1,444 research outputs found
Supernova Remnants and GLAST
It has long been speculated that supernova remnants represent a major source
of cosmic rays in the Galaxy. Observations over the past decade have
ceremoniously unveiled direct evidence of particle acceleration in SNRs to
energies approaching the knee of the cosmic ray spectrum. Nonthermal X-ray
emission from shell-type SNRs reveals multi-TeV electrons, and the dynamical
properties of several SNRs point to efficient acceleration of ions.
Observations of TeV gamma-ray emission have confirmed the presence of energetic
particles in several remnants as well, but there remains considerable debate as
to whether this emission originates with high energy electrons or ions. Equally
uncertain are the exact conditions that lead to efficient particle
acceleration.
Based on the catalog of EGRET sources, we know that there is a large
population of Galactic gamma-ray sources whose distribution is similar to that
of SNRs. With the increased resolution and sensitivity of GLAST, the gamma-ray
SNRs from this population will be identified. Their detailed emission
structure, along with their spectra, will provide the link between their
environments and their spectra in other wavebands to constrain emission models
and to potentially identify direct evidence of ion acceleration in SNRs. Here I
summarize recent observational and theoretical work in the area of cosmic ray
acceleration by SNRs, and discuss the contributions GLAST will bring to our
understanding of this problem.Comment: 5 pages, to be published in "The Proceedings of the First
International GLAST Symposium", February 5-8, 2007, Stanford University, AIP,
Eds. S. Ritz, P. F. Michelson, and C. Meega
Multiband Nonthermal Radiative Properties of HESS J1813-178
The source HESS J1813-178 was detected in the survey of the inner Galaxy in
TeV gamma-rays, and a SNR G12.8-0.0 was identified in the radio band to be
associated with it. The PWN embedded in the SNR is powered by an energetic
pulsar PSR J1813-1749, which was recently discovered. Whether the TeV
gamma-rays originate from the SNR shell or the PWN is uncertain now. We
investigate theoretically the multiwavelength nonthermal radiation from the
composite SNR G12.8-0.0. The emission from the particles accelerated in the SNR
shell is calculated based on a semianalytical method to the nonlinear diffusive
shock acceleration mechanism. In the model, the magnetic field is
self-generated via resonant streaming instability, and the dynamical reaction
of the field on the shock is taken into account. Based on a model which couples
the dynamical and radiative evolution of a PWN in a non-radiative SNR, the
dynamics and the multi-band emission of the PWN are investigated. The particles
are injected with a spectrum of a relativistic Maxwellian plus a power law
high-energy tail with an index of -2.5. Our results indicate that the radio
emission from the shell can be well reproduced as synchrotron radiation of the
electrons accelerated by the SNR shock; with an ISM number density of 1.4
cm^{-3} for the remnant, the gamma-ray emission from the SNR shell is
insignificant, and the observed X-rays and VHE gamma-rays from the source are
consistent with the emission produced by electrons/positrons injected in the
PWN via synchrotron radiation and IC scattering, respectively; the resulting
gamma-ray flux for the shell is comparable to the detected one only with a
relatively larger density of about 2.8 cm^{-3}. The VHE gamma-rays of HESS
J1813-178 can be naturally explained to mainly originate from the nebula
although the contribution of the SNR shell becomes significant with a denser
ambient medium.Comment: 7 pages, 6 figures. Accepted for publication in Ap
Fermi-LAT Observations of Supernova Remnant Kesteven 79
In this paper we report on the detection of -ray emission coincident
with the Galactic supernova remnant Kesteven 79 (Kes 79). We analysed
approximately 52 months of data obtained with the Large Area Telescope (LAT) on
board the Fermi Gamma-ray Space Telescope. Kes 79 is thought to be interacting
with adjacent molecular clouds based on the presence of strong CO J = 1
0 and HCO J = 1 0 emission and the detection
of 1720 MHz line emission towards the east of the remnant. Acceleration of
cosmic rays is expected to occur at SNR shocks, and SNRs interacting with dense
molecular clouds provide a good testing ground for detecting and analysing the
production of -rays from the decay of into two -ray
photons. This analysis investigates -ray emission coincident with Kes
79, which has a detection significance of . Additionally we
present an investigation of the spatial and spectral characteristics of Kes 79
using multiple archival XMM-Newton observations of this remnant. We determine
the global X-ray properties of Kes 79 and estimate the ambient density across
the remnant. We also performed a similar analysis for Galactic SNR Kesteven 78
(Kes 78), but due to large uncertainties in the -ray background model,
no conclusion can be made about an excess of GeV -ray associated with
the remnant.Comment: Accepted by ApJ; 16 pages, 5 figures, 6 table
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