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Exciting times for neutrino astronomy!

15 Mar 2021, 13:06 UTC
Exciting times for neutrino astronomy!

15 March 2021 – In the past weeks, not one but two exciting observations were published by the IceCube collaboration! A neutrino was observed that could be correlated to a Tidal Disruption Event observed by the Zwicky Transien Faciliy and for the first time a particle shower was observed at the energy of the Glashow resonance. KM3NeT congratulates the colleagues of IceCube with these remarkable observations that show the increasing power of neutrino astronomy and multi-messenger observation.
A high-energy neutrino detected in the direction of a Tidal Disruption Event
The IceCube Neutrino Observatory constantly monitors the sky, searching for high-energy neutrinos emitted from the most energetic phenomena in our Universe. When they find one, they send an alert to the astronomy community, hoping other instruments could also see an electromagnetic signal from the same location in the sky. In  October 2019, they had a hit! 
In April 2019, the Zwicky Transient Facility observed a light signal as expected from a Tidal Disruption Event. An tidal eruption in astrophysics refers to the shredding of a star coming close to a black hole. In October 2019, IceCube recorded a high-energy neutrino of which the direction pointed to the tidal eruption AT2019dsg recorded by the Zwicky Transition Facility. The leading IceCube team at DESY, Germany determined that the probability of having by chance a high-energy neutrino correlated with this astrophysical event, is of the order of  0.2%.
This electromagnetic radiation – neutrino correlation might be the first one from this source population. More data, and hopefully more correlated observations, are needed to fully characterise the tidal eruption phenomenon. Our colleagues in the Mediterranean Sea, the ANTARES Collaboration, also searched for neutrinos from AT2019dsg. 
KM3NeT will be a tremendous asset in this quest.  Our realtime multi-messenger astronomy program will allow us to send an alert when an interesting neutrino candidate is detected in KM3NeT but also respond to alerts sent by partners detecting electromagnetic or gravitational waves.

As the star approaches the black hole, the enormous tidal forces strech it more and more until it is finally shred. Credits DESY, Science Communication Lab.
A particle shower detected at the Glashow resonance
The second exciting event is the first observation by the IceCube Collaboration has reported the first observation of a particle shower at the energy of the Glashow resonance. This process, predicted 60 years ago by S. Glashow, occurs when an electron anti-neutrino interacts with an electron. At a very high energy (6.3 PeV), there is a resonance effect and the interaction probability for this anti-neutrino is 300 times larger than that of the other neutrino flavours at the same energy.  
The process only happens for an electron anti-neutrino, and does not for the electron neutrino or the other neutrino flavours. This process therefore gives the possibility to probe the content of the high-energy astrophysical flux of neutrinos and constrain the mechanism that has produced them at the source. Indeed, depending on the production channel (for example whether accelerated protons interact with matter or with light) we will expect a different ratio of neutrino vs anti-neutrino. With only one event, we cannot yet differentiate between the possible production models. 
The KM3NeT/ARCA detector in KM3NeT will be sensitive in this energy range and will contribute to hopefully detect more of these Glashow resonance events. With more data, we will be able to use these events to better understand the processes occurring in the most energetic phenomena in our Universe.
Read the ins and outs of the result in the associated Nature news and views written by Carla Distefano, researcher in the KM3NeT Collaboration at https://www.nature.com/articles/d41586-021-00486-1 

Credit IceCube Collaboration.
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