Studies of Fermi data indicate an excess of GeV gamma rays around the Galactic center (GC), possibly due to dark matter. We show that young gamma-ray pulsars can yield a similar signal. First, a high concentration of GC supernovae naturally leads to
a population of kicked pulsars symmetric about the GC. Second, while very-young pulsars with soft spectra reside near the Galactic plane, pulsars with spectra that have hardened with age accumulate at larger angles. This combination, including unresolved foreground pulsars, traces the morphology and spectrum of the Excess.
Observations of high-z galaxies and gamma-ray bursts now allow for empirical studies during reionization. However, even deep surveys see only the brightest galaxies at any epoch and must extrapolate to arbitrary lower limits to estimate the total rat
e of star formation. We first argue that the galaxy populations seen in LBG surveys yield a GRB rate at z > 8 that is an order of magnitude lower than observed. We find that integrating the inferred UV luminosity functions down to M_UV ~ -10 brings LBG- and GRB-inferred SFR density values into agreement up to z ~ 8. GRBs, however, favor a far larger amount of as yet unseen star formation at z > 9. We suggest that the SFR density may only slowly decline out to z ~ 11, in accord with WMAP and Planck reionization results, and that GRBs may be useful in measuring the scale of this multitude of dwarf galaxies.
The IceCube experiment recently detected the first flux of high-energy neutrinos in excess of atmospheric backgrounds. We examine whether these neutrinos originate from within the same extragalactic sources as ultrahigh-energy cosmic rays. Starting f
rom rather general assumptions about spectra and flavors, we find that producing a neutrino flux at the requisite level through pion photoproduction leads to a flux of protons well below the cosmic-ray data at ~10^18 eV, where the composition is light, unless pions/muons cool before decaying. This suggests a dominant class of accelerator that allows for cosmic rays to escape without significant neutrino yields.
Neutrinos and gravitational waves are the only direct probes of the inner dynamics of a stellar core collapse. They are also the first signals to arrive from a supernova and, if detected, establish the moment when the shock wave is formed that unbind
s the stellar envelope and later initiates the optical display upon reaching the stellar surface with a burst of UV and X-ray photons, the shock breakout (SBO). We discuss how neutrino observations can be used to trigger searches to detect the elusive SBO event. Observation of the SBO would provide several important constraints on progenitor structure and the explosion, including the shock propagation time (the duration between the neutrino burst and SBO), an observable that is important in distinguishing progenitor types. Our estimates suggest that next generation neutrino detectors could exploit the overdensity of nearby SNe to provide several such triggers per decade, more than an order of magnitude improvement over the present.
Isotropy is a key assumption in many models of cosmic-ray electrons and positrons. We find that simulation results imply a critical energy of ~10-1000 GeV above which electrons and positrons can spend their entire lives in streams threading magnetic
fields, due to energy losses. This would restrict the number of electron/positron sources contributing at Earth, likely leading to smooth electron and positron spectra, as is observed. For positrons, this could be as few as one, with an enhanced flux that would ease energetics concerns of a pulsar origin of the positron excess, or even zero, bringing dark matter into play. We conclude that ideas about electron/positron propagation based on either isotropic diffusion or turbulent fields must be changed.
The legacy of solar neutrinos suggests that large neutrino detectors should be sited underground. However, to instead go underwater bypasses the need to move mountains, allowing much larger water Cherenkov detectors. We show that reaching a detector
mass scale of ~5 Megatons, the size of the proposed Deep-TITAND, would permit observations of neutrino mini-bursts from supernovae in nearby galaxies on a roughly yearly basis, and we develop the immediate qualitative and quantitative consequences. Importantly, these mini-bursts would be detected over backgrounds without the need for optical evidence of the supernova, guaranteeing the beginning of time-domain MeV neutrino astronomy. The ability to identify, to the second, every core collapse in the local Universe would allow a continuous death watch of all stars within ~5 Mpc, making practical many previously-impossible tasks in probing rare outcomes and refining coordination of multi-wavelength/multi-particle observations and analysis. These include the abilities to promptly detect otherwise-invisible prompt black hole formation, provide advance warning for supernova shock-breakout searches, define tight time windows for gravitational-wave searches, and identify supernova impostors by the non-detection of neutrinos. Observations of many supernovae, even with low numbers of detected neutrinos, will help answer questions about supernovae that cannot be resolved with a single high-statistics event in the Milky Way.
