421 research outputs found
Self-consistency of relativistic observables with general relativity in the white dwarf-neutron star binary pulsar PSR J1141-6545
Here we report timing measurements of the relativistic binary pulsar PSR
J1141-6545 that constrain the component masses and demonstrate that the orbital
period derivative \dot Pb = (-4+/-1)x10^-13 is consistent with gravitational
wave emission as described by the general theory of relativity. The mass of the
neutron star and its companion are 1.30+/-0.02 Mo and 0.986+/-0.020 Mo
respectively, suggesting a white dwarf companion, and extending the range of
systems for which general relativity provides a correct description. On
evolutionary grounds, the progenitor mass of PSR J1141-6545 should be near the
minimum for neutron star production. Its mass is two standard deviations below
the mean of the other neutron stars, suggesting a relationship between
progenitor and remnant masses.Comment: 10 pages, 2 figures, revised version to Ap J Letter
High time-resolution observations of the Vela pulsar
We present high time resolution observations of single pulses from the Vela
pulsar (PSR B0833-45) made with a baseband recording system at observing
frequencies of 660 and 1413 MHz. We have discovered two startling features in
the 1413 MHz single pulse data. The first is the presence of giant micro-pulses
which are confined to the leading edge of the pulse profile. One of these
pulses has a peak flux density in excess of 2500 Jy, more than 40 times the
integrated pulse peak. The second new result is the presence of a large
amplitude gaussian component on the trailing edge of the pulse profile. This
component can exceed the main pulse in intensity but is switched on only
relatively rarely. Fluctutation spectra reveal a possible periodicity in this
feature of 140 pulse periods. Unlike the rest of the profile, this component
has low net polarization and emits predominantly in the orthogonal mode. This
feature appears to be unique to the Vela pulsar. We have also detected
microstructure in the Vela pulsar for the first time. These same features are
present in the 660 MHz data. We suggest that the full width of the Vela pulse
profile might be as large as 10 ms but that the conal edges emit only rarely.Comment: 6 pages, 5 figures, In Press with ApJ Letter
PSR J1909-3744, a Binary Millisecond Pulsar with a Very Small Duty Cycle
We report the discovery of PSR J1909-3744, a 2.95 millisecond pulsar in a
nearly circular 1.53 day orbit. Its narrow pulse width of 43 microseconds
allows pulse arrival times to be determined with great accuracy. We have
spectroscopically identified the companion as a moderately hot (T = 8500 K)
white dwarf with strong absorption lines. Radial velocity measurements of the
companion will yield the mass ratio of the system. Our timing data suggest the
presence of Shapiro delay; we expect that further timing observations, combined
with the mass ratio, will allow the first accurate determination of a
millisecond pulsar mass. We have measured the timing parallax and proper motion
for this pulsar which indicate a transverse velocity of 140 (+80/-40) km/s.
This pulsar's stunningly narrow pulse profile makes it an excellent candidate
for precision timing experiments that attempt to detect low frequency
gravitational waves from coalescing supermassive black hole binaries.Comment: 12 pages, 4 figures. Accepted for publication in ApJ
Pulsars in Globular Clusters with the SKA
Globular clusters are highly efficient radio pulsar factories. These pulsars
can be used as precision probes of the clusters' structure, gas content,
magnetic field, and formation history; some of them are also highly interesting
in their own right because they probe exotic stellar evolution scenarios as
well as the physics of dense matter, accretion, and gravity. Deep searches with
SKA1-MID and SKA1-LOW will plausibly double to triple the known population.
