H. Sol

Paris Diderot University, Lutetia Parisorum, Île-de-France, France

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Publications (319)1177.25 Total impact

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    ABSTRACT: One of the key open questions in the study of relativistic jets is their interaction with the environment. Here, we study the initial evolution of both electron-proton and electron-positron relativistic jets, focusing on their lateral interaction with the ambient plasma. We trace the generation and evolution of the toroidal magnetic field generated by both kinetic Kelvin-Helmholtz (kKH) and Mushroom instabilities (MI). This magnetic field collimates the jet. We show that in electron-proton jet, electrons are perpendicularly accelerated with jet collimation. The magnetic polarity switches from the clockwise to anti-clockwise in the middle of jet, as the instabilities weaken. For the electron-positron jet, we find strong mixture of electron-positron with the ambient plasma, that results in the creation of a bow shock. Merger of magnetic field current filaments generate density bumps which initiate a forward shock. The strong mixing between jet and ambient particles prevents full development of the jet on the studied scale. Our results therefore provide a direct evidence for both jet collimation and particle acceleration in the created bow shock. Differences in the magnetic field structures generated by electron-proton and electron-positron jets may contribute to observable differences in the polarized properties of emission by electrons.
    Preview · Article · Nov 2015
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    ABSTRACT: The Fermi/LAT instrument has detected about two thousands Extragalactic High Energy (E > 100 MeV) gamma-ray sources. One of the brightest is 3FGL 1603.9-4903, associated to the radio source PMN J1603-4904. Its nature is not yet clear, it could be either a very peculiar BL Lac or a CSO (Compact Symmetric Object) radio source, considered as the early stage of a radio galaxy. The latter, if confirmed, would be the first detection in gamma-rays for this class of objects. Recently a redshift z=0.18 +/- 0.01 has been claimed on the basis of the detection of a single X-ray line at 5.44 +/- 0.05 keV interpreted as a 6.4 keV (rest frame) fluorescent line. We aim to investigate the nature of 3FGL 1603.9-4903/PMN J1603-4904 using optical to NIR spectroscopy. We observed PMN J1603-4904 with the UV-NIR VLT/X-shooter spectrograph for two hours. We extracted spectra in the VIS and NIR range that we calibrated in flux and corrected for telluric absorption and we systematically searched for absorption and emission features. The source was detected starting from ~6300 Ang down to 24000 Ang with an intensity comparable to the one of its 2MASS counterpart and a mostly featureless spectrum. The continuum lacks absorption features and thus is non-stellar in origin and likely non-thermal. On top of this spectrum we detected three emission lines that we interpret as the Halpha-[NII] complex, the [SII] 6716,6731 doublet and the [SIII] 9530 line, obtaining a redshift estimate of z= 0.2321 +/- 0.0004. The equivalent width of the Halpha-[NII] complex implies that PMN J1603-4904 does not follow the observational definition of BL Lac, the line ratios suggest that a LINER/Seyfert nucleus is powering the emission. This new redshift measurement implies that the X-ray line previously detected should be interpreted as a 6.7 keV line which is very peculiar.
    Preview · Article · Oct 2015 · Astronomy and Astrophysics
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    ABSTRACT: List of contributions from the CTA Consortium presented at the 34th International Cosmic Ray Conference, 30 July - 6 August 2015, The Hague, The Netherlands.
    Full-text · Article · Aug 2015
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    ABSTRACT: We report on the first completely simultaneous observation of a gamma-ray burst (GRB) using an array of Imaging Atmospheric Cherenkov Telescopes, which is sensitive to photons in the very high energy (VHE) γ -ray range (100 GeV). On 2006 June 2, the Swift Burst Alert Telescope (BAT) registered an unusually soft γ -ray burst (GRB 060602B). The burst position was under observation using the High Energy Stereoscopic System (HESS) at the time the burst occurred. Data were taken before, during, and after the burst. A total of 5 hr of observations were obtained during the night of 2006 June 2–3, and five additional hours were obtained over the next three nights. No VHE γ -ray signal was found during the period covered by the HESS observations. The 99% confidence level flux upper limit (> 1 TeV) for the prompt phase (9 s) of GRB 060602B is 2.9 × 10 −9 erg cm −2 s −1 . Due to the very soft BAT spectrum of the burst compared with other Swift GRBs and its proximity to the Galactic center, the burst is likely associated with a Galactic X-ray burster, although the possibility of it being a cosmological GRB cannot be ruled out. We discuss the implications of our flux limits in the context of these two bursting scenarios.
