Neil Gehrels Swift Observatory


The Neil Gehrels Swift Observatory, previously called the Swift Gamma-Ray Burst Mission, is a NASA space observatory designed to detect gamma-ray bursts. It was launched on November 20, 2004, aboard a Delta II rocket. Headed by principal investigator Neil Gehrels, NASA Goddard Space Flight Center, the mission was developed in a joint partnership between Goddard and an international consortium from the United States, United Kingdom, and Italy. The mission is operated by Pennsylvania State University as part of NASA's Medium Explorers program.

Overview

Swift is a multi-wavelength space observatory dedicated to the study of gamma-ray bursts. Its three instruments work together to observe GRBs and their afterglows in the gamma-ray, X-ray, ultraviolet, and optical wavebands.
Based on continuous scans of the area of the sky with one of the instrument's monitors, Swift uses momentum wheels to autonomously slew into the direction of possible GRBs. The name "Swift" is not a mission-related acronym, but rather a reference to the instrument's rapid slew capability, and the nimble bird of the same name. All of Swift discoveries are transmitted to the ground and those data are available to other observatories which join Swift in observing the GRBs.
In the time between GRB events, Swift is available for other scientific investigations, and scientists from universities and other organizations can submit proposals for observations.
The Swift Mission Operation Center, where commanding of the satellite is performed, is located in State College, Pennsylvania and operated by the Pennsylvania State University and industry subcontractors. The Swift main ground station is located at the Broglio Space Centre near Malindi on the coast of Eastern Kenya, and is operated by the Italian Space Agency. The Swift Science Data Center and archive are located at the Goddard Space Flight Center outside Washington D.C. The UK Swift Science Data Centre is located at the University of Leicester.
The Swift spacecraft bus was built by Spectrum Astro, which was later acquired by General Dynamics Advanced Information Systems, which was in turn acquired by Orbital Sciences Corporation.

Instruments

Burst Alert Telescope (BAT)

The BAT detects GRB events and computes its coordinates in the sky. It covers a large fraction of the sky. It locates the position of each event with an accuracy of 1 to 4 arc-minutes within 15 seconds. This crude position is immediately relayed to the ground, and some wide-field, rapid-slew ground-based telescopes can catch the GRB with this information. The BAT uses a coded-aperture mask of 52,000 randomly placed 5 mm lead tiles, 1 meter above a detector plane of 32,768 four mm CdZnTe hard X-ray detector tiles; it is purpose-built for Swift. Energy range: 15–150 keV.

X-ray Telescope (XRT)

The XRT can take images and perform spectral analysis of the GRB afterglow. This provides more precise location of the GRB, with a typical error circle of approximately 2 arcseconds radius. The XRT is also used to perform long-term monitoring of GRB afterglow light-curves for days to weeks after the event, depending on the brightness of the afterglow. The XRT uses a Wolter Type I X-ray telescope with 12 nested mirrors, focused onto a single MOS charge-coupled device similar to those used by the XMM-Newton EPIC MOS cameras. On-board software allows fully automated observations, with the instrument selecting an appropriate observing mode for each object, based on its measured count rate. The telescope has an energy range of 0.2–10 keV.

Ultraviolet/Optical Telescope (UVOT)

After Swift has slewed towards a GRB, the UVOT is used to detect an optical afterglow. The UVOT provides a sub-arcsecond position and provides optical and ultra-violet photometry through lenticular filters and low resolution spectra through the use of its optical and UV grisms. The UVOT is also used to provide long-term follow-ups of GRB afterglow lightcurves. The UVOT is based on the XMM-Newton mission's Optical Monitor instrument, with improved optics and upgraded onboard processing computers.
On November 9, 2011, UVOT photographed the asteroid 2005 YU55 as the asteroid made a close flyby of the Earth. On June 3, 2013, UVOT unveiled a massive ultraviolet survey of the nearby Magellanic Clouds.

Mission goals

The Swift mission has four key scientific objectives:
Swift was launched on November 20, 2004, at 17:16 UTC aboard a Delta II 7320-10C from Cape Canaveral Air Force Station and reached a near-perfect orbit of altitude, with an inclination of 20.6°.
On December 4, an anomaly occurred during instrument activation when the Thermo-Electric Cooler Power Supply for the X-Ray Telescope did not turn on as expected. The XRT Team at Leicester and Penn State University were able to determine on December 8 that the XRT would be usable even without the TEC being operational. Additional testing on December 16 did not yield any further information as to the cause of the anomaly.
On December 17 at 07:28:30 UTC, the Swift Burst Alert Telescope triggered and located on board an apparent gamma-ray burst during launch and early operations. The spacecraft did not autonomously slew to the burst since normal operation had not yet begun, and autonomous slewing was not yet enabled. Swift had its first GRB trigger during a period when the autonomous slewing was enabled on January 17, 2005, at about 12:55 UTC. It pointed the XRT telescope to the on-board computed coordinates and observed a bright X-ray source in the field of view.
On February 1, 2005, the mission team released the first light picture of the UVOT instrument and declared Swift operational.
By May 2010, Swift had detected more than 500 GRBs.
By October 2013, Swift had detected more than 800 GRBs.
On October 27, 2015, Swift detected its 1,000th GRB, an event named and located in the constellation Eridanus.
On January 10, 2018, NASA announced that the Swift spacecraft had been renamed the Neil Gehrels Swift Observatory in honor of mission PI Neil Gehrels, who died in early 2017.

Notable detections