About the GRB Region information pages

Index page

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.

Overview

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.

In detail

Each page has the same layout: summary information, useful links, catalogue images, UVOT images, XRT SPER data, catalogue searches. These items are discussed in detail below.

Summary information

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.

Useful links

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.

Catalogue Images

The third section of the page shows blue DSS and J-band 2MASS images, centred on the BAT position, with the Swift positions marked. These images are thumbnails and link to larger version; the FITS versions are also provided. Note: Unfortunately the 2MASS image returned by the 2MASS image server does not always cover the entire BAT field of view

UVOT images

Any processed UVOT images received via GCN appear next on the page. Blue circles on the image mark the positions of the catalogued sources listed in the catalogue searches section of the page. The Swift GRB positions from BAT, XRT and UVOT are also marked if available. The small images on the main web page are links to larger versions. The UVOT filter and exposure details appear below each image.

XRT Sper data

A brief summary of the XRT SPER data is also provided, if such data have been received. The number of SPER images received to date is listed and an image of the field is shown. If a source was found, details of this source are listed. For full details of the SPER data analysis, see the SPER documentation page, or Evans et al. (2009).

Catalogue searches

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.

Columns common to all tables

Offset: Distance from the GRB in arcseconds.
RA: The right ascension (J2000) in decimal degrees.
Dec: Declination (J2000) in decimal degrees
Query: A link which will search all Vizier catalogues for objects within 5 arcseconds of the object detailed in this row.

Table-specific information

SIMBAD: This table details objects contained in SIMBAD. In addition to the common columns detailed above, the first name SIMBAD returns for each object, and the list of magnitudes contained in SIMBAD, are also provided.
X-ray sources: This table presents known X-ray sources, found from the Master X-ray catalogue. The count-rate of the object, the name of the database table originally containing the object and the observatory which detected it are listed.
Galaxies: This table lists catalogued objects which are marked as galaxies or extended sources. The list of catalogues queried is provided beneath the table. The redshift (if available), magnitudes and source catalogue are the additional columns in this table.
Stars: This table details catalogued objects which are marked as stars or point sources. The list of catalogues queried is provided beneath the table. The magnitudes and source catalogue are the additional columns in this table.

Updating the page

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.