Gamma-ray bursts (GRBs) are the most powerful explosions the Universe has seen since the Big Bang. They occur approximately once per day and are brief, but intense, flashes of gamma radiation. They come from all different directions of the sky and last from a few milliseconds to a few hundred seconds. So far scientists do not know what causes them. Do they signal the birth of a black hole in a massive stellar explosion? Are they the product of the collision of two neutron stars? Or is it some other exotic phenomenon that causes these bursts?
With Swift, a NASA mission with international participation, scientists have a tool dedicated to answering these questions and solving the gamma-ray burst mystery. Its three instruments give scientists the ability to scrutinize gamma-ray bursts like never before. Within seconds of detecting a burst, Swift relays its location to ground stations, allowing both ground-based and space-based telescopes around the world the opportunity to observe the burst's afterglow. Swift is part of NASA's medium explorer (MIDEX) program and was launched into a low-Earth orbit on a Delta 7320 rocket on November 20, 2004. The Principal Investigator is Dr. Neil Gehrels (NASA-GSFC).
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Observations by NASA's Swift spacecraft, now renamed the Neil Gehrels Swift Observatory after the spacecraft's late principal investigator, have captured an unprecedented change in the rotation of a comet. Images taken in May 2017 reveal that comet 41P/Tuttle-Giacobini-Kresák - 41P for short - was spinning three times slower than it was in March, when it was observed by the Discovery Channel Telescope at Lowell Observatory in Arizona.
In honor of Neil Gehrels, who helped develop Swift and served as its principal investigator until his death on Feb. 6, 2017, the Swift Gamma-Ray Burst Explorer has officially been renamed the Neil Gehrels Swift Observatory.
Today the advanced LIGO and Virgo gravitational wave observatories announced the discovery of a new type of gravitational wave signal, likely caused by the collision of two neutron stars. The gravitational wave event occurred on 2017 August 17th, and was accompanied by a gamma-ray burst of short duration. Astronomers across the world began searching for the precise location of this event, quickly tracking it down to the nearby galaxy NGC 4993. Once pin-pointed, the Swift satellite quickly maneuvered to look at the object with its X-ray and UV/optical telescopes. The spacecraft saw no X-rays - a surprise for an event that produced higher-energy gamma rays. Instead, it found a bright and quickly fading flash of ultraviolet (UV) light. This bright UV signal was unexpected and revealed unprecedented details about the aftermath of the collision. The short-lived UV pulse likely came from material blown away by the short-lived disk of debris that powered the gamma-ray burst. The rapid fading of the UV signal suggests that this outflow was expanding with a velocity close to a tenth of the speed of light. The results of the Swift observations were published today on the journal Science. The discovery of this powerful wind was only possible using light, which is why combining gravitational waves and light in what we call 'multi-messenger astronomy' is so important.
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