%0 Journal Article %D 2018 %T Blazar Flares as an Origin of High-energy Cosmic Neutrinos? %A Murase, Kohta %A Oikonomou, Foteini %A Petropoulou, Maria %K astroparticle physics %K Astrophysics - Astrophysics of Galaxies %K Astrophysics - Cosmology and Nongalactic Astrophysics %K Astrophysics - High Energy Astrophysical Phenomena %K galaxies: active %K galaxies: jets %K gamma rays: galaxies %K High Energy Physics - Phenomenology %K neutrinos %K radiation mechanisms: non-thermal %X We consider implications of high-energy neutrino emission from blazar flares, including the recent event IceCube-170922A and the 2014-2015 neutrino flare that could originate from TXS 0506+056. First, we discuss their contribution to the diffuse neutrino intensity taking into account various observational constraints. Blazars are likely to be subdominant in the diffuse neutrino intensity at sub-PeV energies, and we show that blazar flares like those of TXS 0506+056 could make ≲1%-10% of the total neutrino intensity. We also argue that the neutrino output of blazars can be dominated by the flares in the standard leptonic scenario for their γ-ray emission, and energetic flares may still be detected with a rate of ≲ 1 {yr}}-1. Second, we consider multi-messenger constraints on the source modeling. We show that luminous neutrino flares should be accompanied by luminous broadband cascade emission, emerging also in X-rays and γ-rays. This implies that not only γ-ray telescopes like Fermi but also X-ray sky monitors such as Swift and MAXI are critical to test the canonical picture based on the single-zone modeling. We also suggest a two-zone model that can naturally satisfy the X-ray constraints while explaining the flaring neutrinos via either photomeson or hadronuclear processes. %V 865 %P 124 %8 2018/10/1 %@ 0004-637X %G eng %U https://ui.adsabs.harvard.edu/abs/2018ApJ...865..124M %! The Astrophysical Journal