75 research outputs found
The sidereal semi-diurnal variation observed at high zenith angles at Mawson, 1968-1984, and the polarity of the solar main field
High zenith-angle North/South telescopes viewing equatorially and at midlatitudes through 40 MWE of atmosphere have been operating at Mawson since early 1968. It is evident that a sidereal semi-diurnal component of galactic origin has been observed, over and above a possible spurious component proposed by Nagashima, arising from a bi-directional component of the solar anisotropy. Although a very pronounced reduction in the semi-diurnal galactic response followed the reversal of polarity of the solar main field during 1969 to 1971, so far the observations indicate that there has been no recurrence of a larger galactic response following the reversal of polarity around 1981. The possible role of the latitudional extent lambda omicron of the wavy neutral sheet is discussed
Isotropic intensity waves and features of their occurrence
Waves of daily average cosmic ray intensity, dependent on interplanetary magnetic fields (IMF) polarity, have been observed in 1982 (Jacklyn and Pomerantz, 1983) and again in 1983 and 1984. These waves at first appeared to be due to the North-South anisotropy. Further investigation revealed that the waves comprise two components, a large isotropic and a smaller anisotropic component. The anisotropic part is attributed to the North-South anisotropy and is in phase with the larger isotropic component in the Southern Hemisphere. Unlike the North-South anisotropy which is a permanent feature of cosmic ray modulation, the isotropic phenomenon appears to be episodic in character. When present, it is clearly dependent on IMF polarity but does not correlate well with IMF field strength. It is conjectured that the phenomenon might indicate some difference between the intensity regimes above and below the neutral sheet
Australian Cosmic Ray Modulation Research
Australian research into variations of the cosmic ray flux arriving at the
Earth has played a pivotal role for more than 50 years. The work has been
largely led by the groups from the University of Tasmania and the Australian
Antarctic Division and has involved the operation of neutron monitors and muon
telescopes from many sites. In this paper the achievements of the Australian
researchers are reviewed and future experiments are described. Particular
highlights include: the determination of cosmic ray modulation parameters; the
development of modelling techniques of Ground Level Enhancements; the
confirmation of the Tail-In and Loss-Cone Sidereal anisotropies; the Space Ship
Earth collaboration; and the Solar Cycle latitude survey.Comment: 47 pages, 37 figures, LaTeX, invited review, in press PASA 18(1).
HTML version available at http://www.atnf.csiro.au/pasa/18_1/duldig/paper
An Improved Model for Relativistic Solar Proton Acceleration applied to the 2005 January 20 and Earlier Events
This paper presents results on modelling the ground level response of the
higher energy protons for the 2005 January 20 ground level enhancement (GLE).
This event, known as GLE 69, produced the highest intensity of relativistic
solar particles since the famous event on 1956 February 23. The location of
recent X-ray and gamma-ray emission (N14 W61) was near to Sun-Earth connecting
magnetic field lines, thus providing the opportunity to directly observe the
acceleration source from Earth. We restrict our analysis to protons of energy
greater than 450 MeV to avoid complications arising from transport processes
that can affect the propagation of low energy protons. In light of this revised
approach we have reinvestigated two previous GLEs: those of 2000 July 14 (GLE
59) and 2001 April 15 (GLE 60). Within the limitations of the spectral forms
employed, we find that from the peak (06:55 UT) to the decline (07:30 UT)
phases of GLE 69, neutron monitor observations from 450 MeV to 10 GeV are best
fitted by the Gallegos-Cruz & Perez-Peraza stochastic acceleration model. In
contrast, the Ellison & Ramaty spectra did not fit the neutron monitor
observations as well. This result suggests that for GLE 69, a stochastic
process cannot be discounted as a mechanism for relativistic particle
acceleration, particularly during the initial stages of this solar event. For
GLE 59 we find evidence that more than one acceleration mechanism was present,
consistent with both shock and stochastic acceleration processes dominating at
different times of the event. For GLE 60 we find that Ellison & Ramaty spectra
better represent the neutron monitor observations compared to stochastic
acceleration spectra. The results for GLEs 59 and 60 are in agreement with our
previous work.Comment: 42 pages, 10 figures, 10 tables, published in ApJ, August 200
Radio emission from the high-mass X-ray binary BP Cru: first detection
BP Cru is a well known high-mass X-ray binary composed of a late B hypergiant
(Wray 977) and a neutron star, also observed as the X-ray pulsar GX 301-2. No
