Context : We present the results of a long M87 monitoring campaign in very high energy \gamma -rays with the MAGIC-I Cherenkov telescope .

Aims : We aim to model the persistent non-thermal jet emission by monitoring and characterizing the very high energy \gamma -ray emission of M87 during a low state .

Methods : A total of 150 h of data were taken between 2005 and 2007 with the single MAGIC-I telescope , out of which 128.6 h survived the data quality selection .
We also collected data in the X-ray and Fermi –LAT bands from the literature ( partially contemporaneous ) .

Results : No flaring activity was found during the campaign .
The source was found to be in a persistent low-emission state , which was at a confidence level of 7 \sigma .
We present the spectrum between 100 GeV and 2 TeV , which is consistent with a simple power law with a photon index \Gamma = 2.21 \pm 0.21 and a flux normalization at 300 GeV of ( 7.7 \pm 1.3 ) \times 10 ^ { -8 } TeV ^ { -1 } s ^ { -1 } m ^ { -2 } .
The extrapolation of the MAGIC spectrum into the GeV energy range matches the previously published Fermi –LAT spectrum well , covering a combined energy range of four orders of magnitude with the same spectral index .
We model the broad band energy spectrum with a spine layer model , which can satisfactorily describe our data .

Conclusions :