Speaker
Description
XRISM is the seventh Japanese X-ray astronomical satellite planned to be launched in early 2020's, and carries an X-ray charge-coupled device (CCD) camera as one of the two focal plane detectors. The camera has four P-channel back-illuminated CCDs with an imaging area size of 31 mm $\times$ 31 mm arranged in a 2$\times$2 array. The charge transfer inefficiency (CTI) is defined as a fraction of charge loss per one pixel transfer, which is caused by the trap of signal charge with defects in the channel, and the modeling of the CTI is the key of the CCD calibration especially for such a large-format CCD. The CTI depends on several operational/observational parameters: transfer rate, pixel size, X-ray photon energy, X-ray event grade, X-ray photon flux, CCD temperature, and so on. We here present an experimental study on the CTI dependencies on these parameters. X-ray CCD data frames are obtained with different clocking modes, different incident X-ray energy, different X-ray photon flux, and different CCD temperatures. Analyzing this data set allows us to disentangle the degeneracy of the CTI dependencies and build a more reliable CTI correction model. X-ray spectra before and after applying the CTI correction utilizing these results are also shown.
| Submission declaration | Original and unpublished |
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