114 research outputs found
Propagation of Ultra-High-Energy Cosmic Ray Nuclei in Cosmic Magnetic Fields and Implications for Anisotropy Measurements
(Abridged) Recent results from the Pierre Auger Observatory (PAO) indicate
that the composition of ultra-high-energy cosmic rays (UHECRs) with energies
above eV may be dominated by heavy nuclei. An important question is
whether the distribution of arrival directions for such UHECR nuclei can
exhibit observable anisotropy or positional correlations with their
astrophysical source objects despite the expected strong deflections by
intervening magnetic fields. For this purpose, we have simulated the
propagation of UHECR nuclei including models for both the extragalactic
magnetic field and the Galactic magnetic field. Assuming that only iron nuclei
are injected steadily from sources with equal luminosity and spatially
distributed according to the observed large scale structure in the local
Universe, at the number of events published by the PAO so far, the arrival
distribution of UHECRs would be consistent with no auto-correlation at 95%
confidence if the mean number density of UHECR sources
Mpc, and consistent with no cross-correlation with sources within 95%
errors for Mpc. On the other hand, with 1000 events
above eV in the whole sky, next generation experiments can
reveal auto-correlation with more than 99% probability even for Mpc, and cross-correlation with sources with more than 99%
probability for Mpc. In addition, we find that the
contribution of Centaurus A is required to reproduce the currently observed
UHECR excess in the Centaurus region. Secondary protons generated by
photodisintegration of primary heavy nuclei during propagation play a crucial
role in all cases, and the resulting anisotropy at small angular scales should
provide a strong hint of the source location if the maximum energies of the
heavy nuclei are sufficiently high.Comment: 17 pages, 15 figure
INTERGALACTIC MAGNETIC FIELD AND ARRIVAL DIRECTION OF ULTRA-HIGH-ENERGY PROTONS
We studied how the intergalactic magnetic field (IGMF) affects the propagation of super-Greisen-Zatsepin-Kuz'min (GZK) protons that originate from extragalactic sources within the local GZK sphere. To this end, we set up hypothetical sources of ultra-high-energy cosmic rays (UHECRs), virtual observers, and the magnetized cosmic web in a model universe constructed from cosmological structure formation simulations. We then arranged a set of reference objects mimicking active galactic nuclei (AGNs) in the local universe, with which correlations of simulated UHECR events are analyzed. With our model IGMF, the deflection angle between the arrival direction of super-GZK protons and the sky position of their actual sources is quite large with a mean value of similar to 15 degrees and a median value of (0) over tilde similar to 7 degrees-10 degrees. On the other hand, the separation angle between the arrival direction and the sky position of nearest reference objects is substantially smaller with similar to 3 degrees.5-4 degrees, which is similar to the mean angular distance in the sky to nearest neighbors among the reference objects. This is a direct consequence of our model that the sources, observers, reference objects, and the IGMF all trace the matter distribution of the universe. The result implies that extragalactic objects lying closest to the arrival direction of UHECRs are not necessarily their actual sources. With our model for the distribution of reference objects, the fraction of super-GZK proton events, whose closest AGNs are true sources, is less than 1/3. We discussed implications of our findings for correlation studies of real UHECR eventsopen272
The Centaurus A Ultrahigh-Energy Cosmic Ray Excess and the Local Extragalactic Magnetic Field
The ultrahigh-energy cosmic-ray anisotropies discovered by the Pierre Auger
Observatory give the potential to finally address both the particles' origins
and properties of the nearby extragalactic magnetic field (EGMF). We examine
the implications of the excess of ~ 10^20 eV events around the nearby radio
galaxy Centaurus A. We find that, if Cen A is the source of these cosmic rays,
the angular distribution of events constrains the EGMF strength within several
Mpc of the Milky Way to > 20 nG for an assumed primary proton composition. Our
conclusions suggest that either the observed excess is a statistical anomaly or
the local EGMF is stronger then conventionally thought. We discuss the
