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 antenna’s 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.

Figure 1

Schematics of the SCHENBERG detector. The spherical antenna is carefully suspended inside metallic chambers that keep it in vacuum at 4 K.

Figure 2

Plot of the Fourier transform of the lightning’s current.

Figure 3

Schematics of an idealized return stroke with the geometrical and physical parameters used in the calculations.

Figure 4

Plot of the behavior of the current of the lightning as a function of time, modeled according to a Poisson distribution.

Figure 5

Plots of the electric (a)and magnetic (b) fields as functions of time for $\mathrm{D}=1500\mathrm{m}$.

Figure 6

Adimensional envelop of amplitudes as a function of time for modes (a) $\mathrm{m}=0$ and (b) $\mathrm{m}=2$. Notice that the amplitude decays slowly due to the antenna’s high mechanical quality factor.