SGR 1806-20 and the gravitational wave detectors EXPLORER and NAUTILUS

The activity of the soft gamma ray repeater SGR 1806-20 is studied in correlation with the EXPLORER and NAUTILUS data, during the year 2004, for gravitational wave (GW) short signal search. Corresponding to the most significant triggers, the bright outburst on October 5th and the giant flare (GF) on December 27th, the associated GW signature is searched. Two methods are employed for processing the data. With the average-modulus algorithm, the presence of short pulses with energy Egw \geq 1.8 x 10^49 erg is excluded with 90% probability, under the hypothesis of isotropic emission. This value is comparable to the upper limits obtained by LIGO regarding similar sources. Using the cross-correlation method, we find a discrepancy from the null-hypothesis of the order of 1%. This statistical excess is not sufficient to claim a systematic association between the gravitational and the electromagnetic radiations, because the estimated GW upper limits are yet several orders of magnitude far away from the theoretically predicted levels, at least three for the most powerful SGR flare.Comment: Accepted by Physical Review

Background Estimation in a Gravitational Wave Experiment

The problem to estimate the background due to accidental coincidences in the search for coincidences in gravitational wave experiments is discussed. The use of delayed coincidences obtained by orderly shifting the event times of one of the two detectors is shown to be the most correctComment: Latex file. 6 pages, 3 figures. Submitted to the proceeding of the 3 GWDAW workshop (Rome, dic 1999) (International journal of Modern physics D

Conjecture on the Cosmic Ray Spectrum

The PAMELA experiment has shown that a fraction of cosmic rays could be due to proton fluxes generated by the magnetosphere of the planet Jupiter. Thus, a conjecture that astrophysical objects provided by magnetospheres be sources of the cosmic radiation is put forward. With simple geometric considerations the energy spectrum E−2.5 is obtained, independently on the particle species, very close to the experimental CR spectrum, under the hypothesis that particle acceleration mechanisms act uniformly in the magnetospheric region

Personal recollections: Frascati and the search for gravitational waves at the Istituto Nazionale di Fisica Nucleare (INFN)

Along the way named Via Isacco Newton in the Laboratori Nazionali di Frascati (LNF) of the Istituto Italiano di Fisica Nucleare (INFN) in Piazza Albert Einstein one meets a building with the inscription NAUTILUS. In this building a cryogenic detector of gravitational waves is installed, the most sensitive one in the world at the end of the 90s. NAUTILUS started to operate in 1991 and will be turned off in June 2016. I think interesting to remember briefly how it has come to carry out this research in the Frascati National Laboratories. The story begins in 1961, when Edoardo Amaldi attended in Varenna lectures on gravitational waves by Joe Weber. Edoardo Amaldi has been the Sower in Italian postwar physics, at least until the 70s. With great scientific acumen and aware of the responsibility that events had put him in, Amaldi launched many seeds on the soil of Italian physics. Some fell on fertile soil and, especially at the University of Rome, developed, continuing the activities initiated by Enrico Fermi with the group of via Panisperna: elementary particle physics, and then the matter, the physics of universe and gravitation. A few more attempts, however, did not catch on completely. Amaldi had tried to convince some colleague or student to start an experimental activity in the field of General Relativity in Italy. Therefore, when in September 1970 I proposed to him to start an experiment for searching gravitational waves, he was extremely happy, gave all his support and he himself was full time in it. The idea to start research in fundamental physics came to me during my stay at the University of Iowa (USA), where I had spent a few years doing research on cosmic rays and Van Allen radiation belts of the Earth. Being the assistant of Edoardo Amaldi, during the last few years I had heard from him the importance to do experiments in the new fields of physics: gravitational waves (GW) and the infrared cosmic background. So when I told him, the next day after my return from Iowa City, that I wished to start an experiment for the search of gravitational waves, his eyes lighted and he stared at me in a way which I shall never forget. In January 1971 Remo Ruffini1 , who was then at the University of Stanford, sent to Amaldi, on a confidential basis, the proposal of William Fairbank (University of Stanford) and William Hamilton (University of Louisiana) for a large five-ton ultracryogenic antenna equipped with a SQUID transducer. Immediately I decided that also in Rome we would have to make a similar experiment. Since we needed a laboratory that could house the antenna and also served cryogenic physicists I proposed Frascati. In Frascati in 1956 I had worked in the installation of the He liquefier and I had performed diffusion experiments He3 in He4 , first Italian researcher working in Frascati with a scholarship INFN, along with J. Reuss and with the technicians Solinas and Bellatreccia, when still the only place fit for use was the laboratory for the helium liquefier (see fig.2). Amaldi immediately summoned a meeting with the director of the INFN Laboratories in Frascati, Italo Federico Quercia, who appeared favorable to 1Remo Ruffini had just got his laurea degree at the University of Rome with a thesis on relativistic astrophysics. 3 Figure 3: EXPLORER at the SNAM-Progetti in Monterorondo. From left: Pallottino, Modena, Pizzella, Amaldi, Serrani, Carelli, Lucano, Giovanardi and, in the lowest line, a technician and Foco. . start this new activity in the LNF. The next day I went to Frascati to discuss it, but it was clear that the interest had been expressed only in words, as there were already more research to be pursued. However we continued to develop the project, also arousing a lot of interest in theoretical physicists, as Bruno Bertotti, Nicola Cabibbo and Bruno Touschek [2]. Since the beginning we had the important collaboration of Ivo Modena and Giovanni Vittorio Pallottino2 , old fellow adventurers. The experimental activity started at the laboratories of the Snam-Progetti ENI in Monterotondo, by Giorgio Careri who had been the director, for the installation and commissioning of the great detector. SNAM had set up the premises and purchased a liquefier for liquid helium. In the spring of 1974 we moved to Monterotondo where all the pieces began to arrive of the cryostat for the large antenna. I well remember that during this period we had the visit at Monterotondo of Bruno Touschek, with whom we discussed the pilot project ending finally with a toast. In the following years the experiment went on with changing fortunes and, 2GianVittorio Pallottino had been an important coworker for my space experiment on the solar wind. 4 after leaving the SNAM-Projects and after a further attempt to go to Frascati, then unavailable for political reason, we landed in 1980 at CERN, very well received, where finally we realized the cryogenic antenna EXPLORER cooled to 2 K. This antenna has worked continuously until 2010, when the collaboration with CERN was terminated. As for funding, which until 1980 had been secured by the CNR, they were provided by the INFN

