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IceCube Neutrino Linked to Cosmic Source.

FOLLOW-UP OBSERVATIONS ACROSS the electromagnetic spectrum have helped scientists pinpoint the source of a single high-energy neutrino--a barely-there particle that has no electrical charge and almost no mass. The IceCube collaboration announced the probable birthplace of the neutrino, dubbed IceCube-170922A, in the July 13th Science.

The neutrino ghosted through our planet on September 22, 2017, before crashing into an atom in the Antarctic ice. The collision produced a heavy cousin of the electron called a muon, which left a track of dim, bluish light in the IceCube detector. Backtracking from the muon's trajectory, a computer cluster calculated the source's location on the sky and sent an automated alert to telescopes around the world just 43 seconds after the event.

Within hours the space-based Neil Gehrels Swift Observatory had identified the particle's possible source: the blazar TXS 0506+056, whose light and particles travel 3.8 billion light-years to reach Earth. This supermassive black hole sends out twin jets of high-energy radiation, one of which happens to be aimed at Earth. The Fermi Gamma-ray Space Telescope reported that this blazar was flaring at the time of the neutrino event. Observations from more than 20 telescopes confirmed the flare across the electromagnetic spectrum.

With a known object for reference, IceCube scientists searched the archive and discovered that the blazar was associated with a larger-than-expected number of neutrinos detected between 2014 and 2015. Both the neutrino energies and the light collected from the blazar are characteristic of a cosmic particle accelerator.

Oddly, scientists haven't detected neutrinos from flaring blazars much closer to Earth, such as Mkn 425 and Mkn 501. However, the authors calculate the chance of a coincidental alignment between the single neutrino detection and the flare of TXS 0506+056 to be only one in a thousand. Still, Kohta Murase (Penn State) urges caution: "If we look at history, there have been many claims for which such a level of significance eventually went away," he explains. "Definitely, we need more events to establish that blazars are sources of neutrinos."

Caption: The neutrino recorded on September 22, 2017, smashed into Antarctic ice, creating a muon that left the track shown here. Color encodes the time of arrival (red is sooner, blue is later), and the size corresponds to the brightness recorded by individual sensors.

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Title Annotation:PARTICLES; IceCube-170922A
Author:Skuse, Benjamin
Publication:Sky & Telescope
Date:Nov 1, 2018
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