The index page lists the Swift-BAT GRB triggers since 2007. The trigger number, date of the trigger and the presumed name are given. When the page is first created the name is produced from the date, and any other BAT GRB triggers reported that day; if this is incorrect (e.g. another satellite has already reported a burst that day) the name will later be updated manually. If a BAT retraction notice is received, the trigger will be automatically removed from the table. If the trigger is determined not to be a GRB, but no retraction notice is issued, the trigger will be manually removed from the table.
A GRB region page is automatically generated when a Swift/GCN notice containing the line "This is a GRB" is received. There is one page per BAT trigger number and this page is updated when XRT or UVOT position information becomes available (see the updating section below). The purpose of these pages is to collect in one place some summary information about the burst and about the immediate vicinity, allowing potential host galaxies or non-GRB sources of the trigger to be quickly identified, as well as detailing information which may be useful to observers such as the Galactic extinction.
The first section of the page contains two tables of information. The left hand table gives the Swift- BAT, XRT and UVOT positions (if available) of the GRB. These are initially parsed from the GCN Notices, however the XRT position may be updated using SPER data (see updating, below). The Galactic column density (from Kalberla et al. 2005) is also given, as is the Galactic extinction (provided by NED).
The right-hand table gives the most precise of the Swift positions both in ecliptical and Galactic co-ordinates. It also presents the angle between the GRB and the Sun at the time of the trigger. To see how the visibility of the GRB varies with time use the link described in the next section.
Two links are provided next. The first of these opens the Aladin tool (provided you have Java installed). DSS (IR, Red and Blue) 2MASS (JHK) and Skyview images of the region around the GRB are automatically loaded, as are the GSC and NED catalogues.
The second link is to the UKSSDC target visbility Calculator and shows the angle between the Sun and the GRB for a year after the trigger.
The final part of the page contains 4 tables; the results of a series of catalogue searches around the GRB position. The radius of the search and the position sought are given in the header to the section; the search radius defaults to 3.3 arcmin (to provide full coverage of the BAT error circle and UVOT image), and the best available Swift position is used. Each table is initially ordered by increasing distance from the best Swift position (given in the right hand summary table), although clicking on the "Offset" and "Magnitudes" ("Count rate" for the X-ray sources table) will sort the table on that column instead. A second click on the column header will reverse the order.
To keep the page concise, only the first 10 entries are shown in each table; if there are more than 10 items a link to the full list of objects appears below each table. Note that if you chose to sort the table, the full list is sorted. So, for example, if you sort by magnitude instead of distance, the 10 brightest sources in the entire list will be given in the main page, rather than just sorting the 10 closest sources by magnitude.
There are 4 columns which appear in every table; these are described below. Each table also contains several further columns, which are described for each table individually.
The GRB Region Information page is automatically updated whenever a new GCN/SWIFT position notice is received. The page may also be updated when XRT SPER data are processed; these are limited Photom Counting mode event lists delivered every 2 minutes during the first snapshot on a new burst (up to ~2 ks). If the position determined from the SPER has moved by more than half of the old position error, or if the new position error radius is ≤60% of the position error radius, the page will be rebuilt. When the page is being updated it will be temporarily unavailable; a warning page will instead appear. Rebuilding the page typically takes around 15 seconds.