information about emission from BP Cru in other bands than X-rays and optical
has been reported to date in the literature, though massive X-ray binaries
containing black holes can have radio emission from a jet. In order to assess
the presence of a radio jet, we searched for radio emission towards BP Cru
using the Australia Compact Array Telescope during a survey for radio emission
from Be/X-ray transients. We probed the 41.5d orbit of BP Cru with the
Australia Telescope Compact Array not only close to periastron but also close
to apastron. BP Cru was clearly detected in our data on 4, possibly 6, of 12
occasions at 4.8 and 8.6 GHz. Our data suggest that the spectral index of the
radio emission is modulated either by the X-ray flux or the orbital phase of
the system. We propose that the radio emission of BP Cru probably arises from
two components: a persistent component, coming from the mass donor Wray 977,
and a periodic component connected to the accretion onto the neutron star,
possibly coming from a (weak and short lived) jet.Comment: 2 figures, accepted for publication in A+A letter
Ground level muons in coincidence with the solar flare of April 15, 2001
The counting rate of single muon tracks from the Project GRAND proportional
wire chamber array is examined during the Ground Level Event (GLE) of April 15,
2001. The GLE was seen by neutron monitor stations shortly after the time of
the solar X-ray flare. GRAND's single muon data are presented and compared with
neutron monitor data from Climax, Newark, and Oulu. The single muon data have
mean primary hadron energies higher than those of these neutron monitor
stations and so contain information about higher energy hadrons. For the single
muon data for Project GRAND, the GLE is detected at a statistical significance
of 6.1-sigma.Comment: 9 pages, 6 figure
Characterization of acyl chain position in unsaturated phosphatidylcholines using differential mobility-mass spectrometry
Glycerophospholipids (GPs) that differ in the relative position of the two fatty acyl chains on the glycerol backbone (i.e., sn-positional isomers) can have distinct physicochemical properties. The unambiguous assignment of acyl chain position to an individual GP represents a significant analytical challenge. Here we describe a workflow where phosphatidylcholines (PCs) are subjected to ESI for characterization by a combination of differential mobility spectrometry and MS (DMS-MS). When infused as a mixture, ions formed from silver adduction of each phospholipid isomer {e.g., [PC (16:0/18:1) + Ag]+ and [PC (18:1/16:0) + Ag]+} are transmitted through the DMS device at discrete compensation voltages. Varying their relative amounts allows facile and unambiguous assignment of the sn-positions of the fatty acyl chains for each isomer. Integration of the well-resolved ion populations provides a rapid method (\u3c 3 min) for relative quantification of these lipid isomers. The DMS-MS results show excellent agreement with established, but time-consuming, enzymatic approaches and also provide superior accuracy to methods that rely on MS alone. The advantages of this DMS-MS method in identification and quantification of GP isomer populations is demonstrated by direct analysis of complex biological extracts without any prior fractionation
Relativistic Proton Production During the 14 July 2000 Solar Event: The Case for Multiple Source Mechanisms
Protons accelerated to relativistic energies by transient solar and
interplanetary phenomena caused a ground-level cosmic ray enhancement on 14
July 2000, Bastille Day. Near-Earth spacecraft measured the proton flux
directly and ground-based observatories measured the secondary responses to
higher energy protons. We have modelled the arrival of these relativistic
protons at Earth using a technique which deduces the spectrum, arrival
direction and anisotropy of the high-energy protons that produce increased
responses in neutron monitors. To investigate the acceleration processes
involved we have employed theoretical shock and stochastic acceleration
spectral forms in our fits to spacecraft and neutron monitor data. During the
rising phase of the event (10:45 UT and 10:50 UT) we find that the spectrum
between 140 MeV and 4 GeV is best fitted by a shock acceleration spectrum. In
contrast, the spectrum at the peak (10:55 UT and 11:00 UT) and in the declining
phase (11:40 UT) is best fitted with a stochastic acceleration spectrum. We
propose that at least two acceleration processes were responsible for the
production of relativistic protons during the Bastille Day solar event: (1)
protons were accelerated to relativistic energies by a shock, presumably a
coronal mass ejection (CME). (2) protons were also accelerated to relativistic
energies by stochastic processes initiated by magnetohydrodynamic (MHD)
turbulence.Comment: 38 pages, 9 figures, accepted for publication in the Astrophysical
Journal, January, 200
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