8,064 research outputs found
A WENO Algorithm of the Temperature and Ionization Profiles around a Point Source
We develop a numerical solver for radiative transfer problems based on the
weighted essentially nonoscillatory (WENO) scheme modified with anti-diffusive
flux corrections, in order to solve the temperature and ionization profiles
around a point source of photons in the reionization epoch. Algorithms for such
simulation must be able to handle the following two features: 1. the sharp
profiles of ionization and temperature at the ionizing front (I-front) and the
heating front (T-front), and 2. the fraction of neutral hydrogen within the
ionized sphere is extremely small due to the stiffness of the rate equations of
atom processes. The WENO scheme can properly handle these two features, as it
has been shown to have high order of accuracy and good convergence in capturing
discontinuities and complicated structures in fluid as well as to be
significantly superior over piecewise smooth solutions containing
discontinuities. With this algorithm, we show the time-dependence of the
preheated shell around a UV photon source. In the first stage the I-front and
T-front are coincident, and propagate with almost the speed of light. In later
stage, when the frequency spectrum of UV photons is hardened, the speeds of
propagation of the ionizing and heating fronts are both significantly less than
the speed of light, and the heating front is always beyond the ionizing front.
In the spherical shell between the I- and T-fronts, the IGM is heated, while
atoms keep almost neutral. The time scale of the preheated shell evolution is
dependent on the intensity of the photon source. We also find that the details
of the pre-heated shell and the distribution of neutral hydrogen remained in
the ionized sphere are actually sensitive to the parameters used. The WENO
algorithm can provide stable and robust solutions to study these details.Comment: 24 pages, 7 figures, accepted in New Astronom
Electromagnetic emissions from near-horizon region of an extreme Kerr-Taub-Nut black hole
We have studied electromagnetic line emissions from near-horizon region in
the extremal Kerr-Taub-NUT black hole spacetime and then probe the effects of
NUT charge on the electromagnetic line emissions. Due to the presence of the
NUT charge, the equatorial plane is no more a symmetry plane of the KTN
spacetime, which leads to that the dependence of electromagnetic line emission
on the NUT charge for the observer in the Southern Hemisphere differs from that
in the Northern one. Our result indicate that the electromagnetic line emission
in the Kerr-Taub-NUT black hole case is brighter than that in the case of Kerr
black hole for the observer in the equatorial plane or in the Southern
Hemisphere, but it becomes more faint as the observer's position deviates far
from the equatorial plane in the Northern one. Moreover, we also probe effects
of redshift factor on electromagnetic emission from near-horizon region in the
extremal Kerr-Taub-NUT black hole spacetime.Comment: 18 pages, 7 figure
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