3,480 research outputs found
The ROTSE-III Robotic Telescope System
The observation of a prompt optical flash from GRB990123 convincingly
demonstrated the value of autonomous robotic telescope systems. Pursuing a
program of rapid follow-up observations of gamma-ray bursts, the Robotic
Optical Transient Search Experiment (ROTSE) has developed a next-generation
instrument, ROTSE-III, that will continue the search for fast optical
transients. The entire system was designed as an economical robotic facility to
be installed at remote sites throughout the world. There are seven major system
components: optics, optical tube assembly, CCD camera, telescope mount,
enclosure, environmental sensing & protection and data acquisition. Each is
described in turn in the hope that the techniques developed here will be useful
in similar contexts elsewhere.Comment: 19 pages, including 4 figures. To be published in PASP in January,
2003. PASP Number IP02-11
Observations of Microwave Continuum Emission from Air Shower Plasmas
We investigate a possible new technique for microwave measurements of
ultra-high energy cosmic ray (UHECR) extensive air showers which relies on
detection of expected continuum radiation in the microwave range, caused by
free-electron collisions with neutrals in the tenuous plasma left after the
passage of the shower. We performed an initial experiment at the AWA (Argonne
Wakefield Accelerator) laboratory in 2003 and measured broadband microwave
emission from air ionized via high energy electrons and photons. A follow-up
experiment at SLAC (Stanford Linear Accelerator Center) in summer of 2004
confirmed the major features of the previous AWA observations with better
precision and made additional measurements relevant to the calorimetric
capabilities of the method. Prompted by these results we built a prototype
detector using satellite television technology, and have made measurements
indicating possible detection of cosmic ray extensive air showers. The method,
if confirmed by experiments now in progress, could provide a high-duty cycle
complement to current nitrogen fluorescence observations of UHECR, which are
limited to dark, clear nights. By contrast, decimeter microwave observations
can be made both night and day, in clear or cloudy weather, or even in the
presence of moderate precipitation.Comment: 15 pages, 13 figure
Risk Factors for Age-Related Maculopathy
Age-related maculopathy (ARM) is the leading cause of blindness in the elderly. Although beneficial therapeutic strategies have recently begun to emerge, much remains unclear regarding the etiopathogenesis of this disorder. Epidemiologic studies have enhanced our understanding of ARM, but the data, often conflicting, has led to difficulties with drawing firm conclusions with respect to risk for this condition. As a consequence, we saw a need to assimilate the published findings with respect to risk factors for ARM, through a review of the literature appraising results from published cross-sectional studies, prospective cohort studies, case series, and case control studies investigating risk for this condition. Our review shows that, to date, and across a spectrum of epidemiologic study designs, only age, cigarette smoking, and family history of ARM have been consistently demonstrated to represent risk for this condition. In addition, genetic studies have recently implicated many genes in the pathogenesis of age-related maculopathy, including Complement Factor H, PLEKHA 1, and LOC387715/HTRA1, demonstrating that environmental and genetic factors are important for the development of ARM suggesting that gene-environment interaction plays an important role in the pathogenesis of this condition
Status of ANITA and ANITA-lite
We describe a new experiment to search for neutrinos with energies above 3 x
10^18 eV based on the observation of short duration radio pulses that are
emitted from neutrino-initiated cascades. The primary objective of the
ANtarctic Impulse Transient Antenna (ANITA) mission is to measure the flux of
Greisen-Zatsepin-Kuzmin (GZK) neutrinos and search for neutrinos from Active
Galactic Nuclei (AGN). We present first results obtained from the successful
launch of a 2-antenna prototype instrument (called ANITA-lite) that circled
Antarctica for 18 days during the 03/04 Antarctic campaign and show preliminary
results from attenuation length studies of electromagnetic waves at radio
frequencies in Antarctic ice. The ANITA detector is funded by NASA, and the
first flight is scheduled for December 2006.Comment: 9 pages, 8 figures, to be published in Proceedings of International
School of Cosmic Ray Astrophysics, 14th Course: "Neutrinos and Explosive
Events in the Universe", Erice, Italy, 2-13 July 200
Ultra-Relativistic Magnetic Monopole Search with the ANITA-II Balloon-borne Radio Interferometer
We have conducted a search for extended energy deposition trails left by
ultra-relativistic magnetic monopoles interacting in Antarctic ice. The
non-observation of any satisfactory candidates in the 31 days of accumulated
ANITA-II flight data results in an upper limit on the diffuse flux of
relativistic monopoles. We obtain a 90% C.L. limit of order
10^{-19}/(cm^2-s-sr) for values of Lorentz boost factor 10^{10}<gamma at the
anticipated energy E=10^{16} GeV. This bound is stronger than all previously
published experimental limits for this kinematic range.Comment: updated to version accepted by Phys. Rev.
