577 research outputs found
A White Dwarf Merger Paradigm for Supernovae and Gamma-Ray Bursts
Gamma-ray bursts can appear to be a hundred times as luminous as supernovae,
but their underlying energy source(s) have remained a mystery. However, there
has been evidence for some time now of an association of gamma-ray bursts with
supernovae of Type Ib and Ic, a fact which has been exploited by a number of
models, to explain the gamma-ray burst phenomenon. Here we interpret the
results of basic observations of SN 1987A and of pulsars in globular clusters,
to propose the energy source, which powers at least some long-duration
gamma-ray bursts, as core-collapse following the merger of two white dwarfs,
either as stars or stellar cores. The beaming and intrinsic differences among
gamma-ray bursts arise, at least in part, from differing amounts and
composition of the gas in the merged stellar common envelopes, with the more
energetic bursts resulting from mergers within less massive envelopes. In order
for the beams/jets associated with gamma-ray bursts to form in mergers within
massive common envelopes (as with SN 1987A), much of the intervening stellar
material in the polar directions must be cleared out by the time of
core-collapse, or the beams/jets themselves must clear their own path. The
core-collapse produces supernovae of Type Ib, Ic, or II (as with SN 1987A, a
SNa IIp), leaving a weakly magnetized neutron star remnant with a spin period
near 2 milliseconds. There is no compelling reason to invoke any other model to
account for gamma-ray bursts. Far from being an unusual event, SN 1987A is
typical, having the same merger source of initiation as 95% of all supernovae,
the rare exceptions being Ia's induced via gradual accretion from a binary
companion, and Fe catastrophe II's.Comment: 11 pages, 0 figures. Accepted for publication in ApJ Letter
Pulsar-driven Jets in Supernovae, Gamma-Ray Bursts, and the Universe
The bipolarity of Supernova 1987A can be understood through its very early
light curve observed from the CTIO 0.4-m telescope and IUE FES, and following
speckle observations of the `Mystery Spot' by two groups. These indicate a
highly directional beam/jet of light/particles, with initial collimation
factors in excess of 10,000 and velocities in excess of 0.95 c, as an impulsive
event of up to 1e-5 solar masses interacting with circumstellar material. These
can be produced by a model proposed in 1972, by Bolotovskii and Ginzburg, which
employs pulsar emission from polarization currents induced/(modulated faster
than c) beyond the pulsar light cylinder by the periodic electromagnetic field
(supraluminally induced polarization currents -- SLIP). SLIP accounts for the
disruption of progenitors in supernova explosions and their anomalous dimming
at cosmological distances, jets from Sco X-1 and SS 433, the lack/presence of
intermittent pulsations from the high/low luminosity low mass X-ray binaries,
long/short gamma-ray bursts and predicts that their afterglows are the pulsed
optical/near infrared emission associated with these pulsars. SLIP may also
account for the TeV e+/e- results from PAMELA and ATIC, the WMAP `Haze'/Fermi
`Bubbles', and the r-process. SLIP jets from SNe of the first stars may allow
galaxies to form without dark matter, and explain the peculiar,
non-gravitational motions observed from pairs of distant galaxies by GALEX.Comment: This article has been published in the open source journal, Advances
in Astronomy: http://www.hindawi.com/journals/aa/2012/898907 This arXiv
version is out of date. arXiv admin note: substantial text overlap with
arXiv:0909.2604 (Note: but less so by v2, Also Brook Sandford in Ackn. -JM
Directional spectra comparisons between HF radar and a wave model
Directional spectra measurements using HF radar are compared with model data to confirm limitations of the currently available theory that underpins these measurements. In high seas, waveheight is overestimated but it is demonstrated that there is no clear impact on the shape of the spectrum which is in reasonable agreement with the model. The need for increased averaging before inversion is discussed
Nature of cyclical changes in the timing residuals from the pulsar B1642-03
We report an analysis of timing data for the pulsar B1642-03 (J1645-0317)
gathered over the 40-year time span between 1969 and 2008. During this
interval, the pulsar experienced eight glitch-like events with a fractional
increase in the rotation frequency Deltanu/nu=(0.9-2.6)x10^{-9}. We have
revealed two important relations in the properties of these peculiar glitches.
The first result shows that there is a strong linear correlation between the
amplitude of the glitch and the time interval to the next glitch. The second
result shows that the amplitude of the glitches is modulated by a periodic
large-scale sawtooth-like function. As a result of this modulation, the glitch
amplitude varies discretely from glitch to glitch with a step of 1.5x10^{-9} Hz
in the range (2.4-6.9)x10^{-9} Hz. The post-glitch time interval also varies
discretely with a step of about 600 days in the range 900-2700 days. An
analysis of the data showed that three modulation schemes with modulation
periods of 43 years, 53 years and 60 years are possible. The best model is the
60-year modulation scheme including 12 glitches. We make a conclusion that the
nature of the observed cyclical changes in the timing residuals from PSR
B1642-03 is a continuous generation of peculiar glitches whose amplitudes are
modulated by a periodic large-scale sawtooth-like function. As the modulation
function is periodical, the picture of cyclical timing residuals will be
exactly repeated in each modulation period or every 60 years.Comment: 26 pages, 9 figures. Accepted for publication in the Astrophysical
Journa
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