75,610 research outputs found
GRB afterglows: deep Newtonian phase and its application
Gamma-ray burst afterglows have been observed for months or even years in a
few cases. It deserves noting that at such late stages, the remnants should
have entered the deep Newtonian phase, during which the majority of
shock-accelerated electrons will no longer be highly relativistic. To calculate
the afterglows, we must assume that the electrons obey a power-law distribution
according to their kinetic energy, not simply the Lorentz factor.Comment: Poster at the 4th workshop "Gamma-Ray Bursts in the Afterglow Era"
(Rome, 2004), accepted for publication in the proceedings. 4 pages, with 3
figures inserte
Zero modes and charged Skyrmions in graphene bilayer
We show that the electric charge of the Skyrmion in the vector order
parameters that characterize the quantum anomalous spin Hall state and the
layer-antiferromagnet in a graphene bilayer is four and zero, respectively. The
result is based on the demonstration that a vortex configuration in two broken
symmetry states in bilayer graphene with the quadratic band crossing has the
number of zero modes doubled relative to the single layer. The doubling can be
understood as a result of Kramers' theorem implied by the "pseudo time
reversal" symmetry of the vortex Hamiltonian. Disordering the quantum anomalous
spin Hall state by Skyrmion condensation should produce a superconductor of an
elementary charge 4e.Comment: 4+ pages, one table, one figure; (v2) improved pedagogy, new
expression for the Pontryagin index derived, additional explanations; (v3)
new and updated references, minor typos corrected, published versio
Isothermal Shock Formation in Non-Equatorial Accretion Flows around Kerr Black Holes
We explore isothermal shock formation in non-equatorial, adiabatic accretion
flows onto a rotating black hole, with possible application to some active
galactic nuclei (AGNs). The isothermal shock jump conditions as well as the
regularity condition, previously developed for one-dimensional (1D) flows in
the equatorial plane, are extended to two-dimensional (2D), non-equatorial
flows, to explore possible geometrical effects. The basic hydrodynamic
equations with these conditions are self-consistently solved in the context of
general relativity to explore the formation of stable isothermal shocks. We
find that strong shocks are formed in various locations above the equatorial
plane, especially around a rapidly-rotating black hole with the prograde flows
(rather than a Schwarzschild black hole). The retrograde flows are generally
found to develop weaker shocks. The energy dissipation across the shock in the
hot non-equatorial flows above the cooler accretion disk may offer an
attractive illuminating source for the reprocessed features, such as the iron
fluorescence lines, which are often observed in some AGNs.Comment: 22 pages with 11 figures, presented at 5th international conference
on high energy density laboratory astrophysics in Tucson, Arizona. accepted
to Ap
Beaming effects in GRBs and orphan afterglows
The overall dynamical evolution and radiation mechanism of -ray burst
jets are briefly introduced. Various interesting topics concerning beaming in
-ray bursts are discussed, including jet structures, orphan afterglows
and cylindrical jets. The possible connection between -ray bursts and
neutron star kicks is also addressed.Comment: 10 Pages, 4 figures, to appear in a special issue of ApSS. Oral
report presented at "The Multiwavelength Approach to Unidentified Gamma-Ray
Sources" (Hong Kong, June 1 - 4, 2004; Conference organizers: K.S. Cheng and
G.E. Romero
Gaussian Effective Potential and the Coleman's normal-ordering Prescription : the Functional Integral Formalism
For a class of system, the potential of whose Bosonic Hamiltonian has a
Fourier representation in the sense of tempered distributions, we calculate the
Gaussian effective potential within the framework of functional integral
formalism. We show that the Coleman's normal-ordering prescription can be
formally generalized to the functional integral formalism.Comment: 6 pages, revtex; With derivation details and an example added. To
appear in J. Phys.
Beaming Effects in Gamma-Ray Bursts
Based on a refined generic dynamical model, we investigate afterglows from
jetted gamma-ray burst (GRB) remnants numerically. In the relativistic phase,
the light curve break could marginally be seen. However, an obvious break does
exist at the transition from the relativistic phase to the non-relativistic
phase, which typically occurs at time 10 to 30 days. It is very interesting
that the break is affected by many parameters, especially by the electron
energy fraction (xi_e), and the magnetic energy fraction (xi_B^2). Implication
of orphan afterglow surveys on GRB beaming is investigated. The possible
existence of a kind of cylindrical jets is also discussed.Comment: Minor changes; 10 pages, with 9 eps figures embedded. Talk given at
the Sixth Pacific Rim Conference on Stellar Astrophysics (Xi'an, China, July
11-17, 2002). A slightly revised version will appear in the proceeding
Fireball/Blastwave Model and Soft Gamma-ray Repeaters
Soft gamma-ray repeaters are at determined distances and their positions are
known accurately. If observed, afterglows from their soft gamma-ray bursts will
provide important clues to the study of the so called "classical gamma-ray
bursts". On applying the popular fireball/blastwave model of classical
gamma-ray bursts to soft gamma-ray repeaters, it is found that their X-ray and
optical afterglows are detectable. Monitoring of the three repeaters is
solicited.Comment: Already published in 1998 in "Chinese Physics Letters", replaced with
the published version. See astro-ph/0502452 for a more detailed versio
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