    Full-text · Article · Aug 2015
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    Full-text · Article · Aug 2015 · Astronomy and Astrophysics
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    ABSTRACT: Re-observations with the H.E.S.S. telescope array of the very-high-energy (VHE) source HESS J1018-589 A coincident with the Fermi-LAT $\gamma$-ray binary 1FGL J1018.6-5856 have resulted in a source detection significance of more than 9$\sigma$, and the detection of variability ($\chi^2$/$\nu$ of 238.3/155) in the emitted $\gamma$-ray flux. This variability confirms the association of HESS J1018-589 A with the high-energy $\gamma$-ray binary detected by Fermi-LAT, and also confirms the point-like source as a new very-high-energy binary system. The spectrum of HESS J1018-589 A is best fit with a power-law function with photon index $\Gamma = 2.20 \pm 0.14_{\rm stat} \pm 0.2_{\rm sys}$. Emission is detected up to ~20 TeV. The mean differential flux level is $(2.9 \pm 0.4)\times10^{-13}$ TeV$^{-1}$ cm$^{-2}$ s$^{-1}$ at 1 TeV, equivalent to ~1% of the flux from the Crab Nebula at the same energy. Variability is clearly detected in the night-by-night lightcurve. When folded on the orbital period of 16.58 days, the rebinned lightcurve peaks in phase with the observed X-ray and high-energy phaseograms. The fit of the H.E.S.S. phaseogram to a constant flux provides evidence of periodicity at the level of 3$\sigma$. The shape of the VHE phaseogram and measured spectrum suggest a low inclination, low eccentricity system with a modest impact from VHE $\gamma$-ray absorption due to pair production ($\tau$ < 1 at 300 GeV).
    Full-text · Article · Mar 2015 · Astronomy and Astrophysics
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    O. Hervet · C. Boisson · H. Sol
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    ABSTRACT: Ap Lib is one of the rare Low Synchrotron Peaked blazars detected so far at TeV energies. This type of source is not properly modelled by standard one-zone leptonic Synchrotron-self-Compton (SSC) emission scenarios. The aim of this paper is to study the relevance of additional components which should naturally occur in a SSC scenario for a better understanding of the emission mechanisms, especially at very high energies (VHE). Methods. We use simultaneous data from a multi-wavelength campaign of Planck, Swift-UVOT and Swift-XRT telescopes carried out in February 2010, as well as quasi-simultaneous data of WISE, Fermi and H.E.S.S. taken in 2010. The multi-lambda emission of Ap Lib is modelled by a blob-in-jet SSC scenario including the contribution of the base of the VLBI extended jet, the radiative blob-jet interaction, the accretion disk and its associated external photon field. We show that signatures of a strong parsec-scale jet and of an accretion disk emission are present in the SED. We can link the observationnal VLBI jet features from MOJAVE to parameters expected for a VHE emitting blob accelerated near the jet base. The VHE emission appears to be dominated by the inverse-Compton effect of the blob relativistic electrons interacting with the jet synchrotron radiation. In such scenario Ap Lib appears as an intermediate source between BL Lac objects and Flat Spectrum Radio Quasars. Ap Lib could be a bright representative of a specific class of blazars, in which the parsec-scale jet luminosity is no more negligible compared to the blob and contributes to the high energy emission via inverse Compton processes.
    Full-text · Article · Mar 2015 · Astronomy and Astrophysics
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    ABSTRACT: An annihilation signal of dark matter is searched for from the central region of the Milky Way. Data acquired in dedicated on-off observations of the Galactic center region with H.E.S.S. are analyzed for this purpose. No significant signal is found in a total of ∼9 h of on-off observations. Upper limits on the velocity averaged cross section, ⟨σv⟩, for the annihilation of dark matter particles with masses in the range of ∼300 GeV to ∼10 TeV are derived. In contrast to previous constraints derived from observations of the Galactic center region, the constraints that are derived here apply also under the assumption of a central core of constant dark matter density around the center of the Galaxy. Values of ⟨σv⟩ that are larger than 3×10^{-24} cm^{3}/s are excluded for dark matter particles with masses between ∼1 and ∼4 TeV at 95% C.L. if the radius of the central dark matter density core does not exceed 500 pc. This is the strongest constraint that is derived on ⟨σv⟩ for annihilating TeV mass dark matter without the assumption of a centrally cusped dark matter density distribution in the search region.
