Radio Quiet AGNs as Possible Sources of Ultra-high Energy Cosmic Rays (2009)
Pe'er, Asaf, Murase, Kohta, Mészáros, Peter
Active galactic nuclei (AGNs) have been one of the most widely discussed sources of ultrahigh-energy cosmic rays (UHECRs). The recent results of Pierre Auger observatory (PAO) have indicated a...
Escape-limited Model of Cosmic-ray Acceleration Revisited (2009)
Ohira, Yutaka, Murase, Kohta, Yamazaki, Ryo
The spectrum of cosmic rays (CRs) is affected by their escape from an acceleration site. This may have been observed not only in the gamma-ray spectrum of young supernova remnants (SNRs) such as RX...
High-energy emission as a test of the prior emission model for gamma-ray burst afterglows (2009)
Murase, Kohta, Toma, Kenji, Yamazaki, Ryo, Nagataki, Shigehiro, Ioka, Kunihito
We study high-energy gamma-ray afterglow emission from gamma-ray bursts (GRBs) in the prior emission model, which is proposed to explain the plateau phase of the X-ray afterglow. This model predicts...
Probing the central engine of long gamma-ray bursts and hypernovae with gravitational waves (2009)
There are the two common candidates as the viable energy source for the central engine of long gamma-ray bursts (GRBs) and hypernovae (HNe), neutrino annihilation and magnetic fields. We investigate...
Aoi, Junichi, Murase, Kohta, Takahashi, Keitaro, Ioka, Kunihito, Nagataki, Shigehiro
We revisit the high-energy spectral cutoff originating from the electron-positron pair creation in the prompt phase of gamma-ray bursts (GRBs) with numerical and analytical calculations. We show that...
Probing the birth of fast rotating magnetars through high-energy neutrinos (2009)
Murase, Kohta, Meszaros, Peter, Zhang, Bing
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...
Detecting neutrinos and photons is crucial to identifying the sources of ultrahigh-energy cosmic rays (UHECRs), especially for transient sources. We focus on ultrahigh-energy gamma-ray emission from...
Possible Effects of Pair Echoes on Gamma-Ray Burst Afterglow Emission (2008)
Murase, Kohta, Zhang, Bing, Takahashi, Keitaro, Nagataki, Shigehiro
High-energy emission from gamma-ray bursts (GRBs) is widely expected but had been sparsely observed until recently when the Fermi satellite was launched. If >TeV gamma rays are produced in GRBs and...
Implications of Ultra-High-Energy Cosmic Rays for Transient Sources in the Auger Era (2008)
We study about ultra-high-energy cosmic rays (UHECRs) from transient sources, propagating in the Galactic and intergalactic space. Based on the recent observational results, we also estimate upper...
We investigate neutrino emission from gamma-ray bursts (GRBs) under alternative scenarios for prompt emission (the photospheric and synchrotron self-Compton scenarios) rather than the classical...
Detectability of Pair Echos from Gamma-Ray Bursts and Intergalactic Magnetic Fields (2008)
Takahashi, Keitaro, Murase, Kohta, Ichiki, Kiyotomo, Inoue, Susumu, Nagataki, Shigehiro
High-energy emission from gamma-ray bursts (GRBs) can give rise to pair echos, i.e. delayed inverse Compton emission from secondary $e^{\pm}$ pairs produced in $\gamma-\gamma$ interactions with...
Murase, Kohta, Takahashi, Keitaro, Inoue, Susumu, Ichiki, Kiyomoto, Nagataki, Shigehiro
More than a dozen blazars are known to be emitters of multi-TeV gamma rays, often with strong and rapid flaring activity. By interacting with photons of the cosmic microwave and infrared backgrounds,...
Murase, Kohta, Inoue, Susumu, Nagataki, Shigehiro
Accretion and merger shocks in clusters of galaxies are potential accelerators of high-energy protons, which can give rise to high-energy neutrinos through pp interactions with the intracluster gas....
Murase, Kohta, Ioka, Kunihito, Nagataki, Shigehiro, Nakamura, Takashi
Gamma-ray bursts (GRBs) are one of the candidates of ultra-high-energy (around 10^18.5 eV) cosmic-ray (UHECR) sources. We investigate high-energy cosmic-ray acceleration including heavy nuclei in...
The effect of energy amplification variance on the shock-acceleration (2007)
Aoi, Junichi, Murase, Kohta, Nagataki, Shigehiro
The shock-acceleration theory predicts a power-law energy spectrum in the test particle approximation, and there are two ways to calculate a power-law index, Peacock's approximation and Vietri's...
Closure Relations for Electron-Positron Pair-Signatures in Gamma-Ray Bursts (2007)
We present recipes to diagnose the fireball of gamma-ray bursts (GRBs) by combining observations of electron-positron pair-signatures (the pair-annihilation line and the cutoff energy due to the...
Unstable GRB photospheres and electron-positron annihilation lines (2007)
Ioka, Kunihito, Murase, Kohta, Toma, Kenji, Nagataki, Shigehiro, Nakamura, Takashi
We propose an emission mechanism of prompt gamma-ray bursts (GRBs) that can reproduce the observed non-thermal spectra with high radiative efficiencies, >50%. Internal dissipation below a photosphere...
High energy neutrino early afterglows from gamma-ray bursts revisited (2007)
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...
Cosmogenic neutrinos as a probe of the transition from Galactic to extragalactic cosmic rays (2007)
Takami, Hajime, Murase, Kohta, Nagataki, Shigehiro, Sato, Katsuhiko
There are two promising scenarios that explain the ankle, which is a dip in the spectrum of cosmic rays at $\sim 10^{19}$ eV. A scenario interprets the ankle as the transition from Galactic to...
Effects of Cosmic Infrared Background on High Energy Delayed Gamma-Rays from Gamma-Ray Bursts (2007)
Murase, Kohta, Asano, Katsuaki, Nagataki, Shigehiro
Regenerated high-energy emissions from gamma-ray bursts (GRBs) are studied in detail. If the intrinsic primary spectrum extends to the TeV range, these very high-energy photons are absorbed by the...
High Energy Neutrinos and Cosmic-Rays from Low-Luminosity Gamma-Ray Bursts? (2006)
Murase, Kohta, Ioka, Kunihito, Nagataki, Shigehiro, Nakamura, Takashi
The recently discovered gamma-ray burst (GRB) GRB 060218/SN 2006aj is classified as an X-ray Flash with very long duration driven possibly by a neutron star. Since GRB 060218 is very near about 140...
High Energy Neutrino Flashes from Far-Ultraviolet and X-ray Flares in Gamma-Ray Bursts (2006)
Murase, Kohta, Nagataki, Shigehiro
The recent observations of bright optical and x-ray flares by the Swift satellite suggest these are produced by the late activities of the central engine. We study the neutrino emission from...
Murase, Kohta, Nagataki, Shigehiro
High energy neutrino emission from GRBs is discussed. In this paper, by using the simulation kit GEANT4, we calculate proton cooling efficiency including pion-multiplicity and proton-inelasticity in...