The Charge Collection Properties of CVD Diamond

The charge collection properties of CVD diamond have been investigated with ionising radiation. In this study two CVD diamond samples, prepared with electrical contacts have been used as solid state ionisation chambers. The diamonds have been studied with beta particles and 10 keV photons, providing a homogeneous ionisation density and with protons and alpha particles which are absorbed in a thin surface layer. For the latter case a strong decrease of the signal as function of time is observed, which is attributed to polarisation effects inside the diamond. Spatially resolved measurements with protons show a large variation of the charge collection efficiency, whereas for photons and minimum ionising particles the response is much more uniform and in the order of 18%. These results indicate that the applicability of CVD diamond as a position sensitive particle detector depends on the ionisation type and appears to be promising for homogeneous ionisation densities as provided by relativistic charged particles.Comment: 26 pages (Latex), submitted to NIM

GALPROP WebRun: an internet-based service for calculating galactic cosmic ray propagation and associated photon emissions

GALPROP is a numerical code for calculating the galactic propagation of relativistic charged particles and the diffuse emissions produced during their propagation. The code incorporates as much realistic astrophysical input as possible together with latest theoretical developments and has become a de facto standard in astrophysics of cosmic rays. We present GALPROP WebRun, a service to the scientific community enabling easy use of the freely available GALPROP code via web browsers. In addition, we introduce the latest GALPROP version 54, available through this service.Comment: Accepted for publication in Computer Physics Communications. Version 2 includes improvements suggested by the referee. Metadata completed in version 3 (no changes to the manuscript

HAWC Study of the Ultra-high-energy Spectrum of MGRO J1908+06

We report TeV gamma-ray observations of the ultra-high-energy source MGRO J1908+06 using data from the High Altitude Water Cherenkov Observatory. This source is one of the highest-energy known gamma-ray sources, with emission extending past 200 TeV. Modeling suggests that the bulk of the TeV gamma-ray emission is leptonic in nature, driven by the energetic radio-faint pulsar PSR J1907+0602. Depending on what assumptions are included in the model, a hadronic component may also be allowed. Using the results of the modeling, we discuss implications for detection prospects by multi-messenger campaigns

Detailed Analysis of the TeV γ-Ray Sources 3HWC J1928+178, 3HWC J1930+188, and the New Source HAWC J1932+192

The latest High Altitude Water Cherenkov (HAWC) point-like source catalog up to 56 TeV reported the detection of two sources in the region of the Galactic plane at galactic longitude 52° \u3c ℓ \u3c 55°, 3HWC J1930+188 and 3HWC J1928+178. The first one is associated with a known TeV source, the supernova remnant SNR G054.1+00.3. It was discovered by one of the currently operating Imaging Atmospheric Cherenkov Telescope (IACT), the Very Energetic Radiation Imaging Telescope Array System (VERITAS), detected by the High Energy Stereoscopic System (H.E.S.S), and identified as a composite SNR. However, the source 3HWC J1928+178, discovered by HAWC and coincident with the pulsar PSR J1928+1746, was not detected by any IACT despite their long exposure on the region, until a recent new analysis of H.E.S.S. data was able to confirm it. Moreover, no X-ray counterpart has been detected from this pulsar. We present a multicomponent fit of this region using the latest HAWC data. This reveals an additional new source, HAWC J1932+192, which is potentially associated with the pulsar PSR J1932+1916, whose γ-ray emission could come from the acceleration of particles in its pulsar wind nebula. In the case of 3HWC J1928+178, several possible explanations are explored, in an attempt to unveil the origins of the very-high-energy γ-ray emission

Discovery of Localized Regions of Excess 10-TeV Cosmic Rays

An analysis of 7 years of Milagro data performed on a 10-degree angular scale has found two localized regions of excess of unknown origin with greater than 12 sigma significance. Both regions are inconsistent with 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 4.6 sigma, and it is consistent with hard spectrum protons with an exponential cutoff, with the most significant excess at ~10 TeV. Potential causes of these excesses are explored, but no compelling explanations are found.Comment: Submitted to PhysRevLet

The Study of TeV Variability and Duty Cycle of Mrk 421 from 3 Years of Observations with the Milagro Observatory

