442 research outputs found
Limits on the Stochastic Gravitational Wave Background from the North American Nanohertz Observatory for Gravitational Wave
The Double Pulsar: Evidence For Neutron Star Formation Without An Iron Core-Collapse Supernova
The double pulsar system PSR J0737-3039A/B is a double neutron star binary, with a 2.4 hr orbital period, which has allowed measurement of relativistic orbital perturbations to high precision. The low mass of the second-formed neutron star, as well as the low system eccentricity and proper motion, point to a different evolutionary scenario compared to most other known double neutron star systems. We describe analysis of the pulse profile shape over 6 years of observations and present the resulting constraints on the system geometry. We find the recycled pulsar in this system, PSR J0737-3039A, to be a near-orthogonal rotator with an average separation between its spin and magnetic axes of 90 Degree-Sign {+-} 11 Degree-Sign {+-} 5 Degree-Sign . Furthermore, we find a mean 95% upper limit on the misalignment between its spin and orbital angular momentum axes of 3. Degree-Sign 2, assuming that the observed emission comes from both magnetic poles. This tight constraint lends credence to the idea that the supernova that formed the second pulsar was relatively symmetric, possibly involving electron capture onto an O-Ne-Mg core
CoRoT measures solar-like oscillations and granulation in stars hotter than the Sun
Oscillations of the Sun have been used to understand its interior structure.
The extension of similar studies to more distant stars has raised many
difficulties despite the strong efforts of the international community over the
past decades. The CoRoT (Convection Rotation and Planetary Transits) satellite,
launched in December 2006, has now measured oscillations and the stellar
granulation signature in three main sequence stars that are noticeably hotter
than the sun. The oscillation amplitudes are about 1.5 times as large as those
in the Sun; the stellar granulation is up to three times as high. The stellar
amplitudes are about 25% below the theoretic values, providing a measurement of
the nonadiabaticity of the process ruling the oscillations in the outer layers
of the stars.Comment: 7 pages, 4 figure
The Evolution of PSR J0737-3039B and a Model for Relativistic Spin Precession
We present the evolution of the radio emission from the 2.8-s pulsar of the
double pulsar system PSR J0737-3039A/B. We provide an update on the Burgay et
al. (2005) analysis by describing the changes in the pulse profile and flux
density over five years of observations, culminating in the B pulsar's radio
disappearance in 2008 March. Over this time, the flux density decreases by
0.177 mJy/yr at the brightest orbital phases and the pulse profile evolves from
a single to a double peak, with a separation rate of 2.6 deg/yr. The pulse
profile changes are most likely caused by relativistic spin precession, but can
not be easily explained with a circular hollow-cone beam as in the model of
Clifton & Weisberg (2008). Relativistic spin precession, coupled with an
elliptical beam, can model the pulse profile evolution well. This particular
beam shape predicts geometrical parameters for the two bright orbital phases
which are consistent and similar to those derived by Breton et al. (2008).
However, the observed decrease in flux over time and B's eventual disappearance
cannot be easily explained by the model and may be due to the changing
influence of A on B.Comment: 20 pages, 18 figures, Accepted by ApJ on 2 August 201
Spin Tilts in the Double Pulsar Reveal Supernova Spin Angular-Momentum Production
The system PSR J0737-3039 is the only binary pulsar known to consist of two
radio pulsars (PSR J0737-3039 A and PSR J0737-3039 B). This unique
configuration allows measurements of spin orientation for both pulsars: pulsar
A's spin is tilted from the orbital angular momentum by no more than 14 degrees
at 95% confidence; pulsar B's by 130 +/- 1 degrees at 99.7% confidence. This
spin-spin misalignment requires that the origin of most of B's present-day spin
is connected to the supernova that formed pulsar B. Under the simplified
assumption of a single, instantaneous kick during the supernova, the spin could
be thought of as originating from the off-center nature of the kick, causing
pulsar B to tumble to its misaligned state. With this assumption, and using
current constraints on the kick magnitude, we find that pulsar B's
instantaneous kick must have been displaced from the center of mass of the
exploding star by at least 1 km and probably 5--10 km. Regardless of the
details of the kick mechanism and the process that produced pulsar B's current
spin, the measured spin-spin misalignment in the double pulsar system provides
an empirical, direct constraint on the angular momentum production in this
supernova. This constraint can be used to guide core-collapse simulations and
the quest for understanding the spins and kicks of compact objects.Comment: 12 pages, 3 figures, as accepted by Ap
The Double Pulsar Eclipses I: Phenomenology and Multi-frequency Analysis
The double pulsar PSR J0737-3039A/B displays short, 30 s eclipses that arise
around conjunction when the radio waves emitted by pulsar A are absorbed as
they propagate through the magnetosphere of its companion pulsar B. These
eclipses offer a unique opportunity to probe directly the magnetospheric
structure and the plasma properties of pulsar B. We have performed a
comprehensive analysis of the eclipse phenomenology using multi-frequency radio
observations obtained with the Green Bank Telescope. We have characterized the
periodic flux modulations previously discovered at 820 MHz by McLaughlin et
al., and investigated the radio frequency dependence of the duration and depth
of the eclipses. Based on their weak radio frequency evolution, we conclude
that the plasma in pulsar B's magnetosphere requires a large multiplicity
factor (~ 10^5). We also found that, as expected, flux modulations are present
at all radio frequencies in which eclipses can be detected. Their complex
behavior is consistent with the confinement of the absorbing plasma in the
dipolar magnetic field of pulsar B as suggested by Lyutikov & Thompson and such
a geometric connection explains that the observed periodicity is harmonically
related to pulsar B's spin frequency. We observe that the eclipses require a
sharp transition region beyond which the plasma density drops off abruptly.
