Abstract
The detection of inclined air showers (zenith angles
θ
≳ 65°) with kilometer-spaced radio-antenna arrays allows measuring cosmic rays at ultra-high energies (
E
≲ 10
20
eV). Radio and ...particle detector arrays provide independent measurements of the electromagnetic and muonic shower components of inclined air showers, respectively. Combined, these measurements have a large sensitivity to discriminate between air showers initiated by lighter and heavier cosmic rays.
We have developed a precise model of the two-dimensional, highly complex and asymmetric lateral radio-signal distributions of inclined air shower at ground — the “radio-emission footprints”. Our model explicitly describes the dominant geomagnetic emission with a rotationally symmetric lateral distribution function, on top of which additional effects disturb the symmetry. The asymmetries are associated with the interference between the geomagnetic and sub-dominant charge-excess emission as well as with geometrical projection effects, so-called “early-late” effects. Our fully analytic model describes the entire footprint with only two observables: the geometrical distance between the shower impact point at the ground and the shower maximum
d
max
, and the geomagnetic radiation energy
E
geo
. We demonstrate that with this model, the electromagnetic shower energy can be reconstructed by kilometer-spaced antenna arrays with an intrinsic resolution of 5% and a negligible bias.
Context.
Arrays of radio antennas have proven to be successful in astroparticle physics with the observation of extensive air showers initiated by high-energy cosmic rays in the Earth’s atmosphere. ...Accurate determination of the energy scale of the primary particles’ energies requires an absolute calibration of the radio antennas for which, in recent years, the utilization of the Galactic emission as a reference source has emerged as a potential standard.
Aims.
To apply the “Galactic calibration” a proper estimation of the systematic uncertainties on the prediction of the Galactic emission from sky models is necessary, which we aim to quantify on a global level and for the specific cases of selected radio arrays. We further aim to determine the influence of additional natural radio sources on the Galactic calibration.
Methods.
We compared seven different sky models that predict the full-sky Galactic emission in the frequency range from 30 to 408 MHz. We made an inventory of the reference maps on which they rely and used the output of the models to determine their global level of agreement. We subsequently took typical sky exposures and the frequency bands of selected radio arrays into account and repeated the comparison for each of them. Finally, we studied and discuss the relative influence of the quiet Sun, the ionosphere, and Jupiter.
Results.
We find a systematic uncertainty of 14.3% on the predicted power from the Galactic emission, which scales to approximately half of that value as the uncertainty on the determination of the energy of cosmic particles. When looking at the selected radio arrays, the uncertainty on the predicted power varies between 11.7% and 21.5%. The influence of the quiet Sun turns out to be insignificant at the lowest frequencies but increases to a relative contribution of ~30% around 400 MHz.
Radio detection of cosmic rays in the Pierre Auger Observatory Huege, T.
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
05/2010, Letnik:
617, Številka:
1
Journal Article
Recenzirano
Odprti dostop
In small-scale experiments such as CODALEMA and LOPES, radio detection of cosmic rays has demonstrated its potential as a technique for cosmic ray measurements up to the highest energies. Radio ...detection promises measurements with high duty-cycle, allows a direction reconstruction with very good angular resolution, and provides complementary information on energy and nature of the cosmic ray primaries with respect to particle detectors at ground and fluorescence telescopes. Within the Pierre Auger Observatory, we tackle the technological and scientific challenges for an application of the radio detection technique on large scales. Here, we report on the results obtained so far using the Southern Auger site and the plans for an engineering array of radio detectors covering an area of
∼
20
km
2
.
