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• 151. Abramowski, A.
Universität Heidelberg, Germany;Universite ́ Paris Diderot, France;Ecole Polytechnique, France. Univ Paris Diderot, APC, AstroParticule & Cosmology, CNRS,IN2P3,CEA,Irfu, Observ Paris,Sorbonne Paris C, 10 Rue Alice Domon & Leonie Duquet, F-75205 Paris 13, France.
Constraints on axionlike particles with HESS from the irregularity of the PKS 2155-304 energy spectrum2013In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 88, no 10, p. Article ID: 102003-Article in journal (Refereed)
• 152.
Univ Hamburg, Germany.
Univ Paris Diderot, France. Max Planck Inst Kernphys, Germany ; Dublin Inst Adv Studies, Ireland ; Natl Acad Sci Republ Armenia, Armenia. Max Planck Inst Kernphys, Germany. Natl Acad Sci Republ Armenia, Armenia ; Yerevan Phys Inst, Armenia. Humboldt Univ, Germany. Univ Erlangen Nurnberg, Germany. Univ Durham, UK. DESY, Germany ; Univ Potsdam, Germany. Nicolaus Copernicus Astron Ctr, Poland. Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering. Univ Paris Diderot, APC, AstroParticule & Cosmology, CNRS,IN2P3,CEA,Irfu, Observ Paris,Sorbonne Paris C, 10 Rue Alice Domon & Leonie Duquet, F-75205 Paris 13, France.
Discovery of the VHE gamma-ray source HESS J1832-093 in the vicinity of SNR G22.7-0.22015In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 446, no 2, p. 1163-1169Article in journal (Refereed)

The region around the supernova remnant (SNR) W41 contains several TeV sources and has prompted the HESS 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 RA = 18(h)32(m)50(s) +/- 3(stat)(s) +/- 2(syst)(s), Dec = -9 degrees 22'36 '' +/- 32(stat)'' +/- 20(syst)'' (J2000), spatially coincident with a part of the radio shell of the neighbouring remnant G22.7-0.2. The photon spectrum is well described by a power law of index Gamma = 2.6 +/- 0.3(stat) +/- 0.1(syst) and a normalization at 1 TeV of Phi(0) = (4.8 +/- 0.8(stat) +/- 1.0(syst)) x 10(-13) 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 multiwavelength observations will help to shed new light on this intriguing VHE source.

• 153. Abramowski, A.
Univ Paris Diderot, APC, AstroParticule & Cosmology, CNRS,IN2P3,CEA,Irfu, Observ Paris,Sorbonne Paris C, 10 Rue Alice Domon & Leonie Duquet, F-75205 Paris 13, France.
Discovery of TeV gamma-ray emission from PKS 0447-439 and derivation of an upper limit on its redshift2013In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 552, p. A118-Article in journal (Refereed)

Very high-energy gamma-ray emission from PKS 0447-439 was detected with the H. E. S. S. Cherenkov telescope array in December 2009. This blazar is one of the brightest extragalactic objects in the Fermi bright source list and has a hard spectrum in the MeV to GeV range. In the TeV range, a photon index of 3.89 +/- 0.37 (stat) +/- 0.22 (sys) and a flux normalisation at 1 TeV, phi(1) (TeV) = (3.5 +/- 1.1(stat) +/- 0.9(sys)) x 10(-13) cm(-2) s(-1) TeV-1 were found. The detection with H. E. S. S. triggered observations in the X-ray band with the Swift and RXTE telescopes. Simultaneous UV and optical data from Swift UVOT and data from the optical telescopes ATOM and ROTSE are also available. The spectrum and light curve measured with H. E. S. S. are presented and compared to the multi-wavelength data at lower energies. A rapid flare is seen in the Swift XRT and RXTE data, together with a flux variation in the UV band, at a time scale of the order of one day. A firm upper limit of z < 0.59 on the redshift of PKS 0447-439 is derived from the combined Fermi-LAT and H. E. S. S. data, given the assumptions that there is no upturn in the intrinsic spectrum above the Fermi-LAT energy range and that absorption on the extragalactic background light (EBL) is not weaker than the lower limit provided by current models. The spectral energy distribution is well described by a simple one-zone synchrotron self-Compton scenario, if the redshift of the source is less than z less than or similar to 0.4.

