We report on the measurement of coherent radio emission from the electron beam sudden appearance at the Telescope Array Electron Light Source facility. This emission was detected by four independent ...radio detector setups sensitive to frequencies ranging from 50 MHz up to 12.5 GHz. We show that this phenomenon can be understood as a special case of coherent transition radiation by comparing the observed results with simulations. The in-nature application of this signal is given by the emission of cosmic ray or neutrino induced particle cascades traversing different media such as air, rock and ice.
We report on the development status of a single-photon sensor that employs wavelength-shifting and light-guiding techniques to maximize the collection area while minimizing the dark noise rate. The ...sensor is tailored towards application in ice-Cherenkov neutrino detectors embedded in inert and cold, low-radioactivity and UV transparent ice as a detection medium, such as IceCube-Gen2 or MICA. The goal is to decrease the energy threshold as well as to increase the energy resolution and the vetoing capability of the neutrino telescope, when compared to a setup with optical sensors similar to those used in IceCube. The proposed sensor captures photons with wavelengths between 250 nm and 400 nm. These photons are re-emitted with wavelengths above 400 nm by a wavelength shifting coating applied to a 90 mm diameter polymer tube. The tube guides the light towards a small-diameter PMT via total internal reflection. By scaling the results from smaller laboratory prototypes, the total efficiency of the proposed detector for a Cherenkov spectrum is estimated to exceed that of a standard IceCube optical module. The status of the prototype development and the performance of its main components will be discussed.
The High Altitude Water Cherenkov (HAWC) Observatory is a wide-field-of-view gamma-ray observatory that is optimized to detect gamma rays between 300 GeV and several hundred TeV. The HAWC ...Collaboration recently released their third source catalog (3HWC), which contains 65 sources. One of these sources, the ultra-high-energy gamma-ray source 3HWC J1908+063, may exhibit a hardening of the spectral index at the highest energies (above 56 TeV). At least two populations of particles are needed to satisfactorily explain the highest energy emission. This second component could be leptonic or hadronic in origin. If it is hadronic in origin, it would imply the presence of protons with energies up to ~1 PeV near the source. We have searched other 3HWC sources for the presence of this spectral hardening feature. If observed, this would imply that the sources could make good PeVatron candidates.
The Ultra-High-Energy Source MGRO J1908+06 Malone, Kelly; Abeysekara, Anushka Udara; Albert, Andrea ...
Pos : proceedings of science,
07/2021, Letnik:
395
Journal Article
Recenzirano
Odprti dostop
The TeV gamma-ray source MGRO J1908+06 is one of the highest-energy sources known, with observed emission by the High Altitude Water Cherenkov (HAWC) Observatory extending well past 100 TeV. The ...source exhibits both energy-dependent morphology and a spatially-dependent spectral index. The emission is likely to be dominantly leptonic, and associated with the radio-quiet PSR J1907+0602. However, one-population models do not describe the data well; a second particle population is needed to explain the shape of the spectral energy distribution at the highest energies. This component can be well-described by either leptonic or hadronic hypotheses. We discuss this feature and implications for detection by multi-wavelength and multi-messenger experiments.
Abstract
We recently reported on the radio-frequency attenuation length of cold polar ice at Summit Station, Greenland, based on bi-static radar measurements of radio-frequency bedrock echo strengths ...taken during the summer of 2021. Those data also allow studies of (a) the relative contributions of coherent (such as discrete internal conducting layers with sub-centimeter transverse scale) vs incoherent (e.g. bulk volumetric) scattering, (b) the magnitude of internal layer reflection coefficients, (c) limits on signal propagation velocity asymmetries (‘birefringence’) and (d) limits on signal dispersion in-ice over a bandwidth of ~100 MHz. We find that (1) attenuation lengths approach 1 km in our band, (2) after averaging 10 000 echo triggers, reflected signals observable over the thermal floor (to depths of ~1500 m) are consistent with being entirely coherent, (3) internal layer reflectivities are ≈–60
$\to$
–70 dB, (4) birefringent effects for vertically propagating signals are smaller by an order of magnitude relative to South Pole and (5) within our experimental limits, glacial ice is non-dispersive over the frequency band relevant for neutrino detection experiments.
