Cosmic Ray e +/(e- + e+), p-bar/p Ratios Explained by an Injection Model Based on 2 Gamma-ray Observations

We present a model of cosmic ray (CR) injection into the Galactic space based on recent {gamma}-ray observations of supernova remnants (SNRs) and pulsar wind nebulae (PWNe) by the Fermi Large Area Telescope (Fermi) and atmospheric Cherenkov telescopes (ACTs). Steady-state (SS) injection of nuclear particles and electrons (e{sup -}) from the Galactic ensemble of SNRs, and electrons and positrons (e{sup +}) from the Galactic ensemble of PWNe are assumed, with their spectra deduced from {gamma}-ray observations and recent evolution models. The ensembles of SNRs and PWNe are assumed to share the same spatial distributions and the secondary CR production in dense molecular clouds interacting with SNRs is incorporated in the model. Propagation of CRs to Earth is calculated using GALPROP with 2 source distributions and 2 Galaxy halo sizes. We show that this observation-based model reproduces the positron fraction e{sup +}/(e{sup -} + e{sup +}) and antiproton-to-proton ratio ({bar p}/p) reported by PAMELA reasonably well without calling for new sources. Significant discrepancy is found, however, between our model and the e{sup -} + e{sup +} spectrum measured by Fermi below {approx} 20 GeV. Important quantities for Galactic CRs, including their energy injection, average lifetime, and mean gas density along their typical propagation path are also presented

Fermi LAT observations of Pulsar Wind Nebulae

International audienc

Fermi observations of Crab and PWNe

The book will be edited by the organizers, and will be published by Springer as a hard cover in its Astrophysics and Space Science series

Fermi-LAT Observations of the Vela-X region

The Vela supernova remnant is the closest SNR to contain a young active pulsar, PSR B0833-45. The remnant spans about 8deg in diameter and contains regions of nonthermal emission in the radio, X-ray and gamma-ray bands, including Vela X, a pulsar wind nebula (PWN) spanning a region of 2deg * 3deg south-southwest of the pulsar. With a center offset by about 40' from the pulsar, Vela X served as the first prototype for offset PWN as a result of SNR expansion into an inhomogeneous medium; it emits in the radio, X-ray, and TeV Gamma-ray bands. Using recent observations by Fermi-LAT, we are conducting a detailed study of the off-pulse emission in the region of the Vela pulsar. In this talk, we will describe the Fermi-LAT measurement of this region and discuss the origin of the detected gamma-rays

GLAST observations of pulsar wind nebulae

The Gamma-ray Large Area Space Telescope (GLAST) will soon provide a new perspective on gamma-ray emission mechanisms in PWNe. The Large Area Telescope (LAT) will have unprecedented sensitivity in the MeV-GeV energy range and the upper energy reach extends to 300 GeV, overlapping with ground-based gamma-ray telescopes. PWNe have become a common phenomenon at TeV energies and some of these are expected to be detectable by the LAT. The high-energy emission is generally attributed to inverse-Compton scattering of the cosmic microwave background by electrons accelerated in the termination of the pulsar wind. The spectral maximum has been seen for several PWNe in the TeV band, but is expected to occur at lower frequencies for others. Cases where the combined GeV and TeV observations can detect or constrain the inverse-Compton peak are of particular interest for study of the injected particle spectrum and history. We will discuss expectations for the LAT based on the current observations of PWNe and explore the potential impact on the understanding of particle acceleration in these sources

GLAST observations of pulsar wind nebulae

The Gamma-ray Large Area Space Telescope (GLAST) will soon provide a new perspective on gamma-ray emission mechanisms in PWNe. The Large Area Telescope (LAT) will have unprecedented sensitivity in the MeV-GeV energy range and the upper energy reach extends to 300 GeV, overlapping with ground-based gamma-ray telescopes. PWNe have become a common phenomenon at TeV energies and some of these are expected to be detectable by the LAT. The high-energy emission is generally attributed to inverse-Compton scattering of the cosmic microwave background by electrons accelerated in the termination of the pulsar wind. The spectral maximum has been seen for several PWNe in the TeV band, but is expected to occur at lower frequencies for others. Cases where the combined GeV and TeV observations can detect or constrain the inverse-Compton peak are of particular interest for study of the injected particle spectrum and history. We will discuss expectations for the LAT based on the current observations of PWNe and explore the potential impact on the understanding of particle acceleration in these sources

