Entity

Time filter

Source Type


Rieger F.M.,Max Planck Institute for Nuclear Physics | Rieger F.M.,European Associated Laboratory for Gamma Ray Astronomy
International Journal of Modern Physics D | Year: 2011

The environs of supermassive black holes are among the universe's most extreme phenomena. Understanding the physical processes occurring in the vicinity of black holes may provide the key to answer a number of fundamental astrophysical questions including the detectability of strong gravity effects, the formation and propagation of relativistic jets, the origin of the highest energy gamma-rays and cosmic rays, and the nature and evolution of the central engine in active galactic nuclei (AGN). As a step towards this direction, this paper reviews some of the progress achieved in the field based on observations in the very high energy domain. It particularly focuses on nonthermal particle acceleration and emission processes that may occur in the rotating magnetospheres originating from accreting, supermassive black hole systems. Topics covered include direct electric field acceleration in the black hole's magnetosphere, ultra-high energy cosmic ray production, BlandfordZnajek mechanism, centrifugal acceleration and magnetic reconnection, along with the relevant efficiency constraints imposed by interactions with matter, radiation and fields. By way of application, a detailed discussion of well-known sources (Sgr A*; Cen A; M87; NGC1399) is presented. © 2011 World Scientific Publishing Company. Source


Pedaletti G.,University of Heidelberg | Pedaletti G.,Institute Of Ciencies Of Lespai Ieec Csic | Wagner S.J.,University of Heidelberg | Rieger F.M.,Max Planck Institute for Nuclear Physics | Rieger F.M.,European Associated Laboratory for Gamma Ray Astronomy
Astrophysical Journal | Year: 2011

Very high energy (VHE, >100GeV) γ-rays are expected to be emitted from the vicinity of supermassive black holes (SMBHs), irrespective of their activity state. In the magnetosphere of rotating SMBH, efficient acceleration of charged particles can take place through various processes. These particles could reach energies up to E ∼1019eV. VHE γ-ray emission from these particles is then feasible via leptonic or hadronic processes. Therefore, passive systems, where the lack of a strong photon field allows the VHE γ-rays to escape, are expected to be detected by Cherenkov telescopes. We present results from recent VHE experiments on the passive SMBH in the nearby elliptical galaxy NGC 1399. No γ-ray signal has been found, neither by the H.E.S.S. experiment nor in the Fermi data analyzed here. We discuss possible implications for the physical characteristics of the system. We conclude that in a scenario where particles are accelerated in vacuum gaps in the magnetosphere, only a fraction 0.3 of the gap is available for particle acceleration, indicating that the system is unlikely to be able to accelerate protons up to E ∼ 1019eV. © 2011 The American Astronomical Society. All rights reserved. Source


Acero F.,Montpellier University | Aharonian F.,Max Planck Institute for Nuclear Physics | Aharonian F.,Dublin Institute for Advanced Studies | Akhperjanian A.G.,Yerevan Physics Institute | And 178 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2010

The inner 10 pc of our Galaxy contains many counterpart candidates of the very high energy (VHE; >100 GeV) γ-ray point source HESS J1745-290. Within the point spread function of the H.E.S.S. measurement, at least three objects are capable of accelerating particles to VHE and beyond and of providing the observed γ-ray flux. Previous attempts to address this source confusion were hampered by the fact that the projected distances between these objects were of the order of the error circle radius of the emission centroid (34 arcsec, dominated by the pointing uncertainty of the H.E.S.S. instrument). Here we present H.E.S.S. data of the Galactic Centre region, recorded with an improved control of the instrument pointing compared to H.E.S.S. standard pointing procedures. Stars observed during γ-ray observations by optical guiding cameras mounted on each H.E.S.S. telescope are used for off-line pointing calibration, thereby decreasing the systematic pointing uncertainties from 20 to 6 arcsec per axis. The position of HESS J1745-290 is obtained by fitting a multi-Gaussian profile to the background-subtracted γ-ray count map. A spatial comparison of the best-fitting position of HESS J1745-290 with the position and morphology of candidate counterparts is performed. The position is, within a total error circle radius of 13 arcsec, coincident with the position of the supermassive black hole Sgr A* and the recently discovered pulsar wind nebula candidate G359.95-0.04. It is significantly displaced from the centroid of the supernova remnant Sgr A East, excluding this object with high probability as the dominant source of the VHE γ-ray emission. © 2009 The Authors. Journal compilation © 2009 RAS. Source


Acero F.,Montpellier University | Aharonian F.,Max Planck Institute for Nuclear Physics | Aharonian F.,Dublin Institute for Advanced Studies | Akhperjanian A.G.,Yerevan Physics Institute | And 176 more authors.
Astronomy and Astrophysics | Year: 2010

Context. The detection of gamma-rays in the very-high-energy (VHE) range (100 GeV-100 TeV) offers the possibility of studying the parent population of ultrarelativistic particles found in astrophysical sources, so it is useful for understanding the underlying astrophysical processes in nonthermal sources. Aims. The discovery of the VHE gamma-ray source HESS J1507-622 is reported and possibilities regarding its nature are investigated. Methods. The H.E.S.S. array of imaging atmospheric Cherenkov telescopes (IACTs) has a high sensitivity compared with previous instruments (∼1% of the Crab flux in 25 h observation time for a 5σ point-source detection) and has a large field of view (∼5° in diameter). HESS J1507-622 was discovered within the ongoing H.E.S.S. survey of the inner Galaxy, and the source was also studied by means of dedicated multiwavelength observations. Results. A Galactic gamma-ray source, HESS J1507-622, located ∼3.5° from the Galactic plane was detected with a statistical significance >9σ. Its energy spectrum is well fitted by a power law with spectral index Γ = 2.24 ± 0.16stat ± 0.20sys and a flux above 1 TeV of (1.5 ± 0.4 stat ± 0.3sys) × 10-12 cm -2 s-1. Possible interpretations (considering both hadronic and leptonic models) of the VHE gamma-ray emission are discussed in the absence of an obvious counterpart. © ESO 2010. Source


Acero F.,Montpellier University | Aharonian F.,Max Planck Institute for Nuclear Physics | Aharonian F.,Dublin Institute for Advanced Studies | Akhperjanian A.G.,Yerevan Physics Institute | And 184 more authors.
Astronomy and Astrophysics | Year: 2010

Aims. Recent theoretical predictions of the lowest very high energy (VHE) luminosity of SN 1006 are only a factor 5 below the previously published HESS upper limit, thus motivating further in-depth observations of this source. Methods. Deep observations at VHE energies (above 100 GeV) were carried out with the high energy stereoscopic system (HESS) of Cherenkov Telescopes from 2003 to 2008. More than 100 h of data have been collected and subjected to an improved analysis procedure. Results. Observations resulted in the detection of VHE γ-rays from SN 1006. The measured γ-ray spectrum is compatible with a power-law, the flux is of the order of 1% of that detected from the Crab Nebula, and is thus consistent with the previously established HESS upper limit. The source exhibits a bipolar morphology, which is strongly correlated with non-thermal X-rays. Conclusions. Because the thickness of the VHE-shell is compatible with emission from a thin rim, particle acceleration in shock waves is likely to be the origin of the γ-ray signal. The measured flux level can be accounted for by inverse Compton emission, but a mixed scenario that includes leptonic and hadronic components and takes into account the ambient matter density inferred from observations also leads to a satisfactory description of the multi-wavelength spectrum. © 2010 ESO. Source

Discover hidden collaborations