The fields of cosmic ray astrophysics, gamma-ray astrophysics, and neutrino astrophysics have diverged somewhat. But for the air showers in the GeV and TeV energy ranges, the ground-based detector ...techniques have considerable overlaps. VHE gamma-ray astronomy is the observational study measuring the directions, flux, energy spectra, and time variability of the sources of these gamma rays. With the low flux of gamma rays, and the background of charged particle cosmic rays, the distinguishing characteristic of gamma-ray air shower detectors is large size and significant photon to charge particle discrimination. Air shower telescopes for gamma-ray astronomy consist of an array of detectors capable of measuring the passage of particles through the array elements. To maximize signal at energies of a TeV or so, the array needs to be built at high altitude as the maximum number of shower particles is high in the atmosphere. These detectors have included sparse arrays of shower counters, dense arrays of scintillators or resistive plate counters (RPC), buried muon detectors in concert with surface detectors, or many-interaction-deep Water Cherenkov Detectors (WCD). In general these detectors are sensitive over a large field of view, the whole of the sky is a typical sensitivity and perhaps 2/3 of the sky selected for clean analysis, but with only moderate resolution in energy, typically due to shower-to-shower fluctuations and the intrinsic sampling of the detector. These telescopes though, operate continuously, despite weather, moonlight, day or night, and without needing to be pointed to a specific target for essentially a 100\% duty cycle. In this chapter we will examine the performance and characteristics of such detectors. These are contrasted with the Imaging Air Cherenkov Telescopes which also operate in this energy range, and both current and future proposed experiments are described.
Galactic cosmic rays consist of primary and secondary particles. Primary cosmic rays are thought to be energized by first order Fermi acceleration processes at supernova shock fronts within our ...Galaxy. The cosmic rays that eventually reach the Earth from this source are mainly protons and atomic nuclei, but also include electrons. Secondary cosmic rays are created in collisions of primary particles with the diffuse interstellar gas. They are relatively rare but carry important information on the Galactic propagation of the primary particles. The secondary component includes a small fraction of antimatter particles, positrons and antiprotons. In addition, positrons and antiprotons may also come from unusual sources and possibly provide insight into new physics. For instance, the annihilation of heavy supersymmetric dark matter particles within the Galactic halo could lead to positrons or antiprotons with distinctive energy signatures. With the High-Energy Antimatter Telescope (HEAT) balloon-borne instrument, we have measured the abundances of positrons and electrons at energies between 1 and 50 GeV. The data suggest that indeed a small additional antimatter component may be present that cannot be explained by a purely secondary production mechanism. Here we describe the signature of the effect and discuss its possible origin.
The High-Altitude Water Cherenkov (HAWC) observatory in central Mexico is currently the world's only synoptic survey instrument for gamma rays above 1 TeV. Because there is significant interest in ...covering the full TeV sky with a survey instrument, we have examined options for a Southern Hemisphere extension to HAWC. In addition to providing all-sky coverage of TeV sources, a southern site could complement existing surveys of the densest part of the Galactic Plane, provide continuous monitoring of Galactic and extragalactic transient sources in both Hemispheres, and simplify the analysis of spatially extended signals such as diffuse gamma rays and the TeV cosmic-ray anisotropy. To take advantage of the air-shower physics and lower the energy threshold of the experiment as much as possible, a high altitude site above 5000 m a.s.l (vs. 4100 m a.s.l. at the current site in Mexico) has been specified. To facilitate efficient detector construction at such altitudes, the detector tanks would be assembled at lower altitude and delivered to the site. An all-digital communications and data acquisition scheme is proposed. Possible designs include taking advantage of digital optical module technology from the IceCube experiment as well as new custom electronics. We discuss the physics potential of such an experiment, focusing on the energy threshold, angular resolution, and background suppression capability of the experiment, as well as the advantages of full-sky coverage above 1 TeV.
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