581 research outputs found
Radioactive Iron Rain: Transporting Fe in Supernova Dust to the Ocean Floor
Several searches have found evidence of Fe deposition, presumably from
a near-Earth supernova (SN), with concentrations that vary in different
locations on Earth. This paper examines various influences on the path of
interstellar dust carrying Fe from a SN through the heliosphere, with
the aim of estimating the final global distribution on the ocean floor. We
study the influences of magnetic fields, angle of arrival, wind and ocean
cycling of SN material on the concentrations at different locations. We find
that the passage of SN material through the mesosphere/lower thermosphere (MLT)
is the greatest influence on the final global distribution, with ocean cycling
causing lesser alteration as the SN material sinks to the ocean floor. SN
distance estimates in previous works that assumed a uniform distribution are a
good approximation. Including the effects on surface distributions, we estimate
a distance of pc for a SN progenitor. This
is consistent with a SN occurring within the Tuc-Hor stellar group 2.8
Myr ago with SN material arriving on Earth 2.2 Myr ago. We note that the
SN dust retains directional information to within through its
arrival in the inner Solar System, so that SN debris deposition on inert bodies
such as the Moon will be anisotropic, and thus could in principle be used to
infer directional information. In particular, we predict that existing lunar
samples should show measurable Fe differences.Comment: 18 pages, 8 figures. Comments welcom
Near-Earth Supernova Explosions: Evidence, Implications, and Opportunities
There is now solid experimental evidence of at least one supernova explosion within 100 pc of Earth within the last few million years, from measurements of the short-lived isotope â¶â°Fe in widespread deep-ocean samples, as well as in the lunar regolith and cosmic rays. This is the first established example of a specific dated astrophysical event outside the Solar System having a measurable impact on the Earth, offering new probes of stellar evolution, nuclear astrophysics, the astrophysics of the solar neighborhood, cosmic-ray sources and acceleration, multi-messenger astronomy, and astrobiology. Interdisciplinary connections reach broadly to include heliophysics, geology, and evolutionary biology. Objectives for the future include pinning down the nature and location of the established near-Earth supernova explosions, seeking evidence for others, and searching for other short-lived isotopes such as ÂČâ¶Al and ÂČâŽâŽPu. The unique information provided by geological and lunar detections of radioactive â¶â°Fe to assess nearby supernova explosions make now a compelling time for the astronomy community to advocate for supporting multi-disciplinary, cross-cutting research programs
Astrophysical Shrapnel: Discriminating Among Near-Earth Stellar Explosion Sources of Live Radioactive Isotopes
We consider the production and deposition on Earth of isotopes with
half-lives in the range 10 to 10 years that might provide
signatures of nearby stellar explosions, extending previous analyses of
Core-Collapse Supernovae (CCSNe) to include Electron-Capture Supernovae
(ECSNe), Super-Asymptotic Giant Branch (SAGBs) stars, Thermonuclear/Type Ia
Supernovae (TNSNe), and Kilonovae/Neutron Star Mergers (KNe). We revisit
previous estimates of the Fe and Al signatures, and extend these
estimates to include Pu and Mn. We discuss interpretations of
the Fe signals in terrestrial and lunar reservoirs in terms of a nearby
stellar ejection ~2.2 Myr ago, showing that (i) the Fe yield rules out
the TNSN and KN interpretations, (ii) the Fe signals highly constrain a
SAGB interpretation but do not completely them rule out, (iii) are consistent
with a CCSN origin, and (iv) are highly compatible with an ECSN interpretation.
Future measurements could resolve the radioisotope deposition over time, and we
use the Sedov blast wave solution to illustrate possible time-resolved
profiles. Measuring such profiles would independently probe the blast
properties including distance, and would provide additional constraints the
nature of the explosion.Comment: 38 pages, 6 figures. Comments welcom
High Energy Polarization of Blazars : Detection Prospects
Emission from blazar jets in the ultraviolet, optical, and infrared is
polarized. If these low-energy photons were inverse-Compton scattered, the
upscattered high-energy photons retain a fraction of the polarization. Current
and future X-ray and gamma-ray polarimeters such as INTEGRAL-SPI, PoGOLITE,
X-Calibur, Gamma-Ray Burst Polarimeter, GEMS-like missions, ASTRO-H, and
POLARIX have the potential to discover polarized X-rays and gamma-rays from
blazar jets for the first time. Detection of such polarization will open a
qualitatively new window into high-energy blazar emission; actual measurements
of polarization degree and angle will quantitatively test theories of jet
emission mechanisms. We examine the detection prospects of blazars by these
polarimetry missions using examples of 3C 279, PKS 1510-089, and 3C 454.3,
bright sources with relatively high degrees of low-energy polarization. We
conclude that while balloon polarimeters will be challenged to detect blazars
within reasonable observational times (with X-Calibur offering the most
promising prospects), space-based missions should detect the brightest blazars
for polarization fractions down to a few percent. Typical flaring activity of
blazars could boost the overall number of polarimetric detections by nearly a
factor of five to six purely accounting for flux increase of the brightest of
the comprehensive, all-sky, Fermi-LAT blazar distribution. The instantaneous
increase in the number of detections is approximately a factor of two, assuming
a duty cycle of 20% for every source. The detectability of particular blazars
may be reduced if variations in the flux and polarization fraction are
anticorrelated. Simultaneous use of variability and polarization trends could
guide the selection of blazars for high-energy polarimetric observations.Comment: Matches published version in Ap
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