3 research outputs found
A review of the Landau-Pomeranchuk-Migdal effect
Bibliography: pages 57-58.The Bethe-Heitler formula is the correct expression for the energy radiated in the form of bremsstrahlung when a charged particle interacts in isolation with the Coulomb field of a nucleus. When the effects of multiple scattering are taken into account, however, the formula needs modification. This is the Landau-Pomeranchuk-Migdal effect. We review here several approaches for the calculation of the revised spectrum and compare the results with experiment
Can Light Echoes Account for the Slow Decay of Type IIn Supernovae?
The spectra of type IIn supernovae indicate the presence of apre-existing
slow, dense circumstellar wind (CSW). If the CSW extends sufficiently far from
the progenitor star, then dust formation should occur in the wind. The light
from the supernova explosion will scatter off this dust and produce a light
echo. Continuum emission seen after the peak will have contributions from both
this echo as well as from the shock of the ejecta colliding with the CSW, with
a fundamental question of which source dominates the continuum. We calculate
the brightness of the light echo as a function of time for a range of dust
shell geometries, and use our calculations to fit to the light curves of SN
1988Z and SN 1997ab, the two slowest declining IIn supernovae on record. We
find that the light curves of both objects can be reproduced by the echo model.
However, their rate of decay from peak, color at peak and their observed peak
absolute magnitudes when considered together are inconsistent with the echo
model. Furthermore, when the observed values of M are corrected for the
effects of dust scattering, the values obtained imply that these supernovae
have unrealistically high luminosities. We conclude that light echoes cannot
properly account for the slow decline seen in some IIn's, and that the shock
interaction is likely to dominate the continuum emission.Comment: 15 pages, 9 figure