The home of "Big Bird", officially known as neutrino HESE-35, detected by the IceCube Neutrino Observatory at the South Pole in 2012, has been found.

IceCube, a neutrino observatory situated at the South Pole, which is operated by the University of Wisconsin-Madison (USA), originally detected the first neutrinos emitted from outside our solar system and galaxy in 2010. The most energetic neutrino recorded is officially named HESE-35, but is affectionately called Big Bird after a character in the long-running American children's show "Sesame Street". At the time no one knew where "Big Bird" came from; researchers suspected from one of several distant galaxies but had no proof.

A network of radio telescopes, including the Hartebeesthoek Radio Astronomy Observatory (HartRAO), operating as an interferometer or linked radio telescope, has now found Big Bird's home in an extremely distant variable galaxy known as PKS B1424-418, says Dr Jonathan Quick, who is responsible for very long baseline interferometry (VLBI) operations at HartRAO.

What is now HartRAO was originally built in 1961 as a tracking station for lunar and other solar system missions. The facility was operated by the Council for Scientific and Industrial Research on behalf of NASA. In 1974, when NASA left, HartRAO was repurposed for radio astronomy and from 1999 functioned under the National Research Foundation, an entity of the Department of Science and Technology. Today HartRAO is a multidisciplinary facility for both radio astronomy and space geodesy, and exploits the synergies between various disciplines. It operates as a stand-alone radio telescope and as part of an international VLBI network.

Since 1961, HartRAO has participated in many interesting discoveries, e.g. an "earthquake" on a neutron star, flaring extra-galactic sources, episodic and periodic masers, and now the home of Big Bird.

From its orbit above the Earth, the Fermi Large Area Telescope (Fermi-LAT) detected a dramatic outburst of gamma rays from PKS B1424-418, a distant variable galaxy in the vicinity of where IceCube detected Big Bird. Fortunately the long-term monitoring programme, Tracking Active Galactic Nuclei with Austral Milli-arcsecond Interferometry (TANAMI) includes this source in its ongoing observations. In order to achieve milli-arcsecond resolution, the largest possible separation between the cooperating telescopes is required, and HartRAO is uniquely positioned to offer such long baselines in the Southern Hemisphere where PKS B1424-418 is found.

IceCube could not absolutely identify the place where Big Bird came from, but it narrowed it down to nine potential candidates. Fermi-LAT has better resolution, so its gamma ray observations reduced this number to a single candidate, PKS B1424-418. However, it was the monitoring and VLBI data from HartRAO and TANAMI respectively that confirmed PKS B1424-418 was indeed the home of Big Bird. These results will be published in the prestigious journal Nature. The HartRAO monitoring data included in Ms Pfesesani van Zyl's 2016 MSc dissertation is cited in the Nature publication.

There is a 5% chance that the radio flares, gamma ray outburst and detection of neutrinos are a coincidence. This also means that there is a 95% chance we know where Big Bird lives!

About the authors:

Dr Jonathan Quick, PhD (Physics), is head of Very Long Baseline Interferometry at HartRAO, where he has been working for 26 years. Ms Pfesesani van Zyl has completed her MSc and is now carrying out research towards her PhD; she is registered at the University of the Witswatersrand and continues to study extragalactic radio continuum sources at HartRAO.