40 research outputs found
Cosmic-ray propagation with DRAGON2: II. Nuclear interactions with the interstellar gas
Understanding the isotopic composition of cosmic rays (CRs) observed near
Earth represents a milestone towards the identification of their origin. Local
fluxes contain all the known stable and long-lived isotopes, reflecting the
complex history of primaries and secondaries as they traverse the interstellar
medium. For that reason, a numerical code which aims at describing the CR
transport in the Galaxy must unavoidably rely on accurate modelling of the
production of secondary particles. In this work we provide a detailed
description of the nuclear cross sections and decay network as implemented in
the forthcoming release of the galactic propagation code DRAGON2. We present
the secondary production models implemented in the code and we apply the
different prescriptions to compute quantities of interest to interpret local CR
fluxes (e.g., nuclear fragmentation timescales, secondary and tertiary source
terms). In particular, we develop a nuclear secondary production model aimed at
accurately computing the light secondary fluxes (namely: Li, Be, B) above 1
GeV/n. This result is achieved by fitting existing empirical or semi-empirical
formalisms to a large sample of measurements in the energy range 100 MeV/n to
100 GeV/n and by considering the contribution of the most relevant decaying
isotopes up to iron. Concerning secondary antiparticles (positrons and
antiprotons), we describe a collection of models taken from the literature, and
provide a detailed quantitative comparison.Comment: 22 pages, 12 figure
Gleam: the GLAST Large Area Telescope Simulation Framework
This paper presents the simulation of the GLAST high energy gamma-ray
telescope. The simulation package, written in C++, is based on the Geant4
toolkit, and it is integrated into a general framework used to process events.
A detailed simulation of the electronic signals inside Silicon detectors has
been provided and it is used for the particle tracking, which is handled by a
dedicated software. A unique repository for the geometrical description of the
detector has been realized using the XML language and a C++ library to access
this information has been designed and implemented.Comment: 10 pages, Late
A population of gamma-ray emitting globular clusters seen with the Fermi Large Area Telescope
Globular clusters with their large populations of millisecond pulsars (MSPs)
are believed to be potential emitters of high-energy gamma-ray emission. Our
goal is to constrain the millisecond pulsar populations in globular clusters
from analysis of gamma-ray observations. We use 546 days of continuous
sky-survey observations obtained with the Large Area Telescope aboard the Fermi
Gamma-ray Space Telescope to study the gamma-ray emission towards 13 globular
clusters. Steady point-like high-energy gamma-ray emission has been
significantly detected towards 8 globular clusters. Five of them (47 Tucanae,
Omega Cen, NGC 6388, Terzan 5, and M 28) show hard spectral power indices and clear evidence for an exponential cut-off in the range
1.0-2.6 GeV, which is the characteristic signature of magnetospheric emission
from MSPs. Three of them (M 62, NGC 6440 and NGC 6652) also show hard spectral
indices , however the presence of an exponential cut-off
can not be unambiguously established. Three of them (Omega Cen, NGC 6388, NGC
6652) have no known radio or X-ray MSPs yet still exhibit MSP spectral
properties. From the observed gamma-ray luminosities, we estimate the total
number of MSPs that is expected to be present in these globular clusters. We
show that our estimates of the MSP population correlate with the stellar
encounter rate and we estimate 2600-4700 MSPs in Galactic globular clusters,
commensurate with previous estimates. The observation of high-energy gamma-ray
emission from a globular cluster thus provides a reliable independent method to
assess their millisecond pulsar populations that can be used to make
constraints on the original neutron star X-ray binary population, essential for
understanding the importance of binary systems in slowing the inevitable core
collapse of globular clusters.Comment: Accepted for publication in A&A. Corresponding authors: J.
Kn\"odlseder, N. Webb, B. Pancraz
Fermi Large Area Telescope Constraints on the Gamma-ray Opacity of the Universe
The Extragalactic Background Light (EBL) includes photons with wavelengths
from ultraviolet to infrared, which are effective at attenuating gamma rays
with energy above ~10 GeV during propagation from sources at cosmological
distances. This results in a redshift- and energy-dependent attenuation of the
gamma-ray flux of extragalactic sources such as blazars and Gamma-Ray Bursts
(GRBs). The Large Area Telescope onboard Fermi detects a sample of gamma-ray
blazars with redshift up to z~3, and GRBs with redshift up to z~4.3. Using
photons above 10 GeV collected by Fermi over more than one year of observations
for these sources, we investigate the effect of gamma-ray flux attenuation by
the EBL. We place upper limits on the gamma-ray opacity of the Universe at
various energies and redshifts, and compare this with predictions from
well-known EBL models. We find that an EBL intensity in the optical-ultraviolet
wavelengths as great as predicted by the "baseline" model of Stecker et al.
