173 research outputs found
Search for Non-Triggered Gamma Ray Bursts in the BATSE Continuous Records: Preliminary Results
We present preliminary results of an off-line search for non-triggered
gamma-ray bursts (GRBs) in the BATSE daily records for about 5.7 years of
observations. We found more GRB-like events than the yield of the similar
search of Kommers et al. (1998) and extended the Log N - log P distribution
down to 0.1 ph cm s. The indication of a turnover of the
log N - log P at a small P is not confirmed: the distribution is straight at
1.5 decades with the power law index -.6 and cannot be fitted with a standard
candle cosmological model.Comment: 4 pages, LaTeX, to appear in Proceedings "Gamma Ray Bursts in the
Afterglow Era", Rome, November 1998, A&AS, 199
A New Window on Primordial non-Gaussianity
We know very little about primordial curvature perturbations on scales
smaller than about a Mpc. Measurements of the mu-type distortion of the CMB
spectrum provide the unique opportunity to probe these scales over the
unexplored range from 50 to 10^4 Mpc^-1. This is a very clean probe, in that it
relies only on well-understood linear evolution. We point out that correlations
between mu-distortion and temperature anisotropies can be used to test
Gaussianity at these very small scales. In particular the mu-T cross
correlation is proportional to the very squeezed limit of the primordial
bispectrum and hence measures fNL^loc, while mu-mu is proportional to the
primordial trispectrum and measures tauNL. We present a Fisher matrix forecast
of the observational constraints.Comment: 5 pages, one figure. v2: added clarifying comments and references,
fixed typo
Modifications to the Cosmic 21-cm Background Frequency Spectrum by Scattering via electrons in Galaxy Clusters
The cosmic 21-cm background frequency spectrum related to the spin-flip
transition of neutral Hydrogen present during and before the era of
reionization is rich in features associated with physical processes that govern
transitions between the two spin states. The intervening electrons in
foreground galaxy clusters inversely Compton scatter the 21-cm background
spectrum and modify it just as the cosmic microwave background (CMB) spectrum
is modified by inverse-Compton scattering. Towards typical galaxy clusters at
low redshifts, the resulting modification is a few tenths milli-Kelvin
correction to the few tens milli-Kelvin temperature of 21-cm signal relative to
that of the cosmic microwave background black body spectrum. The modifications
are mostly associated with sharp changes in the cosmic 21-cm background
spectrum such as due to the onset of a Lyman- radiation field or
heating of neutral gas. Though low frequency radio interferometers that are now
planned for 21-cm anisotropy measurements are insensitive to the mean 21-cm
spectrum, differential observations of galaxy clusters with these
interferometers can be utilized to indirectly establish global features in the
21-cm frequency spectrum. We discuss the feasibility to detect the spectrum
modified by clusters and find that for upcoming interferometers, while a
detection towards an individual cluster is challenging, one can average signals
over a number of clusters, selected based on the strength of the
Sunyave-Zel'dovich effect at high radio frequencies involving CMB scattering
alone, to establish the mean 21-cm spectrum.Comment: 6 pages, 3 figures, PRD in press; expanded and title changed from v1.
Final version in pres
Evolution of low-frequency features in the CMB spectrum due to stimulated Compton scattering and Doppler-broadening
We discuss a new solution of the Kompaneets-equation for physical situations
in which low frequency photons, forming relatively narrow spectral details, are
Compton scattered in an isotropic, infinite medium with an intense ambient
blackbody field that is very close to full thermodynamic equilibrium with the
free electrons. In this situation the background-induced stimulated Compton
scattering slows down the motion of photons toward higher frequencies by a
factor of 3 in comparison with the solution that only takes into account
Doppler-broadening and boosting. This new solution is important for detailed
computations of cosmic microwave background spectral distortions arising due to
uncompensated atomic transitions of hydrogen and helium in the early Universe.
