522 research outputs found
Views of the La Crosse Tribune on the Versailles Treaty and its rejection by the Senate of the United States, November, 1918 to November, 1920
No full textAuthor Correction: Discovery of a radiation component from the Vela pulsar reaching 20 teraelectronvolts
No full textIn the version of the article initially published, R. Zanin, M. Kerr, S. Johnston, R. M. Shannon and D. A. Smith mistakenly appeared in the main author list but are now instead listed as members of The H.E.S.S. Collaboration et al. in the HTML and PDF versions of the article
Numerical simulations of radiation from blazar jets
No full textWe present a description of our numerical code BLAZAR.
This code calculates spectra and light curves of blazars during
outbursts. The code is based on a model in which the non-thermal
flares in blazars are produced in thin shells propagating down a
conical jet with relativistic velocities. Such shells may represent
layers of a shocked plasma, enclosed between the forward and reverse
fronts of an internal shock. In the model adopted by us, the
production of non-thermal radiation is assumed to be dominated by
electrons and positrons which are accelerated directly, rather then
injected by pair cascades. The code includes synchrotron emission
and inverse-Compton process as the radiation mechanisms. Both
synchrotron photons and external photons are included as the seed
photons for Comptonization. At the present stage, the code is
limited to treat the inverse Compton process only within the Thomson
limit and is specialized to model radiation production in the flat
spectrum radio quasars. As an example, we present the results of
modeling an outburst in 3C 279 – the most extensively monitored
γ-ray – bright quasar
Progress in Monte Carlo design and optimization of the Cherenkov Telescope Array
No full textThe Cherenkov Telescope Array (CTA) will be an instrument covering a wide energy range in very-high-energy (VHE) gamma rays. CTA will include several types of telescopes, in order to optimize the performance over the whole energy range. Both large-scale Monte Carlo (MC) simulations of CTA super-sets (including many different possible CTA layouts as sub-sets) and smaller-scale simulations dedicated to individual aspects were carried out and are on-going. We summarize results of the prior round of large-scale simulations, show where the design has now evolved beyond the conservative assumptions of the prior round and present first results from the on-going new round of MC simulations.Fil: Bernlöhr, K.. Max-Planck-Institut fur Kernphysik; AlemaniaFil: Barnacka, A.. Polish Academy of Sciences; ArgentinaFil: Becherini, Y.. École Polytechnique; FranciaFil: Blanch Bigas, O.. IFAE; EspañaFil: Bouvier, A.. University of California; Estados UnidosFil: Carmona, E.. Max-Planck-Institut fur Physik; AlemaniaFil: Colin, P.. Max-Planck-Institut fur Physik; AlemaniaFil: Decerprit, G.. DESY; AlemaniaFil: di Pierro, F.. Osservatorio Astrofisico di Torino dell’Istituto Nazionale di Astrofisica; ItaliaFil: Dubois, F.. Universidad Complutense de Madrid; EspañaFil: Farnier, C.. Stockholm University; SueciaFil: Funk, S.. Kavli Institute for Particle Astrophysics and Cosmology; Estados UnidosFil: Hermann, G.. Max-Planck-Institut fur Kernphysik; AlemaniaFil: Hinton, J. A.. The University of Leicester; Reino UnidoFil: Humensky, T. B.. Columbia University; Estados UnidosFil: Jogler, T.. Kavli Institute for Particle Astrophysics and Cosmology; Estados UnidosFil: Khélifi, B.. École Polytechnique; FranciaFil: Kihm, T.. Max-Planck-Institut fur Kernphysik; AlemaniaFil: Komin, N.. Universite de Savoie; FranciaFil: Lenain, J. -P.. Université Denis Diderot Paris 7; FranciaFil: López Coto, R.. IFAE; EspañaFil: Maier, G.. DESY; AlemaniaFil: Mazin, D.. Max-Planck-Institut fur Physik; AlemaniaFil: Medina, Maria Clementina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: Moralejo, A.. IFAE; EspañaFil: Moderski, R.. Polish Academy of Sciences; ArgentinaFil: Nolan, S. J.. Durham University; Reino UnidoFil: Ohm, S.. The University of Leicester; Reino UnidoFil: de Oña Wilhelmi, E.. Max-Planck-Institut fur Kernphysik; Alemania33rd International Cosmic Ray ConferenceRío de JaneiroBrasilBrazilian Physical Societ
Klein-Nishina effects in the spectra of non-thermal sources immersed in external radiation fields
No full textWe provide a systematic numerical and analytical study of Klein–Nishina (KN) effects in the spectrum produced by a steady-state, non-thermal source where rapidly accelerated electrons cool by emitting synchrotron radiation and Compton up-scattering ambient photons produced outside the source. We focus on the case where q, the ratio of the ambient radiation field to source magnetic field energy densities, significantly exceeds unity. We show that the KN reduction in the electron Compton cooling rate causes the steady-state electron spectrum to harden at energies γγKN, where γKN= 1/4ε0 and ε0=hν0/mec2 is the characteristic ambient photon energy. This hardening becomes noticeable in the synchrotron radiation from electrons with energies as low as 0.1γKN and changes the synchrotron spectral index relative to its Thomson limit value by as much as Δα 0.75 for q 1. The source synchrotron spectrum thus shows a high-energy 'bump' or excess, even though the electron acceleration spectrum has no such excess. In contrast, the low-energy Compton gamma-ray spectrum shows little distortion because the electron hardening compensates for the KN decline in the scattering rate. For sufficiently high electron energies, however, Compton cooling becomes so inefficient that synchrotron cooling dominates – an effect omitted in most previous studies. The hardening of the electron distribution thus stops, leading to a rapid decline in Compton gamma-ray emission, i.e. a strong spectral break whose location does not depend on the maximum electron energy. This break can limit the importance of Compton gamma-ray pair production on ambient photons and implies that a source's synchrotron luminosity may exceed its Compton luminosity even though q> 1. We discuss the importance of these KN effects in blazars, micro-quasars and pulsar binaries
Gravitational lensing as a probe of compact object populations in the Galaxy
No full textAims.The population of solitary compact objects in the Galaxy is very
difficult to investigate. In this paper we examine the possibility
of using microlensing searches to detect and to analyze the
properties of solitary black holes and neutron stars.
