5,093 research outputs found
Laue gamma-ray lenses for space astrophysics:status and prospects
We review feasibility studies, technological developments and astrophysical
prospects for Laue lenses devoted to hard X-/gamma-ray astronomy observations.Comment: 26 pages, 24 figures. Published in a special issue (Volume 2010
(2010), Article ID 215375, doi:10.1155/2010/215375) of the on-line journal
"X-Ray Optics and Instrumentation", devoted to "X-Ray Focusing: Techniques
and Applications
An upscattering spectral formation model for the prompt emission of Gamma-Ray Bursts
We propose a model for the spectral formation of Gamma Ray Burst (GRB) prompt
emission, where the phenomenological Band's function is usually applied to
describe the GRB prompt emission. We suggest that the GRB prompt emission is
mainly a result of two upscattering processes. The first process is the
Comptonization of relatively cold soft photons of the star off electrons of a
hot shell of plasma of temperature T_e of the order of 10^{9} K (or kT_e~100
keV) that moves sub-relativistically with the bulk velocity V_b substantially
less than the speed of light c. In this phase, the Comptonization parameter Y
is high and the interaction between a blackbody-like soft seed photon
population and hot electrons leads to formation of a saturated Comptonization
spectrum modified by the sub-relativistic bulk outflow. The second process is
an upscattering of the previously Comptonized spectrum by the plasma outflow
once it becomes relativistic. This process gives rise to the high-energy
power-law component above the peak in the EF(E)-diagram where F(E) is the
energy flux. The latter process can be described by a convolution of the
Comptonized spectrum with a broken-power-law Green function. Possible physical
scenarios for this second upscattering process are discussed. In the framework
of our model, we give an interpretation of the Amati relation between the
intrinsic spectral peak photon energy and radiated energy or luminosity, and we
propose a possible explanation of the GRB temporal variability.Comment: 27 pages, 8 figures, accepted for publication in the Astrophysical
Journa
Expected performance of a Laue lens based on bent crystals
In the context of the LAUE project devoted to build a long focal length
focusing optics for soft gamma-ray astronomy (70/100 keV to 600 keV), we
present results of simulation of a Laue lens, based on bent crystals in
different assembling configurations (quasi-mosaic and reflection-like
geometries). The main aim is to significantly overcome the sensitivity limits
of the current generation of gamma-ray telescopes and improve the imaging
capability.Comment: 7 pages, 7 figures, presented at the Space Telescopes and
Instrumentation Symposium 2012: Ultraviolet to Gamma Ray Conference.
Published in Proceedings of the SPIE, Volume 8443, id. 844331-844331-7 (2012
Numerical study of the random field Ising model at zero and positive temperature
In this paper the three dimensional random field Ising model is studied at
both zero temperature and positive temperature. Critical exponents are
extracted at zero temperature by finite size scaling analysis of large
discontinuities in the bond energy. The heat capacity exponent is
found to be near zero. The ground states are determined for a range of external
field and disorder strength near the zero temperature critical point and the
scaling of ground state tilings of the field-disorder plane is discussed. At
positive temperature the specific heat and the susceptibility are obtained
using the Wang-Landau algorithm. It is found that sharp peaks are present in
these physical quantities for some realizations of systems sized and
larger. These sharp peaks result from flipping large domains and correspond to
large discontinuities in ground state bond energies. Finally, zero temperature
and positive temperature spin configurations near the critical line are found
to be highly correlated suggesting a strong version of the zero temperature
fixed point hypothesis.Comment: 11 pages, 14 figure
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