TeV flaring activity with time scales as short as tens of minutes and an orphan TeV flare have been observed from the blazar Markarian 421 (Mrk 421). The TeV emission from Mrk 421 is believed to be produced by leptonic synchrotron self-Compton (SSC) emission. In this scenario, correlations between the X-ray and the TeV fluxes are expected, TeV orphan flares are hardly explained and the activity (measured as duty cycle) of the source at TeV energies is expected to be equal or less than that observed in X-rays if only SSC is considered. To estimate the TeV duty cycle of Mrk 421 and to establish limits on its variability at different time scales, we continuously observed Mrk 421 with the Milagro observatory. Mrk 421 was detected by Milagro with a statistical significance of 7.1 standard deviations between 2005 September 21 and 2008 March 15. The observed spectrum is consistent with previous observations by VERITAS. We estimate the duty cycle of Mrk 421 for energies above 1 TeV for different hypothesis of the baseline flux and for different flare selections and we compare our results with the X-ray duty cycle estimated by Resconi et al. 2009. The robustness of the results is discussed.Comment: 27 pages, 6 figures, ApJ accepte

A Measurement of Time-Averaged Aerosol Optical Depth using Air-Showers Observed in Stereo by HiRes

Air fluorescence measurements of cosmic ray energy must be corrected for attenuation of the atmosphere. In this paper we show that the air-showers themselves can yield a measurement of the aerosol attenuation in terms of optical depth, time-averaged over extended periods. Although the technique lacks statistical power to make the critical hourly measurements that only specialized active instruments can achieve, we note the technique does not depend on absolute calibration of the detector hardware, and requires no additional equipment beyond the fluorescence detectors that observe the air showers. This paper describes the technique, and presents results based on analysis of 1258 air-showers observed in stereo by the High Resolution Fly's Eye over a four year span.Comment: 7 pages, 3 figures, accepted for publication by Astroparticle Physics Journa

Search for Global Dipole Enhancements in the HiRes-I Monocular Data above 10^{18.5} eV

Several proposed source models for Ultra-High Energy Cosmic Rays (UHECRs) consist of dipole distributions oriented towards major astrophysical landmarks such as the galactic center, M87, or Centaurus A. We use a comparison between real data and simulated data to show that the HiRes-I monocular data for energies above 10^{18.5} eV is, in fact, consistent with an isotropic source model. We then explore methods to quantify our sensitivity to dipole source models oriented towards the Galactic Center, M87, and Centaurus A.Comment: 17 pages, 31 figure

Spectrum and Morphology of the Two Brightest Milagro Sources in the Cygnus Region: MGRO J2019+37 and MGRO J2031+41

The Cygnus region is a very bright and complex portion of the TeV sky, host to unidentified sources and a diffuse excess with respect to conventional cosmic-ray propagation models. Two of the brightest TeV sources, MGRO J2019+37 and MGRO J2031+41, are analyzed using Milagro data with a new technique, and their emission is tested under two different spectral assumptions: a power law and a power law with an exponential cutoff. The new analysis technique is based on an energy estimator that uses the fraction of photomultiplier tubes in the observatory that detect the extensive air shower. The photon spectrum is measured in the range 1 to 200 TeV using the last 3 years of Milagro data (2005-2008), with the detector in its final configuration. MGRO J2019+37 is detected with a significance of 12.3 standard deviations ($\sigma$), and is better fit by a power law with an exponential cutoff than by a simple power law, with a probability $>98$% (F-test). The best-fitting parameters for the power law with exponential cutoff model are a normalization at 10 TeV of $7^{+5}_{-2}\times10^{-10}$ $\mathrm{s^{-1}\: m^{-2}\: TeV^{-1}}$, a spectral index of $2.0^{+0.5}_{-1.0}$ and a cutoff energy of $29^{+50}_{-16}$ TeV. MGRO J2031+41 is detected with a significance of 7.3$\sigma$, with no evidence of a cutoff. The best-fitting parameters for a power law are a normalization of $2.4^{+0.6}_{-0.5}\times10^{-10}$ $\mathrm{s^{-1}\: m^{-2}\: TeV^{-1}}$ and a spectral index of $3.08^{+0.19}_{-0.17}$. The overall flux is subject to an $\sim$30% systematic uncertainty. The systematic uncertainty on the power law indices is $\sim$0.1. A comparison with previous results from TeV J2032+4130, MGRO J2031+41 and MGRO J2019+37 is also presented.Comment: 11 pages, 10 figure