(2006) can be ruled out with high confidence.Comment: 42 pages, 12 figures, accepted version (24 Aug.2010) for publication
in ApJ; Contact authors: A. Bouvier, A. Chen, S. Raino, S. Razzaque, A.
Reimer, L.C. Reye
The All-sky Medium Energy Gamma-ray Observatory eXplorer (AMEGO-X) Mission Concept
The All-sky Medium Energy Gamma-ray Observatory eXplorer (AMEGO-X) is
designed to identify and characterize gamma rays from extreme explosions and
accelerators. The main science themes include: supermassive black holes and
their connections to neutrinos and cosmic rays; binary neutron star mergers and
the relativistic jets they produce; cosmic ray particle acceleration sources
including Galactic supernovae; and continuous monitoring of other astrophysical
events and sources over the full sky in this important energy range. AMEGO-X
will probe the medium energy gamma-ray band using a single instrument with
sensitivity up to an order of magnitude greater than previous telescopes in the
energy range 100 keV to 1 GeV that can be only realized in space. During its
three-year baseline mission, AMEGO-X will observe nearly the entire sky every
two orbits, building up a sensitive all-sky map of gamma-ray sources and
emission. AMEGO-X was submitted in the recent 2021 NASA MIDEX Announcement of
Opportunity.Comment: 23 pages, 16 figures, Published Journal of Astronomical Telescopes,
Instruments, and System
Gamma-ray and radio properties of six pulsars detected by the fermi large area telescope
We report the detection of pulsed γ-rays for PSRs J0631+1036, J0659+1414, J0742-2822, J1420-6048, J1509-5850, and J1718-3825 using the Large Area Telescope on board the Fermi Gamma-ray Space Telescope (formerly known as GLAST). Although these six pulsars are diverse in terms of their spin parameters, they share an important feature: their γ-ray light curves are (at least given the current count statistics) single peaked. For two pulsars, there are hints for a double-peaked structure in the light curves. The shapes of the observed light curves of this group of pulsars are discussed in the light of models for which the emission originates from high up in the magnetosphere. The observed phases of the γ-ray light curves are, in general, consistent with those predicted by high-altitude models, although we speculate that the γ-ray emission of PSR J0659+1414, possibly featuring the softest spectrum of all Fermi pulsars coupled with a very low efficiency, arises from relatively low down in the magnetosphere. High-quality radio polarization data are available showing that all but one have a high degree of linear polarization. This allows us to place some constraints on the viewing geometry and aids the comparison of the γ-ray light curves with high-energy beam models
The Third Fermi Large Area Telescope Catalog of Gamma-ray Pulsars
We present 294 pulsars found in GeV data from the Large Area Telescope (LAT)
on the Fermi Gamma-ray Space Telescope. Another 33 millisecond pulsars (MSPs)
discovered in deep radio searches of LAT sources will likely reveal pulsations
once phase-connected rotation ephemerides are achieved. A further dozen optical
and/or X-ray binary systems co-located with LAT sources also likely harbor
gamma-ray MSPs. This catalog thus reports roughly 340 gamma-ray pulsars and
candidates, 10% of all known pulsars, compared to known before Fermi.
Half of the gamma-ray pulsars are young. Of these, the half that are undetected
in radio have a broader Galactic latitude distribution than the young
radio-loud pulsars. The others are MSPs, with 6 undetected in radio. Overall,
>235 are bright enough above 50 MeV to fit the pulse profile, the energy
spectrum, or both. For the common two-peaked profiles, the gamma-ray peak
closest to the magnetic pole crossing generally has a softer spectrum. The
spectral energy distributions tend to narrow as the spindown power
decreases to its observed minimum near erg s, approaching the
shape for synchrotron radiation from monoenergetic electrons. We calculate
gamma-ray luminosities when distances are available. Our all-sky gamma-ray
sensitivity map is useful for population syntheses. The electronic catalog
version provides gamma-ray pulsar ephemerides, properties and fit results to
guide and be compared with modeling results.Comment: 142 pages. Accepted by the Astrophysical Journal Supplemen