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| 2. |
- Ackermann, M., et al.
(författare)
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GeV GAMMA-RAY FLUX UPPER LIMITS FROM CLUSTERS OF GALAXIES
- 2010
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Ingår i: ASTROPHYS J LETT. - 2041-8205. ; 717:1, s. l71-L78
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Tidskriftsartikel (refereegranskat)abstract
- The detection of diffuse radio emission associated with clusters of galaxies indicates populations of relativistic leptons infusing the intracluster medium (ICM). Those electrons and positrons are either injected into and accelerated directly in the ICM, or produced as secondary pairs by cosmic-ray ions scattering on ambient protons. Radiation mechanisms involving the energetic leptons together with the decay of neutral pions produced by hadronic interactions have the potential to produce abundant GeV photons. Here, we report on the search for GeV emission from clusters of galaxies using data collected by the Large Area Telescope on the Fermi Gamma-ray Space Telescope from 2008 August to 2010 February. Thirty-three galaxy clusters have been selected according to their proximity and high mass, X-ray flux and temperature, and indications of non-thermal activity for this study. We report upper limits on the photon flux in the range 0.2-100 GeV toward a sample of observed clusters (typical values (1-5) x 10(-9) photon cm(-2) s(-1)) considering both point-like and spatially resolved models for the high-energy emission and discuss how these results constrain the characteristics of energetic leptons and hadrons, and magnetic fields in the ICM. The volume-averaged relativistic-hadron-to-thermal energy density ratio is found to be <5%-10% in several clusters.
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| 3. |
- Ackermann, M., et al.
(författare)
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SEARCH FOR COSMIC-RAY-INDUCED GAMMA-RAY EMISSION IN GALAXY CLUSTERS
- 2014
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 787:1
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Tidskriftsartikel (refereegranskat)abstract
- Current theories predict relativistic hadronic particle populations in clusters of galaxies in addition to the already observed relativistic leptons. In these scenarios hadronic interactions give rise to neutral pions which decay into gamma rays that are potentially observable with the Large Area Telescope (LAT) on board the Fermi space telescope. We present a joint likelihood analysis searching for spatially extended gamma-ray emission at the locations of 50 galaxy clusters in four years of Fermi-LAT data under the assumption of the universal cosmic-ray (CR) model proposed by Pinzke & Pfrommer. We find an excess at a significance of 2.7 sigma, which upon closer inspection, however, is correlated to individual excess emission toward three galaxy clusters: A400, A1367, and A3112. We discuss these cases in detail and conservatively attribute the emission to unmodeled background systems (for example, radio galaxies within the clusters). Through the combined analysis of 50 clusters, we exclude hadronic injection efficiencies in simple hadronic models above 21% and establish limits on the CR to thermal pressure ratio within the virial radius, R-200, to be below 1.25%-1.4% depending on the morphological classification. In addition, we derive new limits on the gamma-ray flux from individual clusters in our sample.
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| 4. |
- Aleksic, J., et al.
(författare)
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DETECTION OF VERY HIGH ENERGY gamma-RAY EMISSION FROM THE PERSEUS CLUSTER HEAD-TAIL GALAXY IC 310 BY THE MAGIC TELESCOPES
- 2010
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Ingår i: The Astrophysical Journal Letters. - 2041-8205. ; 723:2, s. l207-L212
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Tidskriftsartikel (refereegranskat)abstract
- We report on the detection with the MAGIC telescopes of very high energy (VHE) gamma-rays from IC 310, a head-tail radio galaxy in the Perseus galaxy cluster, observed during the interval 2008 November to 2010 February. The Fermi satellite has also detected this galaxy. The source is detected by MAGIC at a high statistical significance of 7.6 sigma in 20.6 hr of stereo data. The observed spectral energy distribution is flat with a differential spectral index of -2.00 +/- 0.14. The mean flux above 300 GeV, between 2009 October and 2010 February, (3.1 +/- 0.5) x 10(-12) cm(-2) s(-1), corresponds to (2.5 +/- 0.4)% of Crab Nebula units. Only an upper limit, of 1.9% of Crab Nebula units above 300 GeV, was obtained with the 2008 data. This, together with strong hints (>3 sigma) of flares in the middle of 2009 October and November, implies that the emission is variable. The MAGIC results favor a scenario with the VHE emission originating from the inner jet close to the central engine. More complicated models than a simple one-zone synchrotron self-Compton (SSC) scenario, e. g., multi-zone SSC, external Compton, or hadronic, may be required to explain the very flat spectrum and its extension over more than three orders of magnitude in energy.
