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MNRAS, 2009
Determining the escape fraction of ionizing photons during reionization
The fraction of ionizing photons that escape their host galaxies and so are able to ionize hydrogen in the inter-galactic medium (IGM) is a critical parameter in analyses of the reionization era and early galaxy formation. Studies of the reionization history normally suffer from a degeneracy ...
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APJL, 2009
The Star Formation Rate in the Reionization Era as Indicated by Gamma-ray Bursts
High-redshift gamma-ray bursts (GRBs) offer an extraordinary opportunity to study aspects of the early Universe, including the cosmic star formation rate (SFR). Motivated by the two recent highest-z GRBs, GRB 080913 at z = 6.7 and GRB 090423 at z = 8.1, and more than four years of Swift observations...
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PRL, 2009
TeV Gamma Rays from Geminga and the Origin of the GeV Positron Excess
The Geminga pulsar has long been one of the most intriguing MeV-GeV gamma-ray point sources. We examine the implications of the recent Milagro detection of extended, multi-TeV gamma-ray emission from Geminga, finding that this reveals the existence of an ancient, powerful cosmic-ray accelerator that also can plausibly account for the multi-GeV positron excess...
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PRD, 2009
CMSSM Spectroscopy in light of PAMELA and ATIC
Dark matter neutralinos in the constrained minimal supersymmetric model (CMSSM) may account for the recent cosmic ray electron and positron observations reported by the PAMELA and ATIC experiments either through self annihilation or via decay. However, to achieve this, both scenarios require new physics beyond the 'standard' CMSSM...
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APJL, 2008
Discovery of the Dust-Enshrouded Progenitor of SN 2008S with Spitzer
We report the discovery of the progenitor of the recent type IIn SN 2008S in the nearby galaxy NGC 6946. Surprisingly, it was not found in deep, pre-explosion optical images of its host galaxy taken with the Large Binocular Telescope, but only through examination of archival Spitzer mid-IR data...
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PRD, 2008
Conservative Constraints on Dark Matter Annihilation into Gamma Rays
Using gamma-ray data from observations of the Milky Way, Andromeda (M31), and the cosmic background, we calculate conservative upper limits on the dark matter self-annihilation cross section to monoenergetic gamma rays,_{gamma gamma}, over a wide range of dark matter masses...
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APJ, 2008
A Survey About Nothing: Monitoring a Million Supergiants for Failed Supernovae
Extragalactic transient searches have historically been limited to looking for the appearance of new sources such as supernovae. It is now possible to carry out a new kind of survey that will do the opposite, that is, search for the disappearance of massive stars. This will entail the systematic observation of galaxies...
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PRD, 2008
Circumscribing Late Dark Matter Decays Model Independently
A number of theories, spanning a wide range of mass scales, predict dark matter candidates that have lifetimes much longer than the age of the universe, yet may produce a significant flux of gamma rays in their decays today. We constrain such late decaying dark matter scenarios model-independently by utilizing...
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APJL, 2008
An Unexpectedly Swift Rise in the Gamma-ray Burst Rate
The association of long gamma-ray bursts with supernovae naturally suggests that the cosmic GRB rate should trace the star formation history. Finding otherwise would provide important clues concerning these rare, curious phenomena. Using a new estimate of Swift GRB energetics to construct a sample...
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APJL, 2008
Revealing the High-Redshift Star Formation Rate with Gamma-Ray Bursts
While the high-z frontier of star formation rate (SFR) studies has advanced rapidly, direct measurements beyond z ~ 4 remain difficult, as shown by significant disagreements among different results. Gamma-ray bursts, owing to their brightness and association with massive stars, offer hope of clarifying this situation, provided that the GRB rate...
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PRL, 2008
Strong Upper Limits on Sterile Neutrino Warm Dark Matter
Sterile neutrinos are attractive dark matter candidates. Their parameter space of mass and mixing angle has not yet been fully tested despite intensive efforts that exploit their gravitational clustering properties and radiative decays. We use the limits on gamma-ray line emission from the Galactic Center...
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