553 research outputs found
GZK Photons Above 10 EeV
We calculate the flux of "GZK-photons", namely the flux of photons produced
by extragalactic nucleons through the resonant photoproduction of pions, the so
called GZK effect. This flux depends on the UHECR spectrum on Earth, of the
spectrum of nucleons emitted at the sources, which we characterize by its slope
and maximum energy, on the distribution of sources and on the intervening
cosmological backgrounds, in particular the magnetic field and radio
backgrounds. For the first time we calculate the GZK photons produced by
nuclei. We calculate the possible range of the GZK photon fraction of the total
UHECR flux for the AGASA and the HiRes spectra. We find that for nucleons
produced at the sources it could be as large as a few % and as low as 10^{-4}
above 10 EeV. For nuclei produced at the sources the maximum photon fraction is
a factor of 2 to 3 times smaller above 10 EeV but the minimum could be much
smaller than for nucleons. We also comment on cosmogenic neutrino fluxes.Comment: 20 pages, 9 figures (21 panels), iopart.cls and iopart12.clo needed
to typese
Composition of UHECR and the Pierre Auger Observatory Spectrum
We fit the recently published Pierre Auger ultra-high energy cosmic ray
spectrum assuming that either nucleons or nuclei are emitted at the sources. We
consider the simplified cases of pure proton, or pure oxygen, or pure iron
injection. We perform an exhaustive scan in the source evolution factor, the
spectral index, the maximum energy of the source spectrum Z E_{max}, and the
minimum distance to the sources. We show that the Pierre Auger spectrum agrees
with any of the source compositions we assumed. For iron, in particular, there
are two distinct solutions with high and low E_{max} (e.g. 6.4 10^{20} eV and 2
10^{19} eV) respectively which could be distinguished by either a large
fraction or the near absence of proton primaries at the highest energies. We
raise the possibility that an iron dominated injected flux may be in line with
the latest composition measurement from the Pierre Auger Observatory where a
hint of heavy element dominance is seen.Comment: 19 pages, 6 figures (33 panels)- Uses iopart.cls and iopart12.clo- In
version 2: addition of a few sentences and two reference
Calibration of the Logarithmic-Periodic Dipole Antenna (LPDA) Radio Stations at the Pierre Auger Observatory using an Octocopter
An in-situ calibration of a logarithmic periodic dipole antenna with a
frequency coverage of 30 MHz to 80 MHz is performed. Such antennas are part of
a radio station system used for detection of cosmic ray induced air showers at
the Engineering Radio Array of the Pierre Auger Observatory, the so-called
Auger Engineering Radio Array (AERA). The directional and frequency
characteristics of the broadband antenna are investigated using a remotely
piloted aircraft (RPA) carrying a small transmitting antenna. The antenna
sensitivity is described by the vector effective length relating the measured
voltage with the electric-field components perpendicular to the incoming signal
direction. The horizontal and meridional components are determined with an
overall uncertainty of 7.4^{+0.9}_{-0.3} % and 10.3^{+2.8}_{-1.7} %
respectively. The measurement is used to correct a simulated response of the
frequency and directional response of the antenna. In addition, the influence
of the ground conductivity and permittivity on the antenna response is
simulated. Both have a negligible influence given the ground conditions
measured at the detector site. The overall uncertainties of the vector
effective length components result in an uncertainty of 8.8^{+2.1}_{-1.3} % in
the square root of the energy fluence for incoming signal directions with
zenith angles smaller than 60{\deg}.Comment: Published version. Updated online abstract only. Manuscript is
unchanged with respect to v2. 39 pages, 15 figures, 2 table
Multi-resolution anisotropy studies of ultrahigh-energy cosmic rays detected at the Pierre Auger Observatory
We report a multi-resolution search for anisotropies in the arrival
directions of cosmic rays detected at the Pierre Auger Observatory with local
zenith angles up to and energies in excess of 4 EeV ( eV). This search is conducted by measuring the angular power spectrum
and performing a needlet wavelet analysis in two independent energy ranges.
Both analyses are complementary since the angular power spectrum achieves a
better performance in identifying large-scale patterns while the needlet
wavelet analysis, considering the parameters used in this work, presents a
higher efficiency in detecting smaller-scale anisotropies, potentially
providing directional information on any observed anisotropies. No deviation
from isotropy is observed on any angular scale in the energy range between 4
and 8 EeV. Above 8 EeV, an indication for a dipole moment is captured; while no
other deviation from isotropy is observed for moments beyond the dipole one.
