Abstracts

A Stacked Analysis of Cluster-centre AGN with Fermi-LAT Data

Radio-synchrotron and hard X-ray emission establish clusters of galaxies as hosts to significant populations of non-thermal particles, and it is believed that feedback from the central active galactic nucleus (AGN) plays a crucial, cluster-scale role in accelerating these particles, and counteracting the observed cooling flow; driving weak shocks through the intracluster medium and inflating bubbles of relativistic plasma tens of kiloparsecs in extent. Observational evidence for variable high-energy (HE) γ-ray emission associated with the central engine of a number of clusters supports this view.
Motivated by Fermi-LAT detections of active galaxies such as NGC 1275 and M87 (the dominant members of the Perseus and Virgo clusters, respectively), we present a radio-selected sample of 63 such Brightest Cluster Galaxies (BCGs) within cooling-core clusters, treating each as a candidate source of ~GeV γ rays. The standard Fermi-LAT analysis procedure is augmented by a source-specific normalisation of the diffuse γ-ray background, and following a maximum likelihood fitting of the data, the distribution of Test Statistic values across the sample is studied. The counts and model maps for candidate sources below an appropriate critical statistical significance are stacked: imitating a deeper observation of the BCG class than is currently achievable in HE γ rays.

TACTIC: The TRIUMF Annular Chamber for Tracking and Identification of Charged particles

The development of radioactive ion beams (RIBs) has enabled the measurement of many nuclear astrophysically important reactions directly for the first time. TAC-TIC (the TRIUMF Annular Chamber for Tracking and Identification of Charged particles) has been designed and built with the main purpose of measuring these reactions.
At present, the main focus is to measure the cross-section of the 8Li(alpha,n)11B reaction. This reaction has been shown to provide an alternative nucleosynthesis pathway to 12C, playing a pivotal role during the initial stages of the r-process in core-collapse supernovae.
In this talk, I will cover the design and operation of TACTIC, as well as physics motivation and the current status of the 8Li(alpha,n)11B reaction.

Effects of Polarisation on the Small-Sized Telescope Performance for the Cherenkov Telescope Array

 Cherenkov light is polarised and most of the light seen by the SSTs will be highly polarised. This talk examines whether this could significantly affect the light throughput of the Dual Mirror SSTs. Calculations are presented of the expected effects of polarisation on the reflection of light from a mirror of a type likely to be used for the SST and compared with measurements. A calculation of the influence of polarisation on the light throughput of a Dual Mirror SST is shown and the possible influence of polarisation on the images of Cherenkov showers is briefly discussed.

Mass Composition Studies of UHECR with the Surface Detector of the Pierre Auger Observatory

The Pierre Auger Observatory has been designed to unravel the origin of the highest energy cosmic rays. It has been in operation since 2004 in Argentina. The keys to the origin are the mass composition and the energy spectrum. Mass sensitive parameters used so far and the recent results will be shown.

GZK photons are one of the signatures if cosmic rays are dominated by protons and they are also important for astro scenario interpretations. A new approach for ultra high energy photon search using fluctuations in footprints of the shower (trace) will be introduced. As this is a variable based on the surface array (100% duty cycle), it allows investigation of the full Auger data set at the very highest energies. The current state of work and outlook to the future plan (multi parameter analysis) will be presented.

Using SHARC and TIGRESS to investigate astrophysical reaction rates

Astrophysical reaction rates for stellar nuclear reactions depend strongly on the structure of the nuclei involved. From information on the structure of the nuclei involved in reactions, such as resonance energies, spin-parities and partial widths, it is possible to calculate reaction rates even when direct measurement of the rates is not possible. The 18Ne(a,p)21Na and 15O(a,g)19Ne reactions are both important to breakout from the Hot CNO cycles in X-ray bursts. Both reactions involve 4He as a reactant and unstable heavy ions which makes direct measurement difficult. Using SHARC (Silicon Highly-segmented Array for Reactions and Coulex - a set of silicon detectors to measure charged particles) and TIGRESS (TRIUMF-ISAC Gamma-Ray Escape-Suppressed Spectrometer - a Compton-suppressed Germanium array), these reactions can be investigated using cluster transfer reactions from 6Li in a 6Li19F target. Information on the analysis of data from SHARC/TIGRESS is presented along with a discussion of the analysis of the data taken with SHARC/TIGRESS in October 2010 from a 20Na + 6Li19F experiment.

