From the May 2006 issue

Searching for GRBs

Since the 1960s, various spacecraft have contributed to the current body of gamma-ray burst knowledge.
By | Published: May 22, 2006 | Last updated on May 18, 2023
gamma-ray burst
The search for gamma-ray bursts (GRBs) began in the early 1960s, when the U.S. Air Force launched its first gamma-ray detector aboard a Vela satellite. Since that first milestone, various spacecraft have contributed to the current body of GRB knowledge. Here’s a timeline that highlights GRB discoveries and the spacecraft that helped astronomers learn more about these elusive bursts.
October 17, 1963
U.S. Air Force launches the first pair of “Vela” (a name that means vigil, or watch, in Spanish) satellites. The 12 Vela satellites were designed to detect nuclear detonations in Earth’s atmosphere or in space to ensure compliance with the 1963 nuclear test ban treaty. The first 4 Vela satellites were equipped with 12 external X-ray detectors and 18 internal gamma-ray detectors.
July 2, 1967
First gamma-ray burst detected by the Vela 4a,b satellite; however, results were classified until 1973. After analyzing Vela GRB data, Los Alamos National Laboratory scientists publish their conclusion that GRBs are “of cosmic origin” in the Astrophysical Journal.
March 14, 1971
NASA launches the IMP 6 satellite, carrying a gamma-ray detector. While on a mission to observe solar flares, IMP 6 inadvertently observes GRBs.
September 29, 1971
NASA launches the Seventh Orbiting Solar Observatory (OSO-7), which carries a gamma-ray monitor and X-ray telescope. The spacecraft’s X-ray All-sky survey ended July 9, 1974.
Soviet Konus satellite data confirming GRB detection are published.
Interplanetary Network (IPN) gamma-ray detectors placed aboard spacecraft to locate GRBs.
April 5, 1991
NASA launches the Compton Gamma-Ray Observatory with the Burst and Transient Source Experiment (BATSE) onboard. The instrument detects more than 2,700 GRBs from 1991 until 2000. Findings include uniform GRB distribution across the sky, indicating the bursts originate outside the Milky Way.
February 20, 1993
Japan launches the Advanced Satellite for Cosmology and Astrophysics (ASCA). The craft detected iron emission lines from GRB 991216’s afterglow in 1999 that helped determine its distance of about 8 billion light-years.
November 1, 1994
NASA launches the Wind satellite. Onboard are several instruments, including the Transient Gamma-Ray Spectrometer (TGRS) and a Soviet Gamma-Ray Burst Detector known as Konus.
December 30, 1995
NASA launches the Rossi X-ray Timing Explorer (RXTE). RXTE’s All-Sky Monitor (ASM) subsequently detects several GRB X-ray afterglows.
April 30, 1996
The Italian Space Agency and The Netherlands Agency for Aerospace Programs launch the BeppoSAX satellite. The spacecraft observes a variety of celestial sources, including GRBs. On February 28, 1997, astronomers detect the X-ray afterglow of GRB 979228 using BeppoSAX.
July 23, 1999
NASA launches the Chandra X-ray Observatory. On December 21, 1999, Chandra imaged the X-ray afterglow of GRB 991216, bolstering the theory that massive collapsed stars cause at least some GRBs.
October 9, 2000
NASA launches the High Energy Transient Explorer (HETE-2) specifically to detect and locate GRBs. The spacecraft is a collaboration between the United States, Japan, France, and Italy.
October 17, 2002
The European Space Agency launches gamma-ray observatory INTEGRAL (INTErnational Gamma-Ray Astrophysics Laboratory) to observe the gamma-ray sky.
November 20, 2004
NASA launches the Swift satellite. The Swift Gamma-Ray Burst Mission includes three instruments — gamma-ray Burst Alert Telescope (BAT), X-Ray Telescope (XRT), and the Ultraviolet/Optical Telescope (UVOT).