Gamma-Ray Bursts as Multienergy Neutrino Sources

We review theoretical models for nonelectromagnetic emission, mainly neutrinos and cosmic rays, from gamma-ray bursts (GRBs). In various stages of the relativistic jet propagation, cosmic-ray ion acceleration and subsequent neutrino emission are expected. GRBs are popular candidate sources of the highest-energy cosmic rays, and their prompt phase has been most widely discussed. IceCube nondetection of PeV neutrinos coincident with GRBs has put interesting constraints on the standard theoretical prediction. The GRB-UHECR hypothesis can critically be tested by future observations. We also emphasize the importance of searches for GeV-TeV neutrinos, which are expected in the precursor/orphan or prompt phase, and lower-energy neutrinos would be more guaranteed and their detections even allow us to probe physics inside a progenitor star. Not only classical GRBs but also low-power GRBs and transrelativistic supernovae can be promising sources of TeV-PeV neutrinos, and we briefly discuss implications for the cumulative neutrino background discovered by IceCube

High-energy neutrino constraints on cosmic-ray re-acceleration in radio halos of massive galaxy clusters

A fraction of merging galaxy clusters host diffuse radio emission in their central region, termed as a giant radio halo (GRH). The most promising mechanism of GRHs is the re-acceleration of non-thermal electrons and positrons by merger-induced turbulence. However, the origin of these seed leptons has been under debate, and either protons or electrons can be primarily-accelerated particles. In this work, we demonstrate that neutrinos can be used as a probe of physical processes in galaxy clusters, and discuss possible constraints on the amount of relativistic protons in the intra-cluster medium with the existing upper limits by IceCube. We calculate radio and neutrino emission from massive ($>10^{14}M_\odot$) galaxy clusters, using the cluster population model of Nishiwaki & Asano (2022). This model is compatible with the observed statistics of GRHs, and we find that the contribution of GRHs to the isotropic radio background observed with the ARCADE-2 experiment should be subdominant. Our fiducial model predicts the all-sky neutrino flux that is consistent with IceCube's upper limit from the stacking analysis. We also show that the neutrino upper limit gives meaningful constraints on the parameter space of the re-acceleration model, such as the electron-to-proton ratio of primary cosmic-rays and the magnetic field, and in particular the secondary scenario, where the seed electrons mostly originate from inelastic $pp$ collisions, can be constrained even in the presence of re-acceleration.Comment: 12 pages, 6 figures, accepted for publication in Ap

High Energy Neutrino Flashes from Far-Ultraviolet and X-ray Flares in Gamma-Ray Bursts

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 far-ultraviolet and x-ray flares under the late internal shock model. We show that the efficiency of pion production in the highest energy is comparable to or higher than the unity, and the contribution from such neutrino flashes to a diffuse very high energy neutrino background can be larger than that of prompt bursts if the total baryonic energy input into flares is comparable to the radiated energy of prompt bursts. These signals may be detected by IceCube and are very important because they have possibilities to probe the nature of flares (the baryon loading, the photon field, the magnetic field and so on).Comment: 4 pages, 3 figures, version published in PR

The Role of Stochastic Acceleration in the Prompt Emission of Gamma-Ray Bursts: Application to Hadronic Injection

We study effects of particle re-acceleration (or heating) in the post-shock region via magnetohydrodynamic/plasma turbulence, in the context of a mixed hadronic-leptonic model for the prompt emission of gamma-ray bursts (GRBs), using both analytical and numerical methods. We show that stochastically accelerated (or heated) leptons, which are injected via pp and pg reactions and subsequent pair cascades, are plausibly able to reproduce the Band function spectra with alpha~1 and beta~2-3 in the ~MeV range. An additional hard component coming from the proton-induced cascade emission is simultaneously expected, which is compatible with observed extra power-law spectra far above the MeV range. We also discuss the specific implications of hadronic models for ongoing high-energy neutrino observations.Comment: 12 pages, 8 figures, accepted for publication in ApJ, discussions added, typos fixed. Results unchange

Detectability of Pair Echos from Gamma-Ray Bursts and Intergalactic Magnetic Fields

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 intergalactic background radiation. We investigate the detectability of such emission with modern-day gamma-ray telescopes. The spectra and light curves are calculated for a wide range of parameters, applying the formalism recently developed by Ichiki et al. The flux depends strongly on the unknown magnitude and coherence length of intergalactic magnetic fields, and we delineate the range of field strength and redshift that allow detectable echos. Relevant uncertainties such as the high-energy cutoff of the primary gamma-ray spectrum and the intensity of the cosmic infrared background are addressed. GLAST and MAGIC may be able to detect pair echo emission from GRBs with redshift $\lesssim 1$ if the primary spectra extend to $\sim 10 ~ {\rm TeV}$.Comment: 4 pages, 4 figure