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 very high energy (VHE) \u3b3-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 from \u3b3-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 Major Atmospheric Gamma-Ray Imaging Cherenkov (MAGIC) observations yielded a \u3b3-ray signal above 250 GeV of (3.7 \ub1 0.7) per cent of the Crab Nebula flux with a statistical significance of 9.9\u3c3. The multiwavelength observations showed significant variability in essentially all energy bands, including a VHE \u3b3-ray flare that lasted less than one night, which provided unprecedented 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 \ub1 0.29 between ~150 GeV and 1 TeV and an integral flux of (9.3 \ub1 1.9) per cent of the Crab nebula flux above 250 GeV. The spectrum during the non-flaring VHE activity is compatible with 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. \ua9 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society