epframes reads a raw event list of a single CCD and exposure from an EPIC PN ODF () . The input file is specified giving the actual filename or a symbolic form of it (which will be expanded with OAL_expandFileName). The ODF in use is defined via the SAS environment variable SAS_ODF prior to execution. epframes uses the summary file from the ODF to display info about the selected observation and to fill in standard header keywords. The auxiliary, main periodic housekeeping and spacecraft time correlation files corresponding to the selected EPIC PN raw event list are needed for the computation of event time tags.
epframes flags events with faulty coordinates or times in a FLAG column. The flags are bit-masked following the same code as for the MOS (see ). epframes stores statistics about these wrong events in FITS keywords (WRGCOORD, WRGORDER and WRGTIME) in the output event list. The statistics of bad frames is stated in the history of the output file.
The raw event list is converted into a table to be processed by other SAS tasks: The existing columns RAWX, RAWY and ENERGY in the ODF files are renamed to RAWX, RAWY and PHA, respectively. We note that the RAWX and RAWY coordinates in the output file have values increased by +1 with respect to the raw coordinates in the ODF/SDF file. For the same reason epframes adds 1 to the WINDOWX0, WINDOWY0 attributes giving the bottom left corner of the readout window. The PHA values are the event raw amplitudes corrected for column offsets. A CCDNR column gives the overall CCD number (1 - 12).
The FRAME counter column (in TIMING and BURST mode together with the RAWY events coordinate and the srcposition parameter or in the case of withsrccoords=Y srcra and srcdec instead) is used to compute the TIME for each event. The time tag computation is based on equations given in EPIC-EST-OP-002 Sects.8.3.1 and 8.3.2 (version Sept.99) . Please, see the warning in the description of the parameter withsrccoords!
A GTI file is produced listing start and stop times of the observation and taking care of missing or bad frames.
epframes creates an EXPOSURE extension (renamed by evlistcomb to EXPOSUxx, xx = 01 - 12) giving details about frame time tags and integration times. These have been corrected for mode dependent readout gaps (livetime factor FC0).
evlistcomb does not apply changes to the exposure extensions and these thus contain CCD specific information also in the FITS headers (the individual EVENTS extensions are merged and individual FITS header information is lost there). Besides housekeeping related quantities (see Sect.7.2) there is also processing relevant information like the occurence of the SAS infrastructure warning ``InvalidObtValue'' in the keyword OBT_WARN.