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First-of-its-kind multi-wave observatory:

Swift Hunts Gamma-Ray Bursts

Looking For the Afterglow of Gamma Rays, X-Rays, and Ultraviolet and Optical Light

NASA artist concept of Swift in orbit observing a gamma-ray burst
NASA artist concept of Swift in orbit observing a faraway gamma-ray burst across the vast reaches of deep space
click to enlarge
Gamma-ray bursts are the most powerful explosions human beings have seen across the Universe.

Intense energy from the bursts arrive at Earth about once per day as brief flashes of gamma radiation.

The bursts seem to come from all different directions across the sky. They last from a few milliseconds to a few hundred seconds.

Scientists don't know what causes the bursts. They wonder if the bursts are the result of:

  • the birth of a black hole in a massive stellar explosion?
  • the collision of two neutron stars?
  • some other exotic phenomenon?
    In the Swift orbiting observatory, scientists have a tool for researching those questions and solving the mystery.

    What is Swift? Swift is an observatory satellite in orbit above Earth observing gamma-ray bursts, the powerful waves of energy pouring out from incredible and mysterious cosmic explosions.

    Swift was launched November 20, 2004. During its planned two-year mission, Swift is expected to observe more than 200 gamma-ray bursts.

    What it does. When an energy flash occurs, Swift's Burst Alert Telescope detects and locates it across the Universe. Then, the satellite turns to point its X-ray and ultraviolet-optical telescopes for observations.

    In addition, Swift transmits information about the burst to observatories on the ground around the globe. Those telescopes then point toward the gamma-ray burst locations and focus to collect additional data.

    The Burst Alert Telescope was activated successfully in space in December 2004.

    Afterglow. As a multi-wavelength observatory, Swift is first-of-its-kind in the way it is dedicated to the study of gamma-ray bursts. It has three telescopes:
    • gamma ray
    • X-ray
    • ultraviolet and optical combined
    The gamma-ray telescope spots a burst and then all three instruments work together to observe the burst's afterglow at gamma ray, X-ray, ultraviolet and optical wavelengths.

    Quick response. The Burst Alert Telescope (BAT) aboard Swift was built by NASA's Goddard Space Flight Center to detect and locate a gamma-ray burst over a wide portion of the sky. Its data is used to swivel Swift to point at a burst.

    Swift then uses its X-ray Telescope (XRT), built by Pennsylvania State University, the University of Leicester in Great Britain, and the Osservatorio Astronomico di Brera. Swift also uses its UltraViolet Optical Telescope (UVOT), made by Penn State and University College London's Mullard Space Science Laboratory.

    NASA expects Swift to detect more than 100 gamma-ray bursts a year.

    BAT detected its first X-ray pulsar, known to astronomers as V0332+53, in December 2004.

    The mission. NASA has planned these objectives for Swift:
    • Determine the origin of gamma-ray bursts
    • Classify gamma-ray bursts and search for new types
    • Determine how the blastwave evolves and interacts with the surroundings
    • Use gamma-ray bursts to study the early Universe
    • Perform the first sensitive hard X-ray survey of the sky
    Scientists involved with Swift are in the U.S., Great Britain and Italy. Swift mission control center is at Penn State University.

    Swift was launched November 20, 2004, on a Delta 2 rocket from launch pad 17A at Cape Canaveral Air Force Station, Florida, to a 375-mi.-high orbit. Launch had been delayed by Florida hurricanes that had closed the site for a time.

    Swift is designed to operate two years, but may work for five years in space. The life of its battery will determine its working period. The satellite has neither steering thrusters nor onboard propellant.

    What is a CCD? CCD is short for charge coupled device, a very sensitive silicon chip best known for its use as a photodetector in digital cameras.

    When an image is recorded, the CCD is struck by energy arriving in the system from deep space. The CCD converts the energy into electrical energy used to make images of astronomical objects or to analyze how much energy is being received from the objects.

    CCDs began to revolutionize astronomy in the 1990s. While they are more expensive than old-fashioned photographs, CCDs can detect much fainter objects than can ordinary photographs.

    The entire array of 32,768 BAT CCD detectors was turned on on December 11, 2004. The XRT opened its window on the Universe that same day. Three days later, the UVOT window was opened on December 14.

    Unfortunately, as the XRT began to observe the sky in December 2004, a thermoelectric cooler for the CCD X-ray detector didn't work well. A warmer CCD detector could be less sensitive.

    Gamma Rays

    Gamma Rays are extraordinarily powerful electromagnetic waves of energy, or photons, emitted from the center of an atom during a nuclear reaction. They are the most penetrating of all radiation.

    Gamma rays are very-high-energy, short-wavelength electromagnetic radiation like X rays. However, X rays do not originate in nuclei of atoms.

    Gamma rays have a large penetrating and destructive power. Dense materials such as lead, depleted uranium or concrete are used to shield against gamma radiation.

    Gamma-ray bursts were discovered during the Cold War, when the West thought, incorrectly, they were Soviet nuclear tests on the Moon or on other planets.

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