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| 5. |
- Arlen, T., et al.
(författare)
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Constraints on Cosmic Rays, Magnetic Fields, and Dark Matter from Gamma-Ray Observations of the Coma Cluster of Galaxies with VERITAS and Fermi
- 2012
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 757:2
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Tidskriftsartikel (refereegranskat)abstract
- We report the discovery of TeV gamma-ray emission coincident with the shell-type radio supernova remnant (SNR) CTA 1 using the VERITAS gamma-ray observatory. The source, VER J0006+729, was detected as a 6.5 standard deviation excess over background and shows an extended morphology, approximated by a two-dimensional Gaussian of semimajor (semiminor) axis 030 (024) and a centroid 5' from the Fermi gamma-ray pulsar PSR J0007+7303 and its X-ray pulsar wind nebula (PWN). The photon spectrum is well described by a power-law dN/dE = N 0(E/3 TeV)–Γ, with a differential spectral index of Γ = 2.2 ± 0.2stat ± 0.3sys, and normalization N 0 = (9.1 ± 1.3stat ± 1.7sys) × 10–14 cm–2 s–1 TeV–1. The integral flux, F γ = 4.0 ×10–12 erg cm–2 s–1 above 1 TeV, corresponds to 0.2% of the pulsar spin-down power at 1.4 kpc. The energetics, colocation with the SNR, and the relatively small extent of the TeV emission strongly argue for the PWN origin of the TeV photons. We consider the origin of the TeV emission in CTA 1.
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| 6. |
- Pfrommer, H., et al.
(författare)
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Experimental Demonstration of Full-Duplex DOCSIS Signal Transmissions over a Wireline/Wireless-Fibre Access Network
- 2006
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Ingår i: 2006 International Topical Meeting on Microwaves Photonics. ; , s. 89-92
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Konferensbidrag (refereegranskat)abstract
- A fibre-radio access network architecture for simultaneous wireline and wireless transmissions of data over cable service interface specification (DOCSIS) signals is presented. An all-optical harmonic up-conversion technique using a dual-drive Mach-Zehnder modulator (DD-MZM) is employed at the central station while an InGaAsP/InGaAsP multiple quantum well (MQW) asymmetric Fabry-Perot modulator/detector (AFPM) functions as a single optical/electrical transducer performing optical intensity modulation and photodetection simultaneously at the base station. Full-duplex operation is demonstrated for both access types in an indoor laboratory environment as well as in a small-scale outdoor field trial
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| 7. |
- Pfrommer, H., et al.
(författare)
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Full-duplex DOCSIS/wirelessDOCSIS fiber-radio network employing packaged AFPM-based base-stations
- 2006
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Ingår i: IEEE Photonics Technology Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 1041-1135 .- 1941-0174. ; 18:04-jan, s. 406-408
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Tidskriftsartikel (refereegranskat)abstract
- The simultaneous wireline (600 MHz) and wireless (5.5 GHz) transmission of data over cable service interface specification (DOCSIS) signals in a hybrid fiber-radio access network is presented. The DOCSIS signal wireless replica is generated by means of an optical harmonic up-conversion technique based on a dual-drive Mach-Zehnder modulator. The optical signal is fed to a base station (BS) where a packaged asymmetric Fabry-Perot modulator/detector acts simultaneously as a photodetector and an optical modulator. At the BS, the DOCSIS signals can be fed either to a wireline or a wireless access network, in a highly flexible approach. Full-duplex operation has been demonstrated for both access types, including indoor wireless transmission.
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