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Agenda
for the parallel workshop sessions in Astrophysical Messengers (Neutrinos, Gamma-Rays, Cosmic Rays).
All links marked with a⇓ can be used to show/hide the abstracts and presentations.
Click here to show/hide all presentations and abstracts and here for a print version.
You may also download the compact program booklet (PDF, 1.9 MB)
and an abstract booklet (PDF, 0.4 MB).
As long as authors provided us with PDF versions of their slides, the corresponding downloads are available on this page.
Monday – Sep 5, 2011
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14:30 – 16:10 |
Astrophysical Messengers W1 – Cosmic rays
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Parallel Session (Millerzimmer) – Chair:
Pierre Sokolsky
14:30
(15' + 5')
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Anisotropy studies with the Pierre Auger Observatory⇓
slides
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Carla Macolino (LPNHE - Paris)
We report recent results from the Pierre Auger Observatory about the anisotropy of ultra-high energy cosmic ray arrival directions. We present the results on the search for a dipolar anisotropy at the EeV energy scale. Both the phase and the amplitude measurements of the first harmonic modulation in the right-ascension distribution are discussed. For cosmic rays with energies above 55 EeV, we present an update on the search for correlations between their arrival directions and the positions of active galactic nuclei from the Véron-Cetty and Véron catalog. Finally, we also discuss the results of correlation analyses applied to other populations of extragalactic objects.
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14:50
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The nuclear mass composition of UHECR with the Pierre Auger Observatory⇓
slides
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Lorenzo Cazon Boado (LIP)
The Fluorescence Detector of the Pierre Auger Observatory measures the atmospheric depth Xmax where the longitudinal profile of the UHECR (Ultra High Energy Cosmic Ray) induced
electromagnetic cascade reaches its maximum. This is sensitive to the nuclear mass composition of the cosmic rays. Due to its hybrid design, the Pierre Auger Observatory also provides independent experimental observables for the study of the nuclear mass
composition coming from the Surface Detector. We present Xmax distributions and an update of the average and RMS values in different energy bins and compare them to the predictions for different nuclear masses and hadronic models. We also present the results of the composition sensitive parameters derived from the ground level component.
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15:10
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Determination of hadronic interaction characteristics with the Pierre Auger Observatory⇓
slides
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Ralf Ulrich (Karlsruhe Institute of Technology)
The Pierre Auger Observatory measures extensive air showers (EAS) up to the highest energies. One of the biggest challenges in current data analyses is to interpret these data in terms of the primary mass composition. Due to the insufficient constraint of interactions in EAS this is afflicted with large uncertainties. On the other hand, this high sensitivity of EAS to interaction features can be exploited to determine or constrain properties of interactions up to √ s of 450TeV. We demonstrate how specific EAS observations are suited for this task and thus may contribute to limit the uncertainties in the interpretation of air showers. These are the estimation of the muon number at ground level and the study of the hadronic cross-section for particle production via EAS fluctuations.
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15:30
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Search for the nuclei sources in the ultra-high energy cosmic ray data⇓
slides
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Dmitri Semikoz (APC)
We propose a new method to search for heavy nuclei sources, on top of
background, in the Ultra-High Energy Cosmic Ray data. We apply this method to the 69
events recently published by the Pierre Auger Collaboration and find a tail of events for which it
reconstructs the source at a few degrees from the Virgo galaxy cluster.
The probability to have such a cluster of events in some random background is
about 0.7%.
The probability to reconstruct the source at less than 10 degrees from M87 in a data set already containing such a cluster of events is about 0.4%. This may be a hint at the Virgo cluster as a bright ultra-high energy nuclei
source.
We investigate the ability of current and future experiments to validate or rule out this possibility.