• 154.
Universität Hamburg, Germany .
Max-Planck-Institut für Kernphysik, Germany ; Dublin Institute for Advanced Studies, Ireland ; National Academy of Sciences of the Republic of Armenia, Armenia . Max-Planck-Institut für Kernphysik, Germany . National Academy of Sciences of the Republic of Armenia, Armenia ; Yerevan Physics Institute, Armenia. Humboldt-Universität zu Berlin, Germany. University of Namibia, Namibia . University of Amsterdam, The Netherlands . Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering. Ruhr-Universität Bochum, Germany . University of Amsterdam, The Netherlands . Leopold-Franzens-Universität Innsbruck, Austria. Max-Planck-Institut für Kernphysik, Germany. Humboldt-Universität zu Berlin, Germany. University of Adelaide, Australia . North-West University, South Africa . Université Paris Diderot, France. Université Pierre et Marie Curie Paris 6, Université Denis Diderot Paris 7, France. Max-Planck-Institut für Kernphysik, Germany. Université Montpellier 2, France. CEA Saclay, France. CEA Saclay, France. University of Amsterdam, The Netherlands . The University of Warsaw, Poland. Aix-Marseille Université, France. Max-Planck-Institut für Kernphysik, Germany ; Instytut Fizyki Jądrowej PAN, Poland. Max-Planck-Institut für Kernphysik, Germany. Université Pierre et Marie Curie Paris 6, Université Denis Diderot Paris 7, France. Université Montpellier 2, France. University of the Witwatersrand, South Africa . Université Pierre et Marie Curie Paris 6, Université Denis Diderot Paris 7, France. University of the Witwatersrand, South Africa. Universität Heidelberg, Germany . Stockholm University, Sweden. Université Pierre et Marie Curie Paris 6, Université Denis Diderot Paris 7, France. Universität Tübingen, Germany. North-West University, South Africa ; University of Namibia, Namibia. École Polytechnique, France. Max-Planck-Institut für Kernphysik, Germany. University of Adelaide, Australia . Université Paris Diderot, France. Max-Planck-Institut für Kernphysik, Germany. Max-Planck-Institut für Kernphysik, Germany. Dublin Institute for Advanced Studies, Ireland. Univ. Grenoble Alpes, France. The University of Leicester, UK. Nicolaus Copernicus Astronomical Center, Poland. Instytut Fizyki Jądrowej PAN, Poland. Max-Planck-Institut für Kernphysik, Germany. Universität Potsdam, Germany. Max-Planck-Institut für Kernphysik, Germany. Aix-Marseille Université, France. Université Paris Diderot, France. Stockholm University, Sweden. École Polytechnique, France. Université Montpellier 2, France. Universität Hamburg, Germany. Université Montpellier 2, France. Université Savoie Mont-Blanc, France. École Polytechnique, France. Max-Planck-Institut für Kernphysik, Germany. DESY, Germany. Université Paris Diderot, France. Humboldt-Universität zu Berlin, Germany. Université Montpellier 2, France. Université Pierre et Marie Curie Paris 6, Université Denis Diderot Paris 7, France. DESY, Germany. École Polytechnique, France. DSM/Irfu, France. Universität Tübingen, Germany. Uniwersytet Jagielloński, Poland. Université Bordeaux, France. The University of Warsaw, Poland. Leopold-Franzens-Universität Innsbruck, Austria. Universität Erlangen-Nürnberg, Germany. Max-Planck-Institut für Kernphysik, Germany. University of Adelaide, Australia . Universität Hamburg, Germany. Univ. Grenoble Alpes, France. Max-Planck-Institut für Kernphysik, Germany. Université Paris Diderot, France. Max-Planck-Institut für Kernphysik, Germany. Max-Planck-Institut für Kernphysik, Germany. The University of Leicester, UK. Max-Planck-Institut für Kernphysik, Germany. Universität Potsdam, Germany. École Polytechnique, France. Universität Hamburg, Germany. North-West University, South Africa . Université Pierre et Marie Curie Paris 6, Université Denis Diderot Paris 7, France. Universität Erlangen-Nürnberg, Germany. DESY, Germany. Nicolaus Copernicus Astronomical Center, Poland. Universität Heidelberg, Germany. Universität Erlangen-Nürnberg, Germany. Universität Hamburg, Germany. Nicolaus Copernicus University, Poland. Universität Erlangen-Nürnberg, Germany. Université Pierre et Marie Curie Paris 6, Université Denis Diderot Paris 7, France. Université Paris Diderot, France. Université Pierre et Marie Curie Paris 6, Université Denis Diderot Paris 7, France. DESY, Germany. Universität Tübingen, Germany. Nicolaus Copernicus Astronomical Center, Poland. Leopold-Franzens-Universität Innsbruck, Austria. University of the Witwatersrand, South Africa. DSM/Irfu, France. University of Amsterdam, The Netherlands . Université Savoie Mont-Blanc, France. North-West University, South Africa. Université Bordeaux, France. Université Savoie Mont-Blanc, France. University of Adelaide, Australia . Université Paris Diderot, France. DSM/Irfu, France. Université