56239300
An air shower array for LOFAR: LORA
LOFAR is a new form of radio telescope which can detect radio emission from air showers induced by very high-energy cosmic rays. It can also look for radio emission from particle cascades on the Moon induced by ultra high-energy cosmic rays or neutrinos. To complement the radio detection, we are setting up a small particle detector array LORA (LOfar Radboud Air shower array) within an area of ~300 m diameter in the LOFAR core. It will help in triggering and confirming the radio detection of air showers with the LOFAR antennas. In this paper, we present a short overview about LORA and discuss its current status.
18536439
The directional dependence of the lunar Cherenkov technique for UHE neutrino detection
The LUNASKA (Lunar UHE Neutrino Astrophysics with the Square Kilometre Array) project is a theoretical and experimental project developing the lunar Cherenkov technique for the next generation of giant radio-telescope arrays. This contribution presents our simulation results on the directional dependence of the technique for UHE neutrino detection. In particular, these indicate that both the instantaneous sensitivities and time-integrated limits from lunar Cherenkov experiments such as those at Parkes, Goldstone, Kalyazin and ATCA are highly anisotropic. We study the regions of the sky which have not been probed by either these or other experiments, and present the expected sky coverage of future experiments with the SKA. Our results show how the sensitivity of lunar Cherenkov observations to potential astrophysical sources of UHE particles may be maximised by choosing appropriate observation dates and antenna-beam pointing positions.
119255444
Full Monte Carlo simulations of radio emission from extensive air showers with CoREAS
CoREAS is a Monte Carlo simulation code for the calculation of radio emission from extensive air showers. It is based on the "endpoint formalism" for radiation from moving charges implemented directly in CORSIKA. Consequently, the full complexity of the air-shower physics is taken into account without the need for approximations or assumptions on the emission mechanism. We present results of simulations for an unthinned shower performed with CoREAS for both MHz and GHz frequencies. At MHz frequencies, the simulations predict the well-known mixture of geomagnetic and charge excess radiation. At GHz frequencies, the emission is strongly influenced by Cherenkov effects arising from the varying refractive index in the atmosphere. In addition, a qualitative difference in the symmetry of the GHz radiation pattern is observed when compared to the ones at lower frequencies. We also discuss the strong increase in the ground area subtended by the radio emission when going from near-vertical to very inclined geometries, making very inclined air showers the most promising ones for cosmic ray radio detection.
12471534
General description of electromagnetic radiation processes based on instantaneous charge acceleration in "endpoints".
We present a methodology for calculating the electromagnetic radiation from accelerated charged particles. Our formulation-the "endpoint formulation"-combines numerous results developed in the literature in relation to radiation arising from particle acceleration using a complete, and completely general, treatment. We do this by describing particle motion via a series of discrete, instantaneous acceleration events, or "endpoints," with each such event being treated as a source of emission. This method implicitly allows for particle creation and destruction, and is suited to direct numerical implementation in either the time or frequency domains. In this paper we demonstrate the complete generality of our method for calculating the radiated field from charged particle acceleration, and show how it reduces to the classical named radiation processes such as synchrotron, Tamm's description of Vavilov-Cherenkov, and transition radiation under appropriate limits. Using this formulation, we are immediately able to answer outstanding questions regarding the phenomenology of radio emission from ultra-high-energy particle interactions in both the earth's atmosphere and the moon. In particular, our formulation makes it apparent that the dominant emission component of the Askaryan effect (coherent radio-wave radiation from high-energy particle cascades in dense media) comes from coherent "bremsstrahlung" from particle acceleration, rather than coherent Vavilov-Cherenkov radiation.