In recent years, the freely available Monte Carlo code REAS for modelling radio emission from cosmic ray air showers has evolved to include the full complexity of air shower physics. However, it ...turned out that in REAS2 and all other time-domain models which calculate the radio emission by superposing the radiation of the single air shower electrons and positrons, the calculation of the emission contributions was not fully consistent. In this article, we present a revised implementation in REAS3, which incorporates the missing radio emission due to the variation of the number of charged particles during the air shower evolution using an “end-point formalism”. With the inclusion of these emission contributions, the structure of the simulated radio pulses changes from unipolar to bipolar, and the azimuthal emission pattern becomes nearly symmetric. Remaining asymmetries can be explained by radio emission due to the variation of the net charge excess in air showers, which is automatically taken into account in the new implementation. REAS3 constitutes the first self-consistent time-domain implementation based on single particle emission taking the full complexity of air shower physics into account, and is freely available for all interested users.
Interferometric measurements with arrays of radio antennas are a powerful and widely used technique in astronomy. Recently, this technique has been revisited for the reconstruction of extensive air ...showers 1. This “radio-interferometric technique” exploits the coherence in the radio emission emitted by billions of secondary shower particles to reconstruct the shower parameters, in particular the shower axis and depth of the shower maximum X max. The accuracy previously demonstrated on simulations with an idealized detector is very promising. The prospect of an accurate X max measurement for inclined air showers combined with measurements of the electromagnetic energy (also with radio antennas) and the muonic shower content (via ground particle detectors) is very intriguing as it would provide a high sensitivity to the mass of cosmic rays, key information to study their origin. In this article we evaluate the potential of interferometric X max measurements using (simulated) inclined air showers with sparse antenna arrays under realistic conditions. To determine prerequisites for the application of the radio-interferometric technique with various antenna arrays, the influence of inaccuracies in the time synchronisation between antennas and its inter-dependency with the antenna density is investigated in detail. We find a strong correlation between the antenna multiplicity (per event) and the maximum acceptable time jitter, i.e., inaccuracy in the time synchronisation. For data recorded with a time synchronisation accurate to within 1 ns in the commonly used frequency band of 30 MHz to 80 MHz, an antenna multiplicity of >50 is needed to achieve an X max resolution of \({\sigma }_{{X}_{\mathrm{max}}}\lesssim 20\) g cm−2. For data recorded with 2 ns accuracy, already ≳ 200 antennas are needed to achieve this X max resolution. Furthermore, we find no advantage reconstructing X max from data simulated at higher observation frequencies, i.e., up to several hundred MHz. Finally, we provide a generalisation of our results from very inclined air showers to vertical geometries.
The South Pole, which hosts the IceCube Neutrino Observatory, has a complete and around-the-clock exposure to the Galactic Center. Hence, it is an ideal location to search for gamma rays of PeV ...energy coming from the Galactic Center. However, it is hard to detect air showers initiated by these gamma rays using cosmic-ray particle detectors due to the low elevation of the Galactic Center. The use of antennas to measure the radio footprint of these air showers will help in this case, and would allow for a 24/7 operation time. So far, only air showers with energies well above
10
16
eV have been detected with the radio technique. Thus, the energy threshold has to be lowered for the detection of gamma-ray showers of PeV energy. This can be achieved by optimizing the frequency band in order to obtain a higher level of signal-to-noise ratio. With such an approach, PeV gamma-ray showers with high inclination can be measured at the South Pole.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Ultra-high-energy (UHE) cosmic neutrinos interacting with the Moon’s regolith generate particle showers that emit Askaryan radiation. This radiation can be observed from the Earth using ground-based ...radio telescopes like LOFAR. We simulate the effective detection aperture for UHE neutrinos hitting the Moon. Under the same assumptions, results from this work are in good agreement with previous analytic parameterizations and Monte Carlo codes. The dependence of the effective detection aperture on the observing parameters, such as observing frequency and minimum detection threshold, and lunar characteristics like surface topography have been studied. Using a Monte Carlo simulation, we find that the detectable neutrino energy threshold is lowered when we include a realistic treatment of the inelasticity, transmission coefficient, and surface roughness. Lunar surface roughness at large scales enhances the total aperture for higher observation frequencies (
ν
≥
1
GHz
) but has no significant effect on the LOFAR aperture. However, roughness at scales small compared to the wavelength reduces the aperture at all frequencies.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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