  The flux of high energy neutrinos and photons produced in a blazar could get
attenuated when they propagate through the dark matter spike around the central
black hole and the halo of the host galaxy. Using the observation by IceCube of
a few high-energy neutrino events from TXS 0506+056, and their coincident gamma
ray events, we obtain new constraints on the dark matter-neutrino and dark
matter-photon scattering cross sections. Our constraints are orders of
magnitude more stringent than those derived from considering the attenuation
through the intergalactic medium and the Milky Way dark matter halo. When the
cross-section increases with energy, our constraints are also stronger than
those derived from the CMB and large-scale structure.