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15:50
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Enhancements to the Southern Pierre Auger Observatory⇓
slides
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Hans Klages (KIT Karlsruhe)
The southern Pierre Auger Observatory detects cosmic rays above 3×1018 eV since 2004, exploiting a hybrid air shower detection technique, with 1600 water Cherenkov detectors and 24 air fluorescence telescopes on a 3000 km2 site. As low energy enhancement to the observatory three additional telescopes with elevated field of view were built (HEAT). In the field of view of HEAT the density of the detector array was raised by additional water tanks on an area of about 20 km2. This setup enables unbiased hybrid data taking above 1017 eV. The infill area is being equipped with large underground muon detectors (AMIGA). A prototype array of radio antenna stations (AERA), working at 30 to 80 MHz, was installed in the infill. Properties and status of AERA, AMIGA and HEAT will be presented.
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16:50 – 18:50 |
Astrophysical Messengers W2 – Cosmic rays
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Parallel Session (Millerzimmer) – Chair:
Marek Kowalski
16:50
(15' + 5')
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Recent results from Telescope Array⇓
slides
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Daisuke Ikeda (Institute for Cosmic Ray Research, University of Tokyo)
The Telescope Array (TA) experiment, located in the West Desert of Utah, is the largest ultra-high energy cosmic ray (UHECR) observatory in the Northern Hemisphere.
The TA detector consists of three Fluorescence Detectors (FDs) and an array of 507 scintillation surface detectors (SDs). The SDs deployed on a square grid of 1.2 km spacing and cover a total area of ≈700 km2$. Three FD stations are located on the periphery of the SD array.
The observation started in November 2007 for FD and in March 2008 for SD.
Here we present the preliminary results of energy spectra, mass composition, photon search and anisotropy search of UHECRs from the TA three-year operation.
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17:10
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Lorentz invariance violation and chemical composition of ultra high energy cosmic rays⇓
slides
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Luca Maccione (DESY)
Motivated by experimental indications of a significant presence of heavy nuclei in the cosmic ray flux at ultra-high energies (gtrsim 1019 eV), we consider the effects of Planck scale suppressed Lorentz Invariance Violation (LIV) on the propagation of cosmic ray nuclei. In particular we focus on LIV effects on the photodisintegration of nuclei onto the background radiation fields. After a general discussion of the formalism, we present constraints on LIV attainable with present data and an outlook of possible future improvements.
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17:30
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Future projects at Telescope Array⇓
slides
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Pierre Sokolsky (University of Utah)
Future projects and extensions of the Telescope Array will be presented. These include the TALE detector, a Cherenkov array and prototype detectors for sensing cosmic rays using bistatic radar.
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17:50
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Cosmic ray anisotropies observed by the ARGO-YBJ experiment⇓
slides
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Giuseppe Di Sciascio (INFN - Sezione Roma Tor Vergata)
The ARGO-YBJ experiment, located at the Yangbajing Cosmic Ray Laboratory
(Tibet, 4300 m asl, 606 g cm-2), is an EAS-array exploiting the full
coverage approach at high altitude. We analyzed the data taken since
November 2007 looking for anisotropies in the arrival directions of
cosmic rays on different angular scales. The results of the analysis are
reported and compared with other experiments.
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18:10
(15' + 5')
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The JEM-EUSO mission⇓
slides
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Marco Ricci (INFN Laboratori Nazionali Frascati)
The Extreme Universe Space Observatory on Japanese Experiment Module (JEM-EUSO ) is a science mission planned to be launched around the end of 2016 to the International Space Station (ISS) to investigate the nature and origin of Extreme Energy Cosmic Rays (EECR) beyond energy E>5×1019 eV.
JEM-EUSO is a wide-angle telescope (60 degrees full field of view) and consists of high-transmittance Fresnel lenses 2.5 m in diameter, an advanced photo-sensitive detector at the focal surface and a suitable electronics. An infrared camera and a LIDAR system will also be used to monitor the Earth's atmosphere and provide significant information on cloud coverage.
The present status of advancement of the mission will be reported.
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18:30
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UHECR spectra composition and maps by lightest nuclei from nearest universe⇓
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Daniele Fargion (Physics Department and INFN)
UHECR should open a new astronomy window because of rigidity and nearby GZK Universe space. However the earlier 2007 AUGER correlation with the super- galactic plane faded away in 2010. UHECR composition (nuclei) was already on 2007 and it is contradiction with directionality (proton). Since 2007, Cen A is the only nearby (4 Mpc) source where UHECR events are clustering (15-20%). Virgo events are absent. We tried to solve these puzzles assuming UHECR as He like nuclei arriving from nerest Universe and maybe even galactic sources. UHECR secondaries at half energy should also crowd along UHECR tail. GZK neutrino may rise by nuclei fragmentation at tens-hundred TeVs in Icecube and few UHE tau neutrino at PeVs in nearest upward Tau airshower in fluorescence Auger-TA telescopes.