    No preview · Article · Feb 2015 · Physical Review Letters
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    ABSTRACT: The Large Magellanic Cloud, a satellite galaxy of the Milky Way, has been observed with the High Energy Stereoscopic System (H.E.S.S.) above an energy of 100 billion electron volts for a deep exposure of 210 hours. Three sources of different types were detected: the pulsar wind nebula of the most energetic pulsar known N 157B, the radio-loud supernova remnant N 132D and the largest non-thermal X-ray shell - the superbubble 30 Dor C. The unique object SN 1987A is, surprisingly, not detected, which constrains the theoretical framework of particle acceleration in very young supernova remnants. These detections reveal the most energetic tip of a gamma-ray source population in an external galaxy, and provide via 30 Dor C the unambiguous detection of gamma-ray emission from a superbubble.
    Full-text · Article · Jan 2015 · Science
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    ABSTRACT: Very high energy (VHE, $E>$100 GeV) $\gamma$-ray flaring activity of the high-frequency peaked BL Lac object \pg\ has been detected by the \hess\ telescopes. The flux of the source increased by a factor of 3 during the nights of 2012 April 26 and 27 with respect to the archival measurements with hint of intra-night variability. No counterpart of this event has been detected in the \fla\ data. This pattern is consistent with VHE $\gamma$ ray flaring being caused by the injection of ultrarelativistic particles, emitting $\gamma$ rays at the highest energies. The dataset offers a unique opportunity to constrain the redshift of this source at \bestz\ using a novel method based on Bayesian statistics. The indication of intra-night variability is used to introduce a novel method to probe for a possible Lorentz Invariance Violation (LIV), and to set limits on the energy scale at which Quantum Gravity (QG) effects causing LIV may arise. For the subluminal case, the derived limits are $\textrm{E}_{\rm QG,1}>4.10\times 10^{17}$ GeV and $\textrm{E}_{\rm QG,2}>2.10\times 10^{10}$ GeV for linear and quadratic LIV effects, respectively.
    Full-text · Article · Jan 2015 · The Astrophysical Journal
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    ABSTRACT: Puppis A is an interesting ~4 kyr-old supernova remnant (SNR) that shows strong evidence of interaction between the forward shock and a molecular cloud. It has been studied in detail from radio frequencies to high-energy (HE, 0.1-100 GeV) gamma-rays. An analysis of the Fermi-LAT data has shown an extended HE gamma-ray emission with a 0.2-100 GeV spectrum exhibiting no significant deviation from a power law, unlike most of the GeV-emitting SNRs known to be interacting with molecular clouds. This makes it a promising target for imaging atmospheric Cherenkov telescopes (IACTs) to probe the gamma-ray emission above 100 GeV. Very-high-energy (VHE, E >= 0.1 TeV) gamma-ray emission from Puppis A is for the first time searched for with the High Energy Stereoscopic System (H.E.S.S.). The analysis of the H.E.S.S. data does not reveal any significant emission towards Puppis A. The derived upper limits on the differential photon flux imply that its broadband gamma-ray spectrum must exhibit a spectral break or cutoff. By combining Fermi-LAT and H.E.S.S. measurements, the 99% confidence level upper limits on such a cutoff are found to be 450 and 280 GeV, assuming a power law with a simple exponential and a sub-exponential cutoff, respectively. It is concluded that none of the standard limitations (age, size, radiative losses) on the particle acceleration mechanism, assumed to be still on-going at present, can explain the lack of VHE signal. The scenario in which particle acceleration has ceased some time ago is considered as an alternative explanation. The HE/VHE spectrum of Puppis A could then exhibit a break of non-radiative origin, (as observed in several other interacting SNRs, albeit at somewhat higher energies) owing to the interaction with dense and neutral material in particular towards the northeastern region.
