4 research outputs found
Terrestrial Consequences of Spectral and Temporal Variability in Ionizing Photon Events
Gamma-Ray Bursts (GRBs) directed at Earth from within a few kpc may have
damaged the biosphere, primarily though changes in atmospheric chemistry which
admit greatly increased Solar UV. However, GRBs are highly variable in spectrum
and duration. Recent observations indicate that short (~0.1 s) burst GRBs,
which have harder spectra, may be 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, and radioactive decay gamma-ray line radiation
emitted during the light curve phase of supernovae (~10^7 s). 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 terrestrial atmosphere. We find that the ultimate
intensity of atmospheric effects varies only slightly with burst duration from
10^-1 s to 10^8 s. Therefore, the effect of many astrophysical events causing
atmospheric ionization can be approximated without including time development.
Detailed modeling requires specification of the season and latitude of the
event. Harder photon spectra produce greater atmospheric effects for spectra
with peaks up to about 20 MeV, because of greater penetration into the
stratosphere.Comment: 30 pages, to be published in ApJ. Replaced for conformity with
published version, including correction of minor typos and updated reference
Climatic and Biogeochemical Effects of a Galactic Gamma-Ray Burst
It is likely that one or more gamma-ray bursts within our galaxy have
strongly irradiated the Earth in the last Gy. This produces significant
atmospheric ionization and dissociation, resulting in ozone depletion and
DNA-damaging ultraviolet solar flux reaching the surface for up to a decade.
Here we show the first detailed computation of two other significant effects.
Visible opacity of NO2 is sufficient to reduce solar energy at the surface up
to a few percent, with the greatest effect at the poles, which may be
sufficient to initiate glaciation. Rainout of dilute nitric acid is could have
been important for a burst nearer than our conservative nearest burst. These
results support the hypothesis that the characteristics of the late Ordovician
mass extinction are consistent with GRB initiation.Comment: 12 pages, 2 figures, in press at Geophysical Research Letters. Minor
revisions, including details on falsifying the hypothesi