MAGIC detection of short-term variability of the high-peaked BL Lac object 1ES 0806+524

The high-frequency-peaked BL Lac (HBL) 1ES 0806+524 (z = 0.138) was discovered in VHEγ rays in 2008. Until now, the broad-band spectrum of 1ES 0806+524 has been only poorly characterized, in particular at high energies. We analysed multiwavelength observations fromγ rays to radio performed from 2011 January to March, which were triggered by the high activity detected at optical frequencies. These observations constitute the most precise determination of the broad-band emission of 1ES 0806+524 to date. The stereoscopic MAGIC observations yielded aγ-ray signal above 250 GeV of (3.7± 0.7) per cent of the Crab Nebula flux with a statistical significa nce of 9.9σ. The multiwavelength observations showed significant vari ability in essentially all energy bands, including a VHEγ-ray flare that lasted less than one night, which provided unp recedented evidence for short-term variability in 1ES 0806+524. The spectrum of this flare is well described by a power law with a photon index of 2.97± 0.29 between∼150 GeV and 1 TeV and an integral flux of (9.3± 1.9) per cent of the Crab Nebula flux above 250 GeV. The spectrum during the non-flaring VHE activity is compatible w ith the only available VHE observation performed in 2008 with VERITAS when the source was in a low optical state. The broad-band spectral energy distribution can be described with a one-zone Synchrotron Self Compton model with parameters typical for HBLs, indicating that 1ES 0806+524 is not substantially different from the HBLs previously detected.