4,303 research outputs found
Waiting for the Big One: A New Class of SGR Outbursts?
It is suggested that magnetars eventually become unstable to a dynamic
overturning instability that destroys most of their dipole moment in a single
event. It is further suggested that such an instability would produce a
supergiant version of the largest soft gamma ray bursts that have thus far been
observed, and that they could be observed out to tens or even Mpc.
Persistent emission and afterglows from the fireball might confirm positive
identification with nearby galaxies and perhaps provide other distinguishing
features as well.Comment: to appear in M.N.R.A.
Relativistic cosmic ray spectra in the full non-linear theory of shock acceleration
The non-linear theory of shock acceleration was generalized to include wave dynamics. In the limit of rapid wave damping, it is found that a finite ave velocity tempers the acceleration of high Mach number shocks and limits the maximum compression ratio even when energy loss is important. For a given spectrum, the efficiency of relativistic particle production is essentially independent of v sub Ph. For the three families shown, the percentage of kinetic energy flux going into relativistic particles is (1) 72%, 2) 44%, and (3) 26% (this includes the energy loss at the upper energy cuttoff). Even small v sub ph, typical of the HISM, produce quasi-universal spectra that depend only weakly on the acoustic Mach number. These spectra should be close enough to e(-2) to satisfy cosmic ray source requirements
A model for the UHE gamma-rays from Hercules X-1
An outburst of gamma rays with energies E gamma 10 to the 12th power eV was recently detected from the X-ray pulsar Hercules X-1. The outburst had a 3 minute duration and occurred at a time during the 35 day X-ray modulation that is associated with X-ray turnon. The gamma rays also have the same 1.24 second modulation that is observed at X-ray energies. Subsequently a 40 minute outburst was detected at E gamma 10 to the 14th power eV. The interaction of ultrahigh energy particles with a precessing accretion disk explain the observed gamma ray light curve. The constraints one can place on acceleration mechanisms and the possibility that the UHE particles are accelerated by shocks in an accretion flow are explained
Efficient electron heating in relativistic shocks and gamma ray burst afterglow
Electrons in shocks are efficiently energized due to the cross-shock
potential, which develops because of differential deflection of electrons and
ions by the magnetic field in the shock front. The electron energization is
necessarily accompanied by scattering and thermalization. The mechanism is
efficient in both magnetized and non-magnetized relativistic electron-ion
shocks. It is proposed that the synchrotron emission from the heated electrons
in a layer of strongly enhanced magnetic field is responsible for gamma ray
burst afterglows.Comment: revtex
Tail emission from a ring-like jet: its application to shallow decays of early afterglows and to GRB 050709
Similar to the pulsar, the magnetic axis and the spin axis of the gamma-ray
burst source may not lie on the same line. This may cause a ring-like jet due
to collimation of the precessing magnetic axis. We analyze the tail emission
from such a jet, and find that it has a shallow decay phase with temporal index
equal to -1/2 if the Lorentz factor of the ejecta is not very high. This phase
is consistent with the shallow decay phase of some early X-ray afterglow
detected by {\it{swift}}. The ring-like jet has a tail cusp with sharp rising
and very sharp decay. This effect can provide an explanation for the
re-brightening and sharp decay of the X-ray afterglow of GRB 050709.Comment: 6 pages, 2 figures. Accepted by ChJA
On the nature of QPO in the tail of SGR giant flares
A model is presented for the quasiperiodic component of magnetar emission
during the tail phase of giant flares. The model invokes modulation of the
particle number density in the magnetosphere. The magnetospheric currents are
modulated by torsional motion of the surface and we calculate that the
amplitude of neutron star surface oscillation should be ~1% of the NS radius in
order to produce the observed features in the power spectrum. Using an
axisymmetric analytical model for structure of the magnetosphere of an
oscillating NS, we calculate the angular distribution of the optical depth to
the resonant Compton scattering. The anisotropy of the optical depth may be why
QPO are observed only at particular rotational phases.Comment: 7 pages, 4 figures, emulateapj styl
- …