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WARNING: Problems with WMAPS since Oct 1996

Date: Fri, 17 Jan 1997 15:25:48 -0500 (EST)
Subject:  Problems with WMAPS since Oct 1996

	BUG WARNING: Problems with WMAPS since Oct 1996

A bug was recently found in the ftools extractor which affects the weighted
map extension of spectra selected using sky coordinates. This means ROSAT
spectra will be affected (but *not* most ASCA spectra, as the latter are
usually extracted based on a selection in detector, not sky coordinates).
The weighted map should contain the number of counts in each detector pixel
within the selected region (even when selected on a sky image). The bug
flags excluded pixels with a +1 instead of a -1, which means the pixels
were included instead of excluded when the map was used by other tools. For
ROSAT this will yield erroneous arf files from PCARF, and erroneous
particle background spectra from PCPARPHA. This error appears to date back
to the October 1996 release, ftools v3.6. More details can be found on 


along with details on how to fix the problem. We apologise for any
inconveniences this has caused, and thanks to Patrick Wojdowski for
bringing it to the attention of the GOF.