implications of this field, including UHECR scattering from more distant
sources, time delays from transient sources, and the possibility of using
magnetic lensing signatures to attain tighter constraints.Comment: 8 pages, 8 figures; Matches published version in AP
Cosmic Rays Above the Second Knee from Clusters of Galaxies and Associated High-Energy Neutrino Emission
Accretion and merger shocks in clusters of galaxies are potential
accelerators of high-energy protons, which can give rise to high-energy
neutrinos through pp interactions with the intracluster gas. We discuss the
possibility that protons from cluster shocks make a significant contribution to
the observed cosmic rays in the energy range between the second knee around
10^17.5 eV and the ankle around 10^18.5 eV. The accompanying cumulative
neutrino background above PeV may be detectable by upcoming neutrino telescopes
such as IceCube or KM3NeT, providing a test of this scenario as well as a probe
of cosmic-ray confinement properties in clusters.Comment: 4 pages, 2 figures, accepted for publication in APJL, references and
discussions added, results unchange
Ultrahigh Energy Nuclei in the Galactic Magnetic Field
Observations are consistent with a significant fraction of heavy nuclei in
the cosmic ray flux above a few times 10^19 eV. Such nuclei can be deflected
considerably in the Galactic magnetic field, with important implications for
the search of their sources. We perform detailed simulations of heavy nuclei
propagation within recent Galactic magnetic field models. While such models are
not yet sufficiently constrained to predict deflection maps in detail, we find
general features of the distribution of (de-) magnified flux from sources.
Since in most theoretical models sources of heavy nuclei are located in the
local large scale structure of galaxies, we show examples of images of several
nearby galaxy clusters and of the supergalactic plane. Such general features
may be useful to develop efficient methods for source reconstruction from
observed ultrahigh energy cosmic ray arrival directions.Comment: 17 pages, 11 figures. Published in JCA
SIMULATED FARADAY ROTATION MEASURES TOWARD HIGH GALACTIC LATITUDES
We study the Faraday rotation measure (RM) due to the Galactic magnetic field (GMF) toward high Galactic latitudes. The RM arises from the global, regular component as well as from the turbulent, random component of the GMF. We model the former based on observations and the latter using the data of magnetohydrodynamic turbulence simulations. For a large number of different GMF models, we produce mock RM maps around the Galactic poles and calculate various statistical quantities with the RM maps. We find that the observed medians of RMs toward the north and south Galactic poles, 0.0 ?? 0.5 rad m -2 and + 6.3 ?? 0.5 rad m-2, are difficult to explain with any of our many alternate GMF models. The standard deviation of observed RMs, 9 rad m-2, is clearly larger than that of simulated RMs. The second-order structure function of observed RMs is substantially larger than that of simulated RMs, especially at small angular scales. We discuss other possible contributions to RM toward high Galactic latitudes. Besides observational errors and the intrinsic RM of background radio sources against which RM is observed, we suggest that the RM due to the intergalactic magnetic field may account for a substantial fraction of the observed RM. Finally, we note that reproducing the observed medians may require additional components or/and structures of the GMF that are not present in our models.open5
Propagation of ultrahigh energy nuclei in clusters of galaxies: resulting composition and secondary emissions
We study the survival of ultrahigh energy nuclei injected in clusters of
galaxies, as well as their secondary neutrino and photon emissions, using a
complete numerical propagation method and a realistic modeling of the magnetic,
baryonic and photonic backgrounds. It is found that the survival of heavy
nuclei highly depends on the injection position and on the profile of the
magnetic field. Taking into account the limited lifetime of the central source
could also lead in some cases to the detection of a cosmic ray afterglow,
temporally decorrelated from neutrino and gamma ray emissions.
We calculate that the diffusive neutrino flux around 1 PeV coming from
clusters of galaxies may have a chance to be detected by current instruments.
