ACIS CTI Plots

• What are plotted on this page?
• How CTI are computed?
• CTI Plots of Data
• Detrended CTI Plots of Data
• ASCII Data
• Correction Factors for Temperature Adjusted Plot

• An acis evt1 data for CTI observation is extracted from Database
• Comparing CTI data with focal plane temperature along observation time, data are extracted for a specific time period corresponding to each temperature segment. The temperature ranges are quantized like: -119.87, -117.0, -119.54, -119.38, -119.22.... Temperature is in C.
• For each extracted data,
  • If the integration time is more than 600 sec, compute CTI using MTA CTI computing tool. The data are listed in ASCII data The columns are start time, quad 0, quad 1, quad 2, quad3, obsid, stop time, integration time in sec, and focal plane temperature. If 99999 appears, the MTA tool could not compute the value.
  • If the integration time is more than 1000 sec and the observation was done before Jan 2003, the results are used for plotting.
  • If the integration time is more than 2000 sec and the observation was done from Jan 2003, the results are used for plotting.
  • Note that the tables say the integration time is lager than 2000 sec, but this reflects current selection of the integration time. Plotted data older than Jan 2003 could have less than 2,000 sec integration time.
  This crates un-adjusted basic plots (red).
• If the focal plane temperature is colder than or equal to -119.7 C, the data are used to create a plot without any adjustment (light green).
• This data are further refined by selecting only data with the integration time longer than 7,000 seconds (blue).
• If the focal plan temperature is warmer than -119.7 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 (fuchsia). Anything data colder than -119.7 C are used without the correction.
  You may want to read A Step by Step Example of Correcting Temperature Dependence of CTI for a better understanding.
• Similar plots with MIT/ACIS team corrections are also plotted (light blue). 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.
  All data, except for CCD5 and CCD7, are detrended and plotted below.

CTI Plots

Detrended CTI Plots

ASCII Data (Not Adjusted)

Correction Factors for Temperature Adjusted Plot
For Al K alpha
For Mn K alpha
For Ti K alpha

Memo

Does The CTI Correction Factor Changes With Time?

How to Select Data?

A Step by Step Example of Correcting Temperature Dependence of CTI

Last Update: 10/13/2008