6,172 research outputs found
The 2000 Periastron Passage of PSR B1259-63
We report here on a sequence of 28 observations of the binary pulsar system
PSR B1259-63/SS2883 at four radio frequencies made with the Australia Telescope
Compact Array around the time of the 2000 periastron passage. Observations made
on 2000 Sep 1 show that the pulsar's apparent rotation measure (RM) reached a
maximum of rad m, some 700 times the value measured
away from periastron, and is the largest astrophysical RM measured. This value,
combined with the dispersion measure implies a magnetic field in the Be star's
wind of 6 mG. We find that the light curve of the unpulsed emission is similar
to that obtained during the 1997 periastron but that differences in detail
imply that the emission disc of the Be star is thicker and/or of higher
density. The behaviour of the light curve at late times is best modelled by the
adiabatic expansion of a synchrotron bubble formed in the pulsar/disc
interaction. The expansion rate of the bubble km s is
surprisingly low but the derived magnetic field of 1.6 G close to that
expected.Comment: 8 pages, 6 figures, 3 tables, LaTeX (mn.sty). Accepted for
publication in the Monthly Notices of the Royal Astronomical Society. Also
available at http://astronomy.swin.edu.au/staff/tconnors/publications.htm
GRAPE - A Balloon-Borne Gamma-Ray Polarimeter Experiment
This paper reviews the development status of GRAPE (the Gamma-Ray Polarimeter
Experiment), a hard X-ray Compton Polarimeter. The purpose of GRAPE is to
measure the polarization of hard X-rays in the 50-300 keV energy range. We are
particularly interested in X-rays that are emitted from solar flares and
gamma-ray bursts (GRBs), although GRAPE could also be employed in the study of
other astrophysical sources. Accurately measuring the polarization of the
emitted radiation will lead to a better understating of both emission
mechanisms and source geometries. The GRAPE design consists of an array of
plastic scintillators surrounding a central high-Z crystal scintillator. The
azimuthal distribution of photon scatters from the plastic array into the
central calorimeter provides a measure of the polarization fraction and
polarization angle of the incident radiation. The design of the detector
provides sensitivity over a large field-of-view (>pi steradian). The design
facilitates the fabrication of large area arrays with minimal deadspace. This
paper presents the latest design concept and the most recent results from
laboratory tests of a GRAPE science model.Comment: 6 pages; paper presented at the FRASCATI Workshop 2005 on
Multifrequency Behaviour of High Energy Cosmic Sources; submitted to Chinese
Journal of Astronomy and Astrophysic
Cardiac Output Dependency on Exercising Muscle Mass During Ergometer Exercise in Healthy Women
Please refer to the pdf version of the abstract located adjacent to the title
A hard X-ray polarimeter designed for transient astrophysical sources
— This paper discusses the latest progress in the development of GRAPE (Gamma-Ray Polarimeter Experiment), a hard X-ray Compton Polarimeter. The purpose of GRAPE is to measure the polarization of hard X-rays in the 50-300 keV energy range. We are particularly interested in X-rays that are emitted from solar flares and gamma-ray bursts (GRBs). Accurately measuring the polarization of the emitted radiation from these sources will lead, to a better understating of both the emission mechanisms and source geometries. The GRAPE design consists of an array of plastic scintillators surrounding a central high-Z crystal scintillator. We can monitor individual Compton scatters that occur in the plastics and determine whether the photon is photo absorbed by the high-Z crystal or not. A Compton scattered photon that is immediately photo absorbed by the high-Z crystal constitutes a valid event. These valid events provide us with the interaction locations of each incident photon and ultimately produces a modulation pattern for the Compton scattering of the polarized radiation. Comparing with Monte Carlo simulations of a 100% polarized beam, the level of polarization of the measured beam can then be determined. The complete array is mounted on a flat-panel multi-anode photomultiplier tube (MAPMT) that can measure the deposited energies resulting from the photon interactions. The design of the detector allows for a large field-ofview (\u3e π steradian), at the same time offering the ability to be close-packed with multiple modules in order to reduce deadspace. We plan to present in this paper the latest laboratory results obtained from GRAPE using partially polarized radiation sources
Subsonic Longitudinal Performance Coefficient Extraction from Shuttle Flight Data: an Accuracy Assessment for Determination of Data Base Updates
Longitudinal performance comparisons between flight derived and predicted values are presented for the first five NASA Space Shuttle Columbia flights. Though subsonic comparisons are emphasized, comparisons during the transonic and low supersonic regions of flight are included. Computed air data information based on the remotely sensed atmospheric measurements as well as in situ Orbiter Air Data System (ADS) measurements were incorporated. Each air data source provides for comparisons versus the predicted values from the LaRC data base. Principally, L/D, C sub L, and C sub D, comparisons are presented, though some pitching moment results are included. Similarities in flight conditions and spacecraft configuration during the first five flights are discussed. Contributions from the various elements of the data base are presented and the overall differences observed between the flight and predicted values are discussed in terms of expected variations. A discussion on potential data base updates is presented based on the results from the five flights to date
Validation of Bioreactance Non-Invasive Cardiac Output Monitoring In a Male College-Aged Population
Please view abstract in the attached PDF file
Developing a Compton Polarimeter to Measure Polarization of Hard X-Rays in the 50-300 keV Energy Range
This paper discusses the latest progress in the development of GRAPE
(Gamma-Ray Polarimeter Experiment), a hard X-ray Compton Polarimeter. The
purpose of GRAPE is to measure the polarization of hard X-rays in the 50-300
keV energy range. We are particularly interested in X-rays that are emitted
from solar flares and gamma-ray bursts (GRBs). Accurately measuring the
polarization of the emitted radiation from these sources will lead, to a better
understating of both the emission mechanisms and source geometries. The GRAPE
design consists of an array of plastic scintillators surrounding a central
high-Z crystal scintillator. We can monitor individual Compton scatters that
occur in the plastics and determine whether the photon is photo absorbed by the
high-Z crystal or not. A Compton scattered photon that is immediately photo
absorbed by the high-Z crystal constitutes a valid event. These valid events
provide us with the interaction locations of each incident photon and
ultimately produces a modulation pattern for the Compton scattering of the
polarized radiation. Comparing with Monte Carlo simulations of a 100% polarized
beam, the level of polarization of the measured beam can then be determined.