In addition we derive another analytic solution that only includes the
background-induced stimulated Compton scattering and is valid for power-law
ambient radiation fields. This solution might have interesting applications for
radio lines arising inside of bright extra-galactic radio source, where
according to our estimates line shifts because of background-induced stimulated
scattering could be amplified and even exceed the line broadening due to the
Doppler-effect.Comment: 5 pages, 2 figures, submitted to A&
A Compton Up-scattering Model for Soft Lags in the Lower Kilohertz QPO in 4U1608-52
An empirical Compton up-scattering model is described which reproduces both
the fractional amplitude (RMS) vs. energy and the soft time lags in the 830 Hz
QPO observed in 4U1608-52 on Mar. 3, 1996. A combination of two coherent
variations in the coronal and soft photon temperatures (with their relative
contributions determined by enforcing energy conservation) gives rise to the
QPO's energy dependent characteristics. All input parameters to the model, save
a characteristic plasma size and the fraction of Comptonized photons impinging
on the soft photon source, are derived from the time-averaged photon energy
spectrum of the same observation. Fits to the fractional RMS and phase lag data
for this kilohertz QPO imply that the spatial extent of the plasma is in the
range from 4 to 15 km.Comment: 4 pages, 2 figure
Unusual physics of quantum plasmas
We discuss some of the peculiarities of collective phenomena in a quantum plasma. In particular, we consider “elementary” collective phenomena such as charge shielding, volume and surface oscillations in a degenerate quantum plasma, and discuss how they change compared to those in a classical plasma.Обсуждаются некоторые особенности коллективных эффектов в квантовой плазме. В частности, рассматриваются такие “элементарные” коллективные явления, как экранирование заряда, объемные и поверхностные колебания в вырожденной квантовой плазме, и обсуждаются их отличия от аналогичных явлений в классической плазме.Обговорюються деякi особливостi колективних ефектiв у квантовiй плазмi. Зокрема, розглядаються такi “елементарнi” колективнi явища, як екранування заряду, об’ємнi та поверхневi коливання в виродженiй квантовій плазмi, та обговорюються їх вiдмiнностi вiд аналогiчних явищ у класичнiй плазм
Primordial magnetic field and spectral distortion of cosmic background radiation
The role played by a primordial magnetic field during the pre-recombination
epoch is analysed through the cyclotron radiation (due to the free electrons)
it might produce in the primordial plasma. We discuss the constraint implied by
the measurement or lack thereof COBE on this primordial field.Comment: to appear in International Journal of Mod. Phy
Analytical Study on the Sunyaev-Zeldovich Effect for Clusters of Galaxies. II. comparison of covariant formalisms
We study a covariant formalism for the Sunyaev-Zeldovich effects developed in
the previous papers by the present authors, and derive analytic expressions for
the redistribution functions in the Thomson approximation. We also explore
another covariant formalism recently developed by Poutanen and Vurm. We show
that the two formalisms are mathematically equivalent in the Thomson
approximation which is fully valid for the cosmic microwave background photon
energies. The present finding will establish a theoretical foundation for the
analysis of the Sunyaev-Zeldovich effects for the clusters of galaxies.Comment: Accepted version, 7 pages, 1 figure, accepted by Physical Review D
for publicatio
Dispersion and damping of potential surface waves in a degenerate plasma
Potential (electrostatic) surface waves in plasma half-space with degenerate
electrons are studied using the quasi-classical mean-field kinetic model. The
wave spectrum and the collisionless damping rate are obtained numerically for a
wide range of wavelengths. In the limit of long wavelengths, the wave frequency
approaches the cold-plasma limit with
being the plasma frequency, while at short wavelengths, the wave
spectrum asymptotically approaches the spectrum of zero-sound mode propagating
along the boundary. It is shown that the surface waves in this system remain
weakly damped at all wavelengths (in contrast to strongly damped surface waves
in Maxwellian electron plasmas), and the damping rate nonmonotonically depends
on the wavelength, with the maximum (yet small) damping occuring for surface
waves with wavelength of , where is the
Thomas-Fermi length.Comment: 22 pages, 6 figure
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