While existing detectors would see a burst of many neutrinos from a Milky Way supernova, the supernova rate is only a few per century. As an alternative, we propose the detection of ∼ 1 neutrino per supernova from galaxies within 10 Mpc, in which there were at least 9 core-collapse supernovae since 2002. With a future 1-Mton scale detector, this could be a faster method for measuring the supernova neutrino spectrum, which is essential for calibrating numerical models and predicting the redshifted diffuse spectrum from distant supernovae. It would also allow a > ∼ 10 4 times more precise trigger time than optical data alone for high-energy neutrinos and gravitational waves. One of the unsolved problems of astrophysics is how core-collapse supernovae explode. Nuclear fusion reactions in the core of a massive star produce progressively heavier elements until a Chandrasekhar mass of iron is formed, and electron degeneracy pressure cannot support the core under the weight of the stellar envelope. The core collapses until it reaches nuclear densities and neutrino emission begins; then an outgoing bounce shock should form, unbinding the envelope and producing the optical supernova. While successful in nature, in most numerical supernova models, the shock stalls, so that the fate of the entire star is to produce a black hole (after substantial neutrino emission), but no optical supernova.Since the gravitational energy release transferred to neutrinos, about 3× 10 53 erg, is ∼ 100 times greater than the required kinetic energy for the explosion, it is thought that neutrino emission and interactions are a key diagnostic or ingredient of success. However, not enough is directly known about the total energies and temperatures of the neutrino flavors. The ≃ 20 events from SN 1987A were only crudely consistent with expectations forν e , and gave very little information on the other flavors [1]. It is thus essential to collect more supernova neutrino events. A Milky Way supernova would allow detailed measurements, but the supernova rate is only a few per century. If Super-Kamiokande were loaded with GdCl 3 [2], the diffuse supernova neutrino background (DSNB) [3,4,5] could be cleanly detected, probing the supernova neutrino spectrum, but convolved with the rapidly evolving star formation rate [6] up to redshift z ≃ 1.We propose an intermediate regime, in which the number of events per supernova is ∼ 1, instead of ≫ 1 (Milky Way) or ≪ 1 (DSNB), motivated by the serious consideration of 1-Mton scale water-Čerenkov detectors in Japan ), the United States (UNO [8]), and Europe (MEMPHYS [9]). These detectors, which may operate for decades, are intended for proton decay and long-baseline accelerator neutrino oscillation studies,

Abstract. Star-forming galaxies have been predicted to contribute considerably to the diffuse gamma-ray background as they are guaranteed reservoirs of cosmic rays. Assuming that the hadronic interactions responsible for high-energy gamma rays also produce highenergy neutrinos and that O(100) PeV cosmic rays can be produced and confined in starburst galaxies, we here discuss the possibility that star-forming galaxies are also the main sources of the high-energy neutrinos observed by the IceCube experiment. First, we compute the diffuse gamma-ray background from star-forming galaxies, adopting the latest Herschel PEP/HerMES luminosity function and relying on the correlation between the gamma-ray and infrared luminosities reported by Fermi observations. Then we derive the expected intensity of the diffuse high-energy neutrinos from star-forming galaxies including normal and starburst galaxies. Our results indicate that starbursts, including those with active galactic nuclei and galaxy mergers, could be the main sources of the high-energy neutrinos observed by the IceCube experiment. We find that assuming a cosmic-ray spectral index of 2.1-2.2 for all starburst-like galaxies, our predictions can be consistent with both the Fermi and IceCube data, but larger indices readily fail to explain the observed diffuse neutrino flux. Taking the starburst high-energy spectral index as free parameter, and extrapolating from GeV to PeV energies, we find that the spectra harder than E −2.15 are likely to be excluded by the IceCube data, which can be more constraining than the Fermi data for this population.

We present analytic approximations to the optically thin synchrotron and synchrotron self-Compton (SSC) spectra when Klein-Nishina (KN) effects are important and pair production and external radiation fields can be neglected. This theory is useful for analytical treatment of radiation from astrophysical sources, such as gamma-ray bursts (GRBs), active galactic nuclei and pulsar wind nebula, where KN effects may be important. We consider a source with a continuous injection of relativistic electrons with a power-law energy distribution above some typical injection energy. We find that the synchrotron-SSC spectra can be described by a broken power-law, and provide analytic estimates for the break frequencies and power-law indices. In general, we show that the dependence of the KN cross-section on the energy of the upscattering electron results in a hardening of the energy distribution of fast cooling electrons and therefore in a hardening of the observed synchrotron spectrum. As a result the synchrotron spectrum of fast cooling electrons, below the typical injection energy, can be as hard as F ν ∝ ν 0 , instead of the classical ν −1/2 when KN effects are neglected. The synchrotron energy output can be dominated by electrons with energy above the typical injection energy. We solve self-consistently for the cooling frequency and find that the transition between synchrotron and SSC cooling can result in a discontinuous variations of the cooling frequency and the synchrotron and SSC spectra. We demonstrate the application of our results to theory by applying them to prompt and afterglow emission models of GRBs.1 As a result of KN effects the definition of γ c may be more complicated in a small region of the parameter space. We discuss the definition (and value) of γ c in §5.

