9,424 research outputs found
Ultrahigh Energy Cosmic Ray Nuclei from Extragalactic Pulsars and the effect of their Galactic counterparts
The acceleration of ultrahigh energy nuclei in fast spinning newborn pulsars
can explain the observed spectrum of ultrahigh energy cosmic rays and the trend
towards heavier nuclei for energies above eV as reported by the
Auger Observatory. Pulsar acceleration implies a hard injection spectrum () due to pulsar spin down and a maximum energy eV due to the limit on the spin rate of neutron stars. We have
previously shown that the escape through the young supernova remnant softens
the spectrum, decreases slightly the maximum energy, and generates secondary
nuclei. Here we show that the distribution of pulsar birth periods and the
effect of propagation in the interstellar and intergalactic media modifies the
combined spectrum of all pulsars. By assuming a normal distribution of pulsar
birth periods centered at 300 ms, we show that the contribution of
extragalactic pulsar births to the ultrahigh energy cosmic ray spectrum
naturally gives rise to a contribution to very high energy cosmic rays (VHECRs,
between and eV) by Galactic pulsar births. The required
injected composition to fit the observed spectrum depends on the absolute
energy scale, which is uncertain, differing between Auger Observatory and
Telescope Array. The contribution of Galactic pulsar births can also bridge the
gap between predictions for cosmic ray acceleration in supernova remnants and
the observed spectrum just below the ankle, depending on the composition of the
cosmic rays that escape the supernova remnant and the diffusion behavior of
VHECRs in the Galaxy.Comment: 21 pages, 5 figure, JCAP submitte
Economic valuation of development projects : a case study of a non-motorized transport project in India
One of the major difficulties in doing cost-benefit analysis of a development project is to estimate the total economic value of project benefits, which are usually multi-dimensional andinclude goods and services that are not traded in the market. Challenges also arise in aggregating the values of different benefits, which may not be mutually exclusive. This paper uses a contingent valuation approach to estimate the economic value of a non-motorized transport project in Pune, India, across beneficiaries. The heads of households which are potentially affected by the project are presented with a detailed description of the project, and then are asked to vote on whether such a project should be undertaken given different specifications of costs to the households. The total value of the project is then derived from the survey answers. Econometric analysis indicates that the survey responses provide generally reasonable valuation estimates.Transport Economics Policy&Planning,Environmental Economics&Policies,Roads&Highways,Housing&Human Habitats,Economic Theory&Research
IceCube and HAWC constraints on very-high-energy emission from the Fermi bubbles
The nature of the -ray emission from the \emph{Fermi} bubbles is
unknown. Both hadronic and leptonic models have been formulated to explain the
peculiar -ray signal observed by the Fermi-LAT between 0.1-500~GeV. If
this emission continues above 30~TeV, hadronic models of the \emph{Fermi}
bubbles would provide a significant contribution to the high-energy neutrino
flux detected by the IceCube observatory. Even in models where leptonic
-rays produce the \emph{Fermi} bubbles flux at GeV energies, a hadronic
component may be observable at very high energies. The combination of IceCube
and HAWC measurements have the ability to distinguish these scenarios through a
comparison of the neutrino and -ray fluxes at a similar energy scale.
We examine the most recent four-year dataset produced by the IceCube
collaboration and find no evidence for neutrino emission originating from the
\emph{Fermi} bubbles. In particular, we find that previously suggested excesses
are consistent with the diffuse astrophysical background with a p-value of 0.22
(0.05 in an extreme scenario that all the IceCube events that overlap with the
bubbles come from them). Moreover, we show that existing and upcoming HAWC
observations provide independent constraints on any neutrino emission from the
\emph{Fermi} bubbles, due to the close correlation between the -ray and
neutrino fluxes in hadronic interactions. The combination of these results
disfavors a significant contribution from the \emph{Fermi} bubbles to the
IceCube neutrino flux.Comment: 9 pages, 4 figures, to appear in PR
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