Such a region defines a plasmasphere which would be well inside the
magnetospheric boundary of an undisturbed pulsar. It is also two times smaller
than the expected standoff radius calculated using the balance of the wind
pressure from pulsar A and the nominally estimated magnetic pressure of pulsar
B.Comment: 9 pages, 7 figures, 3 tables, ApJ in pres
Limits on the Stochastic Gravitational Wave Background from the North American Nanohertz Observatory for Gravitational Waves
We present an analysis of high-precision pulsar timing data taken as part of
the North American Nanohertz Observatory for Gravitational waves (NANOGrav)
project. We have observed 17 pulsars for a span of roughly five years using the
Green Bank and Arecibo radio telescopes. We analyze these data using standard
pulsar timing models, with the addition of time-variable dispersion measure and
frequency-variable pulse shape terms. Sub-microsecond timing residuals are
obtained in nearly all cases, and the best root-mean-square timing residuals in
this set are ~30-50 ns. We present methods for analyzing post-fit timing
residuals for the presence of a gravitational wave signal with a specified
spectral shape. These optimally take into account the timing fluctuation power
removed by the model fit, and can be applied to either data from a single
pulsar, or to a set of pulsars to detect a correlated signal. We apply these
methods to our dataset to set an upper limit on the strength of the
nHz-frequency stochastic supermassive black hole gravitational wave background
of h_c (1 yr^-1) < 7x10^-15 (95%). This result is dominated by the timing of
the two best pulsars in the set, PSRs J1713+0747 and J1909-3744.Comment: To be submitted to Ap
A precise mass measurement of the intermediate-mass binary pulsar PSR J1802-2124
PSR J1802-2124 is a 12.6-ms pulsar in a 16.8-hour binary orbit with a
relatively massive white dwarf (WD) companion. These properties make it a
member of the intermediate-mass class of binary pulsar (IMBP) systems. We have
been timing this pulsar since its discovery in 2002. Concentrated observations
at the Green Bank Telescope, augmented with data from the Parkes and Nancay
observatories, have allowed us to determine the general relativistic Shapiro
delay. This has yielded pulsar and white dwarf mass measurements of 1.24(11)
and 0.78(4) solar masses (68% confidence), respectively. The low mass of the
pulsar, the high mass of the WD companion, the short orbital period, and the
pulsar spin period may be explained by the system having gone through a
common-envelope phase in its evolution. We argue that selection effects may
contribute to the relatively small number of known IMBPs.Comment: 9 pages, 4 figures, 3 tables, accepted for publication in the
Astrophysical Journa
SimFlex: Statistical Sampling of Computer System Simulation
Timing-accurate full-system multiprocessor simulations can take years because of architecture and application complexity. Statistical sampling makes simulation-based studies feasible by providing ten-thousand-fold reductions in simulation runtime and enabling thousand-way simulation parallelis
A High Braking Index for a Pulsar
We present a phase-coherent timing solution for PSR J1640â4631, a young 206 ms pulsar using X-ray timing observations taken with NuSTAR. Over this timing campaign, we have measured the braking index of PSR J1640â4631 to be n = 3.15 ± 0.03. Using a series of simulations, we argue that this unusually high braking index is not due to timing noise, but is intrinsic to the pulsar's spin-down. We cannot, however, rule out contamination due to an unseen glitch recovery, although the recovery timescale would have to be longer than most yet observed. If this braking index is eventually proven to be stable, it demonstrates that pulsar braking indices greater than three are allowed in nature; hence, other physical mechanisms such as mass or magnetic quadrupoles are important in pulsar spin-down. We also present a 3Ï upper limit on the pulsed flux at 1.4 GHz of 0.018 mJy
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