2,870 research outputs found
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
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
ASCA Detection of Pulsed X-ray Emission from PSR J0631+1036
ASCA's long look at the 288 millisecond radio pulsar, PSR J0631+1036, reveals
coherent X-ray pulsation from this source for the first time. The source was
first detected in the serendipitous Einstein observation and later identified
as a radio pulsar. Possible pulsation in the gamma-ray band has been detected
from the CGRO EGRET data (Zepka, et al. 1996). The X-ray spectrum in the ASCA
band is characterized by a hard power-law type emission with a photon index of
about 2.3, when fitted with a single power-law function modified with
absorption. An additional blackbody component of about 0.14 keV increases the
quality of the spectral fit. The observed X-ray flux is 2.1e-13 ergs/s/cm2 in
the 1-10 keV band. We find that many characteristics of PSR J0631+1036 are
similar to those of middle-aged gamma-ray pulsars such as PSR B1055-52, PSR
B0633+17 (Geminga), and PSR B0656+14.Comment: To appear in ApJ Letter
Transition Radiation Spectra of Electrons from 1 to 10 GeV/c in Regular and Irregular Radiators
We present measurements of the spectral distribution of transition radiation
generated by electrons of momentum 1 to 10 GeV/c in different radiator types.
We investigate periodic foil radiators and irregular foam and fiber materials.
The transition radiation photons are detected by prototypes of the drift
chambers to be used in the Transition Radiation Detector (TRD) of the ALICE
experiment at CERN, which are filled with a Xe, CO2 (15 %) mixture. The
measurements are compared to simulations in order to enhance the quantitative
understanding of transition radiation production, in particular the momentum
dependence of the transition radiation yield.Comment: 18 pages, 15 figures, submitted to Nucl. Instr. Meth. Phys. Res.
Energy loss of pions and electrons of 1 to 6 GeV/c in drift chambers operated with Xe,CO2(15%)
We present measurements of the energy loss of pions and electrons in drift
chambers operated with a Xe,CO2(15%) mixture. The measurements are carried out
for particle momenta from 1 to 6 GeV/c using prototype drift chambers for the
ALICE TRD. Microscopic calculations are performed using input parameters
calculated with GEANT3. These calculations reproduce well the measured average
and most probable values for pions, but a higher Fermi plateau is required in
order to reproduce our electron data. The widths of the measured distributions
are smaller for data compared to the calculations. The electron/pion
identification performance using the energy loss is also presented.Comment: 15 pages, 10 figures, accepted for publication in Nucl.Instrum.Meth.
Space charge in drift chambers operated with the Xe,CO2(15%) mixture
Using prototype modules of the ALICE Transition Radiation Detector we
investigate space charge effects and the dependence of the pion rejection
performance on the incident angle of the ionizing particle. The average pulse
height distributions in the drift chambers operated with the Xe,CO2(15%)
mixture provide quantitative information on the gas gain reduction due to space
charge accumulating during the drift of the primary ionization. Our results
demonstrate that the pion rejection performance of a TRD is better for tracks
which are not at normal incidence to the anode wires. We present detailed
simulations of detector signals, which reproduce the measurements and lend
strong support to our interpretation of the measurements in terms of space
charge effects.Comment: 18 pages, 10 figures, accepted for publication in Nucl.Instrum.Meth.
A. Data files available at http://www-alice.gsi.de/tr
Transition Radiation Spectroscopy with Prototypes of the ALICE TRD
We present measurements of the transition radiation (TR) spectrum produced in
an irregular radiator at different electron momenta. The data are compared to
simulations of TR from a regular radiator.Comment: 4 pages, 5 Figures, Proceedings for "TRDs for the 3rd millennium"
(Sept. 4-7, 2003, Bari, Italy
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Nonperturbative transverse-momentum-dependent effects in dihadron and direct photon-hadron angular correlations in p+p collisions at s =200 GeV
Dihadron and isolated direct photon-hadron angular correlations are measured in p+p collisions at s=200 GeV. The correlations are sensitive to nonperturbative initial-state and final-state transverse momenta kT and jT in the azimuthal nearly back-to-back region ÎÏâŒÏ. To have sensitivity to small transverse momentum scales, nonperturbative momentum widths of pout, the out-of-plane transverse-momentum component perpendicular to the trigger particle, are measured. In this region, the evolution of pout can be studied when several different hard scales are measured. These widths are used to investigate possible effects from transverse-momentum-dependent factorization breaking. When accounting for the longitudinal-momentum fraction of the away-side hadron with respect to the near-side trigger particle, the widths are found to increase with the hard scale; this is qualitatively similar to the observed behavior in Drell-Yan and semi-inclusive deep-inelastic scattering interactions, where factorization is predicted to hold. The momentum widths are also studied as a function of center-of-mass energy by comparing to previous measurements at s=510 GeV. The nonperturbative jet widths also appear to increase with s at a similar xT, which is qualitatively consistent to similar measurements in Drell-Yan interactions. Future detailed global comparisons between measurements of processes where transverse-momentum-dependent factorization is predicted to hold and be broken will provide further insight into the role of color in hadronic interactions
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Nonperturbative-transverse-momentum broadening in dihadron angular correlations in sNN =200 GeV proton-nucleus collisions
The PHENIX collaboration has measured high-pT dihadron correlations in p+p, p+Al, and p+Au collisions at sNN=200 GeV. The correlations arise from inter- and intrajet correlations and thus have sensitivity to nonperturbative effects in both the initial and final states. The distributions of pout, the transverse-momentum component of the associated hadron perpendicular to the trigger hadron, are sensitive to initial- and final-state transverse momenta. These distributions are measured multidifferentially as a function of xE, the longitudinal momentum fraction of the associated hadron with respect to the trigger hadron. The near-side pout widths, sensitive to fragmentation transverse momentum, show no significant broadening between p+Au, p+Al, and p+p. The away-side nonperturbative pout widths are found to be broadened in p+Au when compared to p+p; however, there is no significant broadening in p+Al compared to p+p collisions. The data also suggest that the away-side pout broadening is a function of Ncoll, the number of binary nucleon-nucleon collisions, in the interaction. The potential implications of these results with regard to initial- and final-state transverse-momentum broadening and energy loss of partons in a nucleus, among other nuclear effects, are discussed
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