Discovery of very high-energy gamma-ray emission from the LBL object BL Lacertae

TL;DR

This paper reports the first clear detection of very high-energy gamma-ray emission from the LBL object BL Lacertae, revealing its gamma-ray flux and spectral properties, with observations indicating variability linked to optical activity.

Contribution

First detection of VHE gamma-ray emission from an LBL object, providing new insights into its high-energy behavior and spectral characteristics.

Findings

Detected VHE gamma-ray emission with 5.1 sigma significance in 2005

Measured an integral flux of about 3% of the Crab flux above 200 GeV

Observed no significant gamma-ray flux in 2006, indicating variability

Abstract

The low-frequency peaked BL Lac (LBL) object BL Lacertae was observed with the MAGIC telescope from 2005 August to December (22.2 hr), and from 2006 July to September (26.0 hr). A very high energy (VHE) gamma-ray signal was discovered with a 5.1 sigma excess in the 2005 data. Above 200 GeV, an integral flux of (0.6+-0.2)x10e-11 m-2 s-1 was measured, corresponding to approximately 3% of the Crab flux. The differential spectrum between 150 and 900 GeV is rather steep, with a photon index of -3.6+-0.5. The light curve shows no significant variability during the observations in 2005. For the first time a clear detection of VHE gamma-ray emission from an LBL object was obtained. The 2006 data show no significant excess. This drop in flux follows the observed trend in optical activity