XRT/XIS: Correction of thermal wobbling

Calibration status and caveats

• Correction of thermal wobbling (Ref. Suzaku memo 2007-04)
  The attitude of Suzaku sometimes drifts in both DETX/Y directions with a typical peak-to-peak amplitude about DETX~60" and DETY~30", mainly synchronized with the spacecraft orbital period. This effect blurs the spatial photon distribution on the detector plane and thus causes significant distortion of the core of a point spread function. The empirical method to correct this effect have been investigated and the application to XIS event files is found to improve the accuracy of the derived source positions from 60" to 20" (see Figure 1). The wobbling correction to XIS data will be made, starting from V2.0 processing, with aeattcor, and the new attitude files are scheduled to be released this summer. See Suzaku memo 2007-04 for further information.
  
  Note: the wobbling is not corrected for the Ver1.x data, which would thus contain deviation on the order of DETX~60" and DETY~30". Users who wish to reduce this effect may run the FTOOLS aeattcor and produce event files equivalent to the Ver2 data from the Ver1.x data.
  
  
  Figure 1: (Left) Wobbling-correction before and after. Time-integrated XIS0 images made with (X,Y) columns for HerX-1 are displayed. North(Y) is up and west(X) is to the right. The double circles with a radius of 10 and 20 show the nominal(expected) position of the source. The source peak in the wobbling-corrected image (in the right panel) is closer to the nominal position. Furthermore, a wired PSF shape of the original image is clearly improved. (Right) Distributions of source distances r from the nominal position. The top panel shows the r distribution for 20 observations before wobbling-correction, while the bottom panel shows that after correction.

Related links

• Suzaku memo 2006-34 "The X-ray Telescope onboard Suzaku"
• Suzaku memo 2007-04 "Empirical Correction of Thermal Wobbling"