The EXPLORER gravitational wave antenna: recent improvements and performances

Since the beginning of 2000 the EXPLORER gravity wave (GW) detector has been operated continuously after a stop devoted to improve the apparatus. The antenna has been equipped with a new read-out. The use of a new transducer, characterized by a very small gap, and a dc-SQUID with a high coupling, led to a better sensitivity and a larger bandwidth. The EXPLORER sensitivity in terms of spectral noise amplitude, at present (June 2001), is 10-20 Hz-1/2 over a bandwidth of 35 Hz and 3 × 10-21 Hz-1/2 with a bandwidth of about 6 Hz, corresponding to a sensitivity to short conventional GW bursts of h = 4 × 10-19. The performance is stable and the apparatus is taking data with a duty cycle in excess of 80%.