XRT/XIS: On-axis effective area

Calibration status and caveats

• Energy band: hard band, HEASOFT ver: 6.2 (xissim & xissimarfgen ver 2006-11-26)
  • Flux and photon index (Ref. Suzaku memo 2006-34 )
    The current uncertainty of the effective area of the XRT-XIS system is attributed to a calibrational error of the XRT. Based on the Crab observations in 2005, the on-axis effective area in the 2-10 keV band is well calibrated and accurate to about 2%. Table 1 lists flux and photon index of the Crab spectra, obtained from the power-law model fitting. Their uncertainties in the third and fifth columns of the table are derived by referring to the spectral parameters published by Toor & Seward (1974). On the other hand, the effective area below 1 keV is dependent on thickness of contaminating material on the surface of the XIS sensors and thus considered to show larger uncertainty. At energies < 2keV and >8 keV, the effective area is being calibrated.
    
    

    Table 1: Power-law model parameters of the Crab spectra taken on 2005-Sep

    Sensor	Flux	Flux uncertainty	Photon index	Photon index uncertainty
    XIS nominal position
    XIS0	2.15	3%	2.13+-0.02	1%
    XIS1	2.14	2%	2.07+-0.02	-1%
    XIS2	2.19	5%	2.09+-0.02	-1%
    XIS3	2.13	2%	2.07+-0.02	-1%
    HXD nominal position
    XIS0	1.97	-6%	2.14+-0.02	2%
    XIS1	1.94	-7%	2.09+-0.02	-1%
    XIS2	2.13	2%	2.10+-0.02	0%
    XIS3	2.15	3%	2.06+-0.02	-2%

    
    
    Figure 1: Power-law fit to the Crab spectra of all the four XIS modules taken at the XIS-default position. All parameters were set free, allowing them to vary independently for each XIS module. The fit was carried out in the 1.0-10keV band, but excluding the interval 1.5-2.0 keV where a large systematic error associated with the Si K-edge remains.
    
    
• Energy band: soft band, HEASOFT ver: 6.2
  • Under investigation
    
    
• XIS-HXD cross-calibration
  • Relative normalization factors of the XIS and HXD instruments are shown in Suzaku memo 2006-40
    
    

Related links

• Suzaku memo 2006-34 "The X-ray Telescope onboard Suzaku"
• Suzaku memo 2006-40 "Relative normalizations of XIS and HXD-PIN for V1.2.2.3 data"