Appendix 3: Photon Characteristics

**Table 7:** PSPC and HRI Photon characteristics
Property	PSPC		HRI
	MPE	US	MPE	US
XDET^a	0-8192	1-8192	0-4096	1-4096
YDET^a	0-8192	1-8192	0-4096	1-4096
XPIX^b	$-7680\rightarrow+7680$	1-15360	$-4095\rightarrow+4097$	1-8192
YPIX^b	$-7680\rightarrow+7680$	1-15360	$-4095\rightarrow+4097$	1-8192
Time	S/C time	S/C time	S/C time	S/C time
Raw PHA	1-256	1-256	0-15	0-15
Corr. PHA^c	1-256	0-255	1-1	1-1

^a Pixel position on the detector.
^b Pixel position on the sky. i.e. directly related to RA/DEC.
^c The raw pulse height from the PSPC is corrected for gain effects during the SASS pre-processing. This corrected PHA is related to the energy of the incident photon.

The sky pixels are defined and numbered differently in the US and MPE datafiles. US data increases from bottom to top, so for the PSPC, the bottom left hand corner pixel is 1,1. MPE pixel numbers decrease with increasing Y value, so the bottom left hand pixel is -7680,7680 and the top left hand corner pixel is -7680,-7680. Corrected PH channels have the same meaning in the two datasets, but the US supply channels 0-255 for PSPC data whereas the MPE data ranges from 1-256. The channel 0 PSPC data in the US files may not be used within ASTERIX.