Nadja S. Magalhães

A Geometric Method for Location of Gravitational Wave Sources

We show that the interaction of a gravitational wave with a spherical resonant-mass antenna changes the antennas shape to that of an ellipsoid. These changes in shape always determine the direction of the incoming wave and may provide information on the waves polarization. We present a new approach for determining the position of astrophysical sources of gravitational waves which involves fewer calculations than in earlier methods. We also show how the measured quantities relate to the energy density of the wave.

Possible Resonator Configurations for the Spherical Gravitational Wave Antenna

We solve algebraically the equations of motion for a spherical antenna coupled to an arbitrary number of small resonators, free to move radially, and investigate the conditions under which damping forces can be neglected in the system. We show that in order that the antennas modes be decoupled a preferred distribution of the resonators on its surface should be used. We find that either 5, 6, 10 or 16 resonators can be used as long as they are conveniently positioned on the antennas surface. We calculate and analyse the frequency shift and the signal-to-noise ratio of the coupled system for the various distributions studied.

Braking Indices of Pulsars Obtained in the Presence of an Effective Force

The theoretical calculation of braking indices of pulsars is still an open problem. In this work we present a study on this issue which adapts the model that assumes that pulsars are rotating magnetic dipoles by introducing a compensating component in the energy conservation equation of the system. Such component relates to an effective force that varies with the first power of the tangential velocity of the pulsar’s crust. We tested the proposed model using data available.

Bayesian Inference Applied to Pulsar’s Models

The goal of this work is to apply Bayesian statistics to the problem of pulsars in order to compute the Bayes factor and investigate which one among different EoS could better fit known pulsar data, regarding the rate of decrease of the angular velocity versus the angular velocity itself. We also find the posterior distribution and the best fit for some relevant parameters of the pulsar like the mass and the magnetic field.

A Model for the Braking Indices of Pulsars

Stars known as pulsars are generally modeled as magnetized spheres made of neutrons with high rotation frequency. It is known that such stars are spinning down and this braking is measured by a parameter, n, known as braking index. For the canonical model such parameter should have a single value for all pulsars: n = 3. However, from observations it is known that n diverges from 3. In this work, differently from the canonical model, we have hypothesized the existence of a variation of the moment of inertia of the star through a time-varying radius. Using energy conservation we find the values for the variation of the radius of our pulsar sample. Our results indicate that it may be reasonable to consider that the radius of pulsars can be changing with time.

DATA ANALYSIS OF GRAVITATIONAL WAVES SIGNALS FROM MILLISECONDS PULSARS

The present work is devoted to the detection of monochromatic gravitational wave signals emitted by pulsars using ALLEGROs data detector. We will present the region (in frequency) of millisecond pulsars of the globular cluster 47 Tucanae (NGC 104) in the band of detector. With this result it was possible to analyse the data in the frequency ranges of the pulsars J1748-2446L and J1342+2822c, searching for annual Doppler variations using power spectrum estimates for the year 1999. We tested this method injecting a simulated signal in real data and we were able to detect it.

Astrophysics from data analysis of spherical gravitational wave detectors

The direct detection of gravitational waves will provide valuable astrophysical information about many celestial objects. Also, it will be an important test to general relativity and other theories of gravitation. The gravitational wave detector SCHENBERG has recently undergone its first test run. It is expected to have its first scientific run soon. In this work the data analysis system of this spherical, resonant mass detector is tested through the simulation of the detection of gravitational waves generated during the inspiralling phase of a binary system. It is shown from the simulated data that it is not necessary to have all six transducers operational in order to determine the source’s direction and the wave’s amplitudes.

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. Because of 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 lightnings close to the experiment. Such disturbances may influence the vibrations of the antennas normal modes and mask possible gravitational wave signals. In this work we model the interaction between lightnings 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.

Cosmic-ray noise and gravitational wave antennas at the quantum limit

Abstract When present-day bar antennas reach the standard quantum limit, cosmic rays are expected to become a significant source of noise. In this work, we estimate the influences of single hadrons and muons on such detectors and compare them to those expected for a hypothetical CuAl detector, since next generation resonant-mass detectors are being considered to have antennas made with this material.

The first phase of the Brazilian graviton project: The Mário Schenberg detector

The construction of a CuAl (94%–6%) 0.6-meter diameter truncated icosahedral gravitational wave antenna is currently being proposed in Brazil. The system is planned to feature a sensitivity better than h=10−21 Hz−1/2 at both (4.10.4) kHz and (7.90.8) kHz bandwiths.