Archive

This guide describes the contents and organization of the Swift archive.

Where and when the data are available

The Swift data will be quickly available to the community. The first-look data from the three Swift instruments for a newly discovered GRB and its afterglow are transmitted to the ground via TDRSS. The complete telemetry (including the messages transmitted via TDRSS) is subsequently sent down via the Malindi ground station. There are about 6-7 dumps to Malindi per day and these data are processed and put on-line in the quick-look area within a day. The final merged data are moved over to the main archive about a week after the end of the GRB observation. The timeline showing when the various types of data are available is shown in the following figure.

Figure 1.1: Swift data availability timeline

The three instruments on board Swift, the Figure of Merit (FoM) software, and the on-board command and data handling (C& DH) system, all generate a series of messages for each BAT trigger which are transmitted to the ground using TDRSS. For each trigger, the number of messages that are sent down depends on whether or not the trigger is confirmed by the BAT image processor, and whether or not the observatory slews to the new GRB so it can be observed by the XRT and UVOT. These messages are broadcast via the Gamma-Ray Burst Coordinates Network (GCN) as soon as they arrive on the ground, and later included in the archive. If users want to be notified of these alerts, they should enrol in the GCN (http://gcn.gsfc.nasa.gov). The processing of the data telemetered to Malindi occurs at the Science Data Center (SDC), which produces both the quick-look and the final archive data. Quick-look data are produced after each Malindi dump. This typically results in the same observation (see Chapter 2) being reprocessed several times as new data arrive to fill in any gaps. After each processing, the data are made publicly available within a few hours on the SDC's Quick Look facility.

When an observation is complete, the data flow through the processing pipeline one final time to produce data for the final archive. Therefore, the data for the final archive are generated by the same pipeline and software used for the quick-look data.

When no new processing has occurred on a particular observation for one week, the data are moved from the SDC's Quick Look Facility to the Swift Archive at the HEASARC and the other European archive centers in Italy and UK, and then removed from the Quick Look Facility. Users should be aware that the quick-look data for a given observation may not be complete, especially the early dumps of an observation, and that the contents may change when and if subsequent telemetry dumps arrive.

Overview of the Swift archive

The Swift archive contains all the information, data and software which are needed to analyze Swift data. The Swift archival data are divided into six main areas, which are all populated on different timescales:

Observation data

The Swift data are divided into observations which are identified by a specific sequence number. For each observation, the archive will contain the data generated by the final processing pipeline. The data for an observation include the telemetry converted into FITS format with minimum processing (Level I), the calibrated and filtered data (Level II), and the results from the standard analysis carried out on the Level II data (Level III). The latter category provides a quick overview for each GRB/afterglow observation, and includes BAT light curves in several energy bands and spectra, XRT images, spectra and light curves, and UVOT integrated color images. All data are in FITS format and follow the OGIP standards for high-energy astronomy data. In addition to the FITS files, each observation includes GIF plots which preview the FITS products, and an HTML file which records the processing history. The observation data populate the archive from the start (see the section on the Swift data proprietary period), and is used to create additional catalogs and data products.

TDRSS messages

As mentioned in the previous section, the TDRSS messages also form part of the Swift archive. The messages will be converted into FITS, and the long messages will also be processed in order, for example to reproject the images from the XRT and UVOT and the UVOT finding chart into sky coordinates. The TDRSS data populate the archive immediantly after processed by the SDC.

Trend and Monitoring data

This data set is created as part of the reformatting process of the Malindi data into FITS, and may include files containing monitoring information on specific instrument parameters, or some telemetered data which may not be strictly relevant to the science data. The trend data are organized in directories, each dedicated to a data type, such as background files.

Archival calibration data

The calibration data necessary for data analysis are available in the calibration database (CALDB). The Swift instrument teams have the responsibility of providing the results of their calibration efforts to the Science Support Center (SSC), accompanied by the proper documentation. The files are delivered in FITS format, and follow the recommended CALDB standards. The SSC then delivers the calibration data to the HEASARC and the other data centers in a form suitable for inclusion in the CALDB area. CALDB is populated every time new CALDB files become available or in conjunction with the software releases, if the files impact the software.

GRB Summary products

A typical GRB/afterglow will be followed up in several observations, depending on the brightness of the afterglow in the optical through X-ray regions. In order to give a standard overview of the GRB and its afterglow evolution, summary products will be systematically generated by a processing run at the HEASARC once the afterglow has faded away. These products will include all of the data from the three Swift instruments which are available in the archive. These data sets will start being populated into the Swift public area when software and products mature.

BAT, XRT, and UVOT surveys

Each of the instruments will conduct a survey in their respective energy bands. These surveys will contain information about the serendipitous sources found in the FOV of the three instruments while following GRB afterglows. While the XRT and UVOT will cover only a small fraction of the sky, the survey results for the BAT will effectively form an all-sky survey. Each instrument will produce a source catalog and derived data products, and, depending on the instrument, these will be either associated with individual sources and/or with the FOVs. Each survey will be conducted by combining the appropriate data for that instrument. The analysis of the BAT survey will be performed on a number of different timescales. Data products and catalogs from the XRT, UVOT and BAT will began to populate the Swift archive after the first year of the mission. The XRT survey by is being conducted by ISAC, the BAT survey by the BAT team at GSFC and LANL, and the UVOT survey by the UVOT team members at MSSL.

Database tables

Database tables recording high level information on the observation are used to browse the data. There is one general table and one specific table for each of the instruments describing the specific modes used during the observation. There is also a table dedicated to the TDRSS messages which includes most of the TDRSS messages content.

Proprietary Data Rights

There are no proprietary rights for any of the data obtained by the Swift Observatory. All data will be released to the community as soon as it has been processed by the SDC. The only exception to this was during the initial activation and verification phase of the spacecraft and instruments operation. The verification phase lasted approximately 4.5 months starting from launch.