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. Brad Cenko (NASA-GSFC).
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A pair of distant explosions discovered by NASA's Fermi Gamma-ray Space Telescope and Neil Gehrels Swift Observatory have produced the highest-energy light yet seen from these events, called gamma-ray bursts (GRBs). The record-setting detections, made by two different ground-based observatories, provide new insights into the mechanisms driving gamma-ray bursts.
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GRB 070809 is a short duration gamma-ray burst discovered by the Neil Gehrels Swift Observatory in August 2007. Very recently, a team of astronomers, led by Zhi-Ping Jin from Purple Mountain Observatory, showed that the optical light from GRB070809 had a peculiar behavior. Its luminosity and red color appear different than the standard afterglow emission seen by the X-ray Telescope aboard Swift. Instead, the optical light can be naturally interpreted as a kilonova (also known as macronova), a kind of transient powered by the radioactive decay of heavy elements synthesized in the ejecta of a neutron star collision. The kilonova signal was identified at a distance larger than 1 Gpc, well beyond the reach of the second-generation gravitational wave detectors.
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Galaxy clusters are some of the largest cosmic structures, made of hundreds to thousands of galaxies. They are generally thought to have nearly identical structure and radial profiles. Using NASA's Neil Gehrels Swift Observatory observations of the nearby galaxy cluster CL2015 (Abell 117, z=0.05), researchers found a cluster that does not follow this universal profile: it displays a very low pressure for a cluster of its mass. The low pressure profile of CL2015 is likely due to the low concentration of its matter distribution, i.e. a lack of mass in the cluster center. A paper describing these results is being published in the Astronomy and Astrophysics Journal.
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