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Tuesday – Sep 6, 2011
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14:30 – 16:10 |
Astrophysical Messengers W3
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Parallel Session (Millerzimmer) – Chair:
Hans Klages
14:30
(15' + 5')
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Density imaging of volcanoes with atmospheric muons⇓
slides
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Felix Fehr (LPC Clermont-Ferrand)
A Collaboration between volcanologists, astroparticle- and particle physicists, TOMUVOL, has been formed in 2009 to study tomographic muon imaging of volcanoes with high-resolution tracking detectors.
Presently TOMUVOL is operating a muon telescope based based on Glass Resistive Plate Chambers (GRPCs) at the flank of the Puy de Dôme, an inactive volcanic dome situated in the Massif Central (south-central France).
This contribution presents the geophysical motivations for muon imaging as well as the results after several months of data taking at the Puy de Dôme including measurements of the horizontal muon flux and first radiographic images.
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14:50
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Main results of the PAMELA space experiment after 5 years in orbit⇓
slides
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Marco Ricci (INFN Laboratori Nazionali Frascati)
After five years of data taking in space, the experiment PAMELA is showing very interesting features in cosmic rays, namely in the fluxes of protons, heliums, electrons, that could have significant implications on the production, acceleration and propagation of cosmic rays in the galaxy. In addition, PAMELA measurements of cosmic antiproton and positron fluxes are setting strong constraints to the nature of Dark Matter.
PAMELA is also measuring the radiation environment around the Earth, and has recently discovered an antiproton radiation belt.
The study of particles related to the Solar activity is part of the scientific program of PAMELA too, providing important improvements in the comprehension of the solar modulation mechanisms.
In this talk PAMELA main results will be reviewed.
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15:10
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Restrictions on cosmogenic neutrinos and UHECR from Fermi 3 years data⇓
slides
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Oleg Kalashev (Institute for Nuclear Research RAS)
Ultra-high energy cosmic ray protons accelerated in astrophysical objects produce secondary
electromagnetic cascades during propagation in the cosmic microwave and infrared backgrounds.
Those cascades contribute to the GeV-TeV diffuse photon flux, measured by Fermi LAT experiment.
Recent studies of 3 years of Fermi LAT data have shown that diffuse gamma-ray background at
E>10 GeV is about factor of 2 smaller then original one year data. This affects both models of UHECR
and secondary cosmogenic neutrino fluxes. We show the allowed range of cosmogenic neutrino fluxes
scanning over unknown UHECR parameters such as injected proton maximum energy and power law index,
evolution of sources, systematic shift of UHECR energy scale.
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15:30
(15' + 5')
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The first year IceCube-DeepCore results⇓
slides
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Chang Hyon Ha (Penn State University)
The IceCube Neutrino Observatory includes a tightly spaced inner array in the
deepest ice, called DeepCore, which gives access to low-energy neutrinos
with a sizable surrounding cosmic ray muon veto.
Designed to be sensitive to neutrinos at energies
well below 1 TeV, DeepCore will be used to study diverse physics involving neutrinos,
including Dark Matter, atmospheric neutrinos and their oscillations.
The first year of DeepCore physics data-taking
has been completed, and the performance of
the detector and the first IceCube observation of atmospheric
neutrino-induced cascades are presented.
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15:50
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Recent results of the ANTARES neutrino telescope⇓
slides
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Juan Jose Hernandez-Rey (IFIC-Instituto de Fisica Corpuscular)
The ANTARES deep-sea neutrino telescope, located in the Mediterranean Sea, is sensitive to upgoing neutrinos from potential extraterrestrial sources in the TeV to PeV energy regime. Muon tracks and showers are reconstructed using the recorded arrival time and number of Cherenkov photons detected using an array of photomultipliers distributed along a total of 12 lines anchored to the seabed at a depth of 2475 m. The telescope is operating since 2008. In this contribution, the status of the detector and data taking will be given together with recent physics results on the search for point sources of neutrinos, the indirect search for dark matter and the use of the telescope in conjunction with other astrophysical devices, such as optical, gamma, cosmic ray and gravitational detectors.
