Article

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

ABSTRACT

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.

Download full-text

Full-text

Available from: Felix Spanier
  • Source
    [Show abstract] [Hide abstract]
    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.
    Preview · Article · Jan 2010 · Astronomy and Astrophysics
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We reconsider the emission properties of BL Lac objects emitting in the high-energy γ-ray band, by exploiting the information in the MeV–GeV band obtained by the Large Area Telescope (LAT) on board the Fermi Gamma-Ray Space Telescope in its first three months of operation. To this aim we construct the spectral energy distribution of all the BL Lacs revealed by LAT and of the known TeV BL Lacs not detected by LAT, also including data from the Swift satellite, and model them with a simple one-zone leptonic model. The analysis shows that the BL Lacs detected by LAT (whether or not already detected in the TeV band) share similar physical parameters. While some of the TeV BL Lacs not revealed by LAT have spectral energy distributions and physical parameters very similar to the LAT BL Lacs, one group of objects displays peculiar properties (larger electron energies and smaller magnetic fields), suggesting different physical conditions in the emission region. Finally, we discuss possible criteria to select in an effective manner good new candidates for the Cherenkov telescopes among the LAT sources, presenting a list of predicted fluxes in the very high-energy band calculated including the effects of absorption by extragalactic background light.
    Full-text · Article · Jan 2010 · Monthly Notices of the Royal Astronomical Society
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We discuss a method to constrain the distance of blazars with unknown redshift using combined observations in the GeV and TeV regimes. We assume that the Very High Energies (VHE) spectrum corrected for the absorption through the interaction with the extragalactic background light cannot be harder than the spectrum in the Fermi/Large Area Telescope (LAT) band. Starting from the observed VHE spectral data we derive the EBL-corrected spectra as a function of the redshift z and fit them with power laws to be compared with power-law fits to the LAT data. We apply the method to all TeV blazars detected by LAT with known distance and derive an empirical law describing the relation between the upper limits and the true redshifts that can be used to estimate the distance of unknown redshift blazars. Using different EBL models leads to systematic changes in the derived upper limits. Finally, we use this relation to infer the distance of the unknown redshift blazar PKS 1424+240.
    Full-text · Article · Mar 2010 · Monthly Notices of the Royal Astronomical Society
Show more