MAGIC observations of the giant radio galaxy M87 in a low-emission state between 2005 and 2007

Astronomy and Astrophysics (Impact Factor: 4.38). 07/2012; 544. DOI: 10.1051/0004-6361/201117827
Source: arXiv


We present the results of a long M87 monitoring campaign in very high energy
$\gamma$-rays with the MAGIC-I Cherenkov telescope. We aim to model the
persistent non-thermal jet emission by monitoring and characterizing the very
high energy $\gamma$-ray emission of M87 during a low state. A total of 150\,h
of data were taken between 2005 and 2007 with the single MAGIC-I telescope, out
of which 128.6\,h survived the data quality selection. We also collected data
in the X-ray and \textit{Fermi}--LAT bands from the literature (partially
contemporaneous). No flaring activity was found during the campaign. The source
was found to be in a persistent low-emission state, which was at a confidence
level of $7\sigma$. We present the spectrum between 100\,GeV and 2\,TeV, which
is consistent with a simple power law with a photon index $\Gamma=2.21\pm0.21$
and a flux normalization at 300\,GeV of $(7.7\pm1.3) \times 10^{-8}$ TeV$^{-1}$
s$^{-1}$ m$^{-2}$. The extrapolation of the MAGIC spectrum into the GeV energy
range matches the previously published \textit{Fermi}--LAT spectrum well,
covering a combined energy range of four orders of magnitude with the same
spectral index. We model the broad band energy spectrum with a spine layer
model, which can satisfactorily describe our data.

Download full-text


Available from: Mosè Mariotti,
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The MAGIC two 17 meter diameter Very High Energy (VHE) γ-ray telescopes have now operated for two years in stereoscopic mode. The performance of the instrument has been evaluated: the integral sensitivity for an energy above 300 GeV is 0.76% crab units (10% Crab units differential sensitivity below 100 GeV) and the analysis threshold energy is 50 GeV. Highlights of the last two years of observations are the measurement of the Crab Nebula spectrum from ∼50 GeV to ∼50 TeV; the detection of the Crab pulsar up to an energy of 400 GeV, with energy spectra measured for both P1 and P2; the discovery of two new radiogalaxies at VHE (NGC 1275 and IC-310); the absence of an energy cutoff and the discovery of fast variability in the quasars 3C 279 and PKS 1222+21; the discovery at VHE and the characterization of numerous blazars; upper limits to the VHE emission of the Perseus cluster of galaxies and to Dark Matter annihilation in dwarf Spheroidals and the measurement of the electron+positron spectrum between 100 GeV and 3 TeV. MAGIC is currently undergoing a major upgrade of the readout and trigger electronics, and of the camera of the first telescope.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present a model of γ-ray emission through neutral pion production and decay in two-temperature accretion flows around supermassive black holes. We refine previous studies of such a hadronic γ-ray emission by taking into account (1) relativistic effects in the photon transfer and (2) absorption of γ-ray photons in the radiation field of the flow. We use a fully general relativistic description of both the radiative and hydrodynamic processes, which allows us to study the dependence on the black hole spin. The spin value strongly affects the γ-ray emissivity within ˜10 gravitational radii. The central regions of flows with the total luminosities L ≲ 10- 3 of the Eddington luminosity (LEdd) are mostly transparent to photons with energies below 10 GeV, permitting investigation of the effects of space-time metric. For such L, an observational upper limit on the γ-ray (0.1-10 GeV) to X-ray (2-10 keV) luminosity ratio of L0.1-10 GeV/L2-10 keV ≪ 0.1 can rule out rapid rotation of the black hole; on the other hand, a measurement of L0.1-10 GeV/L2-10 keV ˜ 0.1 cannot be regarded as the evidence of rapid rotation, as such a ratio can also result from a flat radial profile of γ-ray emissivity (which would occur for non-thermal acceleration of protons in the whole body of the flow). At L ≳ 10- 2LEdd, the γ-ray emission from the innermost region is strongly absorbed and the observed γ-rays do not carry information on the value of a. We note that if the X-ray emission observed in Centaurus A comes from an accretion flow, the hadronic γ-ray emission from the flow should contribute significantly to the MeV/GeV emission observed from the core of this object, unless it contains a slowly rotating black hole and protons in the flow are thermal.
    Monthly Notices of the Royal Astronomical Society 06/2013; 432(2):1576-1586. DOI:10.1093/mnras/stt573 · 5.11 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Cosmic ray interactions can be investigated indirectly in γ ray astronomy, with the observation of spectral and morphological features of certain classes of sources. MAGIC is a stereoscopic system of two γ ray telescopes, located at La Palma (Canaries), with access to the energy window between 50 GeV and 30 TeV. Sources of high relevance for the study of very high energy hadronic interactions are active galactic nuclei, as blazars and radio galaxies. MAGIC has detectedabout fifty such extragalactic objects; we will present some where theemission is explained with accelerated hadrons in interaction with ambient photons. We will also mention cosmic ray acceleration in galaxy clusters. Other than that, hadron-hadron interactions are supposed to take place in some supernova remnants in interaction with surrounding molecular clouds; we will show some results, in connection with cosmic rays of galactic origin. Finally, about other possible components, wewill mention the measurement of the diffuse electron and positron spectrum. Trustingly, the close connection between particle physics and astrophysics will contribute in future years to many new interesting observations.
    The European Physical Journal Conferences 06/2013; 52:10002-. DOI:10.1051/epjconf/20125210002
Show more