Parametric Motion Transducer for Gravitational Wave Detectors.

We designed, constructed, and tested (using two different low phase noise electrical pump generators) a cryogenic double-resonant parabridge motion transducer made out of niobium, whose electrical output was amplified by a two stage MESFET cryogenic amplifier. Most of the experimental results agreed well with the theoretical models, and we successfully measured the mechanical Brownian motion of this transducer. We were able to adjust the two electrical bridge resonant frequencies on top of each other at the pump frequency, allowing us to obtain an electromechanical coupling as high as 0.054. This high coupling, corresponding to an rms electric field strength of 1.79 $\times$ 10\sp5 V/m across the capacitor plates, is the highest measured so far for this class of transducers. In one case, we observed a dip in the electrical noise spectrum near the mechanical resonant frequency due to destructive interference between this noise and its reflection from the mechanical resonator. At the bottom of this dip, we measured, for this transducer, an equivalent displacement noise of 4 $\times$ 10\sp{-16} m/$\sqrt{\rm Hz}$ with a systematic error of less than 10%. This measured equivalent displacement noise allows this parametric transducer to detect accelerations of 1.4 $\times$ 10\sp{-8} m/s\sp2 at 929 Hz in a one Hz bandwidth. If coupled to the LSU gravitational wave antenna, a 2.3 $\times$ 10\sp3 kg aluminum bar, this transducer resonator of 0.27 kg would detect gravitational wave strains (h) as small as 6 $\times$ 10\sp{-18}. A large improvement can be achieved if we manage to obtain 50 V\sb{\rm peak} across the transducer\u27s capacitor plates with a 5 MHz crystal oscillator. In this case, we would reach an equivalent displacement noise of 2 $\times$ 10\sp{-17} m/$\sqrt{\rm Hz}$, corresponding to h $\sim$ 3 $\times$ 10\sp{-19}. Further improvement could be obtained by the use of a DC SQUID preamplifier

Search for gravitational-wave bursts in LIGO data at the Schenberg antenna sensitivity range

The Brazilian gravitational-wave detector Mario Schenberg was conceived in the early 2000s and operated until 2016 when it was dismantled. A straight path to evaluate the viability of the reassembly of the Schenberg antenna is to verify the possibility of detecting gravitational wave (GW) signals within its design sensitivity features. The eventual identification of significant signals would operate as motivation for the Schenberg rebuild. As the antenna was dismantled, we can get some indication from the third observing run (O3) data of the LIGO detectors. It is based on the similarity between Schenberg sensitivity and the sensitivity of the interferometers in the O3 [3150-3260] Hz band. We search for signals with milliseconds to a few seconds without making assumptions about their morphology, polarization, and arrival sky direction. The data were analyzed with the coherent WaveBurst pipeline (cWB) with frequencies from 512 Hz to 4096 Hz and the search targets only signals with bandwidth overlapping the Schenberg frequency band. No statistically significant evidence of GW bursts during O3 was found. The null result was used to feature the search efficiency in identifying different simulated signal morphologies and establish upper limits on the GW burst event rate as a function of its strain amplitude. The present search, and consequently Schenberg, is sensitive to sources emitting isotropically 5 x 10e(-6) M_sun c^2 in GWs from a distance of 10 kpc with 50% detection efficiency and with a false alarm rate of 1/100 years. The feasibility of detecting f-modes of neutron stars excited by glitches was also investigated. The Schenberg antenna would need at least 5.3 years of observation run to get a single detection of the f-mode signal, given E_(glitch) approx 10e(-10) M_sun c^2

Can lightning be a noise source for a spherical gravitational wave antenna?

The detection of gravitational waves is a very active research field at the moment. In Brazil the gravitational wave detector is called Mario SCHENBERG. Due to its high sensitivity it is necessary to model mathematically all known noise sources so that digital filters can be developed that maximize the signal-to-noise ratio. One of the noise sources that must be considered are the disturbances caused by electromagnetic pulses due to lightning close to the experiment. Such disturbances may influence the vibrations of the antenna's normal modes and mask possible gravitational wave signals. In this work we model the interaction between lightning and SCHENBERG antenna and calculate the intensity of the noise due to a close lightning stroke in the detected signal. We find that the noise generated does not disturb the experiment significantly.Comment: 5 pages, 6 figure

The Past, Present and Future of the Resonant-Mass Gravitational Wave Detectors

Resonant-mass gravitational waves detectors are reviewed from the concept of gravitational waves and its mathematical derivation, using Einstein's general relativity, to the present status of bars and spherical detectors, and their prospects for the future, which include dual detectors and spheres with non-resonant transducers. The review covers not only the technical aspects of detectors and the science that will be done, but also analyses the subject in a historic perspective, covering the various detection efforts over four decades, starting from Weber's pioneering work.Comment: 49 pages, 45 figures, invited review article, which will be published at Research in Astronomy and Astrophysics (RAA

ISOLAMENTO VERTICAL DO MULTI-NESTED PENDULA PARA DETECTORES INTERFEROMÉTRICOS DE ONDAS GRAVITACIONAIS

Neste trabalho apresentamos os primeiros resultados do estudo do isolamento vertical em um sistema de pêndulos multi-aninhados, para aplicação como isoladores vibracionais passivos dos espelhos da próxima geração de detectores interferométricos de ondas gravitacionais, como o LIGO Voyager. As funções de transferência teórica dos modos verticais indicam um fator de isolamento de até seis ordens de grandeza em 10 Hz. As medições dessas oscilações apresentam frequências de ressonância indesejáveis e indicam que o sistema necessita de melhorias. Aqui propomos algumas soluções para isso, que já estão sendo estudadas

The Schenberg spherical gravitational wave detector: the first commissioning runs

Here we present a status report of the first spherical antenna project equipped with a set of parametric transducers for gravitational detection. The Mario Schenberg, as it is called, started its commissioning phase at the Physics Institute of the University of Sao Paulo, in September 2006, under the full support of FAPESP. We have been testing the three preliminary parametric transducer systems in order to prepare the detector for the next cryogenic run, when it will be calibrated. We are also developing sapphire oscillators that will replace the current ones thereby providing better performance. We also plan to install eight transducers in the near future, six of which are of the two-mode type and arranged according to the truncated icosahedron configuration. The other two, which will be placed close to the sphere equator, will be mechanically non-resonant. In doing so, we want to verify that if the Schenberg antenna can become a wideband gravitational wave detector through the use of an ultra-high sensitivity non-resonant transducer constructed using the recent achievements of nanotechnology