1.3 Instrument Overview

The Swift telescope payload consists of three instruments that work together to provide rapid identification and multiwavelength follow-up of GRBs and their afterglows. The spacecraft autonomously slews within 20 to 75 seconds of detecting a GRB so that the fields of view (FoVs) of the three instruments overlap the location of the burst. Afterglows are monitored as long as they can be detected by the instruments, and the observations provide a reasonable science return. Each afterglow is re-evaluated on a daily basis to determine if observations should be continued. All GRB data are rapidly disseminated to the astrophysics community via a public archive.

The three instruments on board Swift are:

The Burst Alert Telescope (BAT)

The BAT is a wide-field, coded-mask gamma-ray detector that is sensitive to energies of 15-150 keV. It detects GRBs, computes their positions to 1-3 arcminutes, and triggers autonomous slews of the spacecraft to point towards the bursts.

The X-Ray Telescope (XRT)

The XRT is a narrow-field X-ray telescope that localizes a GRB to approximately 2-3 arcseconds, and performs imaging and spectroscopy in the 0.2-10 keV band.

Ultraviolet/Optical Telescope (UVOT)

The UVOT is a narrow-field UV/optical telescope with a 30 cm aperture mirror that operates at wavelengths between 1600 Å and 6000 Å. It provides burst positions to 0.5 arcseconds relative to the stars in its FoV, a finding chart, and performs broad-band imaging on GRB afterglows. The UVOT also has the ability to take grism spectra of GRB afterglows.

The placement of the three instruments on the spacecraft is shown in Figure 1. The ability of Swift to zero in on the position of a transient source is illustrated in Figure 2.

Figure 1: This Figure shows the placement of the three telescopes on Swift.

Figure 2: Rapid localization of GRBs with Swift.