Observations of the Askaryan Effect in Ice
We report on the first observations of the Askaryan effect in ice: coherent
impulsive radio Cherenkov radiation from the charge asymmetry in an
electromagnetic (EM) shower. Such radiation has been observed in silica sand
and rock salt, but this is the first direct observation from an EM shower in
ice. These measurements are important since the majority of experiments to date
that rely on the effect for ultra-high energy neutrino detection are being
performed using ice as the target medium. As part of the complete validation
process for the Antarctic Impulsive Transient Antenna (ANITA) experiment, we
performed an experiment at the Stanford Linear Accelerator Center (SLAC) in
June 2006 using a 7.5 metric ton ice target, yielding results fully consistent
with theoretical expectations.Comment: 4 pages, 5 figures, minor correction
Observational Constraints on the Ultra-high Energy Cosmic Neutrino Flux from the Second Flight of the ANITA Experiment
The Antarctic Impulsive Transient Antenna (ANITA) completed its second
long-duration balloon flight in January 2009, with 31 days aloft (28.5 live
days) over Antarctica. ANITA searches for impulsive coherent radio Cherenkov
emission from 200 to 1200 MHz, arising from the Askaryan charge excess in
ultra-high energy neutrino-induced cascades within Antarctic ice. This flight
included significant improvements over the first flight in the payload
sensitivity, efficiency, and a flight trajectory over deeper ice. Analysis of
in-flight calibration pulses from surface and sub-surface locations verifies
the expected sensitivity. In a blind analysis, we find 2 surviving events on a
background, mostly anthropogenic, of 0.97+-0.42 events. We set the strongest
limit to date for 1-1000 EeV cosmic neutrinos, excluding several current
cosmogenic neutrino models.Comment: 6 pages, 5 figures, submitted to Phys. Rev.
Observation of Ultra-high-energy Cosmic Rays with the ANITA Balloon-borne Radio Interferometer
We report the observation of sixteen cosmic ray events of mean energy of 1.5
x 10^{19} eV, via radio pulses originating from the interaction of the cosmic
ray air shower with the Antarctic geomagnetic field, a process known as
geosynchrotron emission. We present the first ultra-wideband, far-field
measurements of the radio spectral density of geosynchrotron emission in the
range from 300-1000 MHz. The emission is 100% linearly polarized in the plane
perpendicular to the projected geomagnetic field. Fourteen of our observed
events are seen to have a phase-inversion due to reflection of the radio beam
off the ice surface, and two additional events are seen directly from above the
horizon.Comment: 5 pages, 5 figures, new figure adde
Constraints on the Ultra-High Energy Neutrino Flux from Gamma-Ray Bursts from a Prototype Station of the Askaryan Radio Array
We report on a search for ultra-high-energy (UHE) neutrinos from gamma-ray
bursts (GRBs) in the data set collected by the Testbed station of the Askaryan
Radio Array (ARA) in 2011 and 2012. From 57 selected GRBs, we observed no
events that survive our cuts, which is consistent with 0.12 expected background
events. Using NeuCosmA as a numerical GRB reference emission model, we estimate
upper limits on the prompt UHE GRB neutrino fluence and quasi-diffuse flux from
to GeV. This is the first limit on the prompt UHE GRB
neutrino quasi-diffuse flux above GeV.Comment: 14 pages, 8 figures, Published in Astroparticle Physics Journa
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