Fermi-LAT detection of gamma-ray emission in the vicinity of the star forming regions W43 and Westerlund 2

Particle acceleration in massive star forming regions can proceed via a large variety of possible emission scenarios, including high-energy gamma-ray production in the colliding wind zone of the massive Wolf-Rayet binary (here WR 20a and WR121a), collective wind scenarios, diffusive shock acceleration at the boundaries of wind-blown bubbles in the stellar cluster, and outbreak phenomena from hot stellar winds into the interstellar medium. In view of the recent Fermi-LAT detection of HESS J1023-575 (in the vicinity of Westerlund 2), we examine another very high energy (VHE) gamma-ray source, HESS J1848-0145 (in the vicinity of W43), possibly associated with a massive star cluster. Considering data from other wavelengths, in particular X-rays and TeV gamma-rays, we examine the available evidence that the gamma-ray emission from Westerlund 2 and W43 could originate in particles accelerated by the above-mentioned mechanisms in massive star clusters

Disentangling multiple high-energy emission components in the Vela X pulsar wind nebula with the FermiFermi Large Area Telescope

Context. Vela X is a pulsar wind nebula in which two relativistic particle populations with distinct spatial and spectral distributions dominate the emission at different wavelengths. An extended 2° × 3°nebula is seen in radio and GeV gamma rays. An elongated cocoon prevails in X-rays and TeV gamma rays.Aims. We use ~9.5 yr of data from the Fermi Large Area Telescope (LAT) to disentangle gamma-ray emission from the two components in the energy range from 10 GeV to 2 TeV, bridging the gap between previous measurements at GeV and TeV energies.Methods. We determine the morphology of emission associated to Vela X separately at energies 100 GeV, and compare it to the morphology seen at other wavelengths. Then, we derive the spectral energy distribution of the two gamma-ray components over the full energy range.Results. The best overall fit to the LAT data is provided by the combination of the two components derived at energies 100 GeV. The first component has a soft spectrum, spectral index 2.19 ± 0.16−0.22+0.05, and extends over a region of radius 1.°36±0.°04, consistent with the size of the radio nebula. The second component has a harder spectrum, spectral index0.9 ± 0.3−0.1+0.3, and is concentrated over an area of radius 0.°63±0.°03, coincident with the X-ray cocoon that had already been established as accounting for the bulk of the emission at TeV energies.Conclusions. The spectrum measured for the low-energy component corroborates previous evidence for a roll-over of the electron spectrum in the extended radio nebula at energies of a few tens of GeV possibly due to diffusive escape. The high-energy component has a very hard spectrum: if the emission is produced by electrons with a power-law spectrum, the electrons must be uncooled, and there is a hint that their spectrum may be harder than predictions by standard models of Fermi acceleration at relativistic shocks

Cosmic Ray e +/(e- + e+), p-bar/p Ratios Explained by an Injection Model Based on 2 Gamma-ray Observations

We present a model of cosmic ray (CR) injection into the Galactic space based on recent {gamma}-ray observations of supernova remnants (SNRs) and pulsar wind nebulae (PWNe) by the Fermi Large Area Telescope (Fermi) and atmospheric Cherenkov telescopes (ACTs). Steady-state (SS) injection of nuclear particles and electrons (e{sup -}) from the Galactic ensemble of SNRs, and electrons and positrons (e{sup +}) from the Galactic ensemble of PWNe are assumed, with their spectra deduced from {gamma}-ray observations and recent evolution models. The ensembles of SNRs and PWNe are assumed to share the same spatial distributions and the secondary CR production in dense molecular clouds interacting with SNRs is incorporated in the model. Propagation of CRs to Earth is calculated using GALPROP with 2 source distributions and 2 Galaxy halo sizes. We show that this observation-based model reproduces the positron fraction e{sup +}/(e{sup -} + e{sup +}) and antiproton-to-proton ratio ({bar p}/p) reported by PAMELA reasonably well without calling for new sources. Significant discrepancy is found, however, between our model and the e{sup -} + e{sup +} spectrum measured by Fermi below {approx} 20 GeV. Important quantities for Galactic CRs, including their energy injection, average lifetime, and mean gas density along their typical propagation path are also presented