Paris Diderot, France. Université Bordeaux, France. Université Pierre et Marie Curie Paris 6, Université Denis Diderot Paris 7, France. Humboldt-Universität zu Berlin, Germany. Universität Erlangen-Nürnberg, Germany. Max-Planck-Institut für Kernphysik, Germany. Max-Planck-Institut für Kernphysik, Germany. Max-Planck-Institut für Kernphysik, Germany. Université Montpellier 2, France. École Polytechnique, France. Max-Planck-Institut für Kernphysik, Germany. Université Savoie Mont-Blanc, France. Université Montpellier 2, France. Yerevan Physics Institute, Armenia. University of the Free State, South Africa . Ruhr-Universität Bochum, Germany. Stockholm University, Sweden. Max-Planck-Institut für Kernphysik, Germany. Nicolaus Copernicus Astronomical Center, Poland. Universität Heidelberg, Germany. Stockholm University, Sweden. DSM/Irfu, France. Humboldt-Universität zu Berlin, Germany. École Polytechnique, France. Instytut Fizyki Jądrowej PAN, Poland. Humboldt-Universität zu Berlin, Germany. Universität Hamburg, Institut für Experimentalphysik, Germany. Leopold-Franzens-Universität Innsbruck, Austria . DESY, Germany. Max-Planck-Institut für Kernphysik,, Germany ; Now at Institut de Ciències de l’Espai, Spain. Universität Hamburg, Germany. Uniwersytet Jagielloński, Poland. DESY, Germany. Max-Planck-Institut für Kernphysik, Germany. Max-Planck-Institut für Kernphysik, Germany. Humboldt-Universität zu Berlin, Germany. North-West University, Spain. Univ. Grenoble Alpes, France. Univ. Grenoble Alpes, France. DSM/Irfu, France. Université Paris Diderot, France. Max-Planck-Institut für Kernphysik, Germany. Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering. Universität Tübingen, Germany. Université Paris Diderot, France. Universität Heidelberg, Germany. Universität Erlangen-Nürnberg, Germany. Université Paris Diderot, France. Leopold-Franzens-Universität Innsbruck, Austria. Leopold-Franzens-Universität Innsbruck, Austria. Université Montpellier 2, France. Max-Planck-Institut für Kernphysik, Germany. Max-Planck-Institut für Kernphysik, Germany ; ITA Universität Heidelberg, Germany . Dublin Institute for Advanced Studies, Ireland. Université Savoie Mont-Blanc, France. University of Adelaide, Australia . Nicolaus Copernicus Astronomical Center, Poland. Université Paris Diderot, France. Yerevan Physics Institute, Armenia ; National Academy of Sciences of the Republic of Armenia, Armenia. University of Amsterdam, The Netherlands . Université Savoie Mont-Blanc, France. Universität Tübingen, Germany. Universität Tübingen, Germany. Ruhr-Universität Bochum, Germany. DSM/Irfu, France. DESY, Germany. Humboldt-Universität zu Berlin, Germany. Universität Heidelberg, Germany. North-West University, South Africa . University of Amsterdam, The Netherlands . Université Paris Diderot, France. North-West University, South Africa. Stockholm University, Sweden. Universität Hamburg, Germany. Uniwersytet Jagielloński, Poland. University of Namibia, Namibia. Universität Potsdam, Germany ; DESY, Germany. Universität Erlangen-Nürnberg, Germany. DESY, Germany. North-West University, South Africa . Université Denis Diderot Paris 7, France. Université Paris Diderot, France. Dublin Institute for Advanced Studies, Ireland. Université Paris Diderot, France. Universität Hamburg, Germany. Université Savoie Mont-Blanc, France. Universität Erlangen-Nürnberg, Germany. North-West University, South Africa . Universität Erlangen-Nürnberg, Germany. University of the Free State, South Africa . Université Montpellier 2, France. Universität Erlangen-Nürnberg, Germany. North-West University, South Africa. Max-Planck-Institut für Kernphysik, Germany. Université Pierre et Marie Curie Paris 6, Université Denis Diderot Paris 7, France. University of Amsterdam, The Netherlands. University of Adelaide, Australia . Max-Planck-Institut für Kernphysik, Germany. University of the Free State, South Africa . Universität Heidelberg, Germany. Humboldt-Universität zu Berlin, Germany. Stockholm University, Sweden. Ruhr-Universität Bochum, Germany. Max-Planck-Institut für Kernphysik, Germany. The University of Leicester, UK. Universität Heidelberg, Germany . Universität Erlangen-Nürnberg, Germany. Universität Erlangen-Nürnberg, Germany. DSM/Irfu, France. Max-Planck-Institut für Kernphysik, Germany. The University of Leicester, UK. École Polytechnique, France. Universität Heidelberg, Germany. Nicolaus Copernicus Astronomical Center, Poland. Université Paris Diderot, France. École Polytechnique, France. Uniwersytet Jagielloński, Poland.
Discovery of variable VHE gamma-ray emission from the binary system 1FGL J1018.6-58562015In: Astronomy and Astrophysics Supplement Series, ISSN 0365-0138, E-ISSN 1286-4846, Vol. 577, article id A131Article in journal (Refereed)

