22,392 research outputs found
X-Ray Flares from Postmerger Millisecond Pulsars
Recent observations support the suggestion that short-duration gamma-ray
bursts are produced by compact star mergers. The X-ray flares discovered in two
short gamma-ray bursts last much longer than the previously proposed postmerger
energy release time scales. Here we show that they can be produced by
differentially rotating, millisecond pulsars after the mergers of binary
neutron stars. The differential rotation leads to windup of interior poloidal
magnetic fields and the resulting toroidal fields are strong enough to float up
and break through the stellar surface. Magnetic reconnection--driven explosive
events then occur, leading to multiple X-ray flares minutes after the original
gamma-ray burst.Comment: 10 pages, published in Scienc
Coronal magnetic topology and the production of solar impulsive energetic electrons
We investigate two candidate solar sources or active regions (ARs) in
association with a solar impulsive energetic electron (SIEE) event on 2002
October 20. The solar particle release (SPR) times of SIEEs are derived by
using their velocity dispersion with consideration of the instrumental effect.
It is found that there are double electron injections at the Sun. The
low-energy (<13 keV) electron injection coincides with a C6.6 flare in AR10154
and is accompanied with prominent type III radio bursts rather than a stronger
M1.8 flare in AR10160. The M1.8 flare produces, however, faint type III radio
bursts. Whereas electrons of 25 to 300 keV are released 9 min later when a
jet-like CME travels to 2.6 solar radii. We further examine the coronal
magnetic configurations above the two ARs based on the potential field source
surface (PFSS) model. It is found that open field lines, rooted in AR10154 and
well connected to the Earth, provide escaping channels for energetic electrons.
Only a small portion of magnetic fields are opened above AR10160, being
responsible for the faint type III radio bursts. These lines are, however, not
well connected, making it impossible for SIEEs detection by near-Earth
spacecraft. The results appear to establish a physical link between coronal
magnetic topology, formation of type III radio bursts, and production of SIEEs.Comment: A&A Letters, accepte
Intrinsic Parameters of GRB990123 from Its Prompt Optical Flash and Afterglow
We have constrained the intrinsic parameters, such as the magnetic energy
density fraction (), the electron energy density fraction
(), the initial Lorentz factor () and the Lorentz factor
of the reverse external shock (), of GRB990123, in terms of the
afterglow information (forward shock model) and the optical flash information
(reverse shock model). Our result shows: 1) the inferred values of
and are consistent with the suggestion that they may be universal
parameters, comparing to those inferred for GRB970508; 2) the reverse external
shock may have become relativistic before it passed through the ejecta shell.
Other instrinsic parameters of GRB990123, such as energy contained in the
forward shock and the ambient density are also determined and discussed
in this paper.Comment: 5 pages, MN LaTeX style, a few changes made according to referee's
suggestions, references up dated, MNRAS accepte
Quantum criticality and nodal superconductivity in the FeAs-based superconductor KFe2As2
The in-plane resistivity and thermal conductivity of
FeAs-based superconductor KFeAs single crystal were measured down to 50
mK. We observe non-Fermi-liquid behavior at =
5 T, and the development of a Fermi liquid state with when
further increasing field. This suggests a field-induced quantum critical point,
occurring at the superconducting upper critical field . In zero field
there is a large residual linear term , and the field dependence of
mimics that in d-wave cuprate superconductors. This indicates that
the superconducting gaps in KFeAs have nodes, likely d-wave symmetry.
Such a nodal superconductivity is attributed to the antiferromagnetic spin
fluctuations near the quantum critical point.Comment: 4 pages, 4 figures - replaces arXiv:0909.485
Optical Flashes and Very Early Afterglows in Wind Environments
The interaction of a relativistic fireball with its ambient medium is
described through two shocks: a reverse shock that propagates into the
fireball, and a forward shock that propagates into the medium. The observed
optical flash of GRB 990123 has been considered to be the emission from such a
reverse shock. The observational properties of afterglows suggest that the
progenitors of some GRBs may be massive stars and their surrounding media may
be stellar winds. We here study very early afterglows from the reverse and
forward shocks in winds. An optical flash mainly arises from the relativistic
reverse shock while a radio flare is produced by the forward shock. The peak
flux densities of optical flashes are larger than 1 Jy for typical parameters,
if we do not take into account some appropriate dust obscuration along the line
of sight. The radio flare always has a long lasting constant flux, which will
not be covered up by interstellar scintillation. The non-detections of optical
flashes brighter than about 9th magnitude may constrain the GRBs isotropic
energies to be no more than a few ergs and wind intensities to be
relatively weak.Comment: 21 pages, 6 figures, accepted by MNRAS on March 7, 200
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