The University of Western Australia?s Resonant-bar Gravitational Wave Experiment

Abstract

The cryogenic resonant-mass gravitational radiation antenna at the University of Western Australia (UWA) has obtained a noise temperature of <2 mK using a zero order predictor filter. This corresponds to aIms burst strain sensitivity of 7x 10-19 . The antenna has been in continuous operation since August 1993. The antenna operates at about 5 K and consists of a 1· 5 tonne niobium bar with a 710 Hz fundamental frequency, and a closely tuned secondary mass of 0·45 kg effective mass. The vibrational state of the secondary mass is continuously monitored by a 9·5 GHz superconducting parametric transducer. This paper presents the current design and operation of the detector. From a two-mode model we show how we calibrate, characterise and theoretically determine the sensitivity of our detector. Experimental results confirm the theory.

Accurate calibration technique for a resonant-mass gravitational wave detector

“…The bending flap amplifies the displacement of the niobium cylinder and is monitored by a superconducting reentrant cavity transducer, which has been described in detail previously. 6 It is important to have an accurate method of calibration to determine the energy of possible gravitational wave events incident on the detector. Niobe is again unique due to the self-calibration properties of the transducer.…”

A method for detecting gravitational waves coincident with gamma-ray bursts

“…We may compare the results in Figs 2 to 6 with the sensitivity curves provided by Tobar et al (1995) for the NIOBE bar detector. The sensitivity curves show that, within the two resonance bands, the rms noise reaches a level of ∼2 and ∼7×10 −20 , for the plus and minus mode respectively.…”

“…We may now discuss the detection of such a GW burst. We assume that the GW burst bandwidth is much greater than that of the bar detector since the later is typically of the order of ∼0.3 Hz (Tobar et al 1995). The cross‐section for a single bar resonance in response to GWs in such a situation is given by (Paik & Wagoner 1976)…”

“…Here we summarize some main points. For details of the detection methods used for NIOBE and for descriptions of the ZOP algorithm, see Tobar et al (1995), Dhurandhar, Blair & Costa (1996) and Heng et al. (1996).…”

“…Near the resonance frequency, bar detectors are capable of reaching sensitivities of ∼10 −19 –10 −18 (e.g. Tobar et al. 1995) and future sensitivities are expected to reach ∼10 −20 (e.g.…”