arXiv subjects

A. Ortolan

Publications and source records attributed to A. Ortolan.

45 records · Page 3Linked to original sources

arXiv2005

Upper limits on gravitational waves emission in association with the Dec 27 2004 giant flare of SGR1806-20

At the time when the giant flare of SGR1806-20 occurred, the AURIGA "bar" gw detector was on the air with a noise performance close to stationary gaussian. This allows to set relevant upper limits, at a number of frequencies in the vicinities of 900 Hz, on the amplitude of the damped gw wave trains, which, according to current models, could have been emitted, due to the excitation of normal modes of the star associated with the peak in X-rays luminosity.

astro-ph↗

arXiv2005

3-mode detection for widening the bandwidth of resonant gravitational wave detectors

We have implemented a novel scheme of signal readout for resonant gravitational wave detectors. For the first time, a capacitive resonant transducer has been matched to the signal amplifier by means of a tuned high Q electrical resonator. The resulting 3-mode detection scheme widens significantly the bandwidth of the detector. We present here the results achieved by this signal readout equipped with a two-stage SQUID amplifier. Once installed on the AURIGA detector, the one-sided spectral sensitivity obtained with the detector operated at 4.5 K is better than 10^-20 Hz^-1/2 over 110 Hz and in good agreement with the expectations.

gr-qc↗

arXiv2004

Gravitational Waves and GRBs from Tidal Disruption of Stars in the Center of Galaxies

Recent measurements of the Chandra satellite have shown that a supermassive black hole of $M = 2.6 \times 10^{6} M_{\odot}$ is located in the Galactic Center; it seems probable that, from other observations, this fact is common in the majority of galaxies. On the other hand, GRB explosions are typical phenomenon linked to the galactic dynamics. In the present paper we discuss the possibility that GRBs are tidal disruption of stars by supermassive black holes located in the center of galaxies. This conjecture can be tested by a gravitational wave detector of the class of AURIGA.

gr-qc↗

arXiv2003

A Modular Object Oriented Data Acquisition System for the Gravitational Wave AURIGA Experiment

The new Data Acquisition system for the gravitational wave detector AURIGA has been designed from the ground up in order to take advantage of hardware and software platforms that became available in recent years; namely, i386 computers running Linux-based free software. This paper describes how advanced software development technologies, such as Object Oriented design and programming and CORBA infrastructure, were exploited to realize a robust, distributed, flexible, and extensible system. Every agent of the Data Acquisition System runs inside an heavyweight framework, conceived to transparently take care of all the agents intercommunication, synchronization, dataflow. It also presents an unified interface to the command and monitoring tools. The DAQ logic is entirely contained in each agent's specialized code. In the case of AURIGA the dataflow is designed as a three tier: frontend, builder, consumer. Each tier is represented by a set of agents possibly running on different hosts. This system is well fit for projects on scales comparable to the AURIGA experiment: permanent and temporary data storage is based on the Frame format adopted by the gravitational wave community, and the design is reliable and fault-tolerant for low rate systems.

physics.ins-det↗

arXiv2001

Wideband dual sphere detector of gravitational waves

We present the concept of a sensitive AND broadband resonant mass gravitational wave detector. A massive sphere is suspended inside a second hollow one. Short, high-finesse Fabry-Perot optical cavities read out the differential displacements of the two spheres as their quadrupole modes are excited. At cryogenic temperatures one approaches the Standard Quantum Limit for broadband operation with reasonable choices for the cavity finesses and the intracavity light power. A molybdenum detector of overall size of 2 m, would reach spectral strain sensitivities of 2x10^-23/Sqrt{Hz} between 1000 Hz and 3000 Hz.

gr-qc↗

arXiv2001

Correlation between Gamma-Ray bursts and Gravitational Waves

The cosmological origin of $γ$-ray bursts (GRBs) is now commonly accepted and, according to several models for the central engine, GRB sources should also emit at the same time gravitational waves bursts (GWBs). We have performed two correlation searches between the data of the resonant gravitational wave detector AURIGA and GRB arrival times collected in the BATSE 4B catalog. No correlation was found and an upper limit \bbox{$h_{\text{RMS}} \leq 1.5 \times 10^{-18}$} on the averaged amplitude of gravitational waves associated with $γ$-ray bursts has been set for the first time.

gr-qc↗

arXiv2000

Initial operation of the International Gravitational Event Collaboration

The International Gravitational Event Collaboration, IGEC, is a coordinated effort by research groups operating gravitational wave detectors working towards the detection of millisecond bursts of gravitational waves. Here we report on the current IGEC resonant bar observatory, its data analysis procedures, the main properties of the first exchanged data set. Even though the available data set is not complete, in the years 1997 and 1998 up to four detectors were operating simultaneously. Preliminary results are mentioned.

astro-ph↗

arXiv2000

chi sup 2_ testing of optimal filters for gravitational wave signals: An experimental implementation

We have implemented likelihood testing of the performance of an optimal filter within the online analysis of AURIGA, a sub-Kelvin resonant-bar gravitational wave detector. We demonstrate the effectiveness of this technique in discriminating between impulsive mechanical excitations of the resonant-bar and other spurious excitations. This technique also ensures the accuracy of the estimated parameters such as the signal-to-noise ratio. The efficiency of the technique to deal with non-stationary noise and its application to data from a network of detectors are also discussed.

astro-ph↗

arXiv1996

Gravitational-Wave Stochastic Background Detection with Resonant-Mass Detectors

In this paper we discuss how the standard optimal Wiener filter theory can be applied, within a linear approximation, to the detection of an isotropic stochastic gravitational-wave background with two or more detectors. We apply then the method to the AURIGA-NAUTILUS pair of ultra low temperature bar detectors, near to operate in coincidence in Italy, obtaining an estimate for the sensitivity to the background spectral density of $\simeq 10^{-49}\ Hz^{-1}$, that converts to an energy density per unit logarithmic frequency of $\simeq 8\times10^{-5}\timesρ_c$ with $ρ_c\simeq1.9 \times 10^{-26}\ kg/m^3$ the closure density of the Universe. We also show that by adding the VIRGO interferometric detector under construction in Italy to the array, and by properly re- orienting the detectors, one can reach a sensitivity of $\simeq 6 \times10^{-5}\timesρ_c$. We then calculate that the pair formed by VIRGO and one large mass spherical detector properly located in one of the nearby available sites in Italy can reah a sensitivity of $\simeq 2\times10^{-5}\times ρ_c$ while a pair of such spherical detectors at the same sites of AURIGA and NAUTILUS can achieve sensitivities of $\simeq 2 \times10^{-6}ρ_c$.

astro-ph↗