High-energy photons from pair annihilation of dark matter particles contribute to the cosmic gamma-ray background (CGB) observed in a wide energy range. Since dark matter particles are weakly interacting, annihilation can happen only in high density regions such as dark matter halos. The precise shape of the energy spectrum of CGB depends on the nature of dark matter particlestheir mass and annihilation cross section, as well as the cosmological evolution of dark matter halos. In order to discriminate between the signals from dark matter annihilation and other astrophysical sources, however, the information from the energy spectrum of CGB may not be sufficient. We show that dark matter annihilation not only contributes to the mean CGB intensity, but also produces a characteristic anisotropy, which provides a powerful tool for testing the origins of the observed CGB. We develop the formalism based on a halo model approach to analytically calculate the threedimensional power spectrum of dark matter clumping, which determines the power spectrum of annihilation signals. We show that the expected sensitivity of future gamma-ray detectors such as the Gamma Ray Large Area Space Telescope (GLAST) should allow us to measure the angular power spectrum of CGB anisotropy, if dark matter particles are supersymmetric neutralinos and they account for most of the observed mean intensity of CGB in GeV region. On the other hand, if dark matter has a relatively small mass, on the order of 20 MeV, and accounts for most of the CGB in MeV region, then the future Advanced Compton Telescope (ACT) should be able to measure the angular power spectrum in MeV region. As the intensity of photons from annihilation is proportional to the density squared, we show that the predicted shape of the angular power spectrum of gamma rays from dark matter annihilation is different from that due to other astrophysical sources such as blazars and supernovae, whose intensity is linearly proportional to density. Therefore, the angular power spectrum of the CGB provides a "smoking-gun" signature of gamma rays from dark matter annihilation. While the mean CGB intensity expected from dark matter halos with smooth density profiles is smaller than observed, the dark matter substructure within halos may provide the origin of additional "boost" factors for the annihilation signal. Our formalism can be used for any other radiation processes that involve collision of particles.

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We report a measurement of intergalactic magnetic fields using combined data from Atmospheric Cherenkov Telescopes and Fermi Gamma-Ray Space Telescope, based on the spectral data alone. If blazars are assumed to produce both gamma rays and cosmic rays, the observed spectra are not sensitive to the intrinsic spectrum of the source, because, for a distant blazar, secondary photons produced in line-of-sight cosmic-ray interactions dominate the signal. In this case, we find 0.01 fG < B < 30 fG. If one excludes the cosmic-ray component, the 0.01 fG lower limit remains, but the upper limit depends on the spectral properties of the source. We present the allowed ranges for a variety of model parameters.Comment: 13 pages, 3 figure

In the indirect detection of dark matter through its annihilation products, the signals depend on the square of the dark matter density, making precise knowledge of the distribution of dark matter in the Universe critical for robust predictions. Many studies have focused on regions where the dark matter density is greatest, e.g., the galactic center, as well as on the cosmic signal arising from all halos in the Universe. We focus on the signal arising from the whole Milky Way halo; this is less sensitive to uncertainties in the dark matter distribution, and especially for flatter profiles, this halo signal is larger than the cosmic signal. We illustrate this by considering a dark matter model in which the principal annihilation products are neutrinos. Since neutrinos are the least detectable standard model particles, a limit on their flux conservatively bounds the dark matter total self-annihilation cross section from above. By using the Milky Way halo signal, we show that previous constraints using the cosmic signal can be improved on by 1-2 orders of magnitude; dedicated experimental analyses should be able to improve both by an additional 1-2 orders of magnitude.

Intergalactic magnetic fields (IGMFs) can cause the appearance of halos around the gamma-ray images of distant objects because an electromagnetic cascade initiated by a high-energy gamma-ray interaction with the photon background is broadened by magnetic deflections. We report evidence of such gamma-ray halos in the stacked images of the 170 brightest active galactic nuclei (AGNs) in the 11 month source catalog of the Fermi Gamma-Ray Space Telescope. Excess over the point-spread function in the surface brightness profile is statistically significant at 3.5σ (99.95% confidence level), for the nearby, hard population of AGNs. The halo size and brightness are consistent with IGMF, B IGMF ≈ 10 −15 G. The knowledge of IGMF will facilitate the future gamma-ray and charged-particle astronomy. Furthermore, since IGMFs are likely to originate from the primordial seed fields created shortly after the big bang, this potentially opens a new window on the origin of cosmological magnetic fields, inflation, and the phase transitions in the early universe.