389 research outputs found
Gravitational Waves Probe the Coalescence Rate of Massive Black Hole Binaries
We calculate the expected nHz--Hz gravitational wave (GW) spectrum from
coalescing Massive Black Hole (MBH) binaries resulting from mergers of their
host galaxies. We consider detection of this spectrum by precision pulsar
timing and a future Pulsar Timing Array. The spectrum depends on the merger
rate of massive galaxies, the demographics of MBHs at low and high redshift,
and the dynamics of MBH binaries. We apply recent theoretical and observational
work on all of these fronts. The spectrum has a characteristic strain
, just below the detection limit from
recent analysis of precision pulsar timing measurements. However, the amplitude
of the spectrum is still very uncertain owing to approximations in the
theoretical formulation of the model, to our lack of knowledge of the merger
rate and MBH population at high redshift, and to the dynamical problem of
removing enough angular momentum from the MBH binary to reach a GW-dominated
regime.Comment: 31 Pages, 8 Figures, small changes to match the published versio
Quantum effects in gravitational wave signals from cuspy superstrings
We study the gravitational emission, in Superstring Theory, from fundamental
strings exhibiting cusps. The classical computation of the gravitational
radiation signal from cuspy strings features strong bursts in the special null
directions associated to the cusps. We perform a quantum computation of the
gravitational radiation signal from a cuspy string, as measured in a
gravitational wave detector using matched filtering and located in the special
null direction associated to the cusp. We study the quantum statistics
(expectation value and variance) of the measured filtered signal and find that
it is very sharply peaked around the classical prediction. Ultimately, this
result follows from the fact that the detector is a low-pass filter which is
blind to the violent high-frequency quantum fluctuations of both the string
worldsheet, and the incoming gravitational field.Comment: 16 pages, no figur
Gravitational Wave Hotspots: Ranking Potential Locations of Single-Source Gravitational Wave Emission
New Binary and Millisecond Pulsars from Arecibo Drift-Scan Searches
We discuss four recycled pulsars found in Arecibo drift-scan searches. PSR
J1944+0907 has a spin period of 5.2 ms and is isolated. The 5.8-ms pulsar
J1453+19 may have a low-mass companion. We discuss these pulsars in the context
of isolated millisecond pulsar formation and the minimum spin period of neutron
stars. The isolated 56-ms pulsar J0609+2130 is possibly the remnant of a
disrupted double neutron star binary. The 41-ms pulsar J1829+2456 is in a
relativistic orbit. Its companion is most likely another neutron star, making
this the eighth known double neutron star binary system.Comment: 6 pages, 3 figures, to appear in proceedings of Aspen Center for
Physics Conference on ``Binary Radio Pulsars'' Eds. F. Rasio and I. Stair
Correlation between X-ray Lightcurve Shape and Radio Arrival Time in the Vela Pulsar
We report the results of simultaneous observations of the Vela pulsar in
X-rays and radio from the RXTE satellite and the Mount Pleasant Radio
Observatory in Tasmania. We sought correlations between the Vela's X-ray
emission and radio arrival times on a pulse by pulse basis. At a confidence
level of 99.8% we have found significantly higher flux density in Vela's main
X-ray peak during radio pulses that arrived early. This excess flux shifts to
the 'trough' following the 2nd X-ray peak during radio pulses that arrive
later. Our results suggest that the mechanism producing the radio pulses is
intimately connected to the mechanism producing X-rays. Current models using
resonant absorption of radio emission in the outer magnetosphere as a cause of
the X-ray emission are explored as a possible explanation for the correlation.Comment: 6 pages, 5 figures, accepted by Ap
PSR J0609+2130: A disrupted binary pulsar?
We report the discovery and initial timing observations of a 55.7-ms pulsar,
J0609+2130, found during a 430-MHz drift-scan survey with the Arecibo radio
telescope. With a spin-down rate of s s and an
inferred surface dipole magnetic field of only G,
J0609+2130 has very similar spin parameters to the isolated pulsar J2235+1506
found by Camilo, Nice & Taylor (1993). While the origin of these weakly
magnetized isolated neutron stars is not fully understood, one intriguing
possibility is that they are the remains of high-mass X-ray binary systems
which were disrupted by the supernova explosion of the secondary star.Comment: 5 pages, 2 figures, accepted for publication in MNRAS (letters
Limits on the Stochastic Gravitational Wave Background from the North American Nanohertz Observatory for Gravitational Wave
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