Re-observations with the HESS telescope array of the very high-energy (VHE) source HESS J1018-589 A that is coincident with the Fermi-LAT γ-ray binary 1FGL J1018.6-5856 have resulted in a source detection significance of more than 9σ and the detection of variability (χ$^2$/ν of 238.3/155) in the emitted γ-ray flux. This variability confirms the association of HESS J1018-589 A with the high-energy γ-ray binary detected by Fermi-LAT and also confirms the point-like source as a new VHE binary system. The spectrum of HESS J1018-589 A is best fit with a power-law function with photon index Γ = 2.20 \plusmn 0.14$_stat$ \plusmn 0.2$_sys$. Emission is detected up to ~20 TeV. The mean differential flux level is (2.9 \plusmn 0.4) \times 10$^-13$ 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 light curve. When folded on the orbital period of 16.58 days, the rebinned light curve peaks in phase with the observed X-ray and high-energy phaseograms. The fit of the HESS phaseogram to a constant flux provides evidence of periodicity at the level of N$_sigma$\gt 3σ. The shape of the VHE phaseogram and measured spectrum suggest a low-inclination, low-eccentricity system with amodest impact from VHE γ-ray absorption due to pair production (τ \lsim 1 at 300 GeV).

• 155.
Univ Hamburg, Inst Experimentalphys, D-22761 Hamburg, Germany.
Max Planck Inst Kernphys, D-69029 Heidelberg, Germany ; Dublin Inst Adv Studies, Dublin 4, Ireland ; Natl Acad Sci Republ Armenia, Yerevan, Armenia . Max Planck Inst Kernphys, D-69029 Heidelberg, Germany. Natl Acad Sci Republ Armenia, Yerevan, Armenia ; Yerevan Phys Inst, Yerevan 375036, Armenia. Humboldt Univ, Inst Phys, D-12489 Berlin, Germany. Univ Erlangen Nurnberg, Inst Phys, D-91058 Erlangen, Germany. Univ Namibia, Dept Phys, Windhoek, Namibia. Univ Durham, Dept Phys, Durham DH1 3LE, England. DESY, D-15738 Zeuthen, Germany ; Univ Potsdam, Inst Phys & Astron, D-14476 Potsdam, Germany. Nicolaus Copernicus Astron Ctr, PL-00716 Warsaw, Poland. Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering. Nicolaus Copernicus Astron Ctr, PL-00716 Warsaw, Poland. Univ Paris Diderot, APC, AstroParticule & Cosmology, CNRS,IN2P3,CEA,Irfu, Observ Paris,Sorbonne Paris C, 10 Rue Alice Domon & Leonie Duquet, F-75205 Paris 13, France.
The high-energy gamma-ray emission of AP Librae2015In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 573, article id A31Article in journal (Refereed)

