arXiv subjects

Jamie Holder

Publications and source records attributed to Jamie Holder.

27 records · Page 2Linked to original sources

arXiv2015

Atmospheric Cherenkov Gamma-ray Telescopes

The stereoscopic imaging atmospheric Cherenkov technique, developed in the 1980s and 1990s, is now used by a number of existing and planned gamma-ray observatories around the world. It provides the most sensitive view of the very high energy gamma-ray sky (above 30 GeV), coupled with relatively good angular and spectral resolution over a wide field-of-view. This Chapter summarizes the details of the technique, including descriptions of the telescope optical systems and cameras, as well as the most common approaches to data analysis and gamma-ray reconstruction.

astro-ph.IM↗

arXiv2015

VERITAS: HAWC's Neighbour to the North

This paper summarizes a presentation given on the occasion of the inauguration of the High Altitude Water Cherenkov (HAWC) Gamma-ray Observatory in Puebla, Mexico in March 2015. The inauguration of a new facility for the study of astrophysical gamma-rays provides an excellent opportunity to review the technical evolution and the scientific achievements of VERITAS (the Very Energetic Radiation Imaging Telescope Array System) since its own inauguration in 2007. HAWC and VERITAS are separated by only 14 degrees in longitude, and so can view much of the same sky at the same time. In combination with other ground-based facilities, and with the instruments onboard the Fermi Gamma-ray Space Telescope, VERITAS and HAWC will give an unprecedented view of the gamma-ray sky. We provide an overview of VERITAS, and discuss the complementarity of the two observatories for future gamma-ray observations.

astro-ph.HE↗

arXiv2014

Ground-based Gamma Ray Astronomy

This paper is the write-up of a rapporteur talk given by the author at the 33rd International Cosmic Ray Conference in Rio de Janeiro, Brazil, in 2013. It attempts to summarize results and developments in ground-based gamma-ray observations and instrumentation from among the $\sim300$ submissions to the gamma-ray sessions of the meeting. Satellite observations and theoretical developments were covered by a companion rapporteur. Any review of this nature is unavoidably subjective, and incomplete. Nevertheless, the article should provide a useful status report for those seeking an overview of this exciting and fast-moving field.

astro-ph.HE↗

arXiv2013

CF2 White Paper: Status and Prospects of The VERITAS Indirect Dark Matter Detection Program

In this white paper, submitted as a part of Snowmass 2013 (subgroup CF2), we examine the current status and future prospects of the VERITAS indirect dark matter detection program. The VERITAS array of imaging atmospheric Cherenkov telescopes (IACTs), sensitive in the 0.1-50 TeV regime, is in the process of completing a multi-year program aimed at detecting signatures of neutralino dark matter. This program is spread out over a range of astrophysical targets which can potentially yield definitive signatures of neutralino self-annihilation such as dwarf spheroidal galaxies (dSphs) and the center of the Milky Way galaxy. While the program is still in progress, initial results on dSphs have produced very competitive upper limits on the thermally averaged cross-section of neutralino self-annihilation as well as strongly constraining leptophillic dark matter models (such as those inferred from the PAMELA and AMS positron fraction results). As the program continues over the next 5 years, VERITAS observations will yield some of the strongest constraints available from IACTs, pushing down the limit on the thermally averaged cross-section of neutralino self-annihilation to the expected natural thermal relic scale.

astro-ph.HE↗

arXiv2012

TeV Gamma-ray Astronomy: A Summary

The field of TeV gamma-ray astronomy has produced many exciting results over the last decade. Both the source catalogue, and the range of astrophysical questions which can be addressed, continue to expand. This article presents a topical review of the field, with a focus on the observational results of the imaging atmospheric Cherenkov telescope arrays. The results encompass pulsars and their nebulae, supernova remnants, gamma-ray binary systems, star forming regions and starburst and active galaxies.

astro-ph.HE↗

arXiv2011

A New TeV Binary: The Discovery of an Orbital Period in HESS J0632+057

HESS J0632+057 is a variable, point-like source of Very High Energy ($>100$ GeV) gamma-rays located in the Galactic plane. It is positionally coincident with a Be star, it is a variable radio and X-ray source, has a hard X-ray spectrum, and has low radio flux. These properties suggest that the object may be a member of the rare class of TeV/X-ray binary systems. The definitive confirmation of this would be the detection of a periodic orbital modulation of the flux at any wavelength. We have obtained {\it Swift} X-ray telescope observations of the source from MJD 54857 to 55647 (Jan. 2009 - Mar. 2011) to test the hypothesis that HESS J0632+057 is an X-ray/TeV binary. We show that these data exhibit flux modulation with a period of $321 \pm 5$ days and we evaluate the significance of this period by calculating the null hypothesis probability, allowing for stochastic flaring. This periodicity establishes the binary nature of HESS J0632+057.

astro-ph.GA↗

arXiv2009

VERITAS Observations of a "Forbidden Velocity Wing"

The H.E.S.S. extended Galactic plane survey revealed the presence of a new extended TeV gamma-ray source, HESSJ1503-582, with no obvious counterpart at other wavelengths. The source is, however, coincident with an HI structure with a velocity significantly different from that of galactic rotation - a so-called "Forbidden Velocity Wing". These structures have been suggested as the fast moving shells and filaments associated with the oldest supernova remnants in our galaxy. The detection of TeV gamma-ray emission from these structures might indicate that supernova remnants remain efficient particle accelerators for much longer than is commonly believed. Here we report on recent VERITAS observations of one of these structures, FVW 190.2+1.1, which shows a clear shell-like morphology in the HI maps.

astro-ph.HE↗

arXiv2009

VERITAS Observations of LS I +61 303 in the Fermi Era

The high-mass X-ray binary system LS I +61 303 is well known as a rare example of a variable Galactic GeV and TeV gamma-ray emitter. Despite years of study, many aspects of the system remain unclear; the nature of the compact object, the particle acceleration mechanisms and the gamma-ray emission and absorption processes can all be modelled in a variety of different scenarios. Here we report on a deep exposure of LS I +61 303 made with the VERITAS array during the 2008-2009 observing season. These are the first TeV observations made with contemporaneous coverage at lower energies by the LAT onboard Fermi, and as such provide a new set of constraints for system models.

astro-ph.HE↗

arXiv2006

Experimental approaches for 100 TeV gamma-ray astronomy

The high energy end of gamma-ray source spectra might provide important clues regarding the nature of the processes involved in gamma-ray emission. Several galactic sources with hard emission spectra extending up to more than 30TeV have already been reported. Measurements around 100TeV and above should be an important goal for the next generation of high energy gamma-ray astronomy experiments. Here we present several techniques providing the required exposure (100 km^2.h). We focus our study on three Imaging Atmospheric Cherenkov Technique (IACT) based approaches: low elevation observations, large field of view telescopes, and large telescope arrays. We comment on the advantages and disadvantages of each approach and report simulation based estimates of their energy ranges and sensitivities.

astro-ph↗