346 research outputs found
Super-luminous X-ray Emission from the Interaction of Supernova Ejecta with Dense Circumstellar Shells
For supernova powered by the conversion of kinetic energy into radiation due
to the interactions of the ejecta with a dense circumstellar shell, we show
that there could be X-ray analogues of optically super-luminous SNe with
comparable luminosities and energetics. We consider X-ray emission from the
forward shock of SNe ejecta colliding into an optically-thin CSM shell, derive
simple expressions for the X-ray luminosity as a function of the circumstellar
shell characteristics, and discuss the different regimes in which the shock
will be radiative or adiabatic, and whether the emission will be dominated by
free-free radiation or line-cooling. We find that even with normal supernova
explosion energies of 10^51 erg, there exists CSM shell configurations that can
liberate a large fraction of the explosion energy in X-rays, producing
unabsorbed X-ray luminosities approaching 10^44 erg/s events lasting a few
months, or even 10^45 erg/s flashes lasting days. Although the large column
density of the circumstellar shell can absorb most of the flux from the initial
shock, the most luminous events produce hard X-rays that are less susceptible
to photoelectric absorption, and can counteract such losses by completely
ionizing the intervening material. Regardless, once the shock traverses the
entire circumstellar shell, the full luminosity could be available to
observers.Comment: Submitted to MNRAS. 12 pages, 4 figure
Efficient Irregular Wavefront Propagation Algorithms on Hybrid CPU-GPU Machines
In this paper, we address the problem of efficient execution of a computation
pattern, referred to here as the irregular wavefront propagation pattern
(IWPP), on hybrid systems with multiple CPUs and GPUs. The IWPP is common in
several image processing operations. In the IWPP, data elements in the
wavefront propagate waves to their neighboring elements on a grid if a
propagation condition is satisfied. Elements receiving the propagated waves
become part of the wavefront. This pattern results in irregular data accesses
and computations. We develop and evaluate strategies for efficient computation
and propagation of wavefronts using a multi-level queue structure. This queue
structure improves the utilization of fast memories in a GPU and reduces
synchronization overheads. We also develop a tile-based parallelization
strategy to support execution on multiple CPUs and GPUs. We evaluate our
approaches on a state-of-the-art GPU accelerated machine (equipped with 3 GPUs
and 2 multicore CPUs) using the IWPP implementations of two widely used image
processing operations: morphological reconstruction and euclidean distance
transform. Our results show significant performance improvements on GPUs. The
use of multiple CPUs and GPUs cooperatively attains speedups of 50x and 85x
with respect to single core CPU executions for morphological reconstruction and
euclidean distance transform, respectively.Comment: 37 pages, 16 figure
Effective-one-body waveforms calibrated to numerical relativity simulations: coalescence of non-precessing, spinning, equal-mass black holes
We present the first attempt at calibrating the effective-one-body (EOB)
model to accurate numerical-relativity simulations of spinning, non-precessing
black-hole binaries. Aligning the EOB and numerical waveforms at low frequency
over a time interval of 1000M, we first estimate the phase and amplitude errors
in the numerical waveforms and then minimize the difference between numerical
and EOB waveforms by calibrating a handful of EOB-adjustable parameters. In the
equal-mass, spin aligned case, we find that phase and fractional amplitude
differences between the numerical and EOB (2,2) mode can be reduced to 0.01
radians and 1%, respectively, over the entire inspiral waveforms. In the
equal-mass, spin anti-aligned case, these differences can be reduced to 0.13
radians and 1% during inspiral and plunge, and to 0.4 radians and 10% during
merger and ringdown. The waveform agreement is within numerical errors in the
spin aligned case while slightly over numerical errors in the spin anti-aligned
case. Using Enhanced LIGO and Advanced LIGO noise curves, we find that the
overlap between the EOB and the numerical (2,2) mode, maximized over the
initial phase and time of arrival, is larger than 0.999 for binaries with total
mass 30-200Ms. In addition to the leading (2,2) mode, we compare four
subleading modes. We find good amplitude and frequency agreements between the
EOB and numerical modes for both spin configurations considered, except for the
(3,2) mode in the spin anti-aligned case. We believe that the larger difference
in the (3,2) mode is due to the lack of knowledge of post-Newtonian spin
effects in the higher modes.Comment: 15 pages, 8 figures, typos fixed in Eqs.(7-10
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