Observations of the Crab Nebula and Pulsar with VERITAS

TL;DR

This paper reports on VERITAS observations of the Crab Nebula and Pulsar, focusing on measuring the gamma-ray energy spectrum near the inverse-Compton peak and searching for pulsed emission beyond 10 GeV.

Contribution

It provides the first preliminary energy spectrum near the inverse-Compton peak and sets an upper limit on pulsed gamma-ray emission from the Crab Pulsar.

Findings

Preliminary energy spectrum of Crab Nebula obtained.

Upper limit established for pulsed emission beyond 10 GeV.

Validated timing techniques with optical pulsed signal.

Abstract

Observations of the Crab Nebula have proven to be the best tool to calibrate and to characterize the performance of a Cherenkov telescope. Scientifically, it is interesting to measure the energy spectrum of the Crab Nebula close to the inverse-Compton peak where a deviation is expected from the power law seen at energies above 300 GeV. Additionally, it is important to search for pulsed emission from the Crab Pulsar at energies beyond the 10 GeV upper limit of the EGRET pulsar detection. Since current models predict a cut-off in pulsed emission between 10 and 100 GeV, measurements at energies close to this range may help to discriminate between them. We observed the Crab extensively in the 2006-2007 season during the VERITAS 2- and 3-telescope commissioning phases. Using this data set we reconstructed a preliminary energy spectrum of the signal from the Crab Nebula. We also measured the optical pulsed signal to validate our GPS time-stamping and barycentering techniques and obtained an upper limit for the pulsed emission at gamma-ray energies.