Pulse shape selection in very high energy gamma-ray astronomy

Abstract

Very high energy gamma-ray astronomers using the atmospheric Čerenkov technique must contend with a large background of light pulses due to cosmic ray-initiated cascades. Significant advances have been made in developing techniques to reduce this background: the imaging technique can have a figure of merit, q, in excess of 6 near the zenith. However, q decreases as the zenith angle increases. In this paper we describe a new technique based on the temporal Čerenkov pulse shape and show that the use of rise time and FWHM cuts are effective discriminators at all zenith angles. For flat-spectrum sources at large zenith angles q ∼ 2.5. Measured parameter distributions are compared with simulations and the methods of making the cuts are discussed. A sensitivity to cosmic-ray composition is also suggested.

Off mass shell effects in hadron electric dipole moments

“…guaranteeing the Ward-Takahashi identities 3 . For non-confined particles the choice µ = m, where m is the mass of the particle concerned, recovers the results of [23].…”

“…For a review of the topic of Dyson-Schwinger equations and their application to hadron phenomenology see [3]. For examples of the use of the Dyson-Schwinger and Bethe-Salpeter equations in the calculation of hadronic properties see references within [1,3].…”

Cosmic ray composition estimation below the knee of the spectrum from the time structure of Čerenkov light in EAS

“…An isochronous large area mirror, such as those used in TeV gammaray astronomy, viewed by a single photomultiplier tube would fulfill these conditions. The use of such a system for cosmic ray composition measurement has been described in [10], and examined in detail for VHE cosmic rays (E<10TeV) in [1].…”

“…The system was designed to be sensitive to the differences between Čerenkov pulses initiated by gamma-rays and cosmic rays for large zenith angle observations. While no detailed composition analysis was performed, it was noted that the shape of the cosmic ray pulse profiles was inconsistent with a pure proton composition ( [10]).…”

The time structure of Cherenkov images generated by TeV γ-rays and by cosmic rays

“…For more recent work, see e.g. [7] and references given there. The HEGRA system of Cherenkov telescopes now allows us to study the detailed time structure of images of TeV cosmic-ray showers and of γ-ray showers, resolved into individual image pixels of 0.25 • diameter, under conditions where the shower geometry -direction and core distance -is known based on the stereoscopic reconstruction.…”