786 research outputs found
Iron K Lines from Gamma Ray Bursts
We present models for reprocessing of an intense flux of X-rays and gamma
rays expected in the vicinity of gamma ray burst sources. We consider the
transfer and reprocessing of the energetic photons into observable features in
the X-ray band, notably the K lines of iron. Our models are based on the
assumption that the gas is sufficiently dense to allow the microphysical
processes to be in a steady state, thus allowing efficient line emission with
modest reprocessing mass and elemental abundances ranging from solar to
moderately enriched. We show that the reprocessing is enhanced by
down-Comptonization of photons whose energy would otherwise be too high to
absorb on iron, and that pair production can have an effect on enhancing the
line production. Both "distant" reprocessors such as supernova or wind remnants
and "nearby" reprocessors such as outer stellar envelopes can reproduce the
observed line fluxes with Fe abundances 30-100 times above solar, depending on
the incidence angle. The high incidence angles required arise naturally only in
nearby models, which for plausible values can reach Fe line to continuum ratios
close to the reported values.Comment: 37 pages, 10 figures. Ap. J in pres
The Poincaré and related groups are algebraically determined Polish groups
The purpose of this paper is to prove a new topological fact about the Poincar\'{e} and related groups. If is a group, say that is an algebraically determined Polish (i.e., complete separable metric topological) group if, whenever is a Polish group and is an algebraic isomorphism, then is a topological isomorphism. The proper Lorentz group, the proper orthochronous Lorentz group and the Heisenberg group are examples of Polish groups that are not algebraically determined. On the other hand it will be shown that the Lorentz group, the orthochronous Lorentz group and the Poincar\'{e} group and the other closely associated semi-direct products are algebraically determined Polish groups
Modeling of Photoionized Plasmas
In this paper I review the motivation and current status of modeling of
plasmas exposed to strong radiation fields, as it applies to the study of
cosmic X-ray sources. This includes some of the astrophysical issues which can
be addressed, the ingredients for the models, the current computational tools,
the limitations imposed by currently available atomic data, and the validity of
some of the standard assumptions. I will also discuss ideas for the future:
challenges associated with future missions, opportunities presented by improved
computers, and goals for atomic data collection.Comment: 17 pages, 8 figures, to appear in the proceedings of Xray2010,
Utrecht, the Netherlands, March 15-17 201
Nitrogen K-shell photoabsorption
Reliable atomic data have been computed for the spectral modeling of the
nitrogen K lines, which may lead to useful astrophysical diagnostics. Data sets
comprise valence and K-vacancy level energies, wavelengths, Einstein
-coefficients, radiative and Auger widths and K-edge photoionization cross
sections. An important issue is the lack of measurements which are usually
employed to fine-tune calculations so as to attain spectroscopic accuracy. In
order to estimate data quality, several atomic structure codes are used and
extensive comparisons with previous theoretical data have been carried out. In
the calculation of K photoabsorption with the Breit--Pauli -matrix method,
both radiation and Auger damping, which cause the smearing of the K edge, are
taken into account. This work is part of a wider project to compute atomic data
in the X-ray regime to be included in the database of the popular {\sc xstar}
modeling code
An X-Ray Spectroscopic Study of the SMC X-1/Sk 160 System
We have investigated the composition and distribution of the wind of Sk 160,
the supergiant companion of the X-ray star SMC X-1, by comparing an X-ray
spectrum of the source, obtained with the ASCA observatory, during an eclipse
with the computed spectra of reprocessed radiation from circumstellar matter
with various density distributions. We show that the metal abundance in the
wind of Sk 160 is no greater than a few tenths of solar, as has been determined
for other objects in the Magellanic Clouds. We also show that the observed
X-ray spectrum is not consistent with the density distributions of
circumstellar matter of the spherically symmetric form derived for line-driven
winds, nor with the density distribution derived from a hydrodynamic simulation
of the X-ray perturbed and line-driven wind by Blondin & Woo (1995).Comment: 35 pages including 16 figures, uses AASTeX v5.0.2, accepted to Ap
Atomic data for the K-vacancy states of Fe XXIV
As part of a project to compute improved atomic data for the spectral
modeling of iron K lines, we report extensive calculations and comparisons of
atomic data for K-vacancy states in Fe XXIV. The data sets include: (i) energy
levels, line wavelengths, radiative and Auger rates; (ii) inner-shell electron
impact excitation rates and (iii) fine structure inner-shell photoionization
cross sections. The calculations of energy levels and radiative and Auger rates
have involved a detailed study of orbital representations, core relaxation,
configuration interaction, relativistic corrections, cancellation effects and
semi-empirical corrections. It is shown that a formal treatment of the Breit
interaction is essential to render the important magnetic correlations that
take part in the decay pathways of this ion. As a result, the accuracy of the
present A-values is firmly ranked at better than 10% while that of the Auger
rates at only 15%. The calculations of collisional excitation and
photoionization cross sections take into account the effects of radiation and
spectator Auger dampings. In the former, these effects cause significant
attenuation of resonances leading to a good agreement with a simpler method
where resonances are excluded. In the latter, resonances converging to the K
threshold display symmetric profiles of constant width that causes edge
smearing.Comment: 18 pages, 8 figures, submitted to Astronomy & Astrophysics 200
Early X-ray/UV Line Signatures of GRB Progenitors and Hypernovae
We calculate the X-ray/UV spectral line signatures expected from the
interaction of a gamma-ray burst afterglow and a dense pre-burst environment
produced by the progenitor. We explore the conditions under which Fe line and
edge equivalent widths of 1 keV can arise, and discuss the possibility
of gaining information about possible progenitor scenarios using X-ray metal
line spectra in the first few days of a burst. A wind or supernova shell around
the burst produces an X-ray absorption line spectrum and later emission lines,
while a hypernova funnel model produces mainly emission lines. The Fe \ked can
in some cases be more prominent than the Fe \kal line. Under simple assumptions
for the input continuum luminosity, current reports of observed Fe line
luminosities are compatible with an Fe-enriched funnel model, while lower
values are expected in shell models.Comment: revisions to ApJ ms first submitted 8/21/99; uses a higher and
flatter input spectrum, with modified implications suggesting preference for
funnel model
Decay Properties of K-Vacancy States in Fe X-Fe XVII
We report extensive calculations of the decay properties of fine-structure
K-vacancy levels in Fe X-Fe XVII. A large set of level energies, wavelengths,
radiative and Auger rates, and fluorescence yields has been computed using
three different standard atomic codes, namely Cowan's HFR, AUTOSTRUCTURE and
the Breit-Pauli R-matrix package. This multi-code approach is used to the study
the effects of core relaxation, configuration interaction and the Breit
interaction, and enables the estimate of statistical accuracy ratings. The
K-alpha and KLL Auger widths have been found to be nearly independent of both
the outer-electron configuration and electron occupancy keeping a constant
ratio of 1.53+/-0.06. By comparing with previous theoretical and measured
wavelengths, the accuracy of the present set is determined to be within 2 mA.
Also, the good agreement found between the different radiative and Auger data
sets that have been computed allow us to propose with confidence an accuracy
rating of 20% for the line fluorescence yields greater than 0.01. Emission and
absorption spectral features are predicted finding good correlation with
measurements in both laboratory and astrophysical plasmas.Comment: 13 pages, 4 figures. Submitted to A&A. Electronic Table 3-4 available
at http://lheawww.gsfc.nasa.gov/users/palmeri/patrick.htm
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