20,637 research outputs found
On the Common Envelope Efficiency
In this work, we try to use the apparent luminosity versus displacement
(i.e., vs. ) correlation of high mass X-ray binaries (HMXBs) to
constrain the common envelope (CE) efficiency , which is a key
parameter affecting the evolution of the binary orbit during the CE phase. The
major updates that crucial for the CE evolution include a variable
parameter and a new CE criterion for Hertzsprung gap donor stars, both of which
are recently developed. We find that, within the framework of the standard
energy formula for CE and core definition at mass \%, a high value of
, i.e., around 0.8-1.0, is more preferable, while likely can not reconstruct the observed vs.
distribution. However due to an ambiguous definition for the core boundary in
the literature, the used here still carries almost two order of
magnitude uncertainty, which may translate directly to the expected value of
. We present the detailed components of current HMXBs and
their spatial offsets from star clusters, which may be further testified by
future observations of HMXB populations in nearby star-forming galaxies.Comment: 14 pages, 10 figures, 7 tables, accepted for publication in MNRA
High-Energy Gamma-Rays from GRB X-ray Flares
The recent detection of X-ray flares during the afterglow phase of gamma-ray
bursts (GRBs) suggests an inner-engine origin, at radii inside the forward
shock. There must be inverse Compton (IC) emission arising from such flare
photons scattered by forward shock afterglow electrons when they are passing
through the forward shock. We find that this IC emission produces high energy
gamma-ray flares, which may be detected by AGILE, GLAST and ground-based TeV
telescopes. The anisotropic IC scattering between flare photons and forward
shock electrons does not affect the total IC component intensity, but cause a
time delay of the IC component peak relative to the flare peak. The anisotropic
scattering effect may also weaken, to some extent, the suppression effect of
the afterglow intensity induced by the enhanced electron cooling due to flare
photons. We speculate that this IC component may already have been detected by
EGRET from a very strong burst--GRB940217. Future observations by GLAST may
help to distinguish whether X-ray flares originate from late central engine
activity or from external shocks.Comment: 4 pages, Contributed talk presented at "The First GLAST Symposium",
Feb.5-8 2007, Stanford Universit
On the magnetization of gamma-ray burst blast waves
The origin of magnetic fields that permeate the blast waves of gamma-ray
bursts (GRBs) is a long-standing problem. The present paper argues that in four
GRBs revealing extended emission at >100 MeV, with follow-up in the radio,
optical and X-ray domains at later times, this magnetization can be described
as the partial decay of the micro-turbulence that is generated in the shock
precursor. Assuming that the bulk of the extended emission >100 MeV can be
interpreted as synchrotron emission of shock accelerated electrons, we model
the multi-wavelength light curves of GRB 090902B, GRB 090323, GRB 090328 and
GRB 110731A, using a simplified then a full synchrotron calculation with
power-law-decaying microturbulence \epsilon_B \propto t^{\alpha_t} (t denotes
the time since injection through the shock, in the comoving blast frame). We
find that these models point to a consistent value of the decay exponent -0.5 <
\alpha_t < -0.4.Comment: 8 pages, 4 figures - discussion added, conclusions unchanged -
version to appear in MNRA
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