The complete array is mounted on a flat-panel multi-anode photomultiplier tube
(MAPMT) that can measure the deposited energies resulting from the photon
interactions. The design of the detector allows for a large field-of-view (>pi
steradian), at the same time offering the ability to be close-packed with
multiple modules in order to reduce deadspace. We plan to present in this paper
the latest laboratory results obtained from GRAPE using partially polarized
radiation sources.Comment: 10 pages; conference paper presented at the SPIE conference "UV,
X-Ray, and Gamma-Ray Space Instrumentation for Astronomy XIV." To be
published in SPIE Conference Proceedings, vol. 589
Development of a Hard X-Ray Polarimeter for Astrophysics
We have been developing a Compton scatter polarimeter for measuring the linear polarization of hard X-rays (100-300 keV) from astrophysical sources. A laboratory prototype polarimeter has been used to successfully demonstrate the reliability of our Monte Carlo simulation code and to demonstrate our ability to generate a polarized photon source in the lab. Our design concept places a self-containedpolarimeter module on the front-end of a a 5-inch position sensitive PMT (PSPMT). We are currently working on the fabrication of a science model based on this PSPMT concept. Although the emphasis of our development effort is towards measuring hard X-rays from solar flares, our design has the advantage that it is sensitive over a rather large field-of-view (\u3e1 steradian), a feature that makes it especially attractive for γ-ray burst studie
Prospects for GRB Polarimetry with GRAPE
This paper discusses the latest progress in the development of GRAPE (Gamma‐Ray Polarimeter Experiment), a hard X‐ray Compton Polarimeter. The purpose of GRAPE is to measure the polarization of hard X‐rays in the 50–300 keV energy range. We are particularly interested in X‐rays that are emitted from solar flares and gamma‐ray bursts (GRBs). Accurately measuring the polarization of the emitted radiation from these sources will lead to a better understating of both the emission mechanisms and source geometries. The GRAPE design consists of an array of plastic scintillators surrounding a central high‐Z crystal scintillator. We can monitor individual Compton scatters that occur in the plastics and determine whether the photon is photo absorbed by the high‐Z crystal or not. A Compton scattered photon that is immediately photo absorbed by the high‐Z crystal constitutes a valid event. These valid events provide us with the interaction locations of each incident photon and ultimately produces a modulation pattern for the Compton scattering of the polarized radiation. Comparing with Monte Carlo simulations of a 100% polarized beam, the level of polarization of the measured beam can then be determined. The complete array is mounted on a flat‐panel multi‐anode photomultiplier tube (MAPMT) that can measure the deposited energies resulting from the photon interactions. The design of the detector allows for a large field‐of‐view (\u3e π steradian), at the same time offering the ability to be close‐packed with multiple modules in order to reduce deadspace. We present in this paper the latest laboratory results obtained from GRAPE using partially polarized radiation sources along with a brief description of our future plans for the GRAPE design
Development of a hard X-ray polarimeter for astrophysics
We have been developing a Compton scatter polarimeter for measuring the linear polarization of hard X-rays (100-300 keV) from astrophysical sources. A laboratory prototype polarimeter has been used to successfully demonstrate the reliability of our Monte Carlo simulation code and to demonstrate our ability to generate a polarized photon source in the lab. Our design concept places a self-containedpolarimeter module on the front-end of a a 5-inch position sensitive PMT (PSPMT). We are currently working on the fabrication of a science model based on this PSPMT concept. Although the emphasis of our development effort is towards measuring hard X-rays from solar flares, our design has the advantage that it is sensitive over a rather large field-of-view (\u3e1 steradian), a feature that makes it especially attractive for γ-ray burst studies
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