3,086 research outputs found
Onset of Melting in Quark-Gluon Fluid at RHIC
A strong suppression in central Au+Au collisions has been observed
by the PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC). We
develop a hydro+ model in which hot quark-gluon matter is described by
the full (3+1)-dimensional relativistic hydrodynamics and is treated
as an impurity traversing through the matter. The experimental
suppression pattern in mid-rapidity is reproduced well by the sequential
melting of , , and in dynamically expanding
fluid. The melting temperature of directly produced is well
constrained by the participant-number dependence of the suppression
and is found to be about with being the
pseudo-critical temperature.Comment: 5 pages, 5 figures, Submitted to Phys. Rev. C. (Rapid Communication
Gamma-Ray Burst Polarimeter - GAP - aboard the Small Solar Power Sail Demonstrator IKAROS
The small solar power sail demonstrator "IKAROS" is a Japanese engineering
verification spacecraft launched by H-IIA rocket on May 21, 2010 at JAXA
Tanegashima Space Center. IKAROS has a huge sail with 20 m in diameter which is
made of thin polyimide membrane. This sail converts the solar
radiation-pressure into the propulsion force of IKAROS and accelerates the
spacecraft. The Gamma-Ray Burst Polarimeter (GAP) aboard IKAROS is the first
polarimeter to observe the gamma-ray polarization of Gamma-Ray Bursts (GRBs)
during the IKAROS cruising phase. GAP is a tinny detector of 3.8 kg in weight
and 17 cm in size with an energy range between 50-300 keV. The GAP detector
also plays a role of the interplanetary network (IPN) to determine the GRB
direction. The detection principle of gamma-ray polarization is the anisotropy
of the Compton scattering. GAP works as the GRB polarimeter with the full
coincidence mode between the central plastic and the surrounding CsI detectors.
GAP is the first instrument, devoted for the observation of gamma-ray
polarization in the astronomical history. In this paper, we present the GAP
detector and its ground and onboard calibrations.Comment: Submitted to Publications of the Astronomical Society of Japan
(PASJ), 23 pages, 14 figure
suppression in the threshold model at RHIC and LHC energy
In the QGP based threshold model \cite{Blaizot:2000ev,Blaizot:1996nq}, in
addition to the normal nuclear absorption, 's are subjected to an
'anomalous' suppression such that above a threshold density , all
the 's are melted. In the threshold model we have analysed the recent
PHENIX data on the centrality dependence of suppression in Au+Au
collisions at RHIC. Feedback from decay of the state is accounted for.
's are anomalously suppressed above a threshold density,
. Threshold density for anomalous
suppression of the state is uncertain to a large extent, . The fraction of the state can not be determined
unambiguously, depending on the nuclear absorption, it can vary from 20% to
40%. We have also predicted for the suppression in Pb+Pb collisions at LHC
energy. In central Pb+Pb collisions, 's are suppressed by a factor of
3-4. Suppression pattern is rather similar to that in Au+Au collisions, if not
slighty less in central collisions. Using the PHENIX data on the participant
number dependence of the Bjorken energy density, we have also estimated the QGP
formation time. For critical temperature =192 MeV, estimated QGP formation
time ranges between 0.07-0.09 fm/c.Comment: 9 pages, 9 figure
Measuring energy dependent polarization in soft gamma-rays using Compton scattering in PoGOLite
Linear polarization in X- and gamma-rays is an important diagnostic of many
astrophysical sources, foremost giving information about their geometry,
magnetic fields, and radiation mechanisms. However, very few X-ray polarization
measurements have been made, and then only mono-energetic detections, whilst
several objects are assumed to have energy dependent polarization signatures.
