HXD: Energy scale

Calibration status and caveats

• HXD/PIN
  The energy scale of the PIN diodes can be calibrated by using energy spectra of fluorescence lines from GSO scintillators. The fluorescence events can be effectively extracted by selecting only coincidence events between PIN and scintillators of the same well unit. Figure 1 shows the thus-obtained energy spectrum of a PIN diode. By fitting the spectra with four Gaussian profiles and a background continuum, the peak pulse-height channels of the Kalpha1 line were obtained for individual PINs. Figure 2 compares the Gd Kalpha1 peak channels of the 64 PINs between two different periods after the launch. Thus at least for half a year, the PIN gains have stayed constant within one ADC channel (~0.4 keV). The energy scale agrees well with the pre-launch ones measured in an energy range of 20-50 keV, and the accuracy is estimated to be about 1%. Note that there are some PINs that have significant non-linearities above 50keV. See Suzaku memo 2006-37 for information.
  
  
  Figure 1: Energy spectrum of a single PIN diode, in which the coincident events of PIN and GSO are accumulated over a half year. Four Gaussian profiles correspond to the Kalpha1 (43.0 keV), Kalpha2 (42.3 keV), Kbeta1+beta3(48.6 keV) , and Kbeta2(50.0keV) lines.
  
  
  Figure 2: Comparison of the Gd K peak channels of the 64 PINs between two periods, 1-2 and 7-9 months after the launch.
  
  
• HXD/GSO
  in preparation
  
  Figure 3: Typical phoswitch pulse-height spectra of one Well unit, acquired in orbit from a blank sky. The line components utilized to calibrate the gain are indicated with the arrows.