M. Alessandra Papa, University of Rome
The second edition of the Amaldi Conference on Gravitational Waves was held in CERN this year from July 1 to July 4 and brought together more than 150 scientists from 13 different countries. Both experimental and theoretical activity were well represented at the conference and great emphasis was put on issues in data analysis. The programme included plenary talks, contributed communications and a large poster session (27 posters), the latter two divided in five topic workshops: sources, instrumentation, non-gaussian noise sources, data analysis and future.
In the past decade a lot of effort has been spent by the resonant bar detector groups to improve sensitivity and duty cycle of their instruments. So, a great success, and in fact one of the highlights of the conference, is the fact that presently there are five gravitational wave detectors - all bar antennas - in continuous operation in the world: NIOBE, in operation since 1993 at the university of Perth, ALLEGRO, operating since 1991 (with a stop during '95) at Louisiana State University, EXPLORER, taking data since 1990 (with a stop from '92 to '94, apart for a few months during '93), at CERN, NAUTILUS in operation since 1996 at LNF (Frascati, Italy) and the AURIGA detector, at LNL (Legnaro, Italy). The latter, as announced during the conference, had started its first cryogenic run in february '97 and has been in stable operation since then with a best sensitivity around 8 mK.
During the conference an agreement was signed among these groups to exchange data regularly on the basis of a common protocol.
The state of the art regarding the construction of the km-sized interferometric antennas projects VIRGO and LIGO, and of the smaller scale interferometers, TAMA 300 and GE0 600 was also reviewed.
The schedules of all these projects foresee initial operation by the year 2000.
It clearly emerged that a great deal of effort is being made to predict and model gw signals from astrophysical sources, especially black holes (W.H. Lee, R. Price, C.Palomba). B.S. Sathyaprakash showed that it is possible to approximate wave forms of signals from inspiraling compact binaries so that they overlap with the exact wave-form more than thus enhancing the detection probability to more than . Issues regarding signals from binary systems, isolated stars and stochastic background radiation were addressed.
G.Schaefer showed how to compute the secular changes of the orbital parameters of a binary system up to order thanks to ad hoc balance equations between far zone fluxes and near zone losses,
A.F.Zahkarov presented estimates of with characteristic frequency at 1 kHz from kpc for gw emission during non spherical evolution of pre-SN in the framework of PN formalism. The results of E.Mueller from a comprehensive study of asymmetric core collapse supernovae predict for a source at Mpc.
M. Gasperini presented predictions on a gravitational wave background from the pre big-bang phase typical of string cosmological model. At frequencies above 1 Hz, and up to about Hz, the expected spectrum lies orders of magnitude (even 10) above that predicted by standard inflation. Upper limits set by data from detectors are still far from constraining the parameters of the model: the most recent data yield and come from the cross correlation of EXPLORER and NAUTILUS data, whereas the upper border of the predicted value is at . Nevertheless the future is promising because already by cross correlating NAUTILUS, EXPLORER and AURIGA the upper limit could be lowered to .
In the data analysis session various topics were discussed. Hierarchical procedures to overcome the demanding requirements on computing resources needed to apply optimal matched filtering to the search for unknown pulsar signals, have been presented by X.Grave and P. Astone. There have also been a number of presentations (I.M.Pinto, A. Vecchio) on algorithms to estimate coalescing binaries parameters, both for space and ground based experiments. A general point about what statistical approach, if bayesian or frequentist, should be used in gravitational wave data analysis was made by S. Finn in his talk.
Future plans concern both the resonant mass and interferometric detection strategy. In the former category fall the projects for big spherical detectors, of enhanced sensitivity and capable of estimating parameters of the incoming radiation (E.Coccia, J.A. Lobo, S. Merkowitz ). For detection at high frequencies () a local array of small multi mode cylinders has been proposed. S. Frasca has presented data analysis strategies for this instrument. In the latter category there is the space bound interferometer LISA that could make observations in the frequency range for signals from massive black holes and galactic binary stars (J.Hough).