B. Allen

Publications (4)25.44 Total impact

• Source

  Available from: Sabrina Casanova

  Article: Discovery of TeV Gamma-Ray Emission from the Cygnus Region of the Galaxy

  A. A. Abdo, B. Allen, D. Berley, E. Blaufuss, S. Casanova, C. Chen, D. G. Coyne, R. S. Delay, B. L. Dingus, R. W. Ellsworth, [......], A. Shoup, G. Sinnis, A. J. Smith, A. W. Strong, G. W. Sullivan, V. Vasileiou, G. P. Walker, D. A. Williams, X. W. Xu, and G. B. Yodh
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  ABSTRACT: The diffuse gamma radiation arising from the interaction of cosmic-ray particles with matter and radiation in the Galaxy is one of the few probes available to study the origin of the cosmic rays. Data from the Milagro gamma-ray observatory—a water Cerenkov detector that continuously views ~2 sr of the overhead sky—shows that the brightest extended region in the entire northern sky is the Cygnus region of the Galactic plane. The TeV image of the Cygnus region contains at least one new source, MGRO J2019+37, which is 10.9 σ above the isotropic background, as well as correlations with the matter density in the region. However, the gamma-ray flux from the Cygnus region (after excluding MGRO J2019+37) as measured at ~12 TeV exceeds that predicted from a model of cosmic-ray production and propagation. This observation indicates the existence of either hard-spectrum cosmic-ray sources and/or unresolved sources of TeV gamma rays in the region.
  The Astrophysical Journal 12/2008; 658(1):L33. · 6.02 Impact Factor
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  Available from: Sabrina Casanova

  Article: TeV Gamma-Ray Sources from a Survey of the Galactic Plane with Milagro

  A. A. Abdo, B. Allen, D. Berley, S. Casanova, C. Chen, D. G. Coyne, B. L. Dingus, R. W. Ellsworth, L. Fleysher, R. Fleysher, [......], P. M. Saz Parkinson, A. Shoup, G. Sinnis, A. J. Smith, G. W. Sullivan, V. Vasileiou, G. P. Walker, D. A. Williams, X. W. Xu, and G. B. Yodh
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  ABSTRACT: A survey of Galactic gamma-ray sources at a median energy of ~20 TeV has been performed using the Milagro Gamma-Ray Observatory. Eight candidate sources of TeV emission are detected with pretrial significances >4.5 σ in the region of Galactic longitude l [30°, 220°] and latitude b [-10°, 10°]. Four of these sources, including the Crab Nebula and the recently published MGRO J2019+37, are observed with significances >4 σ after accounting for the trials. All four of these sources are also coincident with EGRET sources. Two of the lower significance sources are coincident with EGRET sources, and one of these sources is Geminga. The other two candidates are in the Cygnus region of the Galaxy. Several of the sources appear to be spatially extended. The fluxes of the sources at 20 TeV range from ~25% of the Crab flux to nearly as bright as the Crab.
  The Astrophysical Journal 12/2008; 664(2):L91. · 6.02 Impact Factor
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  Available from: Sabrina Casanova

  Article: A Measurement of the Spatial Distribution of Diffuse TeV Gamma-Ray Emission from the Galactic Plane with Milagro

  A. A. Abdo, B. Allen, T. Aune, D. Berley, E. Blaufuss, S. Casanova, C. Chen, B. L. Dingus, R. W. Ellsworth, L. Fleysher, [......], P. M. Saz Parkinson, A. Shoup, G. Sinnis, A. J. Smith, A. W. Strong, G. W. Sullivan, V. Vasileiou, G. P. Walker, D. A. Williams, and G. B. Yodh
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  ABSTRACT: Diffuse γ-ray emission produced by the interaction of cosmic-ray particles with matter and radiation in the Galaxy can be used to probe the distribution of cosmic rays and their sources in different regions of the Galaxy. With its large field of view and long observation time, the Milagro Gamma Ray Observatory is an ideal instrument for surveying large regions of the northern hemisphere sky and for detecting diffuse γ-ray emission at very high energies. Here the spatial distribution and the flux of the diffuse γ-ray emission in the TeV energy range with a median energy of 15 TeV for Galactic longitude between 30° and 110° and between 136° and 216° and for Galactic latitude between –10° and 10° are determined. The measured fluxes are consistent with predictions of the GALPROP model everywhere, except for the Cygnus region (l [ 65°,85°] ). For the Cygnus region, the flux is twice the predicted value. This excess can be explained by the presence of active cosmic-ray sources accelerating hadrons, which interact with the local dense interstellar medium and produce gamma rays through pion decay.
  The Astrophysical Journal 12/2008; 688(2):1078. · 6.02 Impact Factor
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  Available from: Sabrina Casanova

  Article: Discovery of localized regions of excess 10-TeV cosmic rays.

  A A Abdo, B Allen, T Aune, D Berley, E Blaufuss, S Casanova, C Chen, B L Dingus, R W Ellsworth, L Fleysher, [......], J M Ryan, P M Saz Parkinson, A Shoup, G Sinnis, A J Smith, G W Sullivan, V Vasileiou, G P Walker, D A Williams, G B Yodh
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  ABSTRACT: The 7 year data set of the Milagro TeV observatory contains 2.2 x 10(11) events of which most are due to hadronic cosmic rays. These data are searched for evidence of intermediate scale structure. Excess emission on angular scales of approximately 10 degrees has been found in two localized regions of unknown origin with greater than 12sigma significance. Both regions are inconsistent with pure gamma-ray emission with high confidence. One of the regions has a different energy spectrum than the isotropic cosmic-ray flux at a level of 4.6sigma, and it is consistent with hard spectrum protons with an exponential cutoff, with the most significant excess at approximately 10 TeV. Potential causes of these excesses are explored, but no compelling explanations are found.
  Physical Review Letters 12/2008; 101(22):221101. · 7.37 Impact Factor