arXiv subjects

J. Hall

Publications and source records attributed to J. Hall.

79 records · Page 5Linked to original sources

arXiv2006

Observations of the Unidentified TeV Gamma-Ray Source TeV J2032+4130 with the Whipple Observatory 10 m Telescope

We report on observations of the sky region around the unidentified TeV gamma-ray source TeV J2032+4130 carried out with the Whipple Observatory 10 m atmospheric Cherenkov telescope for a total of 65.5 hrs between 2003 and 2005. The standard two-dimensional analysis developed by the Whipple collaboration for a stand-alone telescope reveals an excess in the field of view at a pre-trials significance level of 6.1 standard deviations. The measured position of this excess is alpha(2000) =20 h 32 m 27 s, delta(2000) = 41 deg 39 min 17 s. The estimated integral flux for this gamma-ray source is about 8% of the Crab-Nebula flux. The data are consistent with a point-like source. Here we present a detailed description of the standard two-dimensional analysis technique used for the analysis of data taken with the Whipple Observatory 10 m telescope and the results for the TeV J2032+4130 campaign. We include a short discussion of the physical mechanisms that may be responsible for the observed gamma-ray emission, based on possible association with known astrophysical objects, in particular Cygnus OB2.

astro-ph↗

arXiv2006

The First VERITAS Telescope

The first atmospheric Cherenkov telescope of VERITAS (the Very Energetic Radiation Imaging Telescope Array System) has been in operation since February 2005. We present here a technical description of the instrument and a summary of its performance. The calibration methods are described, along with the results of Monte Carlo simulations of the telescope and comparisons between real and simulated data. The analysis of TeV $γ$-ray observations of the Crab Nebula, including the reconstructed energy spectrum, is shown to give results consistent with earlier measurements. The telescope is operating as expected and has met or exceeded all design specifications.

astro-ph↗

arXiv2006

TeV Gamma-Ray Observations of the Perseus and Abell 2029 Galaxy Clusters

Galaxy clusters might be sources of TeV gamma rays emitted by high-energy protons and electrons accelerated by large scale structure formation shocks, galactic winds, or active galactic nuclei. Furthermore, gamma rays may be produced in dark matter particle annihilation processes at the cluster cores. We report on observations of the galaxy clusters Perseus and Abell 2029 using the 10 m Whipple Cherenkov telescope during the 2003-2004 and 2004-2005 observing seasons. We apply a two-dimensional analysis technique to scrutinize the clusters for TeV emission. In this paper we first determine flux upper limits on TeV gamma-ray emission from point sources within the clusters. Second, we derive upper limits on the extended cluster emission. We subsequently compare the flux upper limits with EGRET upper limits at 100 MeV and theoretical models. Assuming that the gamma-ray surface brightness profile mimics that of the thermal X-ray emission and that the spectrum of cluster cosmic rays extends all the way from thermal energies to multi-TeV energies with a differential spectral index of -2.1, our results imply that the cosmic ray proton energy density is less than 7.9% of the thermal energy density for the Perseus cluster.

astro-ph↗

arXiv2005

Search for TeV Radiation from Selected Local Group Galaxies

Some candidate dark matter particles, such as neutralinos in supersymmetry, would annihilate producing GeV/TeV gamma rays. We report on recent observations of two dwarf spheroid galaxies, Draco, Ursa Minor, the compact elliptical galaxy M32, and the spiral galaxy M33 with the Whipple 10m gamma-ray telescope. No significant signal was found, and we derived upper limits for the gamma-ray flux from each object. We discuss our astrophysical selection criteria for these galaxies in the context of an indirect search for dark matter and the implications of these flux upper limits on the density of neutralinos.

astro-ph↗

arXiv2005

Development of Bubble Chambers With Enhanced Stability and Sensitivity to Low-Energy Nuclear Recoils

The viability of using a Bubble Chamber for rare event searches and in particular for the detection of dark matter particle candidates is considered. Techniques leading to the deactivation of inhomogeneous nucleation centers and subsequent enhanced stability in such a detector are described. Results from prototype trials indicate that sensitivity to low-energy nuclear recoils like those expected from Weakly Interacting Massive Particles can be obtained in conditions of near total insensitivity to minimum ionizing backgrounds. An understanding of the response of superheated heavy refrigerants to these recoils is demonstrated within the context of existing theoretical models. We comment on the prospects for the detection of supersymmetric dark matter particles with a large $CF_{3}I$ chamber.

astro-ph↗

arXiv2002

The Hadron Hose: Continuous Toroidal Focusing for Conventional Neutrino Beams

We have developed a new focusing system for conventional neutrino beams. The ``Hadron Hose'' is a wire located in the meson decay volume, downstream of the target and focusing horns. The wire is pulsed with high current to provide a toroidal magnetic field which continuously focuses mesons. The hose increases the neutrino event rate and reduces differences between near-field and far-field neutrino spectra for oscillation experiments. We have studied this device as part of the development of the Neutrinos at the Main Injector (NuMI) project, but it might also be of use for other conventional neutrino beams.

hep-ex↗

arXiv2002

The TeV spectrum of H1426+428

The BL Lac object H1426+428 was recently detected as a high energy gamma-ray source by the VERITAS collaboration (Horan et al. 2002). We have reanalyzed the 2001 portion of the data used in the detection in order to examine the spectrum of H1426+428 above 250 GeV. We find that the time-averaged spectrum agrees with a power law of the shape dF/dE = 10^(-7.31 +- 0.15(stat) +- 0.16(syst)) x E^(-3.50 +- 0.35(stat) +- 0.05(syst)) m^(-2)s^(-1)TeV^(-1) The statistical evidence from our data for emission above 2.5 TeV is 2.6 sigma. With 95% c.l., the integral flux of H1426+428 above 2.5 TeV is larger than 3% of the corresponding flux from the Crab Nebula. The spectrum is consistent with the (non-contemporaneous) measurement by Aharonian et al. (2002) both in shape and in normalization. Below 800 GeV, the data clearly favours a spectrum steeper than that of any other TeV Blazar observed so far indicating a difference in the processes involved either at the source or in the intervening space.

astro-ph↗