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ROSAT Status#121: New PSPC Calibration Memo Available

			ROSAT Status Report #121
			      March 9 1995


A new memo is available detailing some new insights into the PSPC energy
calibration problem. The memo discusses the discovery of a significant
problem in the spatial gain correction, and details work in progress
towards a new ftool to correct for both the spatial and temporal gain shift 

The memo, entitled "Status of the PSPC Spatial/Temporal Gain Calibration"
by Snowden, Turner, George, Yusaf, Predehl and Prieto is available 
in html and postscript formats via the World Wide Web from either the 
link on the ROSAT GOF page 

(http://heasarc.gsfc.nasa.gov/docs/rosat/rosgof.html, under "Calibration  

or (more directly) via 


the memo is also available in latex and postscript formats from the
legacy.gsfc anonymous ftp account under 




The SASS PSPC data processing software corrects for time and spatial
variations in the detector gain as part of the conversion from detected
pulse height to pulse invariant channels. Analysis of the in-flight AlK
calibration data has shown that there is an error in the spatial gain
correction currently applied in SASS, and also that there are uncalibrated
effects which need to be considered, requiring some additional correction
based on detector coordinates and arrival time (DETX, DETY, and TIME) of
each event. The AlK data allow us to construct a gain map which can be
used to correct the PI data.  Whether or not the required correction is
pulse-height dependent is not known, and will require considerably more
work to determine.