Neil Gehrels Swift

The Swift gamma-ray mission is a space based observatory designed for prompt multi-wavelength observations of gamma-ray bursts (GRBs) and their associated afterglows. It has been launched on 2004 November 20 from Cape Canaveral. It carries three instruments on-board, covering the gamma-ray (BAT), X-ray (XRT) and UV/optical bands (UVOT). Using these instruments, Swift measures GRB positions with arc-second accuracy, within a few minutes since their discovery, and automatically sends the information to ground based observatories for further follow up. It is the first satellite able to observe GRBs in the X-ray band during the crucial first hours of the afterglow evolution. Swift has been realised by an international team of scientists from United States, Italy and United Kingdom.

The Burst Alert Telescope (BAT) is the instrument that detects the bright initial gamma-ray emission of GRBs. The BAT has a large field of view, allowing it to detect gamma-rays from a large portion of the sky at one time, and locate the source. After the initial detection, Swift slews rapidly and autonomously, bringing the detected burst into the field of view of the sensitive narrow field instruments (XRT and UVOT) that start observing the afterglow. The refined positions determined by XRT and UVOT are transmitted to the ground for optical, infrared and radio follow up. Swift provides spectra and multi-wavelength light-curves for all the duration of the afterglow. Its fast pointing capability allows very early spectroscopy of the bright part of the optical afterglow which is critical for distance determinations.

The combined Swift and ground based telescopes observations are enabling the most comprehensive study of GRBs and their host galaxies up to date.

The main goals of the Swift mission are:

  • the determination of the origin of gamma-ray bursts;
  • the classification of gamma-ray bursts and search for new types;
  • the investigation on how the blast-wave evolves and interacts with the surroundings;
  • probing the early Universe by means of very distant gamma-ray bursts;
  • to perform the first sensitive hard X-ray survey of the sky.

What Swift does:

  • The Burst Alert Telescope triggers on GRB and calculates position to within ~4-arc-min.
  • The Spacecraft autonomously slews to GRB position in 20-70 seconds.
  • The X-ray Telescope determines position to within ~5-arc-sec.
  • The UV/Optical Telescope images the field and transmits a finding chart to ground.