High energy Neutrinos also sometimes referred to as astrophysical neutrinos have previously been observed, but a source has never been well localized. For reference on some useful past work, this article talks about the relevant detection mechanisms and implications as well as some of the predictions: https://arxiv.org/pdf/1801.01551.pdf.
The newest observations (outlined in this paper but not on arxiv right now: http://science.sciencemag.org/content/early/2018/07/11/science.aat2890) are showing strong evidence that the event detected by IceCube in September 2017 is localized to a certain Blazar, Blazar TXS 0506+056. Blazars are very compact quasars (quasi-stellar radio source) that are associated with supermassive black holes at the center of giant galaxies.
Blazars are amongst the most energetic phenomena in the universe and as such have been hypothesized to be a source of astrophysical neutrinos for a long time. Blazars are formed in the same way that all active galactic nuclei (AGNs) are formed at the center of a galaxy around a super massive black hole (SMBH). As gas, dust and occasionally stars spiral inwards towards the SMBH, a hot accretion disk is formed which releases a large amount of energy in the form of photons, electrons, positrons and other elementary particles.
Perpendicular to the plane of the disc, a pair of jets transport energetic plasma away from the AGN. The jet is formed due to large winds and turbulence as well as magnetic fields near the center of the AGN. This jet is where it is hypothesized that we see these astrophysical neutrinos. These jets move at very high velocities with much of the plasma reaching speeds of 95-99% the speed of light.
The new observations which combined multiple wavelengths and many observational devices, have successfully localized the detection to an area of $\sim 1\ \text{arcmin}^2$ and therefore successfully isolates the observation to within the area of influence of a single blazar.
The next questions that must be asked are how the source is creating these neutrinos, primarily whether it is from a relativistic jet and whether or not the jet is baryonic. Now that we know what to observe to find them, it will be easier to continue the search for more information about their origin.