Multimessenger Constraints on Intergalactic Magnetic Fields from the
  Flare of TXS 0506+056
  The origin of magnetic fields in the universe is an open problem. Seed
magnetic fields possibly produced in early times may have survived up to the
present day close to their original form, providing an untapped window to the
primeval universe. The recent observations of high-energy neutrinos from the
blazar TXS 0506+056 in association with an electromagnetic counterpart in a
broad range of wavelengths can be used to probe intergalactic magnetic fields
via the time delay between the neutrinos and gamma rays as well as the time
dependence of the gamma-ray fluxes. Using extensive three-dimensional Monte
Carlo simulations, we present a novel method to constrain these fields. We
apply it to TXS 0506+056 and, for the first time, derive constraints on both
the magnetic-field strength and its coherence length, considering six orders of
magnitude for each.
