uvotattcorr - adjust attitude file with information from UVOT aspect corrections
uvotattcorr attfile=<filename> corrfile=<filename> outfile=<filename>
The Swift spacecraft attitude is available from several sources
in the telemetry. Attitude knowledge onboard is not as fine as
what can be obtained from comparing positions of stars in UVOT
images to catalog positions. In addition, when the spacecraft
transitions between slewing and pointed observations, the source
of attitude information shifts from coarse to fine, resulting in
a noticeable jump in the earliest exposures found in particular
in GRB AT sequences. The purpose of uvotattcorr is to take the
refined position information obtained from 'uvotskycorr' and
apply it to the available spacecraft attitude
information (which is 'atjumpcorr'ed in the pipeline),
creating a more accurate attitude file.
The pipeline attempts to find an aspect solution for each image
in a UVOT observing sequence. The results of these corrections
can then applied to the existing attitude file. Since a sequence
can contain gaps between images (and thus aspect solutions), and
the exposure times can vary from tens of seconds to thousands of
seconds, the offsets are first interpolated before being applied
to the existing attitude. Corrections are considered valid for the
snapshot in which they occur. During a snapshot which has no
aspect corrections, no change is made to the attitude. Otherwise,
the correction at a given time is found by linearly interpolating
between (or extrapolating) the nearest known correction(s).
The solutions to the aspect corrections are found in the housekeeping
file sw*uac.hk. At present, the pipeline creates a new corrected
attitude file, sw*uat.fits, when uvotattcorr is run.
- attfile [filename]
- Swift attitude file (normally sw<obsid>sat.fits).
- corrfile [filename]
- UVOT aspect corrections file (normally sw<obsid>uac.hk).
- outfile [filename]
- Attitude file corrected for UVOT.
- (deltafile = NONE) [filename]
- Delta attitude file. The special value NONE indicates to not create this output.
- (chatter = 3) [integer] <1-5>
- Standard HEAdas chatter parameter.
The following examples illustrate running uvotattcorr
1. run uvotattcorr on a given attitude and corrections file
uvotattcorr attfile=sw12345678012sat.fits corrfile=sw12345678012uac.hk \
uvotskycorr, uvotaspcorr, attjumpcorr