -119.5 C, the data are used to create a plot without any adjustment.
- This data are further refined by selecting only data with the integration time longer than 7,000 seconds.
- If the focal plan temperature is warmer than -119.5 C. A correction is done
for CTI. The correction factor is computed as follows:
- Fit a straight line with time as an independent variable to the data with the focal plane temperature ≤ -119.7 C and the integration time longer than 7000 sec.
- Use the fitted values to remove a time dependent CTI evolution.
- Fit a straight line onto this data, but this time use the focal plane temperature as an independent variable. Set the correction at -119.7 C to zero.
- The resulted The correction factors are in CTI chage per degree.
- Using these correction factors, adjust all CTIs with focal temperature warmer than -119.7 C. Anything data colder than -119.7 C are used without the correction.

- Similar plots with MIT/ACIS team corrections are also plotted. The correction factor for front side CCD is 0.036, and the backside CCD is 0.045.
- To detrace drop amp effect, detrend correction factors are computed
- A corresponding acis stat fits file is extracted from database.
- Selecte out drop amp data for CCD7, and compute an average of the drop amp
- The average is devided by 680 to normalize the correction factor. the value 680 was computed by MIT/ACIS team (08/18/2000).
- The correction factor is added to the CTI to remove drop amp effect.

*
If you have any questions about this page, contact swolk@cfa.harvard.edu.
*

Last Update: Sep 24, 2021.