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16:50 – 18:30 |
Astrophysical Messengers W4
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Parallel Session (Millerzimmer) – Chair:
Marco Roncadelli
16:50
(15' + 5')
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Neutrino spectra and flavor composition on the Hillas plot⇓
slides
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Walter Winter (Universität Würzburg)
We describe energy-dependent neutrino fluxes and flavor ratios of neutrinos produced in cosmic accelerators over 20x24 orders of magnitude in R and B, which are the parameters of the Hillas plot. For this approach, we use a self-consistent model where neutrinos are produced by photohadronic interactions between protons and synchrotron photons from co-accelerated electrons. We especially emphasize magnetic field and flavor effects in the neutrino production chains, including the most relevant neutrino production modes. We also illustrate how the energy-dependent flavor composition can be used to measure physics beyond the Standard Model, and we demonstrate what regions of the Hillas plane can be best probed by existing data, such as IC-40 or Auger.
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17:10
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Classifying and probing flavor transition mechanisms of astrophysical high energy neutrinos⇓
slides
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Kwang-Chang Lai (Chang Gung University)
The flavor ratio of astrophysical neutrinos observed on
the Earth depends on both the initial flavor ratio at the source and flavor transitions taking place during
propagations of these neutrinos. We propose a model independent parametrization which is very convenient for classifying flavor transition models. A few flavor transition models are employed to test our parametrization. We also demonstrate how one can constrain paprameters of the above parametrization by discriminating flavors in the neutrino telescope.
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17:30
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UHECRs and multiple shock acceleration in active galactic nuclei⇓
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Athina Meli (University of Liege)
Sequences of consecutive mild relativistic oblique shock features, have been theorized and eventually observed in many AGN jets.
Here we use by analogy the Comptonisation effect and we propose a scenario of a single injection of
particles which are accelerated consecutively by several oblique (conical) shocks along the axis of an AGN jet.
We use detailed Monte Carlo simulations calculating particle spectra while monitoring the efficiency of the acceleration. Among other we find that the first shock of a sequence of relativistic conical shocks, establishes a power-law spectrum
with ~ E^-2.7. The following consecutive shocks push the spectrum up in energy to the UHECR energy regime rendering flatter distributions with steep cut-offs by leaving a depletion at low energies.
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17:50
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Estimating the significance of a signal in a multi-dimensional search⇓
slides
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Ofer Vitells (Weizmann Institute of Science)
In experiments that are aimed at detecting astrophysical sources such as neutrino telescopes, one usually performs a search over a continuous parameter space. Correctly estimating the p-value of a given
observation thus requires repeated simulations of the entire search, a procedure that may be
prohibitively expansive in terms of CPU resources. Recent results from the theory of random fields
provide powerful tools which may be used to alleviate this difficulty, in a wide range of applications. We review those results and discuss their implementation, with a detailed example applied for
neutrino point source analysis in the IceCube experiment.
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18:10
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A new interpretation of the high energy atmospheric muon charge ratio⇓
slides
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Maximiliano Sioli (Bologna University and INFN)
Recently new experimental measurements of the atmospheric muon charge ratio have been provided up to 10 TeV in the vertical direction. We present a new way to interpret these data and discuss the relation with the atmospheric neutrino flux in the TeV region.
