100 research outputs found
Stability of the nonlinear dynamics of an optically injected VCSEL
Automated protocols have been developed to characterize time series data in terms of stability. These techniques are applied to the output power time series of an optically injected vertical cavity surface emitting laser (VCSEL) subject to varying injection strength and optical frequency detuning between master and slave lasers. Dynamic maps, generated from high resolution, computer controlled experiments, identify regions of dynamic instability in the parameter space. © 2012 Optical Society of America
Discovery of Millisecond Pulsars in the Globular Cluster Omega Centauri
The globular cluster Omega Centauri is the most massive and luminous cluster
in the Galaxy. The -ray source FL8Y J1326.74729 is coincident with
the core of the cluster, leading to speculation that hitherto unknown radio
pulsars or annihilating dark matter may be present in the cluster core. Here we
report on the discovery of five millisecond pulsars in Omega Centauri following
observations with the Parkes radio telescope. Four of these pulsars are
isolated with spin periods of 4.1, 4.2, 4.6 and 6.8 ms. The fifth has a spin
period of 4.8 ms and is in an eclipsing binary system with an orbital period of
2.1 hours. Deep radio continuum images of the cluster centre with the
Australian Telescope Compact Array reveal a small population of compact radio
sources making it likely that other pulsars await discovery. We consider it
highly likely that the millisecond pulsars are the source of the -ray
emission. The long-term timing of these pulsars opens up opportunities to
explore the dynamics and interstellar medium of the cluster.Comment: 8 pages, 2 figures, accepted for publication in the Astrophysical
Journal Letter
Piano Studio Recital, November 26, 2019
Lawrence Halsey, from the studio of Professor Forman
Carter Campbell, from the studio of Professor Kasparov
Andrei S Johnson, from the studio of Professor Lutsyshyn
Joel Sanford, from the studio of Professor Toomey
Sean Hynes, from the studio of Professor Forman
Robert Stahl From the studio of Professor Rayd
Serendipitous Discovery of PSR J1431-6328 as a Highly-Polarized Point Source with the Australian SKA Pathfinder
We identified a highly-polarized, steep-spectrum radio source in a deep image
with the Australian Square Kilometre Array Pathfinder (ASKAP) telescope at 888
MHz. After considering and rejecting a stellar origin for this source, we
discovered a new millisecond pulsar (MSP) using observations from the Parkes
radio telescope. This pulsar has period 2.77 ms and dispersion measure 228.27
pc/cm**3. Although this pulsar does not yet appear to be particularly
remarkable, the short spin period, wide profile and high dispersion measure do
make it relatively hard to discover through traditional blind periodicity
searches. Over the course of several weeks we see changes in the barycentric
period of this pulsar that are consistent with orbital motion in a binary
system, but the properties of any binary need to be confirmed by further
observations. While even a deep ASKAP survey may not identify large numbers of
new MSPs compared to the existing population, it would be competitive with
existing all-sky surveys and could discover interesting new MSPs at high
Galactic latitude without the need for computationally-expensive all-sky
periodicity searches.Comment: ApJ, in pres
Piano Studio Recital, February 19, 2019
Elizabeth Baker, from the studio of Professor Forman
Halsey Lawrence, from the studio of Professor Forman
Joel Sanford, from the studio of Professor Toomey
Brooke Ward, from the studio of Professor Raydo
Robert Stahl, from the studio of Professor Raydo
Nicole Dorobanov, from the studio of Professor Kasparo
Wide Bandwidth Observations of Pulsars C, D and J in 47 Tucanae
We report the first wideband observations of pulsars C, D and J in the
globular cluster 47Tucanae (NGC 104) using the Ultra-Wideband Low (UWL)
receiver system recently installed on the Parkes 64 m radio telescope. The wide
frequency range of the UWL receiver (704-4032 MHz), along with the
well-calibrated system, allowed us to obtain flux density measurements and
polarization pulse profiles. The mean pulse profiles have significant linear
and circular polarization, allowing for determination of the Faraday rotation
measure for each pulsar. Precise measurements of the dispersion measures show a
significant deviation in the value for pulsar D compared to earlier results.
Searches for new pulsars in the cluster are on-going and we have determined
optimal bands for such searches using the Parkes UWL receiver system
Piano Studio Recital, April 23, 2019
Robert Stahl, from the studio of Professor Raydo
Lawrence Halsey, from the studio of Professor Forman
Jerry Davis, from the studio of Professor Lutsyshyn
Joel Sanford, from the studio of Professor Toomey
Jashkal Germelus, from the studio of Professor Lutsyshyn
Andrei S Johnson, from the studio of Professor Lutsyshyn
Nicole Dorobanov, from the studio of Professor Kasparo
Precision orbital dynamics from interstellar scintillation arcs for PSR J0437-4715
Intensity scintillations of radio pulsars are known to originate from
interference between waves scattered by the electron density irregularities of
interstellar plasma, often leading to parabolic arcs in the two-dimensional
power spectrum of the recorded dynamic spectrum. The degree of arc curvature
depends on the distance to the scattering plasma and its transverse velocity
with respect to the line-of-sight. We report the observation of annual and
orbital variations in the curvature of scintillation arcs over a period of 16
years for the bright millisecond pulsar, PSR J0437-4715. These variations are
the signature of the relative transverse motions of the Earth, pulsar, and
scattering medium, which we model to obtain precise measurements of parameters
of the pulsar's binary orbit and the scattering medium itself. We observe two
clear scintillation arcs in most of our 5000 observations and we show that
they originate from scattering by thin screens located at distances pc and pc from Earth. The best-fit scattering model
we derive for the brightest arc yields the pulsar's orbital inclination angle
, and longitude of ascending node,
. Using scintillation arcs for precise astrometry and
orbital dynamics can be superior to modelling variations in the diffractive
scintillation timescale, because the arc curvature is independent of variations
in the level of turbulence of interstellar plasma. This technique can be used
in combination with pulsar timing to determine the full three-dimensional
orbital geometries of binary pulsars, and provides parameters essential for
testing theories of gravity and constraining neutron star masses.Comment: 19 pages, 10 figures. Accepted for publication in Ap
The intertropical convergence zone modulates intense hurricane strikes on the western North Atlantic margin
© The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Scientific Reports 6 (2016): 21728, doi:10.1038/srep21728Most Atlantic hurricanes form in the Main Development Region between 9°N to 20°N along the northern edge of the Intertropical Convergence Zone (ITCZ). Previous research has suggested that meridional shifts in the ITCZ position on geologic timescales can modulate hurricane activity, but continuous and long-term storm records are needed from multiple sites to assess this hypothesis. Here we present a 3000 year record of intense hurricane strikes in the northern Bahamas (Abaco Island) based on overwash deposits in a coastal sinkhole, which indicates that the ITCZ has likely helped modulate intense hurricane strikes on the western North Atlantic margin on millennial to centennial-scales. The new reconstruction closely matches a previous reconstruction from Puerto Rico, and documents a period of elevated intense hurricane activity on the western North Atlantic margin from 2500 to 1000 years ago when paleo precipitation proxies suggest that the ITCZ occupied a more northern position. Considering that anthropogenic warming is predicted to be focused in the northern hemisphere in the coming century, these results provide a prehistoric analog that an attendant northern ITCZ shift in the future may again return the western North Atlantic margin to an active hurricane interval.This research was supported by NSF Awards: OCE-1519578, OCE-1356708, BCS-1118340
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