12C +12 C Fusion Reaction at Low Energies

The 12C +12 C reaction plays a key role in different astrophysical scenarios: from the hydrostactic carbon burning where the uncertainty in the reaction rate of this reaction is directly related to the uncertainty in the mass range determining two extremely different endpoints of stellar evolution, to its role in TP AGB stars, Type Ia supernovae and possible role in superbursts. Considerable effort has therefore been devoted over the years to measure the 12C +12 C reaction at astrophysically relevant energies:1-3MeV. The lowest measured energy is 2.1 MeV, major discrepencies persists in the actual data. The present work analyses the 12C+12C reaction data which was performed in the energy range Ecm=3.40MeV to 4.02MeV. The experiment was carried out with TUDA chamber at TRIUMF using charged particle detection.

Indirect measurements of the 18F(α,p)21Ne reaction with TUDA

The 18F(α,p)21Ne  reaction rate is important for predicting the stellar abundance of 19F and the isotopic ratio of Ne observed in AGB stars, thought to be the main source of F production in the galaxy. However there are still large uncertainties in the cross section of this reaction at the relevant temperatures. An experiment was carried out at TRIUMF, Canada, using the TUDA scattering chamber to study the time reversed reaction 21Ne(p,α)18F. A new method has been used by means of a gas H2 target, allowing an independent calculation of cross section to reduce the uncertainty in previously measured values. The presentation will cover the astrophysical importance of this reaction, previous results and experimental set up for measuring this time reversed reaction.

Utilising higher order moments in the Jeans analysis of dwarf spheroidal galaxies

Studies of the internal kinematics of dwarf spheroidal galaxies (dSphs) indicate that these satellites of the Milky Way have a high mass to luminosity ratio and are thus natural candidates for dark matter searches. By utilising the Jean's equations, it is possible to use the line-of-sight velocity and positions of the dSphs stellar population to gain information about the density profile of the galaxy. N-body simulations for cold dark matter halos have given rise to density ansatzes such as the Navarro-Frenk-White and Einasto profiles which determine the potentially observable rate of dark matter self-annihaltion. These models are fed into the Jean's analysis and are constrained by fitting the solutions to the observed dSph line of sight dispersion, the second moment of stellar velocities. Unfortunately these solutions are also dependent on the velocity anisotropy which allows a degeneracy of density parameterisations and thus an uncertainty in the annihalation cross-section. To break the degeneracy it is desirable to study the higher order moments, though in practice the small stellar populations restricts analysis to the fourth order.  This presentation outlines the statistical treatment of stellar velocities that aims to use the non-gaussian kurtosis profiles to try and break the mass-anisotropy degeneracy and to specify uniquely the distribution of dark matter in dSphs.

Fermi-LAT observations of the galaxy cluster Hydra A

Galaxy clusters are the largest virialized structures in the Universe. The detection of diffuse-radio emission from galaxy clusters indicates populations of relativistic leptons interacting with the intracluster medium. Gamma-ray emission from galaxy clusters, arising from these energetic leptons and the decay of neutral pions produced in hadronic interactions, may be detectable with the Fermi-LAT. Using data from the Fermi-LAT, I will present upper limits on gamma-ray emission from Hydra A, which hosts a cluster scale AGN outburst with extraordinary energetics. These upper limits are then used to constrain the energetics of hadronic and leptonic cosmic rays in Hydra A.

