353 research outputs found
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
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
Constraints on cosmic string tension imposed by the limit on the stochastic gravitational wave background from the European Pulsar Timing Array
We investigate the constraints that can be placed on the cosmic string
tension by using the current Pulsar Timing Array limits on the stochastic
gravitational wave background (SGWB). We have developed a code to compute the
spectrum of gravitational waves (GWs) based on the widely accepted one-scale
model. In its simplest form the one-scale model allows one to vary: (i) the
string tension, G\mu/c^2; (ii) the size of cosmic string loops relative to the
horizon at birth, \alpha; (iii) the spectral index of the emission spectrum, q;
(iv) the cut-off in the emission spectrum, n_*; and (v) the intercommutation
probability, p. The amplitude and slope of the spectrum in the nHz frequency
range is very sensitive to these unknown parameters. We have also investigated
the impact of more complicated scenarios with multiple initial loop sizes, in
particular the 2-\alpha models proposed in the literature and a log-normal
distribution for \alpha. We have computed the constraint on G\mu/c^2 due to the
limit on a SGWB imposed by data from the European Pulsar Timing Array. Taking
into account all the possible uncertainties in the parameters we find a
conservative upper limit of G\mu/c^2<5.3x 10^{-7} which typically occurs when
the loop production scale is close to the gravitational backreaction scale,
\alpha\approx\Gamma G\mu/c^2. Stronger limits are possible for specific values
of the parameters which typically correspond to the extremal cases \alpha\ll
\Gamma G\mu/c^2 and \alpha\gg \Gamma G\mu/c^2. This limit is less stringent
than the previously published limits which are based on cusp emission, an
approach which does not necessarily model all the possible uncertainties. We
discuss the prospects for lowering this limit by two orders of magnitude, or
even a detection of the SGWB, in the very near future in the context of the
Large European Array for Pulsars and the Square Kilometre Array.Comment: 24 pages, 14 figures, accepted for publication in Physical Review D.
Minor corrections and additional comments - updated to match the published
versio
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
Low-frequency gravitational radiation from coalescing massive black hole binaries in hierarchical cosmologies
We compute the expected gravitational wave signal from coalescing massive
black hole (MBH) binaries at the center of galaxies in a hierarchical structure
formation scenario in which seed holes of intermediate mass form far up in the
dark halo merger tree. The merger history of DM halos and MBHs is followed from
z=20 to the present in a LCDM cosmology. MBHs get incorporated through halo
mergers into larger and larger structures, sink to the center owing to
dynamical friction against the DM background, accrete cold material in the
merger remnant, and form MBH binary systems. Stellar dynamical interactions
cause the hardening of the binary at large separations, while gravitational
wave emission takes over at small radii and leads to the final coalescence of
the pair. The integrated emission from inspiraling MBH binaries results in a
gravitational wave background (GWB). The characteristic strain spectrum has the
standard h_c(f)\propto f^{-2/3} behavior only in the range 1E-9<f<1E-6 Hz. At
lower frequencies the orbital decay of MBH binaries is driven by the ejection
of background stars, and h_c(f) \propto f. At higher frequencies, f>1E-6 Hz,
the strain amplitude is shaped by the convolution of last stable circular orbit
emission. We discuss the observability of inspiraling MBH binaries by the
planned LISA. Over a 3-year observing period LISA should resolve this GWB into
discrete sources, detecting ~60 (~250) individual events above a S/N=5 (S/N=1)
confidence level. (Abridged)Comment: 11 pages, 8 figues. Revised version accepted to be published in ApJ
Discussion on number counts corrected and expande
Pulsar timing and the detection of black hole binary systems in globular clusters
The possible existence of intermediate mass binary black holes (IMBBHs) in
globular clusters (GCs) offers a unique geometry in which to detect space-time
oscillations. For certain pulsar-IMBBH configurations possible within a GC, the
usual far-field plane wave approximation for the IMBBH metric perturbation
severely underestimates the magnitude of the induced pulsar pulse
time-of-arrival (TOA) fluctuations. In this letter, the expected TOA
fluctuations induced by an IMBBH lying close to the line-of-sight between a
pulsar and the Earth are calculated for the first time. For an IMBBH consisting
of 10 Msolar and 10^3 Msolar components, a 10 year orbital period, and located
0.1 lyr from the Earth-Pulsar line of sight, the induced pulsar timing residual
amplitude will be of order 5 to 500 ns.Comment: Accepted into ApJ Letters. This is a slightly augmented version
containing one extra figur
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