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Wednesday – Sep 7, 2011
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14:30 – 16:10 |
Astrophysical Messengers W5
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Parallel Session (Millerzimmer) – Chair:
Nepomuk Otte
14:30
(15' + 5')
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Recent results from IceCube on high-energy neutrinos and cosmic rays⇓
slides
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Sebastian Böser (Universität Bonn)
The IceCube observatory with its in-ice detector IceCube and air-shower array IceTop has been completed in January 2011. It now comprises 5484 optical modules and encompasses an instrumented volume of ~1km^3. Already with the data accumulated during construction, a number of important physics results have been achieved, including new limits on high-energy neutrino point sources, transient neutrino sources and the diffuse flux of high-energy neutrinos. Using the abundant muons from atmospheric neutrinos, also anisotropy in the arrival direction of cosmic rays has been observed. From the IceTop array the spectrum of cosmic rays and the composition in the energy region of the knee and above has been measured. I will present these results together with an outlook on possible future extensions.
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14:50
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The KM3NeT project⇓
slides
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Simone Biagi (Bologna University and INFN)
The KM3NeT consortium has been carrying on R&D activities towards the construction of a km3 scale deep sea neutrino telescope to detect high-energy astrophysical neutrinos. It will complement the IceCube detector, already in operation at South Pole, and will have the Galactic center and most of the Galactic plane in its field of view. Recently a technical design report has been published which contains the general description of the KM3NeT deep sea research infrastructure. The KM3NeT research facility will represent also a multidisciplinary marine and Earth science observatory, hosting a network of nodes for long term continuous monitoring of the deep sea environment. The objectives, status and plans of the KM3NeT project will be presented.
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15:10
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Results from high-energy neutrino searches from gamma-ray bursts with IceCube⇓
slides
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Nathan Whitehorn (University of Wisconsin - Madison)
IceCube, a cubic kilometer neutrino detector located in glacial ice at the South Pole, has recently become the first neutrino telescope with a sensitivity below the TeV-PeV neutrino flux predicted from gamma-ray bursts if GRBs are responsible for the observed extragalactic cosmic-ray flux. As these neutrinos are expected on fairly general principles on the assumption of high magnetic fields during cosmic ray acceleration, our results will now begin to directly constrain the possibility of proton acceleration in these sources. New results from searches for this flux using the first 59 strings of IceCube will be presented, as well as implications of this result for cosmic-ray acceleration in GRBs and prospects for the future.
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15:30
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The Askaryan radio array⇓
slides
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Kael Hanson (Universite Libre de Bruxelles)
We are developing an antenna array to be installed in boreholes extending 200 m below the ice surface at the geographic South Pole. ARA will cover a fiducial area of 150 sq. km, chosen to ensure the detection of the flux of neutrinos guaranteed by observations of the GZK cutoff by HiRes and the Pierre Auger Observatory. The first components of ARA were installed during the austral summer of 2010-2011. After three years of operation, the full array sensitivity will exceed that of any other instrument in the 0.1-10 EeV energy range by an order of magnitude. The primary goal of the ARA experiment is to establish the absolute cosmogenic neutrino flux through a modest number of events. This talk will describe the array, its science goals, and give the current status of the project.
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15:50
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GRBs and ultra-high-energy cosmic rays⇓
slides
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Martin Pohl (Universität Potsdam / DESY)
GRBs are a potential source of ultra-high-energy cosmic rays, although reproducing the observed flux at GZK energies requires a relatively efficiency in accelerating and releasing particles. If that were the case, GRBs in the Galaxy should account for intermittent contributions to sub-ankle cosmic-rays. Using a Monte-Carlo method and assuming a source population similar to that of long GRB, we
derive constraints arising from intermittency. It is shown that the
composition and anisotropy at 1e18 eV are difficult to reproduce and require that either the particle mean free path is unusually small of the composition is heavier than suggested by recent Auger data. Therefore, it is highly desirable to reduce the systematic uncertainty in the experimental derivation of the UHECR composition.
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16:50 – 18:30 |
Astrophysical Messengers W6 – Gamma-Rays
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Parallel Session (Millerzimmer) – Chair:
Dieter Horns
16:50
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Highlights from the ARGO-YBJ experiment⇓
slides
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Ivan De Mitri (Università del Salento and INFN)
Very high energy gamma ray astronomy and cosmic ray physics in the 10^12-10^15 eV primary
energy range is among the main scientific goals of ARGO-YBJ.