Measurement of the thermal expansion coefficient of an Al-Mg alloy at ultra-low temperatures

We describe a result coming from an experiment based on an Al-Mg alloy (~ 5% Mg) suspended bar hit by an electron beam and operated above and below the termperature of transition from superconducting to normal state of the material. The amplitude of the bar first longitudinal mode of oscillation, excited by the beam interacting with the bulk, and the energy deposited by the beam in the bar are the quantities measured by the experiment. These quantities, inserted in the equations describing the mechanism of the mode excitation and complemented by an independent measurement of the specific heat, allow us to determine the linear expansion coefficient of the material.Comment: 13 pages, 4 figure

Bispectral pairwise interacting source analysis for identifying systems of cross-frequency interacting brain sources from electroencephalographic or magnetoencephalographic signals

Brain cognitive functions arise through the coordinated activity of several brain regions, which actually form complex dynamical systems operating at multiple frequencies. These systems often consist of interacting subsystems, whose characterization is of importance for a complete understanding of the brain interaction processes. To address this issue, we present a technique, namely the bispectral pairwise interacting source analysis (biPISA), for analyzing systems of cross-frequency interacting brain sources when multichannel electroencephalographic (EEG) or magnetoencephalographic (MEG) data are available. Specifically, the biPISA makes it possible to identify one or many subsystems of cross-frequency interacting sources by decomposing the antisymmetric components of the cross-bispectra between EEG or MEG signals, based on the assumption that interactions are pairwise. Thanks to the properties of the antisymmetric components of the cross-bispectra, biPISA is also robust to spurious interactions arising from mixing artifacts, i.e., volume conduction or field spread, which always affect EEG or MEG functional connectivity estimates. This method is an extension of the pairwise interacting source analysis (PISA), which was originally introduced for investigating interactions at the same frequency, to the study of cross-frequency interactions. The effectiveness of this approach is demonstrated in simulations for up to three interacting source pairs and for real MEG recordings of spontaneous brain activity. Simulations show that the performances of biPISA in estimating the phase difference between the interacting sources are affected by the increasing level of noise rather than by the number of the interacting subsystems. The analysis of real MEG data reveals an interaction between two pairs of sources of central mu and beta rhythms, localizing in the proximity of the left and right central sulci