The discovery of a source of neutrinos and electromagnetic emissions in a blazar represents a new success for multimessenger astronomy

Artist's concept of a blazar emitting neutrinos and gamma rays (Image courtesy IceCube/NASA)
Artist’s concept of a blazar emitting neutrinos and gamma rays (Image courtesy IceCube/NASA)

Various articles published in different journals shows various aspects of a research that allowed to associate a neutrino detected by the IceCube instrument at the South Pole to the blazar known as TXS 0506+056. In an article published in February 2018 in “The Astrophysical Journal Letters” a team led by Simona Paiano of the INAF of Padua showed that connection. In two articles just published in the journal “Science”, groups of scientists from 18 different observatories describe what was defined multimessenger observations of neutrino and electromagnetic emissions and a second analysis showing that other neutrinos detected by IceCube came from the same source.

On September 22, 2017 the IceCube experiment detected a very high energy neutrino, so high that it generated a muon with an energy of 22 TeV (TeraelettronVolt). This was a very rare event because the estimate of the neutrino energy was 290 TeV and this suggested it came from deep space, even from another galaxy. Identified as IceCube-170922A, it became even more special because it started a multimessenger investigation, which means based not only on neutrino detection but also on electromagnetic emissions observations.

The detection of the neutrino only made it impossible to identify its origin but it was possible to infer the direction from which it came and report it to astronomers who could use astronomical ground-based or space observatories that could find the origin of the IceCube-170922A neutrino. NASA’s Fermi space telescope, the Major Atmospheric Gamma-Ray Imaging Cherenkov (MAGIC) telescopes and the Great Telescope Canarias on the island of La Palma helped to identify the source in the blazar TXS 0506+056, indicated as 3Fgl J0509+0541 in Fermi catalog.

Blazars are a type of active galactic nucleus powered by an supermassive black hole that’s active due to a significant amount of materials orbiting it that get heated to the point of emitting intense amounts of electromagnetic radiation. When the materials get swallowed, a part is ajected into jets at the poles that reach very high speeds.

Other space telescopes such as NASA’s Swift and NuSTAR, ESA’s INTEGRAL and others contributed to the research in various ways, helping to gather evidence that the source searched for was in the blazar TXS 0506+056. The data collected also allowed to calculate the distance of the blazar, although with a crude approximation so the various sources provide a measure between 3.5 and 5 billion light years from Earth.

Initially there was another “suspect”, another blazar known as PKS 0502+049 which at the end of 2014 generated a gamma-ray burst, typically associated with the emission of neutrinos. However, eventually the flow of neutrinos from the blazar TXS 0506+056 turned out to be similar to its gamma-ray emissions, a strong indication that those emissions were generated by the same mechanism. It was probably what in the jargon is called a Hadronic flare, an emission of very high energy protons that generate gamma rays and neutrinos. This investigation was described in an article published in the journal “Monthly Notices of the Royal Astronomical Society”.

In the past, sources of neutrino emissions were traced to the Sun and a supernova, this is the first case in which the source of neutrinos from another galaxy is discovered. The comments are very positive also because it’s a new case of multimessenger astronomy, this time with neutrino and electromagnetic emissions detections. The case of gravitational and electromagnetic waves detections in the case of the kilonova shows again how the collaboration among space agencies and scientific institutions from all over the world can lead to great scientific results.

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