660 research outputs found
Discovery of an Energetic Pulsar Associated with SNR G76.9+1.0
We report the discovery of PSR J2022+3842, a 24 ms radio and X-ray pulsar in
the supernova remnant G76.9+1.0, in observations with the Chandra X-ray
telescope, the Robert C. Byrd Green Bank Radio Telescope, and the Rossi X-ray
Timing Explorer (RXTE). The pulsar's spin-down rate implies a rotation-powered
luminosity Edot = 1.2 x 10^{38} erg/s, a surface dipole magnetic field strength
B_s = 1.0 x 10^{12} G, and a characteristic age of 8.9 kyr. PSR J2022+3842 is
thus the second-most energetic Galactic pulsar known, after the Crab, as well
as the most rapidly-rotating young, radio-bright pulsar known. The radio
pulsations are highly dispersed and broadened by interstellar scattering, and
we find that a large (delta-f / f ~= 1.9 x 10^{-6}) spin glitch must have
occurred between our discovery and confirmation observations. The X-ray pulses
are narrow (0.06 cycles FWHM) and visible up to 20 keV, consistent with
magnetospheric emission from a rotation-powered pulsar. The Chandra X-ray image
identifies the pulsar with a hard, unresolved source at the midpoint of the
double-lobed radio morphology of SNR G76.9+1.0 and embedded within faint,
compact X-ray nebulosity. The spatial relationship of the X-ray and radio
emissions is remarkably similar to extended structure seen around the Vela
pulsar. The combined Chandra and RXTE pulsar spectrum is well-fitted by an
absorbed power-law model with column density N_H = (1.7\pm0.3) x 10^{22}
cm^{-2} and photon index Gamma = 1.0\pm0.2; it implies that the Chandra
point-source flux is virtually 100% pulsed. For a distance of 10 kpc, the X-ray
luminosity of PSR J2022+3842 is L_X(2-10 keV) = 7.0 x 10^{33} erg s^{-1}.
Despite being extraordinarily energetic, PSR J2022+3842 lacks a bright X-ray
wind nebula and has an unusually low conversion efficiency of spin-down power
to X-ray luminosity, L_X/Edot = 5.9 x 10^{-5}.Comment: 8 pages in emulateapj format. Minor changes (including a shortened
abstract) to reflect the version accepted for publicatio
A simple approach to estimating three-dimensional supercavitating flow fields
A simple method is formulated for predicting three-dimensional supercavitating flow behind cavitators subject to gravitational acceleration and motion of the cavitator. The method applies slenderbody theory in the context of matched asymptotic expansions to pose an inner problem for the cavity evolution downstream from the locus of cavity detachment. This inner problem is solved by means of a coupled set of equations for the Fourier coefficients characterizing the cavity radius and the velocity potential as a function of downstream location and circumferential location, thus resulting in a two-dimensional multipole solution at each station. For the lowestorder term in the Fourier expansion, it is necessary to match the parabolic inner solution to a fully elliptic outer solution. This step allows the application of any one of a number of methods to solve the axisymmetric problem, which serves as the base solution that is perturbed by the three-dimensional effects. The method is an attempt to formalize the Logvinovich principle of independent cavity section evolution. Results flow past a circular disk cavitator are presented for severalvalues of the cavity Froude number.http://deepblue.lib.umich.edu/bitstream/2027.42/84318/1/CAV2009-final145.pd
Measurement of gravitational spin-orbit coupling in a binary pulsar system
In relativistic gravity, a spinning pulsar will precess as it orbits a
compact companion star. We have measured the effect of such precession on the
average shape and polarization of the radiation from PSR B1534+12. We have also
detected, with limited precision, special-relativistic aberration of the
revolving pulsar beam due to orbital motion. Our observations fix the system
geometry, including the misalignment between the spin and orbital angular
momenta, and yield a measurement of the precession timescale consistent with
the predictions of General Relativity.Comment: 4 pages, accepted to PRL. Version with high-resolution figure 2
available at http://www.astro.ubc.ca/people/stairs/papers/sta04b.ps.g
Probing the Masses of the PSR J0621+1002 Binary System Through Relativistic Apsidal Motion
Orbital, spin and astrometric parameters of the millisecond pulsar PSR
J0621+1002 have been determined through six years of timing observations at
three radio telescopes. The chief result is a measurement of the rate of
periastron advance, omega_dot = 0.0116 +/- 0.0008 deg/yr. Interpreted as a
general relativistic effect, this implies the sum of the pulsar mass, m_1, and
the companion mass, m_2, to be M = m_1 + m_2 = 2.81 +/- 0.30 msun. The
Keplerian parameters rule out certain combinations of m_1 and m_2, as does the
non-detection of Shapiro delay in the pulse arrival times. These constraints,
together with the assumption that the companion is a white dwarf, lead to the
68% confidence maximum likelihood values of m_1 = 1.70(+0.32 -0.29) msun and
m_2 =0.97(+0.27 - 0.15) msun and to the 95% confidence maximum likelihood
values of m_1 = 1.70(+0.59 -0.63) msun and m_2 = 0.97(+0.43 -0.24) msun. The
other major finding is that the pulsar experiences dramatic variability in its
dispersion measure (DM), with gradients as steep as 0.013 pc cm^{-3} / yr. A
structure function analysis of the DM variations uncovers spatial fluctuations
in the interstellar electron density that cannot be fit to a single power law,
unlike the Kolmogorov turbulent spectrum that has been seen in the direction of
other pulsars. Other results from the timing analysis include the first
measurements of the pulsar's proper motion, mu = 3.5 +/- 0.3 mas / yr, and of
its spin-down rate, dP/dt = 4.7 x 10^{-20}, which, when corrected for kinematic
biases and combined with the pulse period, P = 28.8 ms, gives a characteristic
age of 1.1 x 10^{10} yr and a surface magnetic field strength of 1.2 x 10^{9}
G.Comment: Accepted by ApJ, 10 pages, 5 figure
The Triple Pulsar System PSR B1620-26 in M4
The millisecond pulsar PSR B1620-26, in the globular cluster M4, has a white
dwarf companion in a half-year orbit. Anomalously large variations in the
pulsar's apparent spin-down rate have suggested the presence of a second
companion in a much wider orbit. Using timing observations made on more than
seven hundred days spanning eleven years, we confirm this anomalous timing
behavior. We explicitly demonstrate, for the first time, that a timing model
consisting of the sum of two non-interacting Keplerian orbits can account for
the observed signal. Both circular and elliptical orbits are allowed, although
highly eccentric orbits require improbable orbital geometries.