The gamma-ray spectrum of the low-frequency-peaked BL Lac (LBL) object AP Librae is studied, following the discovery of very-high-energy (VHE; E > 100 GeV) gamma-ray emission up to the TeV range by the H.E.S.S. experiment. Thismakes AP Librae one of the few VHE emitters of the LBL type. The measured spectrum yields a flux of (8.8 +/- 1.5(stat) +/- 1.8(sys)) x 10(-12) cm(-2) s(-1) above 130 GeV and a spectral index of Gamma = 2.65 +/- 0.19(stat) +/- 0.20(sys). This study also makes use of Fermi-LAT observations in the high energy (HE, E > 100 MeV) range, providing the longest continuous light curve (5 years) ever published on this source. The source underwent a flaring event between MJD 56 306-56 376 in the HE range, with a flux increase of a factor of 3.5 in the 14 day bin light curve and no significant variation in spectral shape with respect to the low-flux state. While the H.E.S.S. and (low state) Fermi-LAT fluxes are in good agreement where they overlap, a spectral curvature between the steep VHE spectrum and the Fermi-LAT spectrum is observed. The maximum of the gamma-ray emission in the spectral energy distribution is located below the GeV energy range.

• 156. Abramowski, A.
Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering. Univ Paris Diderot, APC, AstroParticule & Cosmology, CNRS,IN2P3,CEA,Irfu, Observ Paris,Sorbonne Paris C, 10 Rue Alice Domon & Leonie Duquet, F-75205 Paris 13, France.
Search for extended gamma-ray emission around AGN with HESS and Fermi-LAT2014In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 562, p. A145-Article in journal (Refereed)

Context. Very-high-energy (VHE; E > 100 GeV) gamma-ray emission from blazars inevitably gives rise to electron-positron pair production through the interaction of these gamma-rays with the extragalactic background light (EBL). Depending on the magnetic fields in the proximity of the source, the cascade initiated from pair production can result in either an isotropic halo around an initially- beamed source or a magnetically- broadened cascade :aux. Aims. Both extended pair-halo (PH) and magnetically broadened cascade (MBC) emission from regions surrounding the blazars 1ES 1101-232, IRS 0229+200, and PKS 2155-304 were searched for using VHE y-ray data taken with the High Energy Stereoscopic System (HESS.) and high-energy (HE; 100 MeV < E < 100 GeV) gamma-ray data with the Fermi Large Area Telescope (LAT). Methods. By comparing the angular distributions of the reconstructed gamma-ray events to the angular profiles calculated from detailed theoretical models, the presence of PH and MBC was investigated. Results. Upper limits on the extended emission around lES 1101-232, lES 0229+200, and PKS 2155-304 are found to be at a level of a few per cent of the Crab nebula flux above 1 TeV, depending on the assumed photon index of the cascade emission. Assuming strong extra-Galactic magnetic field (EGME) values, >10(-12) G, this limits the production of pair haloes developing from electromagnetic cascades. For weaker magnetic fields, in which electromagnetic cascades would result in MBCs. EGMF strengths in the range (0.3-3) x 10(-15) G were excluded for PKS 2155-304 at the 99% confidence level, under the assumption of a 1 Mpc coherence length.

• 157. Abramowski, A.
Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering. Univ Paris Diderot, APC, AstroParticule & Cosmology, CNRS,IN2P3,CEA,Irfu, Observ Paris,Sorbonne Paris C, 10 Rue Alice Domon & Leonie Duquet, F-75205 Paris 13, France.
TeV gamma-ray observations of the young synchrotron-dominated SNRs G1.9+0.3 and G330.2+1.0 with HESS2014In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 441, no 1, p. 790-799Article in journal (Refereed)

