Discovery of very high energy γ-Rays from the blazar S5 0716+714

The Astrophysical Journal (Impact Factor: 5.99). 10/2009; 704(2):L129-L133. DOI: 10.1088/0004-637X/704/2/L129


The MAGIC Collaboration reports the detection of the blazar S5 0716+714 (z = 0.31 +/- 0.08) in very high energy gamma rays. The observations were performed in 2007 November and in 2008 April, and were triggered by the Kungliga Vetenskapliga Akademi telescope due to the high optical state of the object. An overall significance of the signal accounts to S = 5.8 sigma for 13.1 hr of data. Most of the signal (S = 6.9 sigma) comes from the 2008 April data sample during a higher optical state of the object suggesting a possible correlation between the Very High Energy gamma-ray and optical emissions. The differential energy spectrum of the 2008 data sample follows a power law with a photon index of G = 3.45 +/- 0.54(stat) +/- 0.2(syst), and the integral flux above 400 GeV is at the level of (7.5 +/- 2.2(stat) +/- 2.3(syst)) x 10(-12) cm(-2) s(-1), corresponding to a 9% Crab Nebula flux. Modeling of the broadband spectral energy distribution indicates that a structured jet model appears to be more promising in describing the available data than a simple one-zone synchrotron self-Compton model.

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    ABSTRACT: For the BL Lac object S5 0716+714 conflicting apparent velocities of jet component motion have been reported in the literature. This object is an intra-day variable source and suited to investigate a possible correlation between kinematic properties and flux-density variability on different timescales. We (re-)analyze 50 VLBI observations obtained with the VLBA at 5 different frequencies (5 to 43 GHz) between 1992.73 and 2006.32. We analyze the jet component motion in detail taking care not only to account for motion in the radial but also in the orthogonal direction. We study the evolution of the jet ridge line and search for correlations between radio band light curves and the kinematic properties of the jet components. We present an alternative kinematic scenario for jet component motion in S5 0716+714 with apparent stationarity of jet components (with regard to their core separation) with time. Jet components, however, do seem to move significantly non-radially with regard to their position angle and in a direction perpendicular to the major axis of the jet. We discuss a possible correlation between the long-term radio flux-density variability and the kinematics. We conclude that a geometric contribution to the origin of the long-term variability might not be negligible. Subluminal motion has been reported for most of the TeV blazars. Our analysis also confirms this for S5 0716+714. This result increases the number of TeV blazars showing apparent subluminal motion to 7.
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