1,180 research outputs found
Very High Lorentz Factor Fireballs and Gamma-Ray Burst Spectra
Collisionless entrainment of the surrounding matter imports the relativistic
baryon component in the Gamma-Ray Burst (GRB) fireball frame. We show that half
the fireball energy can be transferred from radiation to the comoving hot
motions of baryons under the photosphere. The yet baryon-poor fireball can
reexpand to a very high Lorentz factor (VHLF) \Gamma ~ 10^3-10^6 by its own
relativistic collisionless pressure beyond the photosphere (so-called
collisionless bulk acceleration), leading to internal and external shocks. A
simple synchrotron emission from the VHLF internal shocks produces (i) the
extra power-law spectral component with variability observed in the Fermi GeV
bursts, up to the TeV range for the future Cherenkov Telescope Array (CTA),
(ii) the GeV onset delay with a weak luminosity dependence t_{delay} ~
L^{-1/5}, and (iii) the spectral break of GRB 090926 by the synchrotron cooling
break or the maximum synchrotron cutoff limited by the dynamical time, not by
the e+- creation cutoff. The relativistic baryon component could also heat the
photospheric thermal photons into the main GRB Band spectrum via pp, p\gamma
(Bethe-Heitler and photomeson), and Coulomb thermalization processes. In this
hot photosphere-internal-external shock model, we can predict the
anticorrelation of ~TeV neutrinos and GeV gamma-rays, which may be detectable
using IceCube. The spectral peak and luminosity (Yonetoku) relation is also
reproduced if the progenitor stars are nearly identical. We also discuss the
steep/shallow decay of early X-ray afterglows and short GRBs.Comment: 21 pages, 6 figures, final version to be published in Progress of
Theoretical Physic
Soft hadron production in pp interactions up to ISR energies
Soft hadron production is described as a two-step process, where the
interaction of the partonic constituents of the colliding hadrons leads to the
production of intermediate subsystems (fireballs), which decay subsequently
into hadrons. The weights of the various final states are derived from the
corresponding phase-space factors modified by empirical transition elements.
The results compare well with data at energies between particle production
thresholds and ISR energies. Special emphasis is put on correlation data, which
offer the opportunity to shed some light on the question whether particle
production proceeds via fireballs or strings.Comment: 14 pages, 19 figure
The order, shape and critical point for the quark-gluon plasma phase transition
The order, shape and critical point for the phase transition between the
hadronic matter and quark-gluon plasma are considered in a thermodynamical
consistent approach. The hadronic phase is taken as Van der Waals gas of all
the known hadronic mass spectrum particles GeV as well as Hagedorn
bubbles which correspond hadronic states with mass spectrum GeV. The
density of states for Hagedorn bubbles is derived by calculating the
microcanonical ensemble for a bag of quarks and gluons with specific internal
color-flavor symmetry. The mixed-grand and microcanonical ensembles are derived
for massless and massive flavors. We find Hagedorn bubbles are strongly
suppressed in the dilute hadronic matter and they appear just below the line of
the phase transition. The order of the phase transition depends on Hagedorn
bubble's internal color-flavor structure and the volume fluctuation as well. On
the other hand, the highly compressed hadronic matter undergoes a smooth phase
transition from the gas of known mass spectrum hadrons to another one dominated
by Hagedorn bubbles with specific internal color-flavor structure before the
phase transition to quark-gluon plasma takes place at last. The phase
transition is found a first order for the intermediate and large chemical
potentials. The existence of the tri-critical point depends on the modification
of the bubble's internal structure specified by a phenomenological parameter
in the medium.Comment: 69 pages, 10 figure
Proto-type installation of a double-station system for the optical-video-detection and orbital characterisation of a meteor/fireball in South Korea
We give a detailed description of the installation and operation of a
double-station meteor detection system which formed part of a research &
education project between Korea Astronomy Space Science Institute and Daejeon
Science Highschool. A total of six light-sensitive CCD cameras were installed
with three cameras at SOAO and three cameras at BOAO observatory. A
double-station observation of a meteor event enables the determination of the
three-dimensional orbit in space. This project was initiated in response to the
Jinju fireball event in March 2014. The cameras were installed in
October/November 2014. The two stations are identical in hardware as well as
software. Each station employes sensitive Watec-902H2 cameras in combination
with relatively fast f/1.2 lenses. Various fields of views were used for
measuring differences in detection rates of meteor events. We employed the
SonotaCo UFO software suite for meteor detection and their subsequent analysis.
The system setup as well as installation/operation experience is described and
first results are presented. We also give a brief overview of historic as well
as recent meteor (fall) detections in South Korea. For more information please
consult http://meteor.kasi.re.kr .Comment: Technical/instrumentation description of a professional meteor
detection system, 23 pages, 20 figures (color/monochrome), 5 tables,
submitted to the Journal of Korean Astronomical Society (JKAS,
http://jkas.kas.org/, http://jkas.kas.org/history.html
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