The non-thermal nature of the X-ray emission from the shell-type supernova remnants (SNRs) G1.9+0.3 and G330.2+1.0 is an indication of intense particle acceleration in the shock fronts of both objects. This suggests that the SNRs are prime candidates for very-high-energy (VHE; E > 0.1 TeV) gamma-ray observations. G1.9+0.3, recently established as the youngest known SNR in the Galaxy, also offers a unique opportunity to study the earliest stages of SNR evolution in the VHE domain. The purpose of this work is to probe the level of VHE gamma-ray emission from both SNRs and use this to constrain their physical properties. Observations were conducted with the H. E. S. S. (High Energy Stereoscopic System) Cherenkov Telescope Array over a more than six-year period spanning 2004-2010. The obtained data have effective livetimes of 67 h for G1.9+0.3 and 16 h for G330.2+1.0. The data are analysed in the context of the multiwavelength observations currently available and in the framework of both leptonic and hadronic particle acceleration scenarios. No significant gamma-ray signal from G1.9+0.3 or G330.2+1.0 was detected. Upper limits (99 per cent confidence level) to the TeV flux from G1.9+0.3 and G330.2+1.0 for the assumed spectral index Gamma = 2.5 were set at 5.6 x 10(-1)3 cm(-2) s(-1) above 0.26 TeV and 3.2 x 10(-12) cm(-2) s(-1) above 0.38 TeV, respectively. In a one-zone leptonic scenario, these upper limits imply lower limits on the interior magnetic field to B-G1.9 greater than or similar to 12 mu G for G1.9+0.3 and to B-G330 greater than or similar to 8 mu G for G330.2+1.0. In a hadronic scenario, the low ambient densities and the large distances to the SNRs result in very low predicted fluxes, for which the H.E.S.S. upper limits are not constraining.

• 158. Abramowski, A.
Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering. Univ Paris Diderot, APC, AstroParticule & Cosmology, CNRS,IN2P3,CEA,Irfu, Observ Paris,Sorbonne Paris C, 10 Rue Alice Domon & Leonie Duquet, F-75205 Paris 13, France.
HESS J1818-154, a new composite supernova remnant discovered in TeV gamma rays and X-rays2014In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 562, p. 562-Article in journal (Refereed)

Composite supernova remnants (SNRs) constitute a small subclass of the remnants of massive stellar explosions where non-thermal radiation is observed from both the expanding shell-like shock front and from a pulsar wind nebula (PWN) located inside of the SNR. These systems represent a unique evolutionary phase of SNRs where observations in the radio, X-ray, and gamma-ray regimes allow the study of the co-evolution of both these energetic phenomena. In this article, we report results from observations of the shell-type SNR G15.4+0.1 performed with the High Energy Stereoscopic System (H. E. S. S.) and XMM-Newton. A compact TeV gamma-ray source, HESS J1818-154, located in the center and contained within the shell of G15.4+0.1 is detected by H. E. S. S. and featurs a spectrum best represented by a power-law model with a spectral index of -2.3 +/- 0.3(stat) +/- 0.2(sys) and an integral flux of F(>0.42 TeV) = (0.9 +/- 0.3(stat) +/- 0.2(sys)) x 10(-12) cm(-2) s(-1). Furthermore, a recent observation with XMM-Newton reveals extended X-ray emission strongly peaked in the center of G15.4+0.1. The X-ray source shows indications of an energy-dependent morphology featuring a compact core at energies above 4 keV and more extended emission that fills the entire region within the SNR at lower energies. Together, the X-ray and VHE gamma-ray emission provide strong evidence of a PWN located inside the shell of G15.4+0.1 and this SNR can therefore be classified as a composite based on these observations. The radio, X-ray, and gamma-ray emission from the PWN is compatible with a one-zone leptonic model that requires a low average magnetic field inside the emission region. An unambiguous counterpart to the putative pulsar, which is thought to power the PWN, has been detected neither in radio nor in X-ray observations of G15.4+0.1.

• 159. Abramowski, A.
Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering. Univ Paris Diderot, APC, AstroParticule & Cosmology, CNRS,IN2P3,CEA,Irfu, Observ Paris,Sorbonne Paris C, 10 Rue Alice Domon & Leonie Duquet, F-75205 Paris 13, France.
Flux upper limits for 47 AGN observed with HESS in 2004-20112014In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 564, p. Article ID: A9-Article in journal (Refereed)

Context. About 40% of the observation time of the High Energy Stereoscopic System (H.E.S.S.) is dedicated to studying active galactic nuclei (AGN), with the aim of increasing the sample of known extragalactic very-high-energy (VHE, E > 100 GeV) sources and constraining the physical processes at play in potential emitters.Aims. H.E.S.S. observations of AGN, spanning a period from April 2004 to December 2011, are investigated to constrain their gamma-ray fluxes. Only the 47 sources without significant excess detected at the position of the targets are presented.Methods. Upper limits on VHE fluxes of the targets were computed and a search for variability was performed on the nightly time scale.Results. For 41 objects, the flux upper limits we derived are the most constraining reported to date. These constraints at VHE are compared with the flux level expected from extrapolations of Fermi-LAT measurements in the two-year catalog of AGN. The H.E.S.S. upper limits are at least a factor of two lower than the extrapolated Fermi-LAT fluxes for 11 objects Taking into account the attenuation by the extragalactic background light reduces the tension for all but two of them, suggesting intrinsic curvature in the high-energy spectra of these two AGN.Conclusions. Compilation efforts led by current VHE instruments are of critical importance for target-selection strategies before the advent of the Cherenkov Telescope Array (CTA).

