Donna Weaver / Ray Villard
Space Telescope Science Institute, Baltimore, Md.
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University of Leicester, Leicester, U.K.
Space Telescope Science Institute, Baltimore, Md.
“NASA’s Hubble Space Telescope has provided the strongest evidence yet that short-duration gamma-ray bursts are triggered by the merger of two small, super-dense stellar objects, such as a pair of neutron stars or a neutron star and a black hole.
Credit: NASA, ESA, N. Tanvir (University of Leicester), A. Fruchter (STScI), and A. Levan (University of Warwick)
Release Date: July 30, 2013
The definitive evidence came from Hubble observations in near-infrared light of the fading fireball produced in the aftermath of a short gamma-ray burst (GRB). The afterglow reveals for the first time a new kind of stellar blast called a kilonova, an explosion predicted to accompany a short-duration GRB.
A kilonova is about 1,000 times brighter than a nova, which is caused by the eruption of a white dwarf. Such a stellar blast, however, is only 1/10th to 1/100th the brightness of a typical supernova, the self-detonation of a massive star.
Gamma-ray bursts are mysterious flashes of intense high-energy radiation that appear from random directions in space. Short-duration blasts last at most a few seconds, but they sometimes generate faint afterglows in visible and near-infrared light that continue for several hours or days.
The afterglows have helped astronomers determine that GRBs lie in distant galaxies. The cause of short-duration GRBs, however, remains a mystery. The most popular theory is that astronomers are witnessing the energy released as two compact objects crash together. But, until now, astronomers have not gathered enough strong evidence to prove it, say researchers.
A team of researchers led by Nial Tanvir of the University of Leicester in the United Kingdom has used Hubble to study a recent short-duration burst in near-infrared light. The observations revealed the fading afterglow of a kilonova explosion, providing the “smoking gun” evidence for the merger hypothesis.
‘This observation finally solves the mystery of the origin of short gamma-ray bursts,’ Tanvir said. ‘Many astronomers, including our group, have already provided a great deal of evidence that long-duration gamma-ray bursts (those lasting more than two seconds) are produced by the collapse of extremely massive stars. But we only had weak circumstantial evidence that short bursts were produced by the merger of compact objects. This result now appears to provide definitive proof supporting that scenario.’
In a recent science paper Jennifer Barnes and Daniel Kasen of the University of California, Berkeley, and the Lawrence Berkeley National Laboratory presented new calculations predicting how kilonovas should look. They predicted that the same hot plasma producing the radiation will also act to block the visible light, causing the gusher of energy from the kilonova to flood out in near-infrared light over several days.
An unexpected opportunity to test this model came on June 3 when NASA’s Swift Space Telescope picked up the extremely bright gamma-ray burst, cataloged as GRB 130603B, in a galaxy located almost 4 billion light-years away. Although the initial blast of gamma rays lasted just one-tenth of a second, it was roughly 100 billion times brighter than the subsequent kilonova flash.
The visible-light afterglow was detected at the William Herschel Telescope and its distance was determined with the Gran Telescopio Canarias, both located in the Canary Islands.
‘We quickly realized this was a chance to test Barnes’ and Kasen’s new theory by using Hubble to hunt for a kilonova in near-infrared light,’ Tanvir said. The calculations suggested that the light would most likely be brightest in near-infrared wavelengths about 3 to 11 days after the initial blast. The researchers needed to act quickly before the light faded, so they requested Director’s Discretionary Observing Time with Hubble’s Wide Field Camera 3.
On June 12-13 Hubble searched the location of the initial burst, spotting a faint red object. An independent analysis of the data from another research team confirmed the detection. Subsequent Hubble observations three weeks later, on July 3, revealed that the source had faded away, therefore providing the key evidence it was the fireball from an explosive event.”
See the full article here.
The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA’s Goddard Space Flight Center manages the telescope. The Space Telescope Science Institute (STScI), is a free-standing science center, located on the campus of The Johns Hopkins University and operated by the Association of Universities for Research in Astronomy (AURA) for NASA, conducts Hubble science operations.
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