6,372 research outputs found
Sensitivity of full-sky experiments to large scale cosmic ray anisotropies
The two main advantages of space-based observation of extreme energy
( eV) cosmic rays (EECRs) over ground based
observatories are the increased field of view and the full-sky coverage with
nearly uniform systematics across the entire sky. The former guarantees
increased statistics, whereas the latter enables a clean partitioning of the
sky into spherical harmonics. The discovery of anisotropies would help to
identify the long sought origin of EECRs. We begin an investigation of the
reach of a full-sky space-based experiment such as EUSO to detect anisotropies
in the extreme-energy cosmic-ray sky compared to ground based partial-sky
experiments such as the Pierre Auger Observatory and Telescope Array. The
technique is explained here, and simulations for a Universe with just two
nonzero multipoles, monopole plus either dipole or quadrupole, are presented.
These simulations quantify the advantages of space-based, all-sky coverage.Comment: 11 pages, 8 figure
The Galactic Contribution to IceCube's Astrophysical Neutrino Flux
High energy neutrinos have been detected by IceCube, but their origin remains
a mystery. Determining the sources of this flux is a crucial first step towards
multi-messenger studies. In this work we systematically compare two classes of
sources with the data: Galactic and extragalactic. We assume that the neutrino
sources are distributed according to a class of Galactic models. We build a
likelihood function on an event by event basis including energy, event
topology, absorption, and direction information. We present the probability
that each high energy event with deposited energy TeV in the
HESE sample is Galactic, extragalactic, or background. For Galactic models
considered the Galactic fraction of the astrophysical flux has a best fit value
of and is at 90\% CL. A zero Galactic flux is allowed at
.Comment: Updated with 6 year HESE data from IceCube, accepted for publication
in JCA
A new perspective on the relation between dark energy perturbations and the late-time ISW effect
The effect of quintessence perturbations on the ISW effect is studied for a
mixed dynamical scalar field dark energy (DDE) and pressureless perfect fluid
dark matter. A new and general methodology is developed to track the growth of
the perturbations, which uses only the equation of state (EoS) parameter
of the scalar field DDE,
and the initial values of the the relative entropy perturbation (between the
matter and DDE) and the intrinsic entropy perturbation of the scalar field DDE
as inputs. We also derive a relation between the rest frame sound speed
of an arbitrary DDE component and its EoS . We show that the ISW signal differs from that expected in a
CDM cosmology by as much as +20% to -80% for parameterizations of
consistent with SNIa data, and about 20% for
parameterizations of consistent with SNIa+CMB+BAO data, at 95%
confidence. Our results indicate that, at least in principle, the ISW effect
can be used to phenomenologically distinguish a cosmological constant from DDE.Comment: Accepted for publication at PR
Are High Wage Jobs Hazardous to Your Health? The Myth That Attracting Higher Paying Extractive Industry Jobs Is a Desirable Community Economic Development Strategy
Community/Rural/Urban Development,
Toward a Minimum Branching Fraction for Dark Matter Annihilation into Electromagnetic Final States
Observational limits on the high-energy neutrino background have been used to
place general constraints on dark matter that annihilates only into standard
model particles. Dark matter particles that annihilate into neutrinos will also
inevitably branch into electromagnetic final states through higher-order tree
and loop diagrams that give rise to charged leptons, and these charged
particles can transfer their energy into photons via synchrotron radiation or
inverse Compton scattering. In the context of effective field theory, we
calculate the loop-induced branching ratio to charged leptons and show that it
is generally quite large, typically >1%, when the scale of the dark matter mass
exceeds the electroweak scale, M_W. For a branching fraction >3%, the
synchrotron radiation bounds on dark matter annihilation are currently stronger
than the corresponding neutrino bounds in the interesting mass range from 100
GeV to 1 TeV. For dark matter masses below M_W, our work provides a plausible
framework for the construction of a model for "neutrinos only" dark matter
annihilations.Comment: 18 pages, 4 figures, discussion added, matches version in Phys. Rev.
Magneto-optical imaging of voltage-controlled magnetization reorientation
We study the validity and limitations of a macrospin model to describe the
voltage-controlled manipulation of ferromagnetic magnetization in nickel thin
film/piezoelectric actuator hybrid structures. To this end, we correlate
simultaneously measured spatially resolved magneto-optical Kerr effect imaging
and integral magnetotransport measurements at room temperature. Our results
show that a macrospin approach is adequate to model the magnetoresistance as a
function of the voltage applied to the hybrid, except for a narrow region
around the coercive field - where the magnetization reorientation evolves via
domain effects. Thus, on length scales much larger than the typical magnetic
domain size, the voltage control of magnetization is well reproduced by a
simple Stoner-Wohlfarth type macrospin model
G328.4+0.2 : A large and luminous Crab-like supernova remnant
We report on radio continuum and HI observations of the radio source
G328.4+0.2 using the Australia Telescope Compact Array. Our results confirm
G328.4+0.2 to be a filled-center nebula with no surrounding shell, showing
significant linear polarization and an almost flat spectral index. These
results lead us to conclude that G328.4+0.2 is a Crab-like, or ``plerionic'',
supernova remnant (SNR), presumably powered by an unseen central pulsar. HI
absorption towards G328.4+0.2 puts a lower limit on its distance of 17.4 +/-
0.9 kpc, making it the largest (D=25 pc) and most luminous (L_R = 3e35 erg/s)
Crab-like SNR in the Galaxy. We infer G328.4+0.2 to be significantly older than
the Crab Nebula, but powered by a pulsar which is fast spinning (P<20 ms) and
which has a comparatively low magnetic field (B<1e12 G). We propose G328.4+0.2,
G74.9+1.2 and N157B as a distinct group of large-diameter, high-luminosity
Crab-like SNRs, all powered by fast-spinning low-field pulsars.Comment: 7 pages, 3 embedded EPS figures, uses emulateapj.sty. Accepted to
ApJ. Abstract corrected so that distance is now in kpc, not pc
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