Liquid-immersible electrostatic ultrasonic transducer

A broadband megahertz range electrostatic acoustic transducer for use in a liquid environment is described. A liquid tight enclosure includes a metallic conducting membrane as part of its outside surface and has a means inside the liquid tight enclosure for applying a tension to the membrane and for mounting an electrode such that the flat end of the electrode is aproximately parallel to the membrane. The invention includes structure and a method for ensuring that the membrane and the flat end of the electrode are exactly parallel and a fixed predetermined distance from each other

Puncture Self-Healing Polymers for Aerospace Applications

Space exploration launch costs on the order of $10K per pound provide ample incentive to seek innovative, cost-effective ways to reduce structural mass without sacrificing safety and reliability. Damage-tolerant structural systems can provide a route to avoiding weight penalty while enhancing vehicle safety and reliability. Self-healing polymers capable of spontaneous puncture repair show great promise to mitigate potentially catastrophic damage from events such as micrometeoroid penetration. Effective self-repair requires these materials to heal instantaneously following projectile penetration while retaining structural integrity. Poly(ethylene-co-methacrylic acid) (EMMA), also known as Surlyn is an ionomer-based copolymer that undergoes puncture reversal (self-healing) following high impact puncture at high velocities. However EMMA is not a structural engineering polymer, and will not meet the demands of aerospace applications requiring self-healing engineering materials. Current efforts to identify candidate self-healing polymer materials for structural engineering systems are reported. Rheology, high speed thermography, and high speed video for self-healing semi-crystalline and amorphous polymers will be reported

The afterglows of gamma-ray bursts

Gamma-ray burst astronomy has undergone a revolution in the last three years, spurred by the discovery of fading long-wavelength counterparts. We now know that at least the long duration GRBs lie at cosmological distances with estimated electromagnetic energy release of 10^51–10^53 erg, making these the brightest explosions in the Universe. In this article we review the current observational state, beginning with the statistics of X-ray, optical, and radio afterglow detections. We then discuss the insights these observations have given to the progenitor population, the energetics of the GRB events, and the physics of the afterglow emission. We focus particular attention on the evidence linking GRBs to the explosion of massive stars. Throughout, we identify remaining puzzles and uncertainties, and emphasize promising observational tools for addressing them. The imminent launch of HETE-2 and the increasingly sophisticated and coordinated ground-based and space-based observations have primed this field for fantastic growth

The afterglows of gamma-ray bursts

Gamma-ray burst astronomy has undergone a revolution in the last three years, spurred by the discovery of fading long-wavelength counterparts. We now know that at least the long-duration GRBs lie at cosmological distances with estimated electromagnetic energy release of 10^51–10^53 erg, making these the brightest explosions in the Universe. In this article we review the current observational state, beginning with the statistics of X-ray, optical, and radio afterglow detections. We then discuss the insights these observations have given to the progenitor population, the energetics of the GRB events, and the physics of the afterglow emission. We focus particular attention on the evidence linking GRBs to the explosion of massive stars. Throughout, we identify remaining puzzles and uncertainties, and emphasize promising observational tools for addressing them. The imminent launch of HETE-2 and the increasingly sophisticated and coordinated ground-based and space-based observations have primed this field for fantastic growth

The afterglows of gamma-ray bursts

Gamma-ray burst astronomy has undergone a revolution in the last three years, spurred by the discovery of fading long-wavelength counterparts. We now know that at least the long duration GRBs lie at cosmological distances with estimated electromagnetic energy release of 10^51–10^53 erg, making these the brightest explosions in the Universe. In this article we review the current observational state, beginning with the statistics of X-ray, optical, and radio afterglow detections. We then discuss the insights these observations have given to the progenitor population, the energetics of the GRB events, and the physics of the afterglow emission. We focus particular attention on the evidence linking GRBs to the explosion of massive stars. Throughout, we identify remaining puzzles and uncertainties, and emphasize promising observational tools for addressing them. The imminent launch of HETE-2 and the increasingly sophisticated and coordinated ground-based and space-based observations have primed this field for fantastic growth. This overview is a combined write-up of talks given at this conference and in NASA's Goddard Space Flight Center

