334 research outputs found
Exact solutions for sporadic acceleration of cosmic rays
The steady state spectra of cosmic rays which are subject to a sporadic acceleration process, wherein the gain in energy in each encounter is a finite fraction of the particle energy are discussed. They are derived from a mathematical model which includes the possibility of energy dependent leakage of cosmic rays from the galaxy. Comparison with observations allows limits to be placed on the frequency and efficiency of such encounters
Early observations of the Afterglow of GRB000301c
We report multiband observations of the Optical Transient (OT) associated
with GRB000301c carried out between 2--4 March 2000 using the 2.34-m Vainu
Bappu Telescope (VBT) at Kavalur, India. When combined with other reported
data, the initial decline in the R-band magnitude with log (), the time
since the burst is fit with a slope = -0.70 0.07 which
steepens after about 6.0 days to a slope of = -2.44 0.29.
This change in slope does not occur smoothly but there is an indication for a
bimodal distribution. The available measurements of the evolution of (B--R)
color do not show any discernible evolution in the first 12 days.Comment: 14 pages, 2 postscript figures, Accepted for Publication in ApJ
Letter
Halo of NGC 4631 and models of cosmic-ray transport
The halo of edge on spiral galaxy of NGC 4631 is studied from 327 MHz to 10700 MHz to delineate the models of cosmic ray transport. Preliminary studies show that the spectral steepening as a function of height above the plane can be understood in terms of the simplest cosmic ray transport models, viz., simple isotropic diffusion in an infinite medium
What's old and what's new about neutrinos
To save the laws of conservation of energy, linear and angular momentum, Pauli suggested the possible existence of an elementary particle possessing no electric charge and very little mass called the neutrino, which was emitted in β-decay of the nuclei. Subsequent work over the decades has proved the existence of this particle and has proved its importance not only to the physics of elementary particles but also to astrophysics and cosmology. This article is triggered by the recent experiments which show that the neutrinos of one flavour, as they speed through space, periodically transmogrify onto other flavours. This discovery is comparable to the discovery of the electron in that it provides the basis to new physics beyond the currently accepted Standard Model
The Neutrino Hypothesis for Dark Matter in dwarf spheroidals
The theoretical expectation of the high mass of ≳ 400 eV for the particles constituting the dark matter in dwarf-spheroidals as an artifact of the implicit assumption that the density of particles vanishes at the visible edge. On the contrary if our Galaxy and the dwarf-spheroidals are embedded in a neutrino condensation of the dimensions of the cluster then mv ≃ 10 eV can accommodate all the observations
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