Paper: astro-ph/0604556

Date: Wed, 26 Apr 2006 23:04:45 GMT (758kb)

Title: Terrestrial Consequences of Spectral and Temporal Variability in
Ionizing Photon Events

Authors: Larissa M. Ejzak, Adrian L. Melott, Mikhail V. Medvedev, (University
of Kansas) and Brian C. Thomas (Washburn University)

Comments: 21 pages; submitted to ApJ
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Gamma-Ray Bursts (GRBs) directed at Earth from a few kpc may have damaged the
biosphere. However, GRBs are highly variable in spectra and duration. Recent
observations indicate that short (~0.1 s) burst GRBs, which have harder
spectra, are sufficiently abundant at low redshift that they may offer an
additional significant effect. A much longer timescale is associated with shock
breakout luminosity observed in the soft X-ray (~10^3 s) and UV (~10^5 s)
emission. Here we generalize our atmospheric computations to include a broad
range of peak photon energies and investigate the effect of burst duration
while holding total fluence and other parameters constant. The results can be
used to estimate the probable impact of various kinds of ionizing events (such
as short GRBs, X-ray flashes, supernovae) upon the Earths atmosphere. The
ultimate intensity of atmospheric effects varies only slightly with burst
duration from 10^-1 s to 10^8 s. Longer durations produce delayed onset of
effects. Thus, the effect of many astrophysical events causing atmospheric
ionization can be estimated without including time development. Detailed
modeling requires specification of the season and latitude of the event.
However, harder photon spectra produce greater atmospheric effects for spectra
with peaks up to about 20 MeV, because of greater penetration into the
stratosphere. Additional observational rate and spectral information is needed
to clarify whether the probable effect on terrestrial planets of the harder
spectra of short-burst GRBs could be, despite their lower luminosity,
comparable to that of long-duration GRBs.

\\ ( http://arXiv.org/abs/astro-ph/0604556 , 758kb)