Validating delta-filters for resonant bar detectors of improved bandwidth foreseeing the future coincidence with interferometers

TL;DR

This paper evaluates the effectiveness of delta filters in resonant bar gravitational wave detectors with increased bandwidth, comparing their performance to optimal filters for realistic GW signals like stellar quasi-normal modes.

Contribution

It reassesses the use of delta filters in wider bandwidth resonant detectors and analyzes their impact on SNR and timing accuracy for specific GW signals.

Findings

Delta filters lose SNR compared to optimal filters in wider bandwidths.

Filtering with delta filters introduces timing errors for GW signals.

The shape of the GW waveform significantly affects filter performance.

Abstract

The classical delta filters used in the current resonant bar experiments for detecting GW bursts are viable when the bandwidth of resonant bars is few Hz. In that case, the incoming GW burst is likely to be viewed as an impulsive signal in a very narrow frequency window. After making improvements in the read-out with new transducers and high sensitivity dc-SQUID, the Explorer-Nautilus have improved the bandwidth ($\sim 20$ Hz) at the sensitivity level of $10^{-20}/\sqrt{Hz}$. Thus, it is necessary to reassess this assumption of delta-like signals while building filters in the resonant bars as the filtered output crucially depends on the shape of the waveform. This is presented with an example of GW signals -- stellar quasi-normal modes, by estimating the loss in SNR and the error in the timing, when the GW signal is filtered with the delta filter as compared to the optimal filter.