    Full-text · Article · Dec 2014 · Astronomy and Astrophysics
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    ABSTRACT: We have investigated particle acceleration and emission from shocks and shear flows associated with an unmagnetized relativistic jet plasma propagating into an unmagnetized ambient plasma. Strong electro-magnetic fields are generated in the jet shock via the filamentation (Weibel) instability. Shock field strength and structure depend on plasma composition (($e^{\pm}$ or $e^-$- $p^+$ plasmas) and Lorentz factor. In the velocity shear between jet and ambient plasmas, strong AC ($e^{\pm}$ plasmas) or DC ($e^-$- $p^+$ plasmas) magnetic fields are generated via the kinetic Kelvin-Helmholtz instability (kKHI), and the magnetic field structure also depends on the jet Lorentz factor. We have calculated, self-consistently, the radiation from electrons accelerated in shock generated magnetic fields. The spectra depend on the jet's initial Lorentz factor and temperature via the resulting particle acceleration and magnetic field generation. Our ongoing "Global" jet simulations containing shocks and velocity shears will provide us with the ability to calculate and model the complex time evolution and/or spectral structure observed from gamma-ray bursts, AGN jets, and supernova remnants.
    Full-text · Article · Dec 2014
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    ABSTRACT: Diffuse $\gamma$-ray emission is the most prominent observable signature of celestial cosmic-ray interactions at high energies. While already being investigated at GeV energies over several decades, assessments of diffuse $\gamma$-ray emission at TeV energies remain sparse. After completion of the systematic survey of the inner Galaxy, the H.E.S.S. experiment is in a prime position to observe large-scale diffuse emission at TeV energies. Data of the H.E.S.S. Galactic Plane Survey are investigated in regions off known $\gamma$-ray sources. Corresponding $\gamma$-ray flux measurements were made over an extensive grid of celestial locations. Longitudinal and latitudinal profiles of the observed $\gamma$-ray fluxes show characteristic excess emission not attributable to known $\gamma$-ray sources. For the first time large-scale $\gamma$-ray emission along the Galactic Plane using imaging atmospheric Cherenkov telescopes has been observed. While the background subtraction technique limits the ability to recover modest variation on the scale of the H.E.S.S. field of view or larger, which is characteristic of the inverse Compton scatter-induced Galactic diffuse emission, contributions of neutral pion decay as well as emission from unresolved $\gamma$-ray sources can be recovered in the observed signal to a large fraction. Calculations show that the minimum $\gamma$-ray emission from $\pi^0$-decay represents a significant contribution to the total signal. This detection is interpreted as a mix of diffuse Galactic $\gamma$-ray emission and unresolved sources.
    Full-text · Article · Nov 2014 · Physical Review D
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    ABSTRACT: The region around the supernova remnant (SNR) W41 contains several TeV sources and has prompted the H.E.S.S. Collaboration to perform deep observations of this field of view. This resulted in the discovery of the new very high energy (VHE) source HESS J1832-093, at the position $\rm RA=18^h 32^m 50^s \pm 3^s_{stat} \pm 2^s_{syst}, \rm Dec=-9^\circ 22' 36'' \pm 32''_{stat} \pm 20''_{syst} (J2000)$, spatially coincident with a part of the radio shell of the neighboring remnant G22.7-0.2. The photon spectrum is well described by a power-law of index $\Gamma = 2.6 \pm 0.3_{\rm stat} \pm 0.1_{\rm syst}$ and a normalization at 1 TeV of $\Phi_0=(4.8 \pm 0.8_{\rm stat}\pm 1.0_{\rm syst})\,\times\,10^{-13}\,\rm{cm} ^{-2}\,s^{-1}\,TeV^{-1}$. The location of the gamma-ray emission on the edge of the SNR rim first suggested a signature of escaping cosmic-rays illuminating a nearby molecular cloud. Then a dedicated XMM-Newton observation led to the discovery of a new X-ray point source spatially coincident with the TeV excess. Two other scenarios were hence proposed to identify the nature of HESS J1832-093. Gamma-rays from inverse Compton radiation in the framework of a pulsar wind nebula scenario or the possibility of gamma-ray production within a binary system are therefore also considered. Deeper multi-wavelength observations will help to shed new light on this intriguing VHE source.
