High zenith angle observations of PKS 2155-304 with the MAGIC telescope

TL;DR

This paper reports high zenith angle observations of the blazar PKS 2155-304 using the MAGIC telescope, capturing its variability and spectrum during an extraordinary VHE gamma-ray outburst, expanding understanding of Northern hemisphere observations of such sources.

Contribution

First detailed high zenith angle VHE gamma-ray observations of PKS 2155-304 with MAGIC during an outburst, demonstrating capabilities under challenging conditions.

Findings

Detected significant VHE gamma-ray variability on minute scales.

Measured the spectrum during the outburst.

Observed flux levels reaching about 7 times the Crab Nebula flux.

Abstract

The high frequency peaked BL Lac PKS 2155-304 with a redshift z=0.116 was discovered 1997 in the VHE range by the University of Durham Mark 6 gamma-ray telescope in Australia with a flux corresponding to approx. 0.2 times the Crab Nebula flux. It was later observed and detected with high significance by the Southern observatories CANGAROO and H.E.S.S. establishing this source as the best studied Southern TeV blazar. Detection from the Northern hemisphere was very difficult due to challenging observation conditions under large zenith angles. In July 2006, the H.E.S.S. collaboration reported an extraordinary outburst of VHE gamma-emission. During the outburst, the VHE gamma-ray emission was found to be variable on the time scales of minutes and at a mean flux of approx. 7 times the flux observed from the Crab Nebula. The MAGIC collaboration operates a 17m imaging air Cherenkov Telescope at La Palma (Northern Hemisphere). Follow up observations of the extraordinary outburst have been triggered in a Target of Opportunity program by an alert from the H.E.S.S. collaboration. The measured spectrum and light curve are presented.