13 research outputs found
On the possible sources of gravitational wave bursts detectable today
We discuss the possibility that galactic gravitational wave sources might
give burst signals at a rate of several events per year, detectable by
state-of-the-art detectors. We are stimulated by the results of the data
collected by the EXPLORER and NAUTILUS bar detectors in the 2001 run, which
suggest an excess of coincidences between the two detectors, when the resonant
bars are orthogonal to the galactic plane. Signals due to the coalescence of
galactic compact binaries fulfill the energy requirements but are problematic
for lack of known candidates with the necessary merging rate. We examine the
limits imposed by galactic dynamics on the mass loss of the Galaxy due to GW
emission, and we use them to put constraints also on the GW radiation from
exotic objects, like binaries made of primordial black holes. We discuss the
possibility that the events are due to GW bursts coming repeatedly from a
single or a few compact sources. We examine different possible realizations of
this idea, such as accreting neutron stars, strange quark stars, and the highly
magnetized neutron stars (``magnetars'') introduced to explain Soft Gamma
Repeaters. Various possibilities are excluded or appear very unlikely, while
others at present cannot be excluded.Comment: 24 pages, 20 figure
On the complementarity of pulsar timing and space laser interferometry for the individual detection of supermassive black hole binaries
Gravitational waves coming from Super Massive Black Hole Binaries (SMBHBs)
are targeted by both Pulsar Timing Array (PTA) and Space Laser Interferometry
(SLI). The possibility of a single SMBHB being tracked first by PTA, through
inspiral, and later by SLI, up to merger and ring down, has been previously
suggested. Although the bounding parameters are drawn by the current PTA or the
upcoming Square Kilometer Array (SKA), and by the New Gravitational Observatory
(NGO), derived from the Laser Interferometer Space Antenna (LISA), this paper
also addresses sequential detection beyond specific project constraints. We
consider PTA-SKA, which is sensitive from 10^(-9) to p x 10^(-7) Hz (p=4, 8),
and SLI, which operates from s x 10^(-5) up to 1 Hz (s = 1, 3). A SMBHB in the
range 2x 10^(8) - 2 x 10^(9) solar masses (the masses are normalised to a (1+z)
factor, the red shift lying between z = 0.2 and z=1.5) moves from the PTA-SKA
to the SLI band over a period ranging from two months to fifty years. By
combining three Super Massive Black Hole (SMBH)-host relations with three
accretion prescriptions, nine astrophysical scenarios are formed. They are then
related to three levels of pulsar timing residuals (50, 5, 1 ns), generating
twenty-seven cases. For residuals of 1 ns, sequential detection probability
will never be better than 4.7 x 10^(-4) y^(-2) or 3.3 x 10^(-6) y^(-2) (per
year to merger and per year of survey), according to the best and worst
astrophysical scenarios, respectively; put differently this means one
sequential detection every 46 or 550 years for an equivalent maximum time to
merger and duration of the survey. The chances of sequential detection are
further reduced by increasing values of the s parameter (they vanish for s =
10) and of the SLI noise, and by decreasing values of the remnant spin. REST OF
THE ABSTRACT IN THE PDF FILE.Comment: To appear in the Astrophysical Journa
Measurement of mechanical vibrations excited in aluminium resonators by 0.6 GeV electrons
We present measurements of mechanical vibrations induced by 0.6 GeV electrons
impinging on cylindrical and spherical aluminium resonators. To monitor the
amplitude of the resonator's vibrational modes we used piezoelectric ceramic
sensors, calibrated by standard accelerometers. Calculations using the
thermo-acoustic conversion model, agree well with the experimental data, as
demonstrated by the specific variation of the excitation strengths with the
absorbed energy, and with the traversing particles' track positions. For the
first longitudinal mode of the cylindrical resonator we measured a conversion
factor of 7.4 +- 1.4 nm/J, confirming the model value of 10 nm/J. Also, for the
spherical resonator, we found the model values for the L=2 and L=1 mode
amplitudes to be consistent with our measurement. We thus have confirmed the
applicability of the model, and we note that calculations based on the model
have shown that next generation resonant mass gravitational wave detectors can
only be expected to reach their intended ultra high sensitivity if they will be
shielded by an appreciable amount of rock, where a veto detector can reduce the
background of remaining impinging cosmic rays effectively.Comment: Tex-Article with epsfile, 34 pages including 13 figures and 5 tables.
To be published in Rev. Scient. Instr., May 200
Experimental study of high energy electron interactions in a superconducting aluminum alloy resonant bar
Peak amplitude measurements of the fundamental mode of oscillation of a
suspended aluminum alloy bar hit by an electron beam show that the amplitude is
enhanced by a factor ~3.5 when the material is in the superconducting state.
This result is consistent with the cosmic ray observations made by the resonant
gravitational wave detector NAUTILUS, made of the same alloy, when operated in
the superconducting state. A comparison of the experimental data with the
predictions of the model describing the underlying physical process is also
presented
Vibrational excitation induced by electron beam and cosmic rays in normal and superconductive aluminum bars
We report new measurements of the acoustic excitation of an Al5056
superconductive bar when hit by an electron beam, in a previously unexplored
temperature range, down to 0.35 K. These data, analyzed together with previous
results of the RAP experiment obtained for T > 0.54 K, show a vibrational
response enhanced by a factor 4.9 with respect to that measured in the normal
state. This enhancement explains the anomalous large signals due to cosmic rays
previously detected in the NAUTILUS gravitational wave detector.Comment: 28 pages, 13 figure