These follow-up observations, from VERITAS and other gamma ray observatories, suggest that the source of the neutrino is a blazar—a supermassive black hole with powerful outflowing jets that can change dramatically in brightness over time.This blazar, known as TXS 0506+056, is located at the center of a galaxy that is about four billion light years from Earth.
“This gamma-ray detection, coming as the result of an IceCube neutrino alert, is an excellent and exciting example of the power of what we call multi-messenger astrophysics—observations made through multiple types of signals in the universe,” said Scott Wakely, professor of physics at the University of Chicago and director of the Enrico Fermi Institute. “Chicago has played an important role in building and operating VERITAS from the very beginning. Results like this are why we got into this business.”
Wakely is the head of the UChicago VERITAS group, and served as deputy spokesperson of VERITAS from 2015 to 2018.
Initially, NASA’s Fermi Gamma-ray Space Telescope observed that TXS 0506+056 was several times brighter than usually seen in its all-sky monitoring. Eventually, the MAGIC observatory made a detection of much higher-energy gamma rays within two weeks of the neutrino detection, while VERITAS, H.E.S.S. and HAWC did not detect the blazar in any of their observations during the two weeks following the alert.
Given the importance of higher-energy gamma-ray detections in identifying the possible source of the neutrino, VERITAS continued to observe TXS 0506+056 over the following months, through February 2018, and revealed the source, though at a dimmer state than that detected by MAGIC. This detection confirms the variability of the source in gamma rays, a hallmark of blazars.
The detection of gamma rays coincident with neutrinos is tantalizing, since both particles must be produced in the generation of cosmic rays. Since they were first detected over 100 years ago, cosmic rays—highly energetic …