The detector, located in the Cosmic Ray Observatory of Yangbajing (Tibet, China) at 4300m a.s.l., is a full coverage Extensive Air Shower array consisting of a carpet of Resistive Plate Chambers (RPC) of about 6000m2. The apparatus layout, performance and location ensure a low energy threshold and a full sky coverage for gamma observation, while the hadronic component of the cosmic ray flux can be studied in deep detail in an energy window marked by the transition
from direct to indirect measurements. Important information on hadronic physics at these energies
can also be obtained.
We will report on the main results so far obtained.
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17:10
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The HAWC observatory⇓
slides
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Andreas Tepe (Georgia Institute of Technology)
The High Altitude Water Cherenkov (HAWC) Detector is a new instrument for high energy gamma-ray observation of the sky. HAWC, the successor of Milagro, is currently under construction in Mexico at Sierra Negra at an altitude of 4100m (MSL). Due to its higher altitude, extended surface area and improved design, the sensitivity of HAWC is about 15 times higher than that of Milagro. The main
features of HAWC are its high duty cycle, a wide field of view and a large effective area. HAWC will
study galactic cosmic ray accelerators, active galactic nuclei and the diffuse gamma-ray sky. The large duty cycle and wide field of view make HAWC an ideal detector to the search for transient
sources like GRBs. HAWC\'s two DAQ systems, the main DAQ and the scaler DAQ are well suited for GRB searches.
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17:30
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Cosmic rays, gamma rays and synchrotron radiation from the Milky Way⇓
slides
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Elena Orlando (HEPL/KIPAC Stanford University)
Galactic cosmic rays (CRs), interstellar gamma-ray emission and synchrotron radiation are related topics. CR electrons propagate in the Galaxy and interact with the interstellar medium, producing inverse Compton emission measured in gamma rays and synchrotron emission measured in radio. I present an overview of the latest results with Fermi on the gamma-ray diffuse emission induced by CR protons, nuclei and electrons. I then focus on complementary studies of the synchrotron emission. Relevant observables include spectral indices, their variations and radio maps. We use synchrotron radiation to constrain the low-energy interstellar CR electron spectrum, models of propagation of CRs, and magnetic fields. Surveys over a wide range of radio frequencies are used, including polarization data.
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17:50
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Importance of axion-like particles for very-high-energy astrophysics⇓
slides
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Marco Roncadelli (INFN Pavia)
Many extensions of the Standard Model predict the existence of axion-like particles (ALPs), which are very light spin-zero bosons with a two-photon coupling. We show that photon-ALP oscillations occurring in large-scale magnetic fields can produce harder photon spectra of very-high energy blazars. This effect is detecteble with the CTA and with the HAWC water Cherenkov gamma-ray observatory, and possibly with the currently operating Imaging Atmospheric Cherenkov Telescopes. Moreover, we show that the a new interpretation of the blazars detected so far above 100 GeV arises, according to which the large spread in the values of the observed spectral index is mainly due to the wide spread in the source distances rather than to large variations of their internal physical properties.
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18:10
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Constraints on the intergalactic magnetic field from gamma-ray observations of TeV blazars⇓
slides
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Sergey Ostapchenko (Norwegian University for Science and Technology (NTNU))
We discuss different approaches to infer the properties of the intergalactic magnetic field (IGMF) from gamma-ray observations of blazars. In particular, we investigate constraints on the IGMF properties, resulting from studies of TeV blazars by IACTs and Fermi-LAT and demonstrate
that the non-observation of certain sources by Fermi-LAT indicates that a relatively strong magnetic field fills more than 60% of space, favoring the primordial IGMF origin.
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Thursday – Sep 8, 2011
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14:30 – 16:20 |
Astrophysical Messengers W7 – Gamma-Rays
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Parallel Session (Millerzimmer) – Chair:
Robert Wagner
14:30
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The MAGIC telescopes: performance, results and future perspectives⇓
slides
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Barbara De Lotto (University of Udine & I.N.F.N.)
The MAGIC Cherenkov telescopes are operating in stereoscopic mode since almost two years. The improvements due to the stereoscopic upgrade, an overview on the physics results and the plans for the forthcoming upgrade will be presented.
