Intensive searches for the sources of astrophysical high-
energy neutrinos in the past decade revealed only one source candidate -
the blazar TXS0506+056 (TXS). This first evidence was triggered by a
real-time alert from the IceCube Neutrino Observatory that has been
followed up by numerous "electromagnetic" observations. The available
multiwavelength spectrum of TXS allowed us to constrain a remarkable
number of possible source scenarios with only one observed neutrino.
Although, a preceding neutrino burst from the same source was found in
IceCube's archival the data, the absence of simultaneous multi-
wavelength observations leaves numerous open questions and is
significantly less restrictive. The identification of neutrino sources
and their "hadronic signatures" in the electromagnetic spectrum will
open a new window to the fundamental neutrino properties at extremely
long base lines.