On the Radio Polarization Signature of Efficient and Inefficient Particle Acceleration in Supernova Remnant SN 1006

We present a radio polarization study of SN 1006, based on combined VLA and ATCA observations at 20 cm that resulted in sensitive images with an angular resolution of 10 arcsec. The fractional polarization in the two bright radio and X-ray lobes of the SNR is measured to be 0.17, while in the southeastern sector, where the radio and non-thermal X-ray emission are much weaker, the polarization fraction reaches a value of 0.6 +- 0.2, close to the theoretical limit of 0.7. We interpret this result as evidence of a disordered, turbulent magnetic field in the lobes, where particle acceleration is believed to be efficient, and a highly ordered field in the southeast, where the acceleration efficiency has been shown to be very low. Utilizing the frequency coverage of our observations, an average rotation measure of ~12 rad/m2 is determined from the combined data set, which is then used to obtain the intrinsic direction of the magnetic field vectors. While the orientation of magnetic field vectors across the SNR shell appear radial, a large fraction of the magnetic vectors lie parallel to the Galactic Plane. Along the highly polarized southeastern rim, the field is aligned tangent to the shock, and therefore also nearly parallel to the Galactic Plane. These results strongly suggest that the ambient field surrounding SN 1006 is aligned with this direction (i.e., from northeast to southwest) and that the bright lobes are due to a polar cap geometry. Our study establishes that the most efficient particle acceleration and generation of magnetic turbulence in SN 1006 is attained for shocks in which the magnetic field direction and shock normal are quasi-parallel, while inefficient acceleration and little to no generation of magnetic turbulence obtains for the quasi-perpendicular case.Comment: Accepted for publication in Astronomical Journa

ECONOMIC MODELING OF FARM PRODUCTION AND CONSERVATION DECISIONS IN RESPONSE TO ALTERNATIVE RESOURCE AND ENVIRONMENTAL POLICIES

Environmental Economics and Policy, Farm Management,

Pisces IV submersible observations in the epicentral region of the 1929 Grand Banks earthquake

The PISCES IVsubmersible was used to investigate the upper continental slope around 44 ON, 56 W, near the epicentre of the 1929 Grand Banks earthquake. Four dives in water depths of 800-2000 m were undertaken to observe speci3c features identijied with the SeaMARC I sidescan system in 1983. Two dives were made in the head of Eastern Valley where pebbly mudstones ofprobable Pleistocene age were recognized outcropping on the seafloor. Constructional features of cobbles and boulders, derived by exhumation and reworking of the pebbly mudstone, were also observed. These include gravel/sand bedforms (transverse waves) on the valley floor. Slope failure features in semiconsolidated mudstone were recognized on two dives onto the St. Pierre slope. Exposures in these mudstones are rapidly eroded by intense burrowing by benthic organisms

Using next-generation multi-spectral FRRf to improve current estimates of marine primary production (MPP) within Australian waters

University of Technology Sydney. Faculty of Science.Bio-optical tools remain key technologies to address a long-standing goal in oceanography: to improve understanding of how marine primary productivity (MPP) varies over space and time. A major goal for one particular technique, Fast Repetition Rate fluorometry (FRRf), is to retrieve highly resolute patterns of carbon (C) uptake in situ to improve satellite retrieved predictions of MPP. However, this goal hinges upon the application of a highly-variable, yet poorly-understood conversion factor to scale FRRf-derived electron transport rates (ETRs) to rates of C-uptake. Understanding of the conversion factor, termed the “electron requirement for carbon fixation” (KC) is limited, in particularly for Australian waters where KC has rarely been measured. This thesis focuses on coupled ETR – C-uptake measurements, to examine how key factors drive variability in KC, utilising both laboratory and field studies to isolate the respective influences of growth environment and phytoplankton taxonomy. I performed nutrient addition bioassays upon natural phytoplankton assemblages to demonstrate for the first time how macronutrient availability (N, P and Si) regulates KC at an Australian coastal reference station when nutrient concentrations are low during summer. To examine taxonomic variability of KC together with metrics influencing phytoplankton growth and physiology (cell size and non-photochemical quenching, NPQ), I grew phytoplankton covering a broad range of taxonomic and size classes within a controlled laboratory setting where environmental variability could be excluded. Finally, to examine how well KC could be predicted in a highly-dynamic system with multiple environmental stressors and phytoplankton assemblages, I performed a novel high-throughput assessment of KC (n = 80) along the eastern Australian coast spanning multiple water masses including the Tasman Sea and the East Australian Current (EAC). Prevailing environmental variables, physiological (non-photochemical heat dissipation, NPQɴsᴠ) and phytoplankton community structure (size-fractionated Chl-a) were also measured for each sample to allow evaluation of their respective performance in empirically modelling KC variance. This thesis highlights the importance in characterising both environmental and taxonomic factors to most robustly retrieve KC, but also demonstrates that a single FRRf parameter (NPQɴsᴠ) may reliably explain ~50% of variability in eastern Australian waters. These new findings potentially provide new and unprecedented capacity to retrieve C-fixation rate from FRRf-based productivity assessments, but ultimately require further validation that may be possible through re-visiting past FRRf data sets. These findings are then considered to propose a roadmap to enable broader implementation and uptake of FRRf for widespread assessments of marine (and freshwater) primary productivity into the future

The Radial Structure of SNR N103B

We report on the results from a Chandra ACIS observation of the young, compact, supernova remnant N103B. The unprecedented spatial resolution of Chandra reveals sub-arcsecond structure, both in the brightness and in spectral variations. Underlying these small-scale variations is a surprisingly simple radial structure in the equivalent widths of the strong Si and S emission lines. We investigate these radial variations through spatially resolved spectroscopy using a plane-parallel, non-equilibrium ionization model with multiple components. The majority of the emission arises from components with a temperature of 1 keV: a fully ionized hydrogen component; a high ionization timescale (n_e*t > 10^12 s cm^-3) component containing Si, S, Ar, Ca, and Fe; and a low ionization timescale (n_e*t ~ 10^{11} s cm^-3) O, Ne, and Mg component. To reproduce the strong Fe Kalpha line, it is necessary to include additional Fe in a hot (> 2 keV), low ionization (n_e*t ~ 10^10.8 s cm^-3) component. This hot Fe may be in the form of hot Fe bubbles, formed in the radioactive decay of clumps of 56Ni. We find no radial variation in the ionization timescales or temperatures of the various components. Rather, the Si and S equivalent widths increase at large radii because these lines, as well as those of Ar and Ca, are formed in a shell occupying the outer half of the remnant. A shell of hot Fe is located interior to this, but there is a large region of overlap between these two shells. In the inner 30% of the remnant, there is a core of cooler, 1 keV Fe. We find that the distribution of the ejecta and the yields of the intermediate mass species are consistent with model prediction for Type Ia events.Comment: 34 pages, including 7 tables and 7 figures, Accepted by Ap