Just as time marches on, so do SASS releases. SASS (Standard Analysis Software System) is the MPE supplied software that converts level 0 spacecraft data to the data products that the PI receives. Since the last newsletter, there have been ~20 SASS releases and corresponding installations at GSFC. The group here has gotten very good at installing new SASS releases and has enough processing capacity to eliminate any backlog. Currently we are caught up with AO5 data sent from MPE, and PIs should receive their data within ~5-6 weeks of the observation date. It takes approximately 4 weeks to get data from the spacecraft to the USRSDC on an 8mm tape. The other two weeks are processing and shipping time. To check data status, information on processing will soon be available on the US ROSAT Science Data Center (USRSDC) home page via the WWW. Users will also be able to reach this page from the HEASARC and the ROSAT GOF pages.
Some PIs have been receiving reprocessed AO data. The original reason for the reprocessing was to fix bugs in the older versions of SASS and add improved data products. Some of the fixes include correction of the photon timing problem, better background determination, better source detection, better attitude determination through the use of the WFC startracker in the attitude solution, and better data products such as SIMBAD source correlations for the HRI. The other fundamental reason for the reprocessing is to provide a common data format for the public archive. The Rationalized Data Format (RDF) was developed jointly by the USRSDC and MPE (see ROSAT Newsletter Number 10, pg. 14 for more information) and is a true FITS format. The first RDF release was RDF 0.6 on May 1993 and after many iterations RDF 2.4 was used for the beginning of the reprocessing in May 1994. The ROSAT Results Archive (RRA) (see page 13 in this issue for more information) came into being shortly thereafter and further requirements were imposed on the RDF such as including a light curve and adding various FITS keywords that help researchers make better use of the archival data. This resulted in further RDF releases. To date there have been 28 RDF releases and currently reprocessing is using RDF 3.4. This RDF has been agreed upon by both the USRSDC and MPE to be the final archival version.
Different SASS and RDF versions exist, and now to further confuse everyone there are different processing and reprocessing versions or revisions. REV0 processing refers to ROSAT DAY (RODAY) 28 through RODAY 852 excluding the survey. REV1 starts with RODAY 853 and goes through 1318 (observation dates Sept. 18, 1992 to Dec. 21, 1993). REV2 starts with RODAY 1319 and keeps on going. As a PI, all these reprocessings will only affect REV0 data. If your observation was prior to RODAY 853 you will get a new data set in the mail that was processed using REV2 and these NEW REV2 data will have a 6 month proprietary time period. In general, most observations will not be that greatly affected. All later observations will be reprocessed for the purpose of creating a uniform archive and these data will not be distributed to PIs since the difference between REV1 and REV2 is primarily a matter of formats.
There are two parts to the reprocessing: running SASS as REV2 and reformatting the data using RDF 3.4. The latest SASS (version 7_7) with RDF 3.4 will insure that data will be consistent on both sides of the Atlantic and can be used by the staff to populate the RRA. Currently we have reprocessed data to RODAY 710 (exclusive of days 373-443) using REV2 but we have to apply RDF 3.4 to bring the data to spec. RODAYS 711 to 1318 have to be reprocessed with REV2 and RDF 3.4. RODAYS 1319 to 1780 only have to have RDF 3.4 applied to them (reformatting) while the rest of the data is up to spec.
In summary, AO5 and later data are flowing smoothly while reprocessing is being done to achieve a uniform archive and most importantly to extract data into a format that can be easily accessed by users. In the future, if there are problems (with the gain, for example), the user will probably be able to run project-provided software that will correct this problem. This will be possible because required data such as "raw coordinates" are now accessible in RDF 3.4. This is designed to alleviate the need for future reprocessings.
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