When you download Quick Look or obs data from the Swift archives, you have the option to download the SDC processed data, or locally reprocessed data. The difference between these is only in the XRT data.
The SDC-processed data are those provided by the NASA Swift Data Center (SDC),
which for uniformity are available from the SDC, ASDC (Italy) and our website. These
are not guaranteed to have been processed with the most recent
calibration and software. Also, older datasets are not routinely
reprocessed, so the software and calibration versions used for the SDC
data are not consistent across the archive. The software and CALDB versions used in the
SDC processing are stored as
CALDBVER FITS keywords in
the data files; these will also be reported on the data download page, provided the
version is the same for all of the datasets selected. The SDC standard advice is
that users should reprocess the data themselves after downloading, using
For the locally-reprocessed data, the XRT data have been reprocessed at the UKSSDC in Leicester. As of December 2011, the entire XRT archive has been processed with HEASoft version 6.11, and the CALDB released in June 2011; the data download page will report the HEASoft version used in the local reprocessing of the data. We have also created exposure maps for each dataset which are available for download with the standard products. After a new software release, there will be a short delay while we verify that all of our local code works with the new software, and we will then both switch to using the new release for all incoming data, and completely reprocess the XRT archive. Note that this latter step will take several weeks to complete, during which time the archive will progressively be updated. As you visit the download page for a single ObsID, the page will tell you which software version was used to analyse those data.
Windowed Timing (WT) mode data have only one-dimensional spatial information,
thus to ensure that the source is placed at the correct RA and Dec, for ease of
must be given the correct source co-ordinates. The local reprocessing supplies the values in the
DEC_OBJ FITS keywords. If you are
analysing WT mode data therefore you should verify that these values are
correct for the source you are interested in, and if not, you should
xrtpipeline yourself, even if you downloaded the
If you have any questions about this, please contact the UKSSDC helpdesk on email@example.com.