• 160. Abramowski, A.
Heidelberg University. Univ Paris Diderot, APC, AstroParticule & Cosmology, CNRS,IN2P3,CEA,Irfu, Observ Paris,Sorbonne Paris C, 10 Rue Alice Domon & Leonie Duquet, F-75205 Paris 13, France.
Search for TeV Gamma-ray Emission from GRB 100621A, an extremely bright GRB in X-rays, with HESS2014In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 565, p. 1-6, article id A16Article in journal (Refereed)

The long gamma-ray burst (GRB) 100621A, at the time the brightest X-ray transient ever detected by Swift-XRT in the 0.3-10 keV range, has been observed with the H.E.S.S. imaging air Cherenkov telescope array, sensitive to gamma radiation in the very-high-energy (VHE, >100 GeV) regime. Due to its relatively small redshift of z similar to 0.5, the favourable position in the southern sky and the relatively short follow-up time (<700 s after the satellite trigger) of the H.E.S.S. observations, this GRB could be within the sensitivity reach of the HESS. instrument. The analysis of the HESS. data shows no indication of emission and yields an integral flux upper limit above similar to 380 GeV of 4.2 x 10(-12) cm(-2) s(-1) s (95% confidence level), assuming a simple Band function extension model. A comparison to a spectral-temporal model, normalised to the prompt flux at sub-MeV energies, constraints the existence of a temporally extended and strong additional hard power law, as has been observed in the other bright X-ray GRB 130427A. A comparison between the HESS. upper limit and the contemporaneous energy output in X-rays constrains the ratio between the X-ray and VHE gamma-ray fluxes to be greater than 0.4. This value is an important quantity for modelling the afterglow and can constrain leptonic emission scenarios, where leptons are responsible for the X-ray emission and might produce VHE gamma rays.

• 161.
Univ Hamburg, Inst Expt Phys, D-22761 Hamburg, Germany.
Max Planck Inst Kernphys, D-69029 Heidelberg, Germany. Max Planck Inst Kernphys, D-69029 Heidelberg, Germany. Natl Acad Sci Republ Armenia, Yerevan 0019, Armenia. Humboldt Univ, Inst Phys, D-12489 Berlin, Germany. Univ Namibia, Dept Phys, Windhoek, Namibia. Univ Durham, Dept Phys, Durham DH1 3LE, England. Univ Amsterdam, Astron Inst Anton Pannekoek, GRAPPA, NL-1098 XH Amsterdam, Netherlands. Uniwersytet Jagiellonski, Astron Observ, PL-30244 Krakow, Poland. Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering. Univ Paris Diderot, APC, AstroParticule & Cosmology, CNRS,IN2P3,CEA,Irfu, Observ Paris,Sorbonne Paris C, 10 Rue Alice Domon & Leonie Duquet, F-75205 Paris 13, France.
Search for dark matter annihilation signatures in HESS observations of dwarf spheroidal galaxies2014In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 90, no 11, p. 112012-Article in journal (Refereed)

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 nonthermal high-energy gamma-ray emission or intense star formation. Therefore they are among 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 reanalysis 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 similar to 3.9 x 10(-24) cm(3) s(-1) at a 95% confidence level.

