5,357 research outputs found
A Chandra observation of GRO J1744-28: the bursting pulsar in quiescence
We present a Chandra/ACIS-I observation of GRO J1744-28. We detected a source
at a position of R.A = 17h 44m 33.09s and Dec. = -28degr 44' 27.0'' (J2000.0;
with a 1sigma error of ~0.8 arcseconds), consistent with both ROSAT and
interplanetary network localizations of GRO J1744-28 when it was in outburst.
This makes it likely that we have detected the quiescent X-ray counterpart of
GRO J1744-28. Our Chandra position demonstrates that the previously proposed
infrared counterpart is not related to GRO J1744-28. The 0.5-10 keV luminosity
of the source is 2 - 4 x 10^{33} erg/s (assuming the source is near the
Galactic center at a distance of 8 kpc). We discuss our results in the context
of the quiescent X-ray emission of pulsating and non-pulsating neutron star
X-ray transients.Comment: Accepted for publication in ApJ Letters, 20 February 200
Solution of Orthopositronium lifetime Puzzle
The intrinsic decay rate of orthopositronium formed in powder
is measured using the direct correction method such that the time
dependence of the pick-off annihilation rate is precisely determined. The decay
rate of orthopositronium is found to be , which is consistent with our previous measurements with
about twice the accuracy. Results agree well with the QED
prediction, and also with a result reported very recently using nanoporous
film
Radial Bargmann representation for the Fock space of type B
Let be the probability and orthogonality measure for the
-Meixner-Pollaczek orthogonal polynomials, which has appeared in
\cite{BEH15} as the distribution of the -Gaussian process (the
Gaussian process of type B) over the -Fock space (the Fock space of
type B). The main purpose of this paper is to find the radial Bargmann
representation of . Our main results cover not only the
representation of -Gaussian distribution by \cite{LM95}, but also of
-Gaussian and symmetric free Meixner distributions on . In
addition, non-trivial commutation relations satisfied by -operators
are presented.Comment: 13 pages, minor changes have been mad
The TFP and a pulsed LD: New lidar components
One of the large problems of lidar in practical use is that the price and the weight of a laser and a receiving telescope is too high. To solve this problem, many trials have been made. The system with the TFP (thin film paraboloid) for a receiving telescope and a pulsed LD (laser diode) for a laser source is proposed. It is hoped that as a consequece the lidar system will become very lightweigth and inexpensive
Quiescent Thermal Emission from the Neutron Star in Aql X-1
We report on the quiescent spectrum measured with Chandra/ACIS-S of the
transient, type-I X-ray bursting neutron star Aql X-1, immediately following an
accretion outburst. The neutron star radius, assuming a pure hydrogen
atmosphere and hard power-law spectrum, is =13.4{+5}{-4} (d/5 \kpc)
km. Based on the historical outburst record of RXTE/ASM, the quiescent
luminosity is consistent with that predicted by Brown, Bildsten and Rutledge
from deep crustal heating, lending support to this theory for providing a
minimum quiescent luminosity of transient neutron stars. While not required by
the data, the hard power-law component can account for 18+/-8% of the 0.5-10
keV thermal flux. Short-timescale intensity variability during this observation
is less than 15% rms (3 sigma; 0.0001-1 Hz, 0.2-8 keV). Comparison between the
Chandra spectrum and three X-ray spectral observations made between Oct 1992
and Oct 1996 find all spectra consistent with a pure H atmosphere, but with
temperatures ranging from 145--168 eV, spanning a factor of 1.87+/-0.21 in
observed flux. The source of variability in the quiescent luminosity on long
timescales (greater than years) remains a puzzle. If from accretion, then it
remains to be explained why the quiescent accretion rate provides a luminosity
so nearly equal to that from deep crustal heating.Comment: 15 pages, 1 figure, 2 tables; ApJ, accepte
Direct Observation of the Hyperfine Transition of the Ground State Positronium
We report the first direct measurement of the hyperfine transition of the
ground state positronium. The hyperfine structure between ortho-positronium and
para-positronium is about 203 GHz. We develop a new optical system to
accumulate about 10 kW power using a gyrotron, a mode converter, and a
Fabry-P\'{e}rot cavity. The hyperfine transition has been observed with a
significance of 5.4 standard deviations. The transition probability is measured
to be s for the first time, which
