Discovery of Very High Energy gamma-rays from 1ES 1011+496 at z=0.212

TL;DR

This paper reports the discovery of very high energy gamma-ray emission from the BL Lac object 1ES 1011+496 at a redshift of 0.212, making it the most distant VHE gamma-ray source observed to date, with flux variations linked to optical activity.

Contribution

First detection of VHE gamma-rays from 1ES 1011+496 at z=0.212, establishing it as the most distant source of its kind, and linking gamma-ray flux to optical activity.

Findings

Detected VHE gamma-ray emission with 6.2 sigma significance.

Measured flux above 200 GeV as (1.58±0.32)×10^{-11} photons cm^{-2} s^{-1}.

Redshift determination confirms the source as the most distant VHE emitter.

Abstract

We report on the discovery of Very High Energy (VHE) gamma-ray emission from the BL Lacertae object 1ES1011+496. The observation was triggered by an optical outburst in March 2007 and the source was observed with the MAGIC telescope from March to May 2007. Observing for 18.7 hr we find an excess of 6.2 sigma with an integrated flux above 200 GeV of (1.58$\pm0.32) 10^{-11}$ photons cm$^{-2}$ s$^{-1}$. The VHE gamma-ray flux is >40% higher than in March-April 2006 (reported elsewhere), indicating that the VHE emission state may be related to the optical emission state. We have also determined the redshift of 1ES1011+496 based on an optical spectrum that reveals the absorption lines of the host galaxy. The redshift of z=0.212 makes 1ES1011+496 the most distant source observed to emit VHE gamma-rays up to date.