2,923 research outputs found
Transport of exotic anti-nuclei: I- Fast formulae for antiproton fluxes
The Galactic secondary cosmic ray anti-proton flux calculated with different
propagation models is fairly consistent with data, and the associated
propagation uncertainty is small. This is not the case for any anti-proton
exotic component of the dark matter halo. Detailed propagation models are
mandatory if the ultimate goal is to explain an excess. However, simpler and
faster approximate formulae for anti-protons are an attractive alternative to
quickly check that a given dark matter model is not inconsistent with the
anti-proton observed flux. This paper provides such formulae. In addition, they
could be used to put constraints on new physics in this channel, where an
extensive scan of a large parameter space could otherwise be quite expensive in
computer ressources.Comment: 8 pages, 3 figures (submitted). Stand-alone code for exotic
anti-proton propagation can be downloaded at
http://wwwlapp.in2p3.fr/~taillet/mtc/mtc_code.tar . Paper re-organized
(results unchanged
CRDB: a database of charged cosmic rays
This paper gives a description of a new on-line database
http://lpsc.in2p3.fr/crdb and associated on-line tools (data selection, data
export, plots, etc.) for charged cosmic-ray measurements. The experimental
setups (type, flight dates, techniques) from which the data originate are
included in the database, along with the references to all relevant
publications. The database relies on the MySQL5 engine. The web pages and
queries are based on PHP, AJAX and the jquery, jquery.cluetip, jquery-ui, and
table-sorter third-party libraries. In this first release, we restrict
ourselves to Galactic cosmic rays with Z<=30 and a kinetic energy per nucleon
up to a few tens of TeV/n. This corresponds to more than 200 different
sub-experiments (i.e., different experiments, or data from the same experiment
flying at different times) in as many publications. We set up a cosmic-ray
database and provide tools to sort and visualise the data. New data can be
submitted, providing the community with a collaborative tool to archive past
and future cosmic-ray measurements. Any help/ideas to further expand and/or
complement the database is welcome (please contact [email protected]).Comment: 13 pages, 6 figures: new Sect. 2.3 on Solar modulation parameters in
CRDB v2.1, see http://lpsc.in2p3.fr/crd
Galactic secondary positron flux at the Earth
Secondary positrons are produced by spallation of cosmic rays within the
interstellar gas. Measurements have been typically expressed in terms of the
positron fraction, which exhibits an increase above 10 GeV. Many scenarios have
been proposed to explain this feature, among them some additional primary
positrons originating from dark matter annihilation in the Galaxy. The PAMELA
satellite has provided high quality data that has enabled high accuracy
statistical analyses to be made, showing that the increase in the positron
fraction extends up to about 100 GeV. It is therefore of paramount importance
to constrain theoretically the expected secondary positron flux to interpret
the observations in an accurate way. We find the secondary positron flux to be
reproduced well by the available observations, and to have theoretical
uncertainties that we quantify to be as large as about one order of magnitude.
We also discuss the positron fraction issue and find that our predictions may
be consistent with the data taken before PAMELA. For PAMELA data, we find that
an excess is probably present after considering uncertainties in the positron
flux, although its amplitude depends strongly on the assumptions made in
relation to the electron flux. By fitting the current electron data, we show
that when considering a soft electron spectrum, the amplitude of the excess
might be far lower than usually claimed. We provide fresh insights that may
help to explain the positron data with or without new physical model
ingredients. PAMELA observations and the forthcoming AMS-02 mission will allow
stronger constraints to be aplaced on the cosmic--ray transport parameters, and
are likely to reduce drastically the theoretical uncertainties.Comment: 15 pages, 12 figures. The recent PAMELA data on the positron fraction
(arXiv:0810.4995) have been included and the ensuing discussion has been
extended. Accepted version in A&
Decaying dark matter: a stacking analysis of galaxy clusters to improve on current limits
We show that a stacking approach to galaxy clusters can improve current
limits on decaying dark matter by a factor , with respect to a
single source analysis, for all-sky instruments such as Fermi-LAT. Based on the
largest sample of X-ray-selected galaxy clusters available to date (the MCXC
meta-catalogue), we provide all the astrophysical information, in particular
the astrophysical term for decaying dark matter, required to perform an
analysis with current instruments.Comment: 6 pages, 3 figures, supplementary file available on demand, accepted
for publication in PR
Désaisonnalisation des agrégats monétaires : Mise en place d’une chaîne rénovée.
The analysis of seasonality in economics and the development of new seasonal adjustment procedures have been following new directions in the last twenty years. We study this question through the work performed at the Banque de France (Monetary Statistic and Studies Directorate) to compile new seasonally adjusted (SA) data. A brief discussion of the academic literature show the necessity to complement the existing software with empirical rules fixed by the practitioner in order to make all the methodological choices clear, thus avoiding any ambiguity. In the implementation of the new production process, we focus on the revision policy of some keys parameters of the whole process in order to minimize the subsequent revisions in the publication of SA data. We illustrate this new methodology with SA series relating to monetary aggregates, including loans to enterprises and to households, and provide a detailed analysis of the consistency between flows and outstanding amount SA figures, an issue particularly relevant for monetary an financial data.Seasonal Adjustment Methods ; Monetary Aggregates ; Outliers ; SARIMA Models ; Spectral Analysis.