31685649
SEARCHES FOR POINT-LIKE AND EXTENDED NEUTRINO SOURCES CLOSE TO THE GALACTIC CENTER USING THE ANTARES NEUTRINO TELESCOPE
A search for cosmic neutrino sources using six years of data collected by the ANTARES neutrino telescope has been performed. Clusters of muon neutrinos over the expected atmospheric background have been looked for. No clear signal has been found. The most signal-like accumulation of events is located at equatorial coordinates RA=$-$46.8$^{\circ}$ and Dec=$-$64.9$^{\circ}$ and corresponds to a 2.2$\sigma$ background fluctuation. In addition, upper limits on the flux normalization of an E$^{-2}$ muon neutrino energy spectrum have been set for 50 pre-selected astrophysical objects. Finally, motivated by an accumulation of 7 events relatively close to the Galactic Centre in the recently reported neutrino sample of the IceCube telescope, a search for point sources in a broad region around this accumulation has been carried out. No indication of a neutrino signal has been found in the ANTARES data and upper limits on the flux normalization of an E$^{-2}$ energy spectrum of neutrinos from point sources in that region have been set. The 90% confidence level upper limits on the muon neutrino flux normalization vary between 3.5 and 5.1$\times$10$^{-8}$ GeV$\,$cm$^{-2}$s$^{-1}$, depending on the exact location of the source.
122673987
Coherent Cherenkov radio emission from EeV showers in dense media through thinned simulations
Abstract We explore the feasibility of applying “thinning techniques” to the simulation of EeV electromagnetic showers in ice, salt, and the regolith of the Moon. By comparing the results of thinned showers to full simulations, we show that thinning techniques keep a good level of accuracy in the relevant shower and radio observables, and allow a considerable reduction in computing time. We apply thinning techniques to the simulation of EeV electromagnetic showers including the Landau–Pomeranchuk–Migdal effect. Our study is of the utmost importance for the determination of the sensitivity to extremely energetic neutrinos of experiments looking for radiopulses in dense media.
31097656
Very Early Optical Afterglows of Gamma-Ray Bursts: Evidence for Relative Paucity of Detection
Very early observations with the Swift satellite of γ-ray burst (GRB) afterglows reveal that the optical component is not detected in a large number of cases. This is in contrast to the bright optical flashes previously discovered in some GRBs (e.g., GRB 990123 and GRB 021211). Comparisons of the X-ray afterglow flux to the optical afterglow flux and prompt γ-ray fluence is used to quantify the seemingly deficient optical, and in some cases X-ray, light at these early epochs. This comparison reveals that some of these bursts appear to have higher than normal γ-ray efficiencies. We discuss possible mechanisms and their feasibility for explaining the apparent lack of early optical emission. The mechanisms considered include, foreground extinction, circumburst absorption, Lyα blanketing and absorption due to high-redshift, low-density environments, rapid temporal decay, and intrinsic weakness of the reverse shock. Of these, foreground extinction, circumburst absorption, and high redshift provide the best explanations for most of the nondetections in our sample. There is tentative evidence of suppression of the strong reverse shock emission. This could be because of a Poynting flux-dominated flow or a pure nonrelativistic hydrodynamic reverse shock.
