Swift is a first-of-its-kind multi-wavelength observatory dedicated to the study of gamma-ray burst (GRB) science. Its three instruments work together to observe GRBs and their afterglows at gamma-ray, X-ray, ultraviolet (UV), and optical wavelengths. Swift, part of NASA's medium explorer (MIDEX) program, has been developed by an international collaboration of Italy, the United Kingdom, and the USA. It was launched into a low Earth orbit on a Delta 7320 rocket on November 20, 2004. During the first nine years of operation Swift has observed approximately 900 bursts with a sensitivity approximately three times fainter than the BATSE detector aboard the Compton Gamma-Ray Observatory. Swift's Burst Alert Telescope can detect gamma-ray bursts and relay a position estimate that is accurate to within 1-3 arcminutes to the ground within approximately 15 s. After the initial burst detection, the spacecraft ``swiftly'' (approximately 20 to 75 seconds) and autonomously repoints itself to bring the burst location within the field of view of the sensitive narrow-field X-ray and UV/optical telescopes. Swift provides spectral energy distributions for the bursts and multi-wavelength light curves for the duration of the afterglow. Swift measurements have been of great interest to the astrophysical community. All data products are available to the public via the Internet as soon as they are processed. The Swift mission represents the most comprehensive study of GRB afterglows to date.
The main mission objectives for Swift are to:
Swift has a complement of three co-aligned instruments for studying GRBs and their afterglows: the Burst Alert Telescope (BAT), the X-Ray Telescope (XRT), and the Ultraviolet/Optical Telescope (UVOT). The largest instrument on board Swift is the BAT, which can view approximately one sixth of the sky at a time. It currently localizes approximately 100 GRBs per year. Within seconds of detecting a burst, the spacecraft ``swiftly'' and autonomously repoints itself to aim the XRT and UVOT at the burst to obtain high-precision X-ray and optical positions and spectra. Swift provides detailed multi-wavelength light curves for the duration of the afterglow. Key data taken by Swift are relayed to the ground in near-real time, allowing the Gamma-Ray Burst Coordinates Network (GCN) to immediately distribute it to the world via the internet for follow-up observations and study. Swift also uses the BAT to perform an all-sky survey of hard X-rays that will be significantly more sensitive than any previous survey.
The Swift mission began with an activation phase lasting approximately 45 days. This was followed by a verification phase of approximately three months. On April 5, 2005 the verification phase was completed and regular observations began. All Swift data taken during the activation and verification phases have been made available to the astrophysical community. All data taken after April 5, 2005 are made public as soon as they are processed, usually about three hours after the observations were taken.