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

TL;DR

This study presents the most detailed multiwavelength analysis of the high-peaked BL Lac object 1ES 0806+524, revealing short-term variability including a rapid VHE gamma-ray flare, and characterizing its broad-band emission spectrum.

Contribution

It provides the first detailed multiwavelength characterization of 1ES 0806+524, including detection of rapid VHE gamma-ray variability and a comprehensive spectral energy distribution modeling.

Findings

Detected a VHE gamma-ray flare lasting less than one night.

Measured a gamma-ray signal with 9.9 sigma significance above 250 GeV.

Broad-band spectrum consistent with a typical HBL Synchrotron Self Compton model.

Abstract

The high-frequency-peaked BL Lac (HBL) 1ES 0806+524 (z = 0.138) was discovered in VHE $\gamma$ 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 $\gamma$ 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 a $\gamma$-ray signal above 250 GeV of $(3.7 \pm 0.7)$ per cent of the Crab Nebula flux with a statistical significance of 9.9 $\sigma$. The multiwavelength observations showed significant variability in essentially all energy bands, including a VHE $\gamma$-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 $2.97 \pm 0.29$ between $\sim$150 GeV and 1 TeV and an integral flux of $(9.3 \pm 1.9)$ 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.