28-03-2011, 11:56 AM
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Supernova remnants and γ - ray sources
The particle acceleration mechanism «diffusive shock acceleration,
which naturally leads to a power-law(幂指数) population of relativistic particles.
In the version particles are scattered by magnetohydrodynamic waves repeatedly through the shock front. Electrons suffer synchrotron losses, producing the non-thermal emission from radio to X-rays usually seen in shell-type SNRs.
The maximum energy depend on shock speed and age.
Phenomenological model for the hadronic g-ray emission in SNRs and their environs.
Relativistic Bremsstrahlung
Diffusion of CRs and g-ray spectral evolution
sample and correlation
SNRs coincident with g–ray sources
pulsars within the EGRET error boxes
variability
The energy decreases:
a ratio:
t2 is the actual age of the SNR
we shall assume the initial time t1 as that obtained when the SNR has swept about 5 Mq of interstellar material, starting then the Sedov phase .???
(the typical t1 is 200-2000 years)
ECR1=ECR2» ECR3 » 3qESN/4pR3
he hadronic g-ray flux is;
the flux provided by the previous equation is far too low to produce a detectable EGRET source.
The expected g-ray flux in the Tev region by SNRs
To extrapolate the GeV flux up to TeV energies we assume
the flux in any given energy interval E1–E2 is just,
In any case, this extrapolation will always provide an upper bound to the high-energy photon flux.
The g-ray emissivity at a given energy E from relativistic Bremsstrahlung is
We are interested in the g-ray radiation above 100 MeV,
This same population of relativistic electrons will also radiate at radio wavelengths, via the synchrotron mechanism. The synchrotron spectrum of a power-law electron energy distribution is
the ratio between the g-ray flux emitted by relativistic Bremsstrahlung and the synchrotron emission results
3 Diffusion of CRs and g-ray spectral evolution
The spectrum of g-rays generated through p0-decay at a source of proton density np is
If the proton spectrum Jp(Ep) at the g-ray production site is:
We also expected a power-law spectrum at g-ray
If there is diffusion, we shall have, instead
[f (Ep,r,t)is the distribution function of protons]
f satisfies the well-known diffusion equation
But we obserbved(different from the expected particle population )
Summing up, special care must be taken in analyzing the a priori expectations for the SNR-cloudy medium scenario.
(the distanse to the cloud and the diffusion index)