Multi-messenger Astronomy
"Neutrinos and gamma rays from the same cosmic source have been observed for the first time. The result was published on Science today."
For the first time, it has been possible to identify the source of a cosmic neutrino, thanks to the association with a gamma (high energy photons) source. This extraordinary result, published today in Science, combines data from the IceCube experiment, detecting neutrinos at the South Pole, with those of other 15 experiments, which detect photons at ground and in space. The identified source is a blazar: an active galaxy with a supermassive black hole at its center, emitting jets of energetic particles at nealry the speed of light, at a distance of 4.5 billion light-years, in the direction of Orion.
On September 22 2017, IceCube detected a particularly interesting neutrino: it extremely high energy (290 TeV) hinted that it could originate from a distant, active object. According to models, the production of cosmic neutrinos always comes together with the production of gammas. IceCube thus sent a "neutrino alert" to telescopes around Earth, hoping that their observations would allow for the precise identification of the source.
The Fermi Satellite (NASA), with the telescope LAT, observed, in the direction of the neutrino, the emissions of a gamma ray source, the blazar TXS 0506+056. It immediatly sent out an "astronomical telegram", which made it possible for other 14 detectors to point in the same direction. The MAGIC telescope, in the Canary Islands, oriented its giantic mirrors to the source. With 12 hours of observation, it detected the emission of gamma rays with energies one thousand times larger than those observed by Fermi. It thus contributed with an important piece to complete the puzzle of this discovey. Several other detectors participated and, thanks to the combination of the different observations, it has been possible to confirm as possible source of the neutrino the blazar TXS 0506+056, at the heart of a galaxy a 4.5 billion light-years from Earth.
Alessandro de Angelis, collaborator of LIP and invited professor at IST, founding member of Fermi and for many years scientific PI of MAGIC, followed this discovery closely, and has no doubts that: "this is a result that will be in the physics books of the future. And it was only possible with multi-messenger observations, which imply different particles. This is the astronomy of the 21th century, and this event is the second chapter, nine months after the 2017 graviational wave event".
This unprecedented observation, the result of the newborn multi-messenger astronomy, also provides solid hints towards solving the mistery of the origin of high-energy cosmic rays. Most cosmic rays are protons, charged particles that are deflected by the magnetic fields that fill the space. This prevents us from tracing back their origin. Neutrinos, which are produced by the high-energy protons, are not deflected by magnetic fileds, and interact only very weakly with matter. They can thus point back to their origin. Because it produces neutrinos with energies as high as the one observed by IceCube, we now know that this source is able to accelerate protons to even much higher energies.
Mário Pimenta, president of LIP and full professor at IST, explains how important this result is for the consolidation of multi-messenger astronomy, and for several research lines at LIP: "This result is of extreme importance and confirms a change of paradigm in the observation of the Universe: detectors as different as neutrino, photon and graviational wave detectors, located in completely different places and environments, are today organized in global netowrks. Portugal (LIP), together with scientists from other countries, in particular Brazil, Italy and the Czech Republic, is right now working on the proposal of two new elements of this chain: a gamma ray observatory at an altitude of 5000 m in the Andes, in South America; and an ambitious satellite experiment for the detection of photon in the MeV region."
LIP keeps active another multi-messenger observation channel, the Pierre Auger Observatory, devoted to the observation of charged cosmic rays one thousand times more energetic than the neutrino now observed by ICeCube. The Pierre Auger Observatory is also sensitive to very-high energy photons and neutrinos, and participated in the first multi-messenger observation with gravitational waves, less than one year ago.
Interview with Mário Pimenta, President of LIP
IceCube video on this discovery
More info: IceCube
Links to the papers:
info “Multimessenger observations of a flaring blazar coincident with high-energy neutrino IceCube-170922A,” The IceCube, Fermi-LAT, MAGIC, AGILE, ASAS-SN, HAWC, H.E.S.S, INTEGRAL, Kanata, Kiso, Kapteyn, Liverpool telescope, Subaru, Swift/NuSTAR, VERITAS, and VLA/17B-403 teams. Science 361, eaat1378 (2018). DOI:10.1126/science.aat1378, arXiv
+ info “Neutrino emission from the direction of the blazar TXS 0506+056 prior to the IceCube-170922A alert,” IceCube Collaboration: M.G. Aartsen et al. Science 361, 147-151 (2018). DOI:10.1126/science.aat2890, arXiv