Session F1: Astroparticle Symposium III: VHE Gamma Rays 2

The Milagro Gamma-Ray Telescope -- A New Look at an Old Problem

The origin of the cosmic radiation has remained a mystery since its discovery nearly a century ago. While there are good theoretical reasons to believe that supernovae play an important role in the acceleration of cosmic rays, experimental evidence for the acceleration of nuclei at these sites has proven difficult to obtain. In this talk I will briefly review the history of cosmic rays and discuss some of the new instrumentation that has given us a fresh look at this age-old problem. In particular I will discuss results from the Milagro water Cherenkov telescope and our plans for a future telescope known as HAWC.   

Observations of gamma ray emission from Markarian 501 by the VERITAS Observatory

Markarian 501 is a blazar-type galaxy with an active galactic nucleus (AGN) at a red shift of 0.0337. In blazar type AGN, jets emerging from the vicinity of the core supermassive black hole are chance aligned with the observer. Markarian 501 was observed by the VERITAS TeV gamma ray telescope array between April and June 2009. A total of 1116 minutes of B grade (or better) weather data was selected for this analysis. In this data set Markarian 501 was detected at a significance level of 24.1 sigma, corresponding to a rate of 0.428 gamma-rays/minute. In this talk I will describe the results of this analysis and compare it to previous observations of VHE emission from Markarian 501.   

Sensitivity Study of the Multi-Telescope Array for Ground-Based Gamma-Ray Astronomy

Recently, ground-based very high-energy (VHE) gamma-ray astronomy achieved a remarkable advancement in the development of the observational technique for the registration and study of gamma-ray emission above 100 GeV. Construction of multi-telescope arrays of currently used 12 m class telescopes combined with a few telescopes of much larger reflector size (20-25 m) can drastically improve the sensitivity of ground-based detectors to gamma rays of energy from 10 GeV to 100 GeV. Based on Monte Carlo simulations we have studied the response of such an array of imaging atmospheric Cherenkov telescopes. The sensitivity estimates will be presented at the meeting.   

Development of a wavelet based tool for variability statistical analysis

It can sometimes be problematic to distinguish between variations in data on a light curve due to interesting occurrences and statistical or background noise. By using a simple Haar wavelet transform on the data with error propagation through the coefficients calculation, it becomes possible to establish the confidence level with which variability at specific time scales is observed. Advantages and disadvantages of the Haar wavelets over other basis are discussed and example applications are presented.   

Geminga and the Diffuse Source Sensitivity of Imaging Air Cherenkov Telescopes

Geminga, a supernova~remnant, is a source of high energy (E $>$ 1 GeV) gamma rays. The Milagro, Fermi, and EGRET observatories have detected high energy gamma rays from Geminga below 10 GeV and above 10 TeV energies. Imaging Atmospheric Cherenkov Telescopes (IACTs) such as VERITAS and MAGIC have been unable to detect this source between 100 GeV and 10 TeV energies. In this talk, I have analyzed the sensitivity of various IACT observatories as a function of~the angular extent of observed sources. This analysis demonstrates that IACT sensitivity decreases with increasing source diameter. The large angular extent of Geminga (2.6 degrees, as determined by Milagro) is the likely reason why VERITAS and MAGIC have not yet detected this source.