is in good agreement with the theoretical value of
s
Numerical Investigation of a Coronal Mass Ejection from an Anemone Active Region: Reconnection and Deflection of the 2005 August 22 Eruption
We present a numerical investigation of the coronal evolution of a coronal
mass ejection (CME) on 2005 August 22 using a 3-D thermodynamics
magnetohydrodynamic model, the SWMF. The source region of the eruption was
anemone active region (AR) 10798, which emerged inside a coronal hole. We
validate our modeled corona by producing synthetic extreme ultraviolet (EUV)
images, which we compare to EIT images. We initiate the CME with an
out-of-equilibrium flux rope with an orientation and chirality chosen in
agreement with observations of a H-alpha filament. During the eruption, one
footpoint of the flux rope reconnects with streamer magnetic field lines and
with open field lines from the adjacent coronal hole. It yields an eruption
which has a mix of closed and open twisted field lines due to interchange
reconnection and only one footpoint line-tied to the source region. Even with
the large-scale reconnection, we find no evidence of strong rotation of the CME
as it propagates. We study the CME deflection and find that the effect of the
Lorentz force is a deflection of the CME by about 3 deg/Rsun towards the East
during the first 30 minutes of the propagation. We also produce coronagraphic
and EUV images of the CME, which we compare with real images, identifying a
dimming region associated with the reconnection process. We discuss the
implication of our results for the arrival at Earth of CMEs originating from
the limb and for models to explain the presence of open field lines in magnetic
clouds.Comment: 14 pages, 8 Figures, accepted to Astrophysical Journa
Electron Acceleration by Multi-Island Coalescence
Energetic electrons of up to tens of MeV are created during explosive
phenomena in the solar corona. While many theoretical models consider magnetic
reconnection as a possible way of generating energetic electrons, the precise
roles of magnetic reconnection during acceleration and heating of electrons
still remain unclear. Here we show from 2D particle-in-cell simulations that
coalescence of magnetic islands that naturally form as a consequence of tearing
mode instability and associated magnetic reconnection leads to efficient
energization of electrons. The key process is the secondary magnetic
reconnection at the merging points, or the `anti-reconnection', which is, in a
sense, driven by the converging outflows from the initial magnetic reconnection
regions. By following the trajectories of the most energetic electrons, we
found a variety of different acceleration mechanisms but the energization at
the anti-reconnection is found to be the most important process. We discuss
possible applications to the energetic electrons observed in the solar flares.
We anticipate our results to be a starting point for more sophisticated models
of particle acceleration during the explosive energy release phenomena.Comment: 14 pages, 12 figures (degraded figure quality), 1 table. Accepted for
publication in ApJ
Snowden's revelations and the attitudes of students at Swedish universities
Purpose â Mapping of Swedish students' attitudes toward Snowden's revelations and their effects in the
political and socio-cultural environment of Sweden.
Design/methodology/approach â A questionnaire was answered by 190 Swedish University students.
The quantitative responses to the survey were statistically analysed as well as qualitative considerations
of free text answers.
Findings â Swedish students had a high level of knowledge of Snowden revelations, they actively
searched for information, they gave a positive judgement of Snowden's actions and they were willing to
follow his example in Sweden but not the US. They trusted their country and most of its institutions and
authorities except for secret service agencies and Internet and computer software companies.
Practical implications â Design of education for university students, especially in Information
Technology programs.
Social implications â Developing and applying policies on privacy, surveillance and whistleblowing.
Originality/value â This study is part of a bigger international study to map students' attitudes toward
Snowden's revelations and their opinions about privacy, surveillance and whistleblowing opening up for
cross-cultural analyses. This record was migrated from the OpenDepot repository service in June, 2017 before shutting down
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