The most energetic neutrino yet!!

IceCube has just announced the observation of our most energetic neutrino yet.  The event was in the form of a through-going muon, which means that we saw a piece of the track in our detector, but the track both originated and ended outside of the enclosed volume.  So, we cannot measure the total energy of the neutrino.  Instead, we measure the specific energy loss (energy loss/distance, or dE/dx).  From that, we can estimate the muon energy, in the detector, and, from that, we can, based on an assumption of the neutrino energy spectrum, estimate the probability that neutrino had a range of energies.   We are still working on estimating the neutrino energy, but the total energy loss visible in the detector was 2.6 +/- 0.3 PeV.  This is, of course, a lower limit to the neutrino energy, making it clearly the most energetic neutrino yet observed.  Typically, one expects the neutrino energy to be a couple of times higher than the muon energy.

The event came from the Northern Sky (coordinates R.A.: 110.34 deg and Decl.: 11.48 deg), and we currently estimate the average angular resolution to be 0.27 degrees.   Because it was upward-going, we know that it must be a neutrino, and not cosmic-ray muon background.

The event was recorded on June 11, 2014 (see the link for details), just over a year ago.  We are clearly getting better at processing and analyzing our data more quickly, but there is still room for improvement.

The event was announced as an "Astronomers Telegram," (ATel) a brief announcement which can be issued quickly.  The main purpose of ATels is to get word out quickly about a new transient phenomena (gamma-ray burst, nearby supernova etc.), so that other astronomers can point their telescopes in right direction while the phenomena is still going on.  In our case, there is no reason to expect this to be (or not be) from a transient phenomena, and, if it was, it is probably over now.  But, we are releasing the coordinates now, so that other observatories can see if they can find anything unusual in that direction.   The event is relatively near the equator, so it should be visible from most large observatories.

More information later (probably after the Intl. Cosmic Ray Conference, July 30-Aug. 6th).

Note Added (July 30th).  Unlike Bert, Ernie and Big Bird, we have named this event after a Muppet.