The motion of the pulsar in the inner orbit is very nearly a Keplerian
ellipse, but the tidal effects of the outer companion cause variations in the
orbital elements. We have measured the change in the projected semi-major axis
of the orbit, which is dominated by precession-driven changes in the orbital
inclination. This measurement, along with limits on the rate of change of other
orbital elements, can be used to significantly restrict the properties of the
outer orbit. We find that the second companion most likely has a mass m~0.01
Msun --- it is almost certainly below the hydrogen burning limit (m<0.036 Msun,
95% confidence) --- and has a current distance from the binary of ~35 AU and
orbital period of order one hundred years. Circular (and near-circular) orbits
are allowed only if the pulsar magnetic field is ~3x10^9 G, an order of
magnitude higher than a typical millisecond pulsar field strength. In this
case, the companion has mass m~1.2x10^-3 Msun and orbital period ~62 years.Comment: 12 pages, 6 figures, 3 tables. Very minor clarifications and
rewording. Accepted for publication in the Astrophys.
Chandra Confirmation of a Pulsar Wind Nebula in DA 495
As part of a multiwavelength study of the unusual radio supernova remnant DA
495, we present observations made with the Chandra X-ray Observatory. Imaging
and spectroscopic analysis confirms the previously detected X-ray source at the
heart of the annular radio nebula, establishing the radiative properties of two
key emission components: a soft unresolved source with a blackbody temperature
of 1 MK consistent with a neutron star, surrounded by a nonthermal nebula 40''
in diameter exhibiting a power-law spectrum with photon index Gamma =
1.6+/-0.3, typical of a pulsar wind nebula. The implied spin-down luminosity of
the neutron star, assuming a conversion efficiency to nebular flux appropriate
to Vela-like pulsars, is ~10^{35} ergs/s, again typical of objects a few tens
of kyr old. Morphologically, the nebular flux is slightly enhanced along a
direction, in projection on the sky, independently demonstrated to be of
significance in radio polarization observations; we argue that this represents
the orientation of the pulsar spin axis. At smaller scales, a narrow X-ray
feature is seen extending out 5'' from the point source, a distance consistent
with the sizes of resolved wind termination shocks around many Vela-like
pulsars. Finally, we argue based on synchrotron lifetimes in the estimated
nebular magnetic field that DA 495 represents a rare pulsar wind nebula in
which electromagnetic flux makes up a significant part, together with particle
flux, of the neutron star's wind, and that this high magnetization factor may
account for the nebula's low luminosity.Comment: 26 pages, 5 figures, AASTeX preprint style. Accepted for publication
in The Astrophysical Journa
Millisecond Pulsar Ages: Implications of Binary Evolution and a Maximum Spin Limit
In the absence of constraints from the binary companion or supernova remnant,
the standard method for estimating pulsar ages is to infer an age from the rate
of spin-down. While the generic spin-down age may give realistic estimates for
normal pulsars, it can fail for pulsars with very short periods. Details of the
spin-up process during the low mass X-ray binary phase pose additional
constraints on the period (P) and spin-down rates (Pdot) that may consequently
affect the age estimate. Here, we propose a new recipe to estimate millisecond
pulsar (MSP) ages that parametrically incorporates constraints arising from
binary evolution and limiting physics. We show that the standard method can be
improved by this approach to achieve age estimates closer to the true age
whilst the standard spin-down age may over- or under-estimate the age of the
pulsar by more than a factor of ~10 in the millisecond regime. We use this
approach to analyze the population on a broader scale. For instance, in order
to understand the dominant energy loss mechanism after the onset of radio
emission, we test for a range of plausible braking indices. We find that a
braking index of n=3 is consistent with the observed MSP population. We
demonstrate the existence and quantify the potential contributions of two main
sources of age corruption: the previously known "age bias" due to secular
acceleration and "age contamination" driven by sub-Eddington progenitor
accretion rates. We explicitly show that descendants of LMXBs that have
accreted at very low rates will exhibit ages that appear older than the age of
the Galaxy. We further elaborate on this technique, the implications and
potential solutions it offers regarding MSP evolution, the underlying age
distribution and the post-accretion energy loss mechanism.Comment: Replaced with version published by ApJ. Tables reformatted and minor
changes to the text. Full resolution color figures and movies available at
http://www.kiziltan.org/research.html#age
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