Spatial Origin of Galactic Cosmic Rays in Diffusion Models: I- Standard sources in the Galactic disk
The propagation of Galactic Cosmic Ray nuclei having energies between 100
MeV/nuc and several PeV/nuc is strongly believed to be of diffusive nature. The
particles emitted by a source located in the disk do not pervade the whole
Galaxy, but are rather confined to a smaller region whose spatial extension is
related to the height of the diffusive halo, the Galactic wind and the
spallation rate. Following the pioneering work of Jones (1978), this paper
presents a general study on the spatial origin of cosmic rays, with a
particular attention to the role of spallations and Galactic wind. This
question is different, and to a certain extent disconnected, from that of the
origin of cosmic rays. We find the regions of the disk from which a given
fraction of cosmic rays detected in the Solar neighborhood were emitted
(f-surfaces). After a general study, we apply the results to a realistic source
distribution, with the propagation parameters obtained in our previous
systematic analysis of the observed secondary-to-primary ratios Maurin et al
(2002). The shape and size of these f-surfaces depend on the species as well as
on the values of the propagation parameters. For some of the models preferred
by our previous analysis (i.e. large diffusion slope ), these
f-surfaces are small and in some extreme cases only a fraction of a percent of
the whole Galactic sources actually contribute to the Solar neighborhood Cosmic
Ray flux. Moreover, a very small number of sources may be responsible for more
than 15 % of the flux detected in the Solar neighborhood. This may point
towards the necessity to go beyond the approximations of both homogeneity and
stationarity. Finally, the observed primary composition is dominated by sources
within a few kpc.Comment: revised version, 32 pages, to appear in A&A. Shortened version, with
corresction
Sensitivity studies for the cubic-kilometre deep-sea neutrino telescope KM3NeT
The observation of high-energy neutrinos from astrophysical sources would
substantially improve our knowledge and understanding of the non-thermal
processes in these sources, and would in particular pinpoint the accelerators
of cosmic rays. The sensitivity of different design options for a future
cubic-kilometre scale neutrino telescope in the Mediterranean Sea is
investigated for generic point sources and in particular for some of the
galactic objects from which TeV gamma emmission has recently been observed by
the H.E.S.S. atmospheric Cherenkov telescope. The effect of atmospheric
background on the source detection probabilities has been taken into account
through full simulation. The estimated event rates are compared to previous
results and limits from present neutrino telescopes.Comment: 4 pages, 1 figure, contribution of the 30th International Cosmic Ray
conferenc
Variation of the X-ray non-thermal emission in the Arches cloud
The origin of the iron fluorescent line at 6.4 keV from an extended region
surrounding the Arches cluster is debated and the non-variability of this
emission up to 2009 has favored the low-energy cosmic-ray origin over a
possible irradiation by hard X-rays. By probing the variability of the Arches
cloud non-thermal emission in the most recent years, including a deep
observation in 2012, we intend to discriminate between the two competing
scenarios. We perform a spectral fit of XMM-Newton observations collected from
2000 to 2013 in order to build the Arches cloud lightcurve corresponding to
both the neutral Fe Kalpha line and the X-ray continuum emissions. We reveal a
30% flux drop in 2012, detected with more than 4 sigma significance for both
components. This implies that a large fraction of the studied non-thermal
emission is due to the reflection of an X-ray transient source.Comment: 5 pages, 3 figures, accepted for publication in MNRAS Letter
New results on source and diffusion spectral features of Galactic cosmic rays: I- B/C ratio
In a previous study (Maurin et al., 2001), we explored the set of parameters
describing diffusive propagation of cosmic rays (galactic convection,
reacceleration, halo thickness, spectral index and normalization of the
diffusion coefficient), and we identified those giving a good fit to the
measured B/C ratio. This study is now extended to take into account a sixth
free parameter, namely the spectral index of sources. We use an updated version
of our code where the reacceleration term comes from standard minimal
reacceleration models. The goal of this paper is to present a general view of
the evolution of the goodness of fit to B/C data with the propagation
parameters. In particular, we find that, unlike the well accepted picture, and
in accordance with our previous study, a Kolmogorov-like power spectrum for
diffusion is strongly disfavored. Rather, the analysis points towards
along with source spectra index . Two
distinct energy dependences are used for the source spectra: the usual
power-law in rigidity and a law modified at low energy, the second choice being
only slightly preferred. We also show that the results are not much affected by
a different choice for the diffusion scheme. Finally, we compare our findings
to recent works, using other propagation models. This study will be further
refined in a companion paper, focusing on the fluxes of cosmic ray nuclei.Comment: 32 pages, 13 figures, accepted in A&
- …