Methods.Evolution of single and binary stars is followed using the StarTrac
New constraints on the mid-IR EBL from the HESS discovery of VHE gamma-rays from 1ES 0229+200
No full textAims.To investigate the very high energy (VHE: >100 GeV) γ-ray emission from the high-frequency peaked BL Lac 1ES 0229+200. Methods: Observations of 1ES 0229+200 at energies above 580 GeV were performed with the High Energy Stereoscopic System (HESS) in 2005 and 2006. Results: 1ES 0229+200 is discovered by HESS to be an emitter of VHE photons. A signal is detected at the 6.6σ level in the HESS observations (41.8 h live time). The integral flux above 580 GeV is (9.4±1.5_stat±1.9_syst) × 10-13 cm-2 s-1, corresponding to ~1.8% of the flux observed from the Crab Nebula. The data show no evidence for significant variability on any time scale. The observed spectrum is characterized by a hard power law (Γ = 2.50±0.19_stat±0.10_syst) from 500 GeV to ~15 TeV. Conclusions: The high-energy range and hardness of the observed spectrum, coupled with the object's relatively large redshift (z = 0.1396), enable the strongest constraints so far on the density of the Extragalactic Background Light (EBL) in the mid-infrared band. Assuming that the emitted spectrum is not harder than Γ_int ≈ 1.5, the HESS data support an EBL spectrum ∝λ-1 and density close to the lower limit from source counts measured by Spitzer, confirming the previous indications from the HEGRA data of 1ES 1426+428 (z=0.129). Irrespective of the EBL models used, the intrinsic spectrum of 1ES 0229+200 is hard, thus locating the high-energy peak of its spectral energy distribution above a few TeV.Aharonian, F.; Akhperjanian, A. G.; Barres de Almeida, U.; Bazer-Bachi, A. R.; Behera, B.; Beilicke, M.; Benbow, W.; Bernlöhr, K.; Boisson, C.; Bolz, O.; Borrel, V.; Braun, I.; Brion, E.; Brown, A. M.; Bühler, R.; Bulik, T.; Büsching, I.; Boutelier, T.; Carrigan, S.; Chadwick, P. M.; Chounet, L.-M.; Clapson, A. C.; Coignet, G.; Cornils, R.; Costamante, L.; Dalton, M.; Degrange, B.; Dickinson, H. J.; Djannati-Ataï, A.; Domainko, W.; O'C. Drury, L.; Dubois, F.; Dubus, G.; Dyks, J.; Egberts, K.; Emmanoulopoulos, D.; Espigat, P.; Farnier, C.; Feinstein, F.; Fiasson, A.; Förster, A.; Fontaine, G.; Funk, Seb.; Füßling, M.; Gallant, Y. A.; Giebels, B.; Glicenstein, J. F.; Glück, B.; Goret, P.; Hadjichristidis, C.; Hauser, D.; Hauser, M.; Heinzelmann, G.; Henri, G.; Hermann, G.; Hinton, J. A.; Hoffmann, A.; Hofmann, W.; Holleran, M.; Hoppe, S.; Horns, D.; Jacholkowska, A.; de Jager, O. C.; Jung, I.; Katarzyński, K.; Kendziorra, E.; Kerschhaggl, M.; Khélifi, B.; Keogh, D.; Komin, Nu.; Kosack, K.; Lamanna, G.; Latham, I. J.; Lemière, A.; Lemoine-Goumard, M.; Lenain, J.-P.; Lohse, T.; Martin, J. M.; Martineau-Huynh, O.; Marcowith, A.; Masterson, C.; Maurin, D.; Maurin, G.; McComb, T. J. L.; Moderski, R.; Moulin, E.; de Naurois, M.; Nedbal, D.; Nolan, S. J.; Ohm, S.; Olive, J.-P.; de Oña Wilhelmi, E.; Orford, K. J.; Osborne, J. L.; Ostrowski, M.; Panter, M.; Pedaletti, G.; Pelletier, G.; Petrucci, P.-O.; Pita, S.; Pühlhofer, G.; Punch, M.; Ranchon, S.; Raubenheimer, B. C.; Raue, M.; Rayner, S. M.; Renaud, M.; Ripken, J.; Rob, L.; Rolland, L.; Rosier-Lees, S.; Rowell, G.; Rudak, B.; Ruppel, J.; Sahakian, V.; Santangelo, A.; Schlickeiser, R.; Schöck, F.; Schröder, R.; Schwanke, U.; Schwarzburg, S.; Schwemmer, S.; Shalchi, A.; Sol, H.; Spangler, D.; Stawarz, Ł.; Steenkamp, R.; Stegmann, C.; Superina, G.; Tam, P. H.; Tavernet, J.-P.; Terrier, R.; van Eldik, C.; Vasileiadis, G.; Venter, C.; Vialle, J. P.; Vincent, P.; Vivier, M.; Völk, H. J.; Volpe, F.; Wagner, S. J.; Ward, M.; Zdziarski, A. A.; Zech,
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