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).
All Swift systems are operating normally.
Type Ia supernovae are violent stellar explosions used by astronomers to measure the accelerating expansion of the Universe. They are commonly theorized to be the thermonuclear explosions of a white dwarf star that is part of a binary system. How this white dwarf goes from binary star system to Type Ia supernova is a vivid matter of debate. New observations made by the Swift satellite provided an unprecedented clue to the origin of Type Ia explosions. The UVOT telescope aboard Swift started observing the Type Ia supernova iPTF14atg only four days after the explosion, and unveiled a bright pulse of ultraviolet emission. This is consistent with theoretical expectations of collision between material being ejected from a supernova explosion and the companion star from which it has been accreting matter. Alternative models, involving the merger of two white dwarfs, are instead disfavored by the Swift data. These results show that early time ultraviolet observations of young supernovae could hold the key to fully understanding the pre-explosion interaction between a supernova's white dwarf progenitor and its companion.
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The Swift Data Center is now reprocessing the Swift data for the entire mission in chronological order using the current version of the SDC pipeline (v. 3.16.08). All the data for 2005 have been reprocessed and delivered to the HEASARC. The archives in Italy and UK are currently populating their archives with the new data. Currently the reprocessing rate is about 3 months per month.
A team of astronomers found that type Ia supernovae commonly used to measure distances in the universe fall into distinct populations not recognized before. The data collected with Swift were crucial because the differences between the populations are subtle in visible light, which had been used to detect type Ia supernovae previously, but became obvious only through Swift's dedicated follow-up observations in the ultraviolet. These findings have important implications for our understanding of how fast the universe has been expanding since the Big Bang: the study concludes that some of the reported acceleration of the universe can be explained by color differences between the two groups of supernovae, leaving less acceleration than initially reported. This would, in turn, require less dark energy than currently assumed.
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