2006-34: The X-ray Telescope onboard Suzaku - HEASARC - NASA

Fig. 8. Locations of the optical axis of each XRT-I module in the focal plane determined from the observationsof the Crab Nebula in 2005 August–September. This figure implies that the image on each XISdetector becomes brightest when a target star is placed at the position of the corresponding cross. Thedotted circles are drawn every 30 ′′ in radius from the XIS-default position (see the text).the average.3.2. Effective AreaIn-flight calibration of the effective area has been carried out with the version 0.7 processeddata (Mitsuda et al. 2006) of the Crab Nebula both at the XIS/HXD-default positions.The observations were carried out in 2005 September 15–16 (§3.1). The data were taken inthe normal mode with the 0.1 s burst option in which the CCD is exposed during 0.1 s out ofthe full-frame read-out time of 8 s, in order to avoid event pile-up and telemetry saturation.The exposure time of 0.1 s is, however, comparable to the frame transfer time of 0.025 s. Asa matter of fact, the Crab image is elongated in the frame-transfer direction due to so-calledout-of-time events, as shown in Fig. 9. Accordingly, the background-integration regions with asize of 126 by 1024 pixels are taken at the left and right ends of the chip for the XIS-defaultposition, perpendicularly to the frame-transfer direction, as shown in the left panel of Fig. 9.For observations at the HXD-default observation, the image center is shifted from the XISdefaultposition in the direction perpendicular to the frame-transfer direction for XIS0 andXIS3. Hence we can adopt the same background-integration regions as those of the XIS-defaultposition for these two XIS modules. For XIS1 and XIS2, on the other hand, the image shiftoccurs in the frame-transfer direction, as shown in the right panel of Fig. 9. We thus take a13