118186858
Experimental status of weak radiative decays
A summary of data for the weak radiative decays of hyperons (baryon{r arrow}baryon+photon) is presented. Branching ratios and asymmetry parameters are given. Comparison with theoretical models is given. (AIP)
118376389
The Carina Project. IV. Radial Velocity Distribution
We present new and accurate radial velocity (RV) measurements of luminous stars of all ages (old horizontal branch, intermediate-age red clump, and young blue plume, as well as red giants of a range of ages: 20.6 ≤ V ≤ 22) in the Carina dwarf spheroidal galaxy, based on low-resolution spectra collected with the FORS2 multiobject slit spectrograph at the VLT. This data set was complemented by RV measurements based on medium- and high-resolution archive spectra of brighter (V 20.6) Carina targets collected with the GIRAFFE multiobject fiber spectrograph at the VLT. The combined sample includes more than 21,340 individual spectra of ≈2000 stars covering the entire body of the galaxy. The mean (RV = 220.4 ± 0.1 km s-1) and the dispersion (σ = 11.7 ± 0.1 km s-1) of the RV distribution of candidate Carina stars (~1210 objects, 180 ≤ RV ≤ 260 km s-1, 4σ) agree quite well with similar measurements available in the literature. To further improve the statistics, the accurate RV measurements recently provided by Walker et al. were also added to the current data set. We ended up with a sample of ~1370 RV measurements of candidate Carina stars that is ≈75% larger than any previous Carina RV sample. We found that the hypothesis that the Carina RV distribution is Gaussian can be discarded at 99% confidence level. The mean RV across the body of the galaxy varies from ~220 km s-1 at a distance of 7' (~200 pc) from the center to ~223 km s-1 at 13' (~400 pc, 6σ level) and flattens out to a constant value of ~221 km s-1 at larger distances (600 pc, 4σ level). Moreover, and even more importantly, we found that in the Carina regions where the mean RV is smaller, the dispersion is also smaller, and the RV distribution is more centrally peaked (i.e., the kurtosis attains larger values). The difference in mean RV is more than 4 km s-1 (9σ level) when moving from east to west and more than 3 km s-1 (~7σ level) when moving from north to south. The RV gradient appears to be in the direction of the Carina proper motion. However, this parameter is affected by large uncertainties to reach a firm conclusion. There is evidence of a secondary maximum in RV across the Carina center (|D| ≤ 200 pc). The occurrence of a secondary feature across the Carina center is also supported by the flat-topped radial distribution based on the photometric catalog. These findings are reminiscent of a substructure with transition properties that are already detected in dwarf ellipticals, and they call for confirmation by independent investigations.
53048052
TANAMI Blazars in the IceCube PeV Neutrino Fields
ABSTRACT The IceCube Collaboration has announced the discovery of a neutrino ﬂux in excess of the atmospheric background. Due to thesteeply falling atmospheric background spectrum, events at PeV energies are most likely of extraterrestrial origin. We present themultiwavelength properties of the six radio brightest blazars positionally coincident with these events using contemporaneous data ofthe TANAMI blazar sample, including high-resolution images and spectral energy distributions. Assuming the X-ray to -ray emissionoriginates in the photoproduction of pions by accelerated protons, the integrated predicted neutrino luminosity of these sources is largeenough to explain the two detected PeV events. Key words. neutrinos – galaxies: active – quasars: general 1. Introduction The detection of neutrinos at PeV energies in excess of the at-mospheric background reported by the IceCube Collaboration(Aartsen et al. 2013; IceCube Collaboration 2013) has prompteda quest to identify their extraterrestrial sources. The two eventswith PeV energies (event 20, dubbed ‘Ernie’ and event 14,‘Bert’, hereafter E20 and E14), detected between May 2010 andMay 2012
7763998
Swift UVOT detection of GRB 050318
We present observations of GRB 050318 by the Ultraviolet/Optical Telescope (UVOT) on board the Swift observatory. The data are the first detections of a gamma-ray burst (GRB) afterglow decay by the UVOT instrument, launched specifically to open a new window on these transient sources. We showcase UVOT's ability to provide multicolor photometry and the advantages of combining UVOT data with simultaneous and contemporaneous observations from the high-energy detectors on the Swift spacecraft. Multiple filters covering 1800-6000 A reveal a red source with a spectral slope steeper than the simultaneous X-ray continuum. Spectral fits indicate that the UVOT colors are consistent with dust extinction by systems at z = 1.2037 and 1.4436, redshifts where absorption systems have been preidentified. However, the data can be most easily reproduced with models containing a foreground system of neutral gas redshifted by z = 2.8 ± 0.3. For both of the above scenarios, spectral and decay slopes are, for the most part, consistent with fireball expansion into a uniform medium, provided a cooling break occurs between the energy ranges of the UVOT and Swift's X-ray instrumentation.