arXiv subjects

César A. Costa

Publications and source records attributed to César A. Costa.

6 recordsLinked to original sources

arXiv2019

Gravitational Waves From Pulsars Due To Their Magnetic Ellipticity

We discuss some aspects of de Araujo, Coelho & Costa (2016, 2017) concerning the role of a time dependent magnetic ellipticity on the pulsars' braking indices and on the putative gravitational waves (GWs) these objects can emit. Since only nine of more than 2000 known pulsars have accurately measured braking indices, it is of interest to extend this study to all known pulsars, in particular as regards GW generation. In summary, our results show a pessimistic prospect for the detection of GWs generated by these pulsars, even for advanced detectors such as aLIGO and AdVirgo, and the planned Einstein Telescope, would not be able to detect these pulsar, if the ellipticity has magnetic origin.

astro-ph.HE↗

arXiv2017

Gravitational waves from pulsars in the context of magnetic ellipticity

In one of our previous articles we have considered the role of a time dependent magnetic ellipticity on pulsars' braking indices and on the putative gravitational waves these objects can emit. Since only nine of more than 2000 known pulsars have accurately measured braking indices, it is of interest to extend this study to all known pulsars, in particular to what concerns the gravitational waves generation. To do so, as shown in our previous article, we need to know some pulsars' observable quantities such as: periods and their time derivatives, and estimated distances to the Earth. Moreover, we also need to know the pulsars' masses and radii, for which, in here we are adopting current fiducial values. Our results show that the gravitational wave amplitude is at best $h \sim 10^{-28}$. This leads to a pessimistic prospect for the detection of gravitational waves generated by these pulsars, even for Advanced LIGO and Advanced Virgo, and the planned Einstein Telescope, whether the ellipticity has magnetic origin.

astro-ph.SR↗

arXiv2016

Gravitational Waves from Pulsars and Their Braking Indices: The Role of a Time Dependent Magnetic Ellipticity

We study the role of time dependent magnetic ellipticities ($ε_{B}$) on the calculation of the braking index of pulsars. Moreover, we study the consequences of such a $ε_{B}$ on the amplitude of gravitational waves (GWs) generated by pulsars with measured braking indices. We show that, since the ellipticity generated by the magnetic dipole is extremely small, the corresponding amplitude of GWs is much smaller than the amplitude obtained via the spindown limit.

astro-ph.HE↗

arXiv2008

Solution of the inverse problem in spherical gravitational wave detectors using a model with independent bars

The direct detection of gravitational waves will provide valuable astrophysical information about many celestial objects. The SCHENBERG has already undergone its first test run. It is expected to have its first scientific run soon. In this work a new data analysis approach is presented, called method of independent bars, which can be used with SCHENBERG's data . We test this method through the simulation of the detection of gravitational waves. With this method we find the source's direction without the need to have all six transducers operational. Also we show that the method is a generalization of another one, already described in the literature, known as the mode channels method.

gr-qc↗

arXiv2003

The Mario Schenberg Gravitational Wave Detector: A mathematical model for its quadrupolar oscilations

In this work we present a mathematical model for the mechanical response of the Brazilian Mario SCHENBERG gravitational wave (GW) detector to such waves. We found the physical parameters that are involved in this response assuming a linear elastic theory. Adopting this approach we determined the system's resonance frequencies for the case when six $i$-mode mechanical resonators are coupled to the antenna surface according to the arrangement suggested by Johnson and Merkowitz: the truncated icosahedron configuration. This configuration presents special symmetries that allow for the derivation of an analytic expression for the mode channels, which can be experimentally monitored and which are directly related to the tensorial components of the GW. Using this model we simulated how the system behaves under a gravitational sinewave quadrupolar force and found the relative amplitudes that result from this excitation. The mechanical resonators made the signal $\approx 5340$ times stronger. We found $i+1$ degenerate triplets plus $i$ non-degenerate system mode resonances within a band around ${3.17-3.24\rm{kHz}}$ that are sensitive to signals higher than ${\tilde h\sim 10^{-22}\rm{Hz}^{-1/2}}$ when we considerate the effects of thermal noise only.

gr-qc↗

arXiv2003

Response of the Brazilian gravitational wave detector to signals from a black hole ringdown

It is assumed that a black hole can be disturbed in such a way that a ringdown gravitational wave would be generated. This ringdown waveform is well understood and is modelled as an exponentially damped sinusoid. In this work we use this kind of waveform to study the performance of the SCHENBERG gravitational wave detector. This first realistic simulation will help us to develop strategies for the signal analysis of this Brazilian detector. We calculated the signal-to-noise ratio as a function of frequency for the simulated signals and obtained results that show that SCHENBERG is expected to be sensitive enough to detect this kind of signal up to a distance of $\sim 20\mathrm{kpc}$.

gr-qc↗