• 162.
Univ Hamburg Inst Expt Phys, D-22761 Hamburg, Germany.
Max Planck Inst Kernphys, D-69029 Heidelberg, Germany ; Dublin Inst Adv Studies, Dublin 2, Ireland ; Natl Acad Sci Republ Armenia, Yerevan 0019, Armenia . Max Planck Inst Kernphys, D-69029 Heidelberg, Germany. Natl Acad Sci Republ Armenia, Yerevan 0019, Armenia ; Yerevan Phys Inst, Yerevan 375036, Armenia. Humboldt Univ, Inst Phys, D-12489 Berlin, Germany. Univ Namibia, Dept Phys, Windhoek, Namibia. Univ Durham, Dept Phys, Durham DH1 3LE, England. Univ Amsterdam, Astron Inst Anton Pannekoek, Gravitat Astroparticle Phys Amsterdam GRAPPA, NL-1098 XH Amsterdam, Netherlands. Uniwersytet Jagiellonski, Obserwatorium Astronomiczne, PL-30244 Krakow, Poland ; Harvard Smithsonian Ctr Astrophys, Cambridge, MA 02138 USA . Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering. Univ Paris Diderot, APC, AstroParticule & Cosmology, CNRS,IN2P3,CEA,Irfu, Observ Paris,Sorbonne Paris C, 10 Rue Alice Domon & Leonie Duquet, F-75205 Paris 13, France.
The exceptionally powerful TeV gamma-ray emitters in the Large Magellanic Cloud2015In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 347, no 6220, p. 406-412Article in journal (Refereed)

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 nonthermal x-ray shell, the superbubble 30 Dor C. The unique object SN 1987A is, unexpectedly, not detected, which constrains the theoretical framework of particle acceleration in very young supernova remnants. These detections reveal the most energetic tip of a g-ray source population in an external galaxy and provide via 30 Dor C the unambiguous detection of g-ray emission from a superbubble.

• 163.
Univ Hamburg, Germany.
Max Planck Inst Kernphys,Germany ; Dublin Inst Adv Studies, Ireland ; Natl Acad Sci Republ Armenia, Armenia. Max Planck Inst Kernphys,Germany. Natl Acad Sci Republ Armenia, Armenia ; Yerevan Phys Inst, Armenia. Humboldt Univ, Germany. Univ Namibia, Namibia. Univ Durham, UK. Univ Amsterdam, Netherlands. Uniwersytet Jagiellonski, Poland. Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering. Univ Paris Diderot, APC, AstroParticule & Cosmology, CNRS,IN2P3,CEA,Irfu, Observ Paris,Sorbonne Paris C, 10 Rue Alice Domon & Leonie Duquet, F-75205 Paris 13, France.
THE 2012 FLARE OF PG 1553+113 SEEN WITH HESS AND FERMI-LAT2015In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 802, no 1, article id 65Article in journal (Refereed)

Very high energy (VHE, E > 100 GeV)gamma-ray flaring activity of the high-frequency peaked BL Lac object PG 1553 + 113 has been detected by the H.E.S.S. 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 a hint of intra-night variability. No counterpart of this event has been detected in the Fermi-Large Area Telescope data. This pattern is consistent with VHE gamma(-)ray flaring being caused by the injection of ultrarelativistic particles, emitting.-rays at the highest energies. The dataset offers a unique opportunity to constrain the redshift of this source at z = 0.49 +/- 0.04 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 E-QG,E- 1 > 4.10 x 10(17) GeV and E-QG,E- 2 > 2.10 x 10(10) GeV for linear and quadratic LIV effects, respectively.

• 164.
Universität Hamburg, Germany.
Max-Planck-Institut für Kernphysik, Germany ; Dublin Institute for Advanced Studies, Ireland ; National Academy of Sciences of the Republic of Armenia, Armenia. Max-Planck-Institut für Kernphysik, Germany. Yerevan Physics Institute, Armenia ; National Academy of Sciences of the Republic of Armenia, Armenia. Humboldt-Universität zu Berlin, Germany. University of Namibia, Namibia. University of Durham, UK. University of Amsterdam, The Netherlands. Uniwersytet Jagielloński, Poland. Linnaeus University, Faculty of Technology, Department of Physics and Electrical Engineering.
H.E.S.S. reveals a lack of TeV emission from the supernova remnant Puppis A: (Research Note)2015In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 575, article id A81Article in journal (Refereed)

Context. Puppis A is an interesting similar to 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 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.

Aims. Very-high-energy (VHE, E >= 0.1 TeV) gamma-ray emission from Puppis A has been, for the first time, searched for with the High Energy Stereoscopic System (HESS.).

Methods. Stereoscopic imaging of Cherenkov radiation from extensive air showers is used to reconstruct the direction and energy of the incident gamma-rays in order to produce sky images and source spectra. The profile likelihood method is applied to find constraints on the existence of a potential break or cutoff in the photon spectrum.

Results. The analysis of the HESS. 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 HESS. 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 continuing 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 NE region.

• 165.