Bugs: reproject_events

The match parameter does not accept images as input. The warning message

# reproject_events (CIAO 4.4): Error: failed to open match file foo.img

does not make this clear to users.

reproject_events does not update the FITS keywords that describes the limits of the X and Y columns (TLMIN/TLMAX). These limits are used, for example by ds9, when displaying an event file to know the range of values to bin over.

If the reprojection involves a large field of view, eg making a mosaic, then the reprojected events may be located at x,y values outside the original TLMIN/TLMAX limits and the data will appear to have been cropped.

Setting the match parameter to an invalid RA/Dec (eg RA < 0 or Dec > 90 value does not trigger a warning and the tool will run to completion with undetermined results.

If the subspaces of the two files don't match - e.g. observation A was taken with S5 and that chip wasn't used in observation B - all the events are dropped from the output file (not just those on the chip that's missing).

The bug may also be described as: the tool needs one good time interval (GTI) per chip, otherwise the time for the other CCDs is set to zero.

The *NOM values from the original (unprojected) input file are copied to the output file. These values need to be updated to match the new WCS in order for dmcoords to work properly.

Running without updating the header will result in a warning from dmcoords:

unix% dmcoords reproj.fits
# dmcoords (CIAO): Warning: RA_NOM DEC_NOM different from WCS

# dmcoords (CIAO): RA_NOM DEC_NOM = 224.013371 -68.725793 
                                  WCS = 224.013323 -68.725752 

The spatial filter is recorded in the file subspace, but it is not reprojected when reproject_events is run. When reproject_events changes the sky tangent point, the region in the subspace is "shifted" in the reference frame.

In many cases, users run into this problem when they do the following order of events:

1. Use a spatial filter to select certain ACIS chips (e.g. just the ACIS-I array)
2. Run reproject_events on the filtered event file
3. Attempt to extract spectra with a source list.

The final output has zero exposure and/or empty GTIs because the source list and the initial, unshifted region filter (stored in the file subspace) don't intersect.

Workaround:

Use the DM subspace-editing capabilities to delete the filter specification written in the file subspace:

unix% dmcopy "reprojected_file.fits[subspace -sky]" reprojected_file_fix.fits

An alternative is to run reproject_events before applying any spatial filtering.