In this paper we investigate whether detection of energy dependent polarization
from cosmic sources is possible using the Compton technique, in particular with
the proposed PoGOLite balloon-experiment, in the 25-100 keV range. We use
Geant4 simulations of a PoGOLite model and input photon spectra based on Cygnus
X-1 and accreting magnetic pulsars (100 mCrab). Effective observing times of 6
and 35 hours were simulated, corresponding to a standard and a long duration
flight respectively. Both smooth and sharp energy variations of the
polarization are investigated and compared to constant polarization signals
using chi-square statistics. We can reject constant polarization, with energy,
for the Cygnus X-1 spectrum (in the hard state), if the reflected component is
assumed to be completely polarized, whereas the distinction cannot be made for
weaker polarization. For the accreting pulsar, constant polarization can be
rejected in the case of polarization in a narrow energy band with at least 50%
polarization, and similarly for a negative step distribution from 30% to 0%
polarization.Comment: 11 pages, 12 figures; updated to match version accepted for
publication in Astroparticle Physics (only minor changes
Magnetic Field Structure of the Crab Pulsar Wind Nebula Revealed with IXPE
We report a detailed study of the magnetic-field structure of the Crab pulsar
wind nebula, using the X-ray polarization data in 2--8~keV obtained with the
Imaging X-ray Polarimetry Explorer. Contamination of the pulsar emission to the
data of the nebula region was removed through application of a stringent
pulsation phase-cut, extracting a phase range of 0.7--1.0 only. We found that
the electric field vector polarization angle (PA) was about from
north to east with the polarization degree (PD) of about 25\% at the pulsar
position, indicating that the direction of the toroidal magnetic field is
perpendicular to the pulsar spin axis in the region close to the termination
shock. The PA gradually deviated from the angle as an increasing function of
the distance from the pulsar. There was a region of a low PD to the west of the
X-ray torus. Although such a region is expected to be located at the torus
edge, where geometrical depolarization due to a steep spatial variation of the
PA is expected, the observed low-PD region positionally deviated from the edge.
We found that the region of low PD positionally coincided with a dense filament
seen in the optical band, and conjecture that the low-PD region may be produced
through deflection of the pulsar wind. By comparing the values of the PD at the
pulsar position between the data and a model, in which toroidal and turbulent
magnetic fields were considered, we estimated the fractional energy of the
turbulent magnetic field to be about of the total. We also evaluated a
potential polarization of the northern jet in the nebula and derived the PD and
PA to be about and , respectively.Comment: This is a pre-copyedited, author-produced version of an article
accepted for publication in PASJ following peer revie
Development of a Time Projection Chamber Using Gas Electron Multipliers (GEM-TPC)
We developed a prototype time projection chamber using gas electron
multipliers (GEM-TPC) for high energy heavy ion collision experiments. To
investigate its performance, we conducted a beam test with 3 kinds of gases
(Ar(90%)-CH4(10%), Ar(70%)-C2H6(30%) and CF4). Detection efficiency of 99%, and
spatial resolution of 79 m in the pad-row direction and 313 m in the
drift direction were achieved. The test results show that the GEM-TPC meets the
requirements for high energy heavy ion collision experiments. The configuration
and performance of the GEM-TPC are described.Comment: 18 pages, 12 figures, published online in Nucl. Instr. and Meth.
Simulating Cherenkov Telescope Array observation of RX J1713.7-3946
We perform simulations of Cherenkov Telescope Array (CTA) observations of a
young supernova remnant RX J1713.7-3946. This target is not only one of the
brightest sources ever discovered in very high-energy gamma rays but also well
observed in other wavebands. In X-rays, the emission is dominated by
synchrotron radiation, which links directly to the existence of high-energy
electrons. Radio observations of CO and HI gas have revealed a highly
inhomogeneous medium surrounding the SNR, such as clumpy molecular clouds.
Therefore gamma rays from hadronic interactions are naturally expected.
However, the spectrum in GeV energy range measured by Fermi/LAT indicates more
typical of leptonic emission from accelerated electrons. Despite lots of
multi-wavelength information, the competing interpretations have led to much
uncertainty in the quest of unraveling the true origin of the gamma-ray
emission from RX~J1713.7--3946. CTA will achieve highest performance ever in
sensitivity, angular resolution, and energy resolution. We estimate CTA
capability to examine the emission mechanisms of the gamma rays through
simulated spatial distribution, spectra, and their time variation.Comment: 8 pages, 3 figures. In Proceedings of the 34th International Cosmic
Ray Conference (ICRC2015), The Hague, The Netherlands. All CTA contributions
at arXiv:1508.0589
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