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ASCA Guest Observer Facility

Ascascreen rejected all my data!

What to do when ascascreen skips all your files

When you run ascascreen, you first interact with a Perl shell program that prompts you for the screening criteria. Then the Perl shell writes these criteria into command and selection files. Finally, it starts up xselect, which uses the command file (the prefix.xco file, by name, where prefix is the session name you chose) and the selection files (prefix_mkf.sel, prefix_obscat.sel and for the GIS, prefix_randc.reg) to implement your screening criteria.

In the xselect stage, during the sisclean or extract commands, it is normal to see an occasional message:

Skipping file: /data/ASCA/raw/ft930601_0923_0416S000102M.fits

This arises when the given file lies wholly outside the timing filters being applied. In the xselect session run by the prefix.xco file, these filters are entered through the select mkf command.

However, sometimes the extract or sisclean stages of ascascreen will skip all, or all but one or two of the files in your data, leaving you with very few photons. There are two possible causes for this effect: Too restrictive mkf selections and, for GIS only, a bug in FRFread.

Too restrictive mkf selections

One cause is that, due to some peculiarity in your data, the normal screening criteria are too restrictive. As an example, consider the following: one of the standard criteria restricts the deviation of the satellite from the mean pointing for the observation. Suppose, however, that the observation is short, and the satellite took too long to settle down. Then the mean pointing could be off from the stable pointing enough to cause a normal setting for the angular deviation to reject most of the data.

To diagnose such problems as these, look at the prefix_mkf.sel file (prefix is the session name you chose in ascascreen.) It consists of a series of Boolean relations. The LHS of each relation is the name of a parameter in the mkf file, which is the file that contains the digest form of the housekeeping information used to do the data screening. The RHS is the value(s) that constrains it. You can use the mkfbin command to plot the mkf parameters, and plot mkf to plot them. For instance, if the prefix_mkf.sel file read:

You could say:
> Give print-out time interval >[40] 
xsel:ASCA > plot mkf
The available parameters are:
- ----------------------------
 0 - TIME
 1 - SAA
 2 - ELV
 3 - COR
 6 - G2_L1
> Enter independent variable ( 0 for TIME ) >[0] 
> Enter dependent variables (e.g. 1-6) >[1-2] 1-6
Then you can examine the plots to see which parameter is causing the rejection, and how much you have to relax the bounds to get the data to pass. Also, if you provide this information to the ASCA GOF, it will be much easier for us to figure out what is unique in your data, and what this might mean for your analysis.

Bug in FRFread (GIS data only)

When mkfilter, the program which creates mkf files, was upgraded to mkfilter2, a bug in FRFread became apparent in the form of currupt mkf files. Versions of FRFread up to 3.027 incorrectly truncated the GIS HK files under certain circumstances; the bug was not noticed before because mkfilter, the version used in Rev 0 processing, did not use the HK files as input. As a result, the G2_L1 and G3_L1 columns in the mkf file remain undefined for most of the file. Since these parameters are used in the routine cleaning for the GIS instrument, this bug will result in the rejection of a substantial fraction of your GIS data.

To see if this is the case for your data, start up xselect, set the datadirectory to wherever your data resides, and issue the commands:

xsel:ASCA > mkfbin "G2_L1 G3_L1"
> Give print-out time interval >[40]
xsel:ASCA > plot mkf
The available parameters are:
- ----------------------------
0 - TIME
1 - G2_L1
2 - G3_L1
> Enter independent variable ( 0 for TIME ) >[0] 0
> Enter dependent variables (e.g. 1-6) >[] 1-2
Look at the plot, and if the values are -99.9 for most of the plot, your mkf file has been corrupted by this bug.

The bug was fixed in August 1995. If you happen to have data affected by this, please obtain a newer version from the archive.

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This file was last modified on Tuesday, 09-Mar-2004 11:18:04 EST

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