A Study of Key States in 22Mg Contributing to Breakout from the Hot-CNO cycle in X-Ray Bursters

The 18Ne(alpha,p)21Na reaction is considered a crucial process governing breakout conditions from the Hot-CNO cycle at temperatures of  ~1GK, leading to energy generation and further nucleosynthesis through the rp-process in X-Ray Bursters (XRBs). Directly measurements of
stellar reaction rates in this energy regime are fraught with difficulties including requirements for high beam intensities and identification of state properties close to the alpha-particle reaction
threshold.
Key states of interest can be studied utilising a high-intensity radioactive 21Na beam through scattering of protons from a hydrogen-rich target, in order to extract state spin-parity from observed angular distributions. We present preliminary analysis of the data taken using the TIGRESS and BAMBINO detector arrays at TRIUMF, Vancouver.

A Terrestrial Search for Dark Contents of the Vacuum and Dark Energy, Using Atom Interferometry

We are designing and constructing a 2m atom interferometer at the University of Liverpool in conjunction with the Cockcroft Institute.
This presentation will discuss atom interferometry and how it can be used to explore the parameter space for a terrestrial search for dark energy and the dark contents of the vacuum.

S-process Abundances : How Small Cross Section Measurements can have Large Effects

In massive stars at low metallicity the exists a discrepancy in s-process abundance calculations for the elements strontium to barium.  The 17O(alpha, gamma)21Ne reaction is crucial to differentiating between conflicting theoretical models which, at present, produce a difference of up to 10^4 in the abundance of these nuclei.  Measurements of this reaction have been performed at the TRIUMF laboratory, Vancouver, and results will be discussed.

A search for correlation of the highest energy cosmic rays with nearby luminous matter

Ultra High Energy Cosmic Rays with energies greater than 10^19.6 eV are rare, yet fascinating particles whose sources and acceleration mechanisms remain unknown. Since 2004 when operations started, the Pierre Auger Observatory in Argentina has detected ~100 such particles. Nucleons and nuclei with this energy suffer severe energy losses due to interaction with the cosmic microwave background within a few megaparsecs of propagation, so the sources of the UHECRs observed on Earth must lie in the nearby universe. Due to their high magnetic rigidity UHECRs are expected to point back to their sources within a few degrees if they are not highly charged, hence a correlation between the arrival directions of the UHECRs and the positions of their sources is expected. In my talk I will explain how we use the observed UHECR arrival direction distribution to select between proposed models for the origin of UHECRs.

Measuring the 18F(p,g)19Ne reaction at TRIUMF

The observation of γ-rays from nova outbursts will provide theorists with a unique opportunity to test the predictions of current models. Assuming that the nuclear reaction rates are sufficiently well known, such observational data would allow the underlying hydrodynamics of these models to be put to the test. The decay of 18F is the major source of γ-rays from novae, hence knowledge of the abundance of this isotope is important in nova models.

The uncertainty in the final abundance of 18F in novae is dominated by the uncertainty in its rate of destruction via the 18F(p,α)15O reaction. However, studies also show a sensitivity to the 18F(p,γ)19Ne reaction which is also uncertain and has only been investigated directly in an experiment once before.

An upper limit on the 18F(p,γ)19Ne 665keV resonance strength has been experimentally determined using radioactive beam at ISAC. 18F beam was produced and sent to a windowless gas target of hydrogen in DRAGON where 19Ne recoils were then observed in an ion chamber located at the end of the recoil separator. The findings indicate that this resonance contributes much less to the 18F abundance at the highest nova temperatures than previously thought.

The Askaryan Radio Array - Detecting GZK neutrinos using the Antarctic Ice Sheet

Ultra High Energy Neutrinos provide an exciting opportunity to study Particle Physics at energies unobtainable by terrestrial accelerators and also to study Astrophysics using this unique messenger. The Askaryan Radio Array (ARA) is a radio detection experiment designed to detect UHE neutrinos interacting in the Antarctic ice.  ARA is being constructed in a phased approach, with two stations currently deployed near the South Pole. I will present the design goals, current construction status and work on data acquisition currently being undertaken at UCL.

 

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