    Full-text · Article · Nov 2014 · Monthly Notices of the Royal Astronomical Society
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    ABSTRACT: Dwarf spheroidal galaxies of the Local Group are close satellites of the Milky Way characterized by a large mass-to-light ratio and are not expected to be the site of non-thermal high-energy gamma-ray emission or intense star formation. Therefore they are amongst the most promising candidates for indirect dark matter searches. During the last years the High Energy Stereoscopic System (H.E.S.S.) of imaging atmospheric Cherenkov telescopes observed five of these dwarf galaxies for more than 140 hours in total, searching for TeV gamma-ray emission from annihilation of dark matter particles. The new results of the deep exposure of the Sagittarius dwarf spheroidal galaxy, the first observations of the Coma Berenices and Fornax dwarves and the re-analysis of two more dwarf spheroidal galaxies already published by the H.E.S.S. Collaboration, Carina and Sculptor, are presented. In the absence of a significant signal new constraints on the annihilation cross-section applicable to Weakly Interacting Massive Particles (WIMPs) are derived by combining the observations of the five dwarf galaxies. The combined exclusion limit depends on the WIMP mass and the best constraint is reached at 1-2 TeV masses with a cross-section upper bound of ~3.9x10-24 cm^3 s-1 at a 95% confidence level.
    Full-text · Article · Oct 2014 · Physical Review D
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    ABSTRACT: We have investigated the generation of magnetic fields associated with velocity shear between an unmagnetized relativistic (core) jet and an unmagnetized sheath plasma by the kinetic Kelvin-Helmholtz instability for different mass ratios (mi/me = 1, 20, and 1836) and different jet Lorentz factors. We found that electron-positron cases have alternating magnetic fields instead of the DC magnetic fields found in electron-ion cases. We have also investigated particle acceleration and shock structure associated with an unmagnetized relativistic jet propagating into an unmagnetized plasma for electron-positron and electron-ion plasmas. Strong magnetic fields generated in the trailing shock lead to transverse deflection and acceleration of the electrons. We have self-consistently calculated the radiation from the electrons accelerated in the turbulent magnetic fields for different jet Lorentz factors. We find that the synthetic spectra depend on the bulk Lorentz factor of the jet, the jet temperature, and the strength of the magnetic fields generated in the shock.
    Full-text · Article · Sep 2014
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    ABSTRACT: In this paper we report on the analysis of all the available optical and very high-energy $\gamma$-ray ($>$200 GeV) data for the BL Lac object PKS 2155$-$304, collected simultaneously with the ATOM and H.E.S.S. telescopes from 2007 until 2009. This study also includes X-ray (RXTE, Swift) and high-energy $\gamma$-ray (Fermi-LAT) data. During the period analysed, the source was transitioning from its flaring to quiescent optical states,and was characterized by only moderate flux changes at different wavelengths on the timescales of days and months. A flattening of the optical continuum with an increasing optical flux can be noted in the collected dataset, but only occasionally and only at higher flux levels. We did not find any universal relation between the very high-energy $\gamma$-ray and optical flux changes on the timescales from days and weeks up to several years. On the other hand, we noted that at higher flux levels the source can follow two distinct tracks in the optical flux-colour diagrams, which seem to be related to distinct $\gamma$-ray states of the blazar. The obtained results therefore indicate a complex scaling between the optical and $\gamma$-ray emission of PKS 2155$-$304, with different correlation patterns holding at different epochs, and a $\gamma$-ray flux depending on the combination of an optical flux and colour rather than a flux alone.
    Full-text · Article · Aug 2014 · Astronomy and Astrophysics
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    ABSTRACT: This letter reports the discovery of a remarkably hard spectrum source, HESS J1641-463, by the High Energy Stereoscopic System (H.E.S.S.) in the very-high energy (VHE) domain. HESS J1641-463 remained unnoticed by the usual analysis techniques due to confusion with the bright nearby source HESS J1640-465. It emerged at a significance level of 8.5 standard deviations after restricting the analysis to events with energies above 4 TeV. It shows a moderate flux level of F(E > 1 TeV) = (3.64 +/- 0.44_stat +/- 0.73_sys) x 10^-13 cm^-2s-1, corresponding to 1.8% of the Crab Nebula flux above the same energy, and a hard spectrum with a photon index of Gamma = 2.07 +/- 0.11_stat +/- 0.20_sys. It is a point-like source, although an extension up to Gaussian width of sigma = 0.05 deg cannot be discounted due to uncertainties in the H.E.S.S. PSF. The VHE gamma-ray flux of HESS J1641-463 is found to be constant over the observed period when checking time binnings from year-by-year to the 28 min exposures timescales. HESS J1641-463 is positionally coincident with the radio supernova remnant SNR G338.5+0.1. No X-ray candidate stands out as a clear association, however Chandra and XMM-Newton data reveal some potential weak counterparts. Various VHE gamma-ray production scenarios are discussed. If the emission from HESS J1641-463 is produced by cosmic ray protons colliding with the ambient gas, then their spectrum must extend up to at least a few hundred TeV. The energy released in accelerating these particles could account for the entire energy budget of the galactic cosmic ray population above a few TeV.