The corresponding -values obtained after accounting for searches blindly
performed at several angular scales, are in the case of
the angular power spectrum, and in the case of the needlet
analysis. While these results are consistent with previous reports making use
of the same data set, they provide extensions of the previous works through the
thorough scans of the angular scales.Comment: Published version. Added journal reference and DOI. Added Report
Numbe
Ultrahigh-energy neutrino follow-up of Gravitational Wave events GW150914 and GW151226 with the Pierre Auger Observatory
On September 14, 2015 the Advanced LIGO detectors observed their first
gravitational-wave (GW) transient GW150914. This was followed by a second GW
event observed on December 26, 2015. Both events were inferred to have arisen
from the merger of black holes in binary systems. Such a system may emit
neutrinos if there are magnetic fields and disk debris remaining from the
formation of the two black holes. With the surface detector array of the Pierre
Auger Observatory we can search for neutrinos with energy above 100 PeV from
point-like sources across the sky with equatorial declination from about -65
deg. to +60 deg., and in particular from a fraction of the 90% confidence-level
(CL) inferred positions in the sky of GW150914 and GW151226. A targeted search
for highly-inclined extensive air showers, produced either by interactions of
downward-going neutrinos of all flavors in the atmosphere or by the decays of
tau leptons originating from tau-neutrino interactions in the Earth's crust
(Earth-skimming neutrinos), yielded no candidates in the Auger data collected
within s around or 1 day after the coordinated universal time (UTC)
of GW150914 and GW151226, as well as in the same search periods relative to the
UTC time of the GW candidate event LVT151012. From the non-observation we
constrain the amount of energy radiated in ultrahigh-energy neutrinos from such
remarkable events.Comment: Published version. Added journal reference and DOI. Added Report
Numbe
Azimuthal asymmetry in the risetime of the surface detector signals of the Pierre Auger Observatory
The azimuthal asymmetry in the risetime of signals in Auger surface detector
stations is a source of information on shower development. The azimuthal
asymmetry is due to a combination of the longitudinal evolution of the shower
and geometrical effects related to the angles of incidence of the particles
into the detectors. The magnitude of the effect depends upon the zenith angle
and state of development of the shower and thus provides a novel observable,
, sensitive to the mass composition of cosmic rays
above eV. By comparing measurements with predictions from
shower simulations, we find for both of our adopted models of hadronic physics
(QGSJETII-04 and EPOS-LHC) an indication that the mean cosmic-ray mass
increases slowly with energy, as has been inferred from other studies. However,
the mass estimates are dependent on the shower model and on the range of
distance from the shower core selected. Thus the method has uncovered further
deficiencies in our understanding of shower modelling that must be resolved
before the mass composition can be inferred from .Comment: Replaced with published version. Added journal reference and DO
LSST: from Science Drivers to Reference Design and Anticipated Data Products
(Abridged) We describe here the most ambitious survey currently planned in
the optical, the Large Synoptic Survey Telescope (LSST). A vast array of
science will be enabled by a single wide-deep-fast sky survey, and LSST will
have unique survey capability in the faint time domain. The LSST design is
driven by four main science themes: probing dark energy and dark matter, taking
an inventory of the Solar System, exploring the transient optical sky, and
mapping the Milky Way. LSST will be a wide-field ground-based system sited at
Cerro Pach\'{o}n in northern Chile. The telescope will have an 8.4 m (6.5 m
effective) primary mirror, a 9.6 deg field of view, and a 3.2 Gigapixel
camera. The standard observing sequence will consist of pairs of 15-second
exposures in a given field, with two such visits in each pointing in a given
night. With these repeats, the LSST system is capable of imaging about 10,000
square degrees of sky in a single filter in three nights. The typical 5
point-source depth in a single visit in will be (AB). The
project is in the construction phase and will begin regular survey operations
by 2022. The survey area will be contained within 30,000 deg with
, and will be imaged multiple times in six bands, ,
covering the wavelength range 320--1050 nm. About 90\% of the observing time
will be devoted to a deep-wide-fast survey mode which will uniformly observe a
18,000 deg region about 800 times (summed over all six bands) during the
anticipated 10 years of operations, and yield a coadded map to . The
remaining 10\% of the observing time will be allocated to projects such as a
Very Deep and Fast time domain survey. The goal is to make LSST data products,
including a relational database of about 32 trillion observations of 40 billion
objects, available to the public and scientists around the world.Comment: 57 pages, 32 color figures, version with high-resolution figures
available from https://www.lsst.org/overvie
Anisotropy studies around the galactic centre at EeV energies with the Auger Observatory
Data from the Pierre Auger Observatory are analyzed to search for
anisotropies near the direction of the Galactic Centre at EeV energies. The
exposure of the surface array in this part of the sky is already significantly
larger than that of the fore-runner experiments. Our results do not support
previous findings of localized excesses in the AGASA and SUGAR data. We set an
upper bound on a point-like flux of cosmic rays arriving from the Galactic
Centre which excludes several scenarios predicting sources of EeV neutrons from
Sagittarius . Also the events detected simultaneously by the surface and
fluorescence detectors (the `hybrid' data set), which have better pointing
accuracy but are less numerous than those of the surface array alone, do not
show any significant localized excess from this direction.Comment: Matches published versio
Evidence for a mixed mass composition at the `ankle' in the cosmic-ray spectrum
We report a first measurement for ultra-high energy cosmic rays of the
correlation between the depth of shower maximum and the signal in the water
Cherenkov stations of air-showers registered simultaneously by the fluorescence
and the surface detectors of the Pierre Auger Observatory. Such a correlation
measurement is a unique feature of a hybrid air-shower observatory with
sensitivity to both the electromagnetic and muonic components. It allows an
accurate determination of the spread of primary masses in the cosmic-ray flux.
Up till now, constraints on the spread of primary masses have been dominated by
systematic uncertainties. The present correlation measurement is not affected
by systematics in the measurement of the depth of shower maximum or the signal
in the water Cherenkov stations. The analysis relies on general characteristics
of air showers and is thus robust also with respect to uncertainties in
hadronic event generators. The observed correlation in the energy range around
the `ankle' at differs significantly from
expectations for pure primary cosmic-ray compositions. A light composition made
up of proton and helium only is equally inconsistent with observations. The
data are explained well by a mixed composition including nuclei with mass . Scenarios such as the proton dip model, with almost pure compositions, are
thus disfavoured as the sole explanation of the ultrahigh-energy cosmic-ray
flux at Earth.Comment: Published version. Added journal reference and DOI. Added Report
Numbe
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