Time-dependent neutrino emission from Mrk 421 during flares and predictions for IceCube

摘要

Blazars are prime candidate sources for the high energy neutrinos recentlydetected by IceCube. Being one of the brightest sources in the extragalacticX-ray and $\gamma$-ray sky as well as one of the nearest blazars to Earth, Mrk421 is an excellent source for testing the scenario of the blazar-neutrinoconnection. Here, we model the spectral energy distribution of Mrk 421 during a13-day flare in 2010 with unprecedented multi-wavelength coverage, andcalculate the respective neutrino flux. We find a correlation between the $>1$PeV neutrino and photon fluxes, in all energy bands. Using typical IceCubethrough-going muon event samples with good angular resolution and highstatistics, we derive the mean event rate above 100 TeV ($\sim0.57$ evt/yr) andshow that it is comparable to that expected from a four-month quiescent periodin 2009. Due to the short duration of the flare, an accumulation of similarflares over several years would be necessary to produce a meaningful signal forIceCube. To better assess this, we apply the correlation between the neutrinoand $\gamma$-ray fluxes to the 6.9 yr Fermi-LAT light curve of Mrk 421. We findthat the mean event count above 1 PeV for the full IceCube detector livetime is$3.59\pm0.60$ ($2.73\pm0.38$) $\nu_\mu+\bar{\nu}_\mu$ with (without) majorflares included in our analysis. This estimate exceeds, within theuncertainties, the $95\%$ ($90\%$) threshold value for the detection of one ormore muon (anti-)neutrinos. Meanwhile, the most conservative scenario, where nocorrelation of $\gamma$-rays and neutrinos is assumed, predicts $1.60\pm0.16$$\nu_\mu+\bar{\nu}_\mu$ events. We conclude that a non-detection of high-energyneutrinos by IceCube would probe the neutrino/$\gamma$-ray flux correlationduring major flares or/and the hadronic contribution to the blazar emission.