The MAGIC collaboration observed BL Lacertae for 22.2 hr during 2005 August to December and for 26 hr during 2006 July to September .
The source is the historical prototype and eponym of a class of low-frequency peaked BL Lacertae ( LBL ) objects .
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 \pm 0.2 ) \times 10 ^ { -11 } ~ { } { cm } ^ { -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 \pm 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 with a signal below previous upper limits .
The 2006 data show no significant excess .
This drop in flux follows the observed trend in optical activity .