Kohta Murase 교수

We consider implications of the IceCube signal for hadronuclear ($pp$) scenarios of neutrino sources such as galaxy clusters/groups and star-forming galaxies. Since the observed neutrino flux is comparable to the diffuse $\ensuremath{\gamma}$-ray background flux obtained by Fermi, we place new, strong upper limits on the source spectral index, $\ensuremath{\Gamma}\ensuremath{\lesssim}2.1--2.2$. In addition, the new IceCube data imply that these sources contribute at least 30%--40% of the diffuse

The latest IceCube data suggest that the all-flavor cosmic neutrino flux may be as large as 10^{-7} GeV cm^{-2} s^{-1} sr^{-1} around 30 TeV. We show that, if sources of the TeV-PeV neutrinos are transparent to γ rays with respect to two-photon annihilation, strong tensions with the isotropic diffuse γ-ray background measured by Fermi are unavoidable, independently of the production mechanism. We further show that, if the IceCube neutrinos have a photohadronic (pγ) origin, the sources are expect

Abstract Detection of the IceCube-170922A neutrino coincident with the flaring blazar TXS 0506+056, the first and only ∼3 σ high-energy neutrino source association to date, offers a potential breakthrough in our understanding of high-energy cosmic particles and blazar physics. We present a comprehensive analysis of TXS 0506+056 during its flaring state, using newly collected Swift , NuSTAR , and X-shooter data with Fermi observations and numerical models to constrain the blazar’s particle accele

We study high-energy neutrino production in inner jets of radio-loud active galactic nuclei (AGN), taking into account effects of external photon fields and the blazar sequence. We show that the resulting diffuse neutrino intensity is dominated by quasar-hosted blazars, in particular, flat spectrum radio quasars, and that PeV-EeV neutrino production due to photohadronic interactions with broadline and dust radiation is unavoidable if the AGN inner jets are ultrahigh-energy cosmic-ray (UHECR) sou

We study high-energy neutrino production in collimated jets inside progenitors of gamma-ray bursts (GRBs) and supernovae, considering both collimation and internal shocks. We obtain simple, useful constraints, using the often overlooked point that shock acceleration of particles is ineffective at radiation-mediated shocks. Classical GRBs may be too powerful to produce high-energy neutrinos inside stars, which is consistent with IceCube nondetections. We find that ultralong GRBs avoid such constr

Tenuous wind bubbles, which are formed by the spin-down activity of central compact remnants, are relevant in some models of fast radio bursts (FRBs) and superluminous supernovae (SNe). We study their high-energy signatures, focusing on the role of pair-enriched bubbles produced by young magnetars, rapidly rotating neutron stars, and magnetized white dwarfs. (i) First, we study the nebular properties and the conditions allowing for escape of high-energy gamma-rays and radio waves, showing that t

The spectra of BL Lac objects and Fanaroff-Riley I radio galaxies are commonly explained by the one-zone leptonic synchrotron self-Compton (SSC) model. Spectral modeling of correlated multiwavelength data gives the comoving magnetic field strength, the bulk outflow Lorentz factor, and the emission region size. Assuming the validity of the SSC model, the Hillas condition shows that only in rare cases such sources accelerate protons to much above 10 19 eV, so 10 20 eV ultra-high-energy cosmic rays

We consider limits on the local ($z=0$) density (${n}_{0}$) of extragalactic neutrino sources set by the nondetection of steady high-energy neutrino sources producing $\ensuremath{\gtrsim}50\text{ }\text{ }\mathrm{TeV}$ muon multiplets in the present IceCube data, taking into account the redshift evolution, luminosity function, and neutrino spectrum of the sources. We show that the lower limit depends moderately on source spectra and strongly on redshift evolution. We find ${n}_{0}\ensuremath{\g

High energy neutrino emission from gamma-ray bursts (GRBs) is discussed. In this paper, by using the simulation kit GEANT4, we calculate proton cooling efficiency including pion-multiplicity and proton-inelasticity in photomeson production. First, we estimate the maximum energy of accelerated protons in GRBs. Using the obtained results, neutrino flux from one burst and a diffuse neutrino background are evaluated quantitatively. We also take account of cooling processes of pion and muon, which ar

Mysteries about the origin of high-energy cosmic neutrinos have deepened by the recent IceCube measurement of a large diffuse flux in the 10-100 TeV range. Based on the standard disk-corona picture of active galactic nuclei (AGN), we present a phenomenological model enabling us to systematically calculate the spectral sequence of multimessenger emission from the AGN coronae. We show that protons in the coronal plasma can be stochastically accelerated up to PeV energies by plasma turbulence, and

Gamma-ray bursts (GRBs) are one of the candidates of ultrahigh-energy ($\ensuremath{\gtrsim}{10}^{18.5}\text{ }\text{ }\mathrm{eV}$) cosmic-ray (UHECR) sources. We investigate high-energy cosmic-ray acceleration including heavy nuclei in GRBs by using Geant 4, and discuss its various implications, taking both high-luminosity (HL) and low-luminosity (LL) GRBs into account. This is because LL GRBs may also make a significant contribution to the observed UHECR flux if they form a distinct populatio

Late time decay of very heavy dark matter is considered as one of the possible explanations for diffuse PeV neutrinos observed in IceCube. We consider implications of multimessenger constraints, and show that proposed models are marginally consistent with the diffuse γ-ray background data. Critical tests are possible by a detailed analysis and identification of the sub-TeV isotropic diffuse γ-ray data observed by Fermi and future observations of sub-PeV γ rays by observatories like HAWC or Tibet

A new class of core-collapse supernovae (SNe) has been discovered in recent years by optical/infrared surveys; these SNe suggest the presence of one or more extremely dense ($\ensuremath{\sim}{10}^{5\ensuremath{-}11}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}3}$) shells of circumstellar material (CSM) on ${10}^{2\ensuremath{-}4}\text{ }\text{ }\mathrm{AU}$ scales. We consider the collisions of the SN ejecta with these massive CSM shells as potential cosmic-ray (CR) accelerators. If $\ensuremat

The high energy neutrino emission from gamma-ray bursts (GRBs) has been expected in various scenarios. In this paper, we study the neutrino emission from early afterglows of GRBs, especially under the reverse-forward shock model and late prompt emission model. In the former model, the early afterglow emission occurs due to dissipation made by an external shock with the circumburst medium (CBM). In the latter model, internal dissipation such as internal shocks produces the shallow decay emission

We investigate the high-energy neutrino emission expected from newly born magnetars surrounded by their stellar ejecta. Protons might be accelerated up to 0.1--100 EeV energies possibly by, e.g., the wave dissipation in the winds, leading to hadronic interactions in the stellar ejecta. The resulting PeV-EeV neutrinos can be detected by IceCube/KM3Net with a typical peak time scale of a few days after the birth of magnetars, making the characteristic soft-hard-soft behavior. Detections would be i