    Full-text · Article · Aug 2014 · The Astrophysical Journal Letters
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    Full-text · Dataset · Jul 2014
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    ABSTRACT: Previous observations with HESS have revealed the existence of an extended very-high-energy (VHE; E>100 GeV) gamma-ray source, HESS J1834-087, coincident with the SNR W41. The origin of the gamma-ray emission has been further investigated with HESS and the Fermi-LAT. The gamma-ray data provided by 61h (HESS) and 4 yrs (Fermi LAT) of observations cover over 5 decades in energy (1.8GeV - 30TeV). The morphology and spectrum of the TeV and GeV sources have been studied and multi-wavelength data have been used to investigate the origin of the observed emission. The TeV source can be modeled with a sum of two components: one point-like and one significantly extended (sig_TeV = 0.17{\deg}), both centered on SNR W41 and exhibiting spectra described by a power law of index 2.6. The GeV source detected with Fermi is extended (sig_GeV =0.15{\deg}) and morphologically matches the VHE emission. Its spectrum can be described by a power-law with index 2.15 and joins smoothly the one of the whole TeV source. A break appears in the spectra around 100 GeV. Two main scenarios are proposed to explain the emission: a pulsar wind nebula (PWN) or the interaction of SNR W41 with a molecular cloud. X-ray observations suggest the presence of a point-like source (pulsar candidate) near the center of the SNR and non-thermal X-ray diffuse emission which could arise from a potential PWN. The PWN scenario is supported by the match of of the TeV and GeV positions with the putative pulsar. However, the overall spectrum is reproduced by a 1-zone leptonic model only if an excess of low-energy electrons is injected by a high spin-down power pulsar. This low-energy component is not needed if the point-like TeV source is unrelated to the extended GeV and TeV sources. The interacting SNR scenario is supported by the spatial coincidence between the gamma-ray sources, the detection of OH maser lines and the hadronic modeling.
    Full-text · Article · Jul 2014 · Astronomy and Astrophysics

Publication Stats

9k Citations
1,177.25 Total Impact Points

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Institutions

  • 2008-2014
    • Paris Diderot University
      • • AstroParticule et Cosmologie (APC) UMR 7164
      • • Laboratoire Univers et Théories (LUTH) UMR 8102
      Lutetia Parisorum, Île-de-France, France
    • Max Planck Institute for Nuclear Physics
      Heidelburg, Baden-Württemberg, Germany
    • University Joseph Fourier - Grenoble 1
      Grenoble, Rhône-Alpes, France
  • 2013
    • IT University of Copenhagen
      København, Capital Region, Denmark
  • 2012
    • Universität Heidelberg
      Heidelburg, Baden-Württemberg, Germany
    • KTH Royal Institute of Technology
      • Department of Physics
      Tukholma, Stockholm, Sweden
  • 2011
    • University of Hamburg
      • Institut für Experimentalphysik
      Hamburg, Hamburg, Germany
  • 2007-2011
    • Humboldt-Universität zu Berlin
      • Department of Physics
      Berlín, Berlin, Germany
  • 2001-2011
    • French National Centre for Scientific Research
      • Laboratoire de l'univers et de ses théories (LUTH)
      Paris, Ile-de-France, France
  • 2010
    • Dublin Institute for Advanced Studies
      Dublin, Leinster, Ireland
  • 2009
    • Ruhr-Universität Bochum
      • Institut für Theoretische Physik I
      Bochum, North Rhine-Westphalia, Germany
  • 1986-2008
    • Observatoire de Paris
      Lutetia Parisorum, Île-de-France, France
  • 2004
    • University of Alabama in Huntsville
      • Department of Physics
      Huntsville, Alabama, United States
  • 1999
    • Institut d'astrophysique de Paris
      Lutetia Parisorum, Île-de-France, France
    • Byurakan Astrophysical Observatory
      Kaznafar, Aragatsotn Province, Armenia
  • 1981-1990
    • École Polytechnique
      • Centre de Physique Théorique
      Paliseau, Île-de-France, France