M 87 is one of the closest ( z=0.00436 ) extragalactic sources emitting at very-high-energies ( VHE , E > 100 GeV ) .
The aim of this work is to locate the region of the VHE gamma-ray emission and to describe the observed broadband spectral energy distribution ( SED ) during the low VHE gamma-ray state .
The data from M 87 collected between 2012 and 2015 as part of a MAGIC monitoring programme are analysed and combined with multi-wavelength data from Fermi -LAT , Chandra , HST , EVN , VLBA and the Liverpool Telescope .
The averaged VHE gamma-ray spectrum can be fitted from \sim 100 GeV to \sim 10 TeV with a simple power law with a photon index of ( -2.41 \pm 0.07 ) , while the integral flux above 300 GeV is ( 1.44 \pm 0.13 ) \times 10 ^ { -12 } \mathrm { cm } ^ { -2 } \mathrm { s } ^ { -1 } .
During the campaign between 2012 and 2015 , M 87 is generally found in a low emission state at all observed wavelengths .
The VHE gamma-ray flux from the present 2012-2015 M 87 campaign is consistent with a constant flux with some hint of variability ( \sim 3 \sigma ) on a daily timescale in 2013 .
The low-state gamma-ray emission likely originates from the same region as the flare-state emission .
Given the broadband SED , both a leptonic synchrotron self Compton and a hybrid photo-hadronic model reproduce the available data well , even if the latter is preferred .
We note , however , that the energy stored in the magnetic field in the leptonic scenario is very low suggesting a matter dominated emission region . Keywords : galaxies : active - galaxies : individual : M 87 - galaxies : jets - gamma rays : galaxies - radiation mechanisms : non-thermal