IceCube 170922A, a high-energy neutrino detected by the IceCube Neutrino Observatory in 2017, was generated by a jet-jet collision within TXS 0506+056, an active galaxy some 3.8 billion light-years away, according to new research.
The IceCube Neutrino Observatory is represented in this illustration by strings of sensors under the ice. Image credit: NASA / Fermi / Aurore Simonnet, Sonoma State University.
The home galaxy of the IceCube 170922A event is a so-called BL Lacertae (Lac) object, a type of active galactic nucleus.
“Active galactic nuclei are the most energetic objects in our Universe. Powered by a supermassive black hole, matter is being accreted and streams of plasma — so-called jets — are launched into intergalactic space,” said Dr. Silke Britzen of the Max Planck Institute for Radio Astronomy and colleagues.
“BL Lac objects form a special class of these active galactic nuclei, where the jet is directly pointing at us and dominating the observed radiation.”
“IceCube-170922A appears to originate from the BL Lac object TXS 0506+056.”
This image shows the sky in gamma rays with energies greater than 1 billion electron volts across a broad region centered on TXS 0506+056, located about 4 billion light-years away. Image credit: NASA / DOE / Fermi LAT Collaboration.
The researchers analyzed nine years of archival IceCube data and found evidence for an enhanced neutrino activity in TXS 0506+056 between September 2014 and March 2015.
“Other BL Lac Objects show properties quite similar to those of TXS 0506+056. However, it is a bit of a mystery why only TXS 0506+056 was identified as neutrino emitter,” they said.
“We wanted to unravel what makes TXS 0506+056 special, to understand the neutrino creation process and to localize the emission site and studied a series of high resolution radio images of the jet.”
Surprisingly, they found an unexpected interaction between jet material in TXS 0506+056.
“While jet plasma is usually assumed to flow undisturbed in a kind of channel, the situation seems different in TXS 0506+056,” they noted.
“The cosmic collision can be explained by new jet material clashing into older jet material.”
“A strongly curved jet structure provides the proper set up for such a scenario. Another explanation involves the collision of two jets in the same source.”
“In both scenarios, it is the collision of jetted material which generates the neutrino.”
The IceCube 170922A neutrino event appears to originate in the interaction zone of the two jets in TXS 0506+056. Image credit: IceCube Collaboration / MOJAVE / S. Britzen / M. Zajacek.
In addition to the collision of jetted material, the team also found evidence for a precession of the central jet of TXS 0506+056.
“This precession can in general be explained by the presence of a supermassive black hole binary or the Lense-Thirring precession effect as predicted by Einstein’s theory of general relativity,” said co-author Dr. Michal Zajaček, a researcher at the Warsaw Center for Theoretical Physics.”
“The latter could also be triggered by a second, more distant black hole in the centre. Both scenarios lead to a wandering of the jet direction, which we observe.”
The study was published in the October 2019 issue of the journal Astronomy & Astrophysics.
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S. Britzen et al. 2019. A cosmic collider: Was the IceCube neutrino generated in a precessing jet-jet interaction in TXS 0506+056? A&A 630, A103; doi: 10.1051/0004-6361/201935422