Such searches will only require one to a few tied-array beams, and can be done
during early commissioning of the telescope - before an all-sky pulsar survey
using hundreds to thousands of tied-array beams is feasible. With SKA2 it will
be possible to observe most of the active radio pulsars within a large fraction
of the Galactic globular clusters, an estimated population of 600 - 3700
observable pulsars (those beamed towards us). This rivals the total population
of millisecond pulsars that can be found in the Galactic field; fully
characterizing it will provide the best-possible physical laboratories as well
as a rich dynamical history of the Galactic globular cluster system.Comment: 15 pages, 5 figures, to be published in: "Advancing Astrophysics with
the Square Kilometre Array", Proceedings of Science, PoS(AASKA14)04
On the Eccentricities and Merger Rates of Double Neutron Star Binaries and the Creation of "Double Supernovae"
We demonstrate that a natural consequence of an asymmetric kick imparted to
neutron stars at birth is that the majority of double neutron star binaries
should possess highly eccentric orbits. This leads to greatly accelerated
orbital decay, due to the enormous increase in the emission of gravitational
radiation at periastron as originally demonstrated by Peters (1964). A uniform
distribution of kick velocities constrained to the orbital plane would result
in ~24% of surviving binaries coalescing at least 10,000 times faster than an
unperturbed circular system. Even if the planar kick constraint is lifted, ~6%
of bound systems still coalesce this rapidly. In a non-negligible fraction of
cases it may even be possible that the system could coalesce within 10 years of
the final supernova, resulting in what we might term a "double supernova''. For
systems resembling the progenitor of PSR J0737-3039A, this number is as high as
\~9% (in the planar kick model). Whether the kick velocity distribution extends
to the range required to achieve this is still unclear. We do know that the
observed population of binary pulsars has a deficit of highly eccentric systems
at small orbital periods. In contrast, the long-period systems favour large
eccentricities, as expected. We argue that this is because the short-period
highly eccentric systems have already coalesced and are thus selected against
by pulsar surveys. This effect needs to be taken into account when using the
scale-factor method to estimate the coalescence rate of double neutron star
binaries. We therefore assert that the coalesence rate of such binaries is
underestimated by a factor of several.Comment: 7 pages, 6 figures, submitted to Ap
Implications of the PSR 1257+12 Planetary System for Isolated Millisecond Pulsars
The first extrasolar planets were discovered in 1992 around the millisecond
pulsar PSR 1257+12. We show that recent developments in the study of accretion
onto magnetized stars, plus the existence of the innermost, moon-sized planet
in the PSR 1257+12 system, suggest that the pulsar was born with approximately
its current rotation frequency and magnetic moment. If so, this has important
implications for the formation and evolution of neutron star magnetic fields as
well as for the formation of planets around pulsars. In particular, it suggests
that some and perhaps all isolated millisecond pulsars may have been born with
high spin rates and low magnetic fields instead of having been recycled by
accretion.Comment: 17 pages including one figure, uses aaspp4, accepted by Ap
Discovery of Five Recycled Pulsars in a High Galactic Latitude Survey
We present five recycled pulsars discovered during a 21-cm survey of
approximately 4,150 deg^2 between 15 deg and 30 deg from the galactic plane
using the Parkes radio telescope. One new pulsar, PSR J1528-3146, has a 61 ms
spin period and a massive white dwarf companion. Like many recycled pulsars
with heavy companions, the orbital eccentricity is relatively high (~0.0002),
consistent with evolutionary models that predict less time for circularization.
The four remaining pulsars have short spin periods (3 ms < P < 6 ms); three of
these have probable white dwarf binary companions and one (PSR J2010-1323) is
isolated. PSR J1600-3053 is relatively bright for its dispersion measure of
52.3 pc cm^-3 and promises good timing precision thanks to an intrinsically
narrow feature in its pulse profile, resolvable through coherent dedispersion.
In this survey, the recycled pulsar discovery rate was one per four days of
telescope time or one per 600 deg^2 of sky. The variability of these sources
implies that there are more millisecond pulsars that might be found by
repeating this survey.Comment: 15 pages, 3 figures, accepted for publication in Ap
Determination of the geometry of the PSR B1913+16 system by geodetic precession
New observations of the binary pulsar B1913+16 are presented. Since 1978 the
leading component of the pulse profile has weakend dramatically by about 40%.
For the first time, a decrease in component separation is observed, consistent
with expectations of geodetic precession. Assuming the correctness of general
relativity and a circular hollow-cone like beam, a fully consistent model for
the system geometry is developed. The misalignment angle between pulsar spin
and orbital momentum is determined giving direct evidence for an asymmetric
kick during the second supernova explosion. It is argued that the orbital
inclination angle is 132\fdg8 (rather than 47\fdg2). A prediction of this
model is that PSR B1913+16 will not be observable anymore after the year 2025.Comment: 16 pages, incl. 5 figures, accepted for publication in Ap
Simian immunodeficiency virus infection in wild-caught chimpanzees from Cameroon
Simian immunodeficiency viruses (SIVcpz) infecting chimpanzees (Pan troglodytes) in west central Africa are the closest relatives to all major variants of human immunodeficiency virus type 1 ([HIV-1]; groups M, N and O), and have thus been implicated as the source of the human infections; however, information concerning the prevalence, geographic distribution, and subspecies association of SIVcpz still remains limited. In this study, we tested 71 wild-caught chimpanzees from Cameroon for evidence of SIVcpz infection. Thirty-nine of these were of the central subspecies (Pan troglodytes troglodytes), and 32 were of the Nigerian subspecies (Pan troglodytes vellerosus), as determined by mitochondrial DNA analysis. Serological analysis determined that one P. t. troglodytes ape (CAM13) harbored serum antibodies that cross-reacted strongly with HIV-1 antigens; all other apes were seronegative. To characterize the newly identified virus, 14 partially overlapping viral fragments were amplified from fecal virion RNA and concatenated to yield a complete SIVcpