Very high energy gamma ray observations of southern hemisphere blazars

Abstract

This thesis is concerned with very high energy γ-ray observations of blazars observable from the southern hemisphere. The data presented were obtained using the recently deployed University of Durham Mark 6 high sensitivity Čerenkov telescope. Chapters 1 and 2 are introductory; the subjects of γ-ray astronomy, extensive air showers, Čerenkov light production, the development of the atmospheric Čerenkov technique and the current status of TeV astronomy are discussed. Chapter 3 introduces the telescopes operated by the University of Durham. The Mark 6 telescope, designed to have a low threshold energy and a high resolution imaging system, is discussed in detail. Chapter 4 presents the calibration and analysis techniques routinely applied to data obtained with the Mark 6 telescope. The chapter concludes with a set of moment parameter selections designed to reject a significant fraction of the cosmic ray cascades, while retaining the majority of γ-rays cascades. These selections have resulted in a 5σ detection of PSR 1706-44. Chapter 5 discusses active galactic nuclei and in particular blazars. Topics included are recent high energy observations; the differences between the radio/X-ray selected BL Lacs and flat spectrum radio quasars; the infrared background; high energy flux variability and γ-ray production mechanisms within these objects. The chapter concludes with a list of possible very high energy γ-ray emitting blazars observable with the Mark 6 Čerenkov telescope. Chapter 6 presents the results from four of these very high-energy γ-ray blazar candidates; PKS 0548-322, PKS 1514-24, PKS 2005-489 and PKS 2155-304. There is no evidence for γ-ray emission from these sources, either in the form of a steady flux or variable activity. Three sigma integral flux upper limits above 300 GeV are produced for these objects and the implications of these observations are discussed. The conclusions are presented in Chapter 7 as well as ideas for future work.