184 research outputs found
Multi-messenger constraints to the local emission of cosmic-ray electrons
The data on the inclusive flux of cosmic positrons and electrons
() have been recently collected from GeV to tens of TeV energies by
several experiments with unprecedented precision. In addition, the Fermi-LAT
Collaboration has provided a new energy spectrum for the upper bounds on the
dipole anisotropy. This observable can bring information on the
emission from local Galactic sources, notably measured with high precision at
radio frequencies. We develop a framework in which and measured at
Earth from GeV up to tens of TeV energies have a composite origin. A dedicated
analysis is deserved to Vela YZ and Cygnus Loop Supernova Remnants (SNRs), for
which we consider two different models for the injection of . We
investigate the consistency of these models using the three physical
observables: the radio flux from Vela YZ and Cygnus Loop at all the available
frequencies, the flux from five experiments from the GeV to tens of
TeV energy, the dipole anisotropy upper limits from 50 GeV to about 1
TeV. We find that the radio flux for these nearby SNRs strongly constraints the
properties of the injection electron spectrum, partially compatible with the
looser constraints derived from the flux data. We also perform a
multi-wavelength multi-messenger analysis by fitting simultaneously the radio
flux on Vela YZ and Cygnus Loop and the flux, and checking the
outputs against the dipole anisotropy data. Remarkably, we find a
model which is compatible with all the flux data, the radio data for
Vela YZ and Cygnus Loop, and with the anisotropy upper bounds. We show the
severe constraints imposed by the most recent data on the dipole
anisotropy.Comment: 20 pages, 9 figures. Accepted for publication in the JCAP. Changes in
v3: discussion and results extended to include an evolutionary model for the
injection of cosmic-ray electrons in SNR
Novel interpretation of the latest AMS-02 cosmic-ray electron spectrum
The latest AMS-02 data on cosmic ray electrons show a break in the energy
spectrum around 40 GeV, with a change in the slope of about 0.1. We perform a
combined fit to the newest AMS-02 positron and electron flux data above 10 GeV
using a semi-analytical diffusion model where sources includes production of
pairs from pulsar wind nebulae (PWNe), electrons from supernova remnants (SNRs)
and both species from spallation of hadronic cosmic rays with interstellar
medium atoms. We demonstrate that within our setup the change of slope in the
AMS-02 electron data is well explained by the interplay between the flux
contributions from SNRs and from PWNe. In fact, the relative contribution to
the data of these two populations changes by a factor of about 13 from 10 to
1000 GeV. The PWN contribution has a significance of at least ,
depending on the model used for the propagation, interstellar radiation field
and energy losses. We checked the stability of this result against low-energy
effects by solving numerically the transport equation. as well as adding
possible breaks in the injection spectrum of SNRs. The effect of the energy
losses alone, when the inverse Compton scattering is properly computed within a
fully numerical treatment of the Klein-Nishina cross section, cannot explain
the break in the flux data, as recently proposed in the literature.Comment: 13 pages, 6 figures and supplemental material. Phys.Rev.D 104 (2021)
8, 08301
Evidences of low-diffusion bubbles around Galactic pulsars
Recently, a few-degrees extended -ray halo in the direction of
Geminga pulsar has been detected by HAWC, Milagro and Fermi-LAT. These
observations can be interpreted with positrons () and electrons ()
accelerated by Geminga pulsar wind nebula (PWN), released in a Galactic
environment with a low diffusion coefficient (), and inverse Compton
scattering (ICS) with the interstellar radiation fields. We inspect here how
the morphology of the ICS -ray flux depends on the energy, the pulsar
age and distance, and the strength and extension of the low-diffusion bubble.
In particular we show that -ray experiments with a peak of sensitivity
at TeV energies are the most promising ones to detect ICS halos. We perform a
study of the sensitivity of HAWC, HESS and the future CTA experiment finding
that, with efficiencies of the order of a few %, the first two experiments
should have already detected a few tens of ICS halos while the latter will
increase the number of detections by a factor of 4. We then consider a sample
of sources associated to PWNe and detected in the HESS Galactic plane survey
and in the second HAWC catalog. We use the information available in these
catalogs for the -ray spatial morphology and flux of these sources to
inspect the value of around them and the injection spectrum.
All sources are detected as extended with a -ray emission extended
about pc. Assuming that most of the accelerated by these
sources have been released in the interstellar medium, the diffusion
coefficient is cm/s at 1 TeV, i.e. two orders of
magnitude smaller than the value considered to be the average in the Galaxy.
These observations imply that Galactic PWNe have low-diffusion bubbles with a
size of at least 80 pc.Comment: 21 pages, 11 figures. Phys.Rev.D 101 (2020) 10, 10303
Contribution of pulsars to cosmic-ray positrons in light of recent observation of inverse-Compton halos
The hypothesis that pulsar wind nebulae (PWNe) can significantly contribute
to the excess of the positron () cosmic-ray flux has been consolidated
after the observation of a -ray emission at TeV energies of a few
degree size around Geminga and Monogem PWNe, and at GeV energies for Geminga at
a much larger extension. The -ray halos around these PWNe are
interpreted as due to electrons () and accelerated and escaped by
their PWNe, and inverse Compton scattering low-energy photons of the
interstellar radiation fields. The extension of these halos suggests that the
diffusion around these PWNe is suppressed by two orders of magnitude with
respect to the average in the Galaxy. We implement a two-zone diffusion model
for the propagation of accelerated by the Galactic population of PWNe. We
consider pulsars from the ATNF catalog and build up simulations of the PWN
Galactic population. In both scenarios, we find that within a two-zone
diffusion model, the total contribution from PWNe and secondary is at the
level of AMS-02 data, for an efficiency of conversion of the pulsar spin down
energy in of . For the simulated PWNe, a
uncertainty band is determined, which is of at least one order of magnitude
from 10 GeV up to few TeV. The hint for a decreasing flux at TeV energies
is found, even if it is strongly connected to the chosen value of the radius of
the low diffusion bubble around each source.Comment: 10 pages, 7 figures. Figures 2, 3 and 5 updated. Results unchange
Frequent, complex and vivid dream-like/hallucinatory experiences during NREM sleep parasomnia episodes
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