| Archive | List of SWIFT Catalogs |
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The BAT can operate several configuration modes simultaneously. Each of the simultaneous modes is listed in separate records within this table. For a given time interval, there are several records (partially overlapping in time), each describing a single configuration/mode. The BAT modes collect data for the entire FOV but also have the capability to record rates (tag mask rate) for up to a few specific sky positions (typically 3) that correspond to a pre-assigned target ID. It is possible that at least two or more of these positions do not coincide with the BAT or NFI pointing position and therefore the target ID does necessarily coincide with Target_ID of the BAT or NFI pointing position. This table records for the position (RA and Dec) and Target_ID parameters the correct values associated to each of the mask tag data.
The Swift catalog was compiled from 4 catalogues: Tycho-2, GVCS III, NGC, and the Yale Bright Star Catalog. All catalogs were preprocessed before compiling the Swift catalog to achieve uniform columns and units. Next, they were merged into one catalogue before eliminating "red" objects and precessing all coordinates to epoch 2000.0. The catalog was then corrected for missing decimal points. Finally, the catalog was sorted by R.A. for ease of locating objects within the catalogue. The original catalog contained 239,853 objects brighter than 12.0 mags.
This table records high-level information for each Swift observation and provides access to the data archive. Each record is associated with a single observation that contains data from all instruments on board Swift. The BAT is the large field of view instrument and operates in the 10-300 keV energy band. The narrow field instruments, XRT and UVOT, operate in the X-ray and UV/optical regime, respectively.
An observation is defined as a collection of snapshots, where a snapshot is defined as the time spent observing the same position continuously. Because of observing constraints, the length of a snapshot can be shorter than a single orbit and it can be interrupted because the satellite will point in a different direction of the sky or because the time allocated to that observation ends.
The typical Swift observing strategy for a Gamma Ray Burst (GRB) and/or afterglow, consists of a serious of observations aimed at following the GRB and its afterglow evolution. This strategy is achieved with two different type of observations named Automatic Targets and Pre-Planned Targets. The Automatic Target is initiated on board soon after an event is triggered by the BAT. The Figure of Merit (FOM) algorithm, part of the observatory's autonomy, decides if it is worth requesting a slew maneuver to point the narrow field instruments (NFI) on Swift, XRT and UVOT, in the direction of the trigger. If the conditions to slew to the new position are satisfied, the Automatic Target observation takes place; all the instruments have a pre-set standard configuration of operating modes and filters and about 20000 seconds on source will be collected. The Pre-Planned Target observations instead are initiated from the ground once the trigger is known. These observations are planned on ground and uploaded onto the spacecraft.
This database table is derived from the Swift TDRSS messages sent on ground soon after a BAT trigger occurs on-board. For each trigger there are associated up to 14 messages, however not all are always generated and sent on ground. The messages are generated on board by the BAT, XRT and UVOT instruments and the Figure of Merit part of the observatory's autonomy. The BAT and XRT can each have five different message types. The UVOT and FOM can each have two different message types. These TDRSS messages are the results of the on-board data processing of the three instruments and some contain data products. They are first distributed via the GCN and later archived. The BAT messages are: alert, 'ack' containing the position, or 'nack' if the position could not be calculated, a lightcurve and scaled map. The XRT messages are: centroid containing the position, an image (if the position has been calculated), centroid error if the position could not be calculated, spectra in Low Rate Photodiode and Windowed Timing modes, a lightcurve. The UVOT messages are: finding chart containing star positions and a subimage centered on the XRT position. The FOM messages are used to indicate if the FOM will or will not observe the new target and if the spacecraft will (or will not) request a slew for the new target.
The parameters in this database table are a collection of high level information taken from the following messages : the BAT alert, 'ack' or 'nack' message, the FOM messages, the XRT position and image. If the information is not available the fields are left blank. All messages are provided as data products within this database table.
The UVOT runs only one type of configuration filter/mode/window in a given time interval. This database table, therefore, contains for a given time interval a single record that describes one configuration.
The XRT runs only one type of configuration mode/window in a given time interval. The table therefore contains for a given time interval a single record that describes one configuration. A new record is generated when the following is changing within an observation: new operating mode , new pointing mode, or new window configuration.
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