The Dark Side of ROTSE-III Prompt GRB Observations

We present several cases of optical observations during gamma-ray bursts (GRBs) which resulted in prompt limits but no detection of optical emission. These limits constrain the prompt optical flux densities and the optical brightness relative to the gamma-ray emission. The derived constraints fall within the range of properties observed in GRBs with prompt optical detections, though at the faint end of optical/gamma flux ratios. The presently accessible prompt optical limits do not require a different set of intrinsic or environmental GRB properties, relative to the events with prompt optical detections.Comment: ApJ accepted. 20 pages in draft manuscript form, which includes 6 pages of tables and 2 figure

Status of the ROTSE-III telescope network

ROTSE-III is a homogeneous worldwide array of 4 robotic telescopes. They were designed to provide optical observations of γ-ray burst (GRB) afterglows as close as possible to the start of γ-ray emission. ROTSE-III is fulfilling its potential for GRB science, and provides optical observations for a variety of astrophysical sources in the interim between GRB events

Looking Into the Fireball: ROTSE-III and Swift Observations of Early GRB Afterglows

We report on a complete set of early optical afterglows of gamma-ray bursts (GRBs) obtained with the ROTSE-III telescope network from March 2005 through June 2007. This set is comprised of 12 afterglows with early optical and Swift/XRT observations, with a median ROTSE-III response time of 45 s after the start of gamma-ray emission (8 s after the GCN notice time). These afterglows span four orders of magnitude in optical luminosity, and the contemporaneous X-ray detections allow multi-wavelength spectral analysis. Excluding X-ray flares, the broadband synchrotron spectra show that the optical and X-ray emission originate in a common region, consistent with predictions of the external forward shock in the fireball model. However, the fireball model is inadequate to predict the temporal decay indices of the early afterglows, even after accounting for possible long-duration continuous energy injection. We find that the optical afterglow is a clean tracer of the forward shock, and we use the peak time of the forward shock to estimate the initial bulk Lorentz factor of the GRB outflow, and find 100<Gamma_0<1000, consistent with expectations.Comment: 31 pages, 5 figures, submitted to Ap

The Broadband Afterglow of GRB980329

We present radio observations of the afterglow of the bright gamma-ray burst GRB980329 made between one month and several years after the burst, a re-analysis of previously published submillimeter data, and late-time optical and near-infrared (NIR) observations of the host galaxy. From the absence of a spectral break in the optical/NIR colors of the host galaxy, we exclude the earlier suggestion that GRB980329 lies at a redshift of z >~5. We combine our data with the numerous multi-wavelength observations of the early afterglow, fit a comprehensive afterglow model to the entire broadband dataset, and derive fundamental physical parameters of the blast-wave and its host environment. Models for which the ejecta expand isotropically require both a high circumburst density and extreme radiative losses from the shock. No low density model (n << 10 cm^{-3}) fits the data. A burst with a total energy of ~ 10^{51} erg, with the ejecta narrowly collimated to an opening angle of a few degrees, driven into a surrounding medium with density ~ 20 cm^{-3}, provides a satisfactory fit to the lightcurves over a range of redshifts.Comment: 27 pages, incl. 6 figures, minor revisions (e.g. added/updated references) Accepted by Ap

The Anomalous Early Afterglow of GRB 050801

The ROTSE-IIIc telescope at the H.E.S.S. site, Namibia, obtained the earliest detection of optical emission from a Gamma-Ray Burst (GRB), beginning only 21.8 s from the onset of Swift GRB 050801. The optical lightcurve does not fade or brighten significantly over the first ~250 s, after which there is an achromatic break and the lightcurve declines in typical power-law fashion. The Swift/XRT also obtained early observations starting at 69 s after the burst onset. The X-ray lightcurve shows the same features as the optical lightcurve. These correlated variations in the early optical and X-ray emission imply a common origin in space and time. This behavior is difficult to reconcile with the standard models of early afterglow emission.Comment: 5 pages, 1 figure. Accepted for publication in ApJ Letter