The observation of single sources in neutrinos and in gamma rays produced by
ultrahigh energy cosmic rays will be more difficult. Signals coming from lower
energy cosmic rays (E < 1 PeV), if they exist, might however be detected by
Fermi, for reasonable sets of parameters.Comment: 19 pages, 15 figures, version to appear in ApJ (minor changes
SEEDS direct imaging of the RV-detected companion to V450 Andromedae, and characterization of the system
We report the direct imaging detection of a low-mass companion to a young,
moderately active star V450 And, that was previously identified with the radial
velocity method. The companion was found in high-contrast images obtained with
the Subaru Telescope equipped with the HiCIAO camera and AO188 adaptive optics
system. From the public ELODIE and SOPHIE archives we extracted available
high-resolution spectra and radial velocity (RV) measurements, along with RVs
from the Lick planet search program. We combined our multi-epoch astrometry
with these archival, partially unpublished RVs, and found that the companion is
a low-mass star, not a brown dwarf, as previously suggested. We found the
best-fitting dynamical masses to be and
M. We also performed spectral analysis of
the SOPHIE spectra with the iSpec code. The Hipparcos time-series photometry
shows a periodicity of d, which is also seen in SOPHIE spectra as an
RV modulation of the star A. We interpret it as being caused by spots on the
stellar surface, and the star to be rotating with the given period. From the
rotation and level of activity, we found that the system is
Myr old, consistent with an isochrone analysis ( Myr). This
work may serve as a test case for future studies of low-mass stars, brown
dwarfs and exoplanets by combination of RV and direct imaging data.Comment: 15 pages, 9 figures, 7 tables, to appear in Ap
New highly radioactive particles derived from Fukushima Daiichi Reactor Unit 1 : Properties and environmental impacts
A contaminated zone elongated toward Futaba Town, north-northwest of the Fukushima Daiichi Nuclear Power Plant (FDNPP), contains highly radioactive particles released from reactor Unit 1. There are uncertainties associated with the physio-chemical properties and environmental impacts of these particles. In this study, 31 radioactive particles were isolated from surface soils collected 3.9Â km north-northwest of the FDNPP. Two of these particles have the highest particle-associated 134+137Cs activity ever reported for Fukushima (6.1Â ĂÂ 105 and 2.5Â ĂÂ 106Â Bq per particle after decay-correction to March 2011). The new, highly-radioactive particle labeled FTB1 is an aggregate of flaky silicate nanoparticles with an amorphous structure containing ~0.8Â wt% Cs, occasionally associated with SiO2 and TiO2 inclusions. FTB1 likely originates from the reactor building, which was damaged by a H2 explosion, after adsorbing volatilized Cs. The 134+137Cs activity in the other highly radioactive particle labeled FTB26 exceeded 106Â Bq. FTB26 has a glassy carbon core and a surface that is embedded with numerous micro-particles: PbâSn alloy, fibrous Al-silicate, Ca-carbonate or hydroxide, and quartz. The isotopic signatures of the micro-particles indicate neutron capture by B, Cs volatilization, and adsorption of natural Ba. The composition of the micro-particles on FTB26 reflects the composition of airborne particles at the moment of the H2 explosion. Owing to their large size, the health effects of the highly radioactive particles are likely limited to external radiation during static contact with skin; the highly radioactive particles are thus expected to have negligible health impacts for humans. By investigating the mobility of the highly radioactive particles, we can better understand how the radiation dose transfers through environments impacted by Unit 1. The highly radioactive particles also provide insights into the atmospheric conditions at the time of the Unit 1 explosion and the physio-chemical phenomena that occurred during reactor meltdown.Peer reviewe
Multiphase induction motor drives - a technology status review
The area of multiphase variable-speed motor drives in general and multiphase induction motor drives in particular has experienced a substantial growth since the beginning of this century. Research has been conducted worldwide and numerous interesting developments have been reported in the literature. An attempt is made to provide a detailed overview of the current state-of-the-art in this area. The elaborated aspects include advantages of multiphase induction machines, modelling of multiphase induction machines, basic vector control and direct torque control schemes and PWM control of multiphase voltage source inverters. The authors also provide a detailed survey of the control strategies for five-phase and asymmetrical six-phase induction motor drives, as well as an overview of the approaches to the design of fault tolerant strategies for post-fault drive operation, and a discussion of multiphase multi-motor drives with single inverter supply. Experimental results, collected from various multiphase induction motor drive laboratory rigs, are also included to facilitate the understanding of the drive operatio
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