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14:50
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The Crab pulsar above 100 GeV⇓
slides
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Nepomuk Otte (University of California Santa Cruz)
It has been long thought that gamma-ray emission from pulsars cuts off sharply above a few GeV and that no emission would be observable above 100 GeV. With the VERITAS array of four imaging atmospheric Cherenkov telescopes we conducted a deep observation of the Crab pulsar and detected significant pulsed emission above 100 GeV. We discuss the detection and put it into context with present theoretical interpretation.
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15:05
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Observations of the Crab pulsar above 25 GeV with the MAGIC telescope⇓
slides
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Stefan Klepser (IFAE, Barcelona)
The emission mechanism of pulsars is not fully understood yet, although the discovery of the first pulsar was more than 40 years ago. There were two major theoretical models which explain the pulsation, namely, the Polar Cap model and the Outer Gap model. The detection of the Crab pulsar above 25 GeV by MAGIC in 2008 excluded the Polar Cap model. The exponential cutoff spectra of many gamma-ray pulsars measured by Fermi-LAT since 2008 also excluded the Polar Cap model and supported the Outer Gap model. However, comparison of the energy spectrum of the Crab pulsar in Fermi-LAT energies (100 MeV to a few tens of GeV) and that in MAGIC energies (25 GeV to above100 GeV) revealed that the spectrum does not roll off as fast as the exponential cutoff above 25 GeV but that it extends following a power law, i.e. even Outer Gap model is not valid for the Crab pulsar. Here we would like to present the results of MAGIC observations of the Crab pulsar in the last three years. Observations were performed in two different modes, mono-mode with a threshold of 25 GeV and stereo-mode with a threshold of 50 GeV.
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15:20
(15' + 5')
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Very high energy optical depth of the universe⇓
slides
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Dieter Horns (Universität Hamburg)
At sufficiently large energies, the Universe becomes optically thick due to pair production processes with the background photon field. We have investigated the transition from optically thin to the expected optically thick regime using all available spectral data points from very high energy emitting blazars at red-shifts from 0.004 to 0.536. We have carried out an unbiased search to find the transition under the assumption of a minimum background photon field. Using this guaranteed background radiation field, we have found with 3 st.deviations indications that the Universe appears less opticall thick than expected. We rule out systematic effects related to instruments or data selection by carrying out a mock-analysis on a null-sample of Galactic sources.
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15:40
(15' + 5')
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Prospects for a dark matter annihilation signal towards the Sagittarius dwarf galaxy with ground based Cherenkov telescopes⇓
slides
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Aion Viana (CEA Saclay)
Dwarf galaxies are widely believed to be among the best targets for indirect dark
matter(DM) searches using high-energy gamma rays; and indeed gamma-ray emission from these objects has long been a subject of detailed study for ground-based atmospheric Cherenkov telescopes. Here, we update current exclusion limits obtained on the Sagittarius dwarf galaxy, in light of recent realistic DM halo models. The limits are extrapolated to the sensitivities of future Cherenkov Telescope Arrays. For 200 h of observation time, the sensitivity reaches 10$^{-25}$ cm$^{3}$s$^{-1}$. Possible astrophysical backgrounds from gamma-ray sources are studied. It is shown that the background from millisecond pulsars in a globular cluster contained within Sagittarius may limit the sensitivity to DM annihilation.
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16:00
(15' + 5')
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Searching for primordial black holes with the VERITAS gamma-ray experiment⇓
slides
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Gordana Tešić (McGill University)
VERITAS is an array of four 12 m Cherenkov gamma-ray telescopes located in southern Arizona. It detects very-high-energy (VHE) gamma rays with energies between 100 GeV and 30 TeV, which originate from non-thermal processes in various astrophysical environments. VHE gamma rays could also be produced by evaporating primordial black holes (PBHs). Setting a limit on PBHs is important for cosmology, particle physics and quantum gravity. According to some theoretical models, PBHs evaporate and could produce bursts of VHE gamma rays detectable with VERITAS. We present the results from a search in the VERITAS data sample for evidence of gamma-ray bursts due to evaporating PBHs. A new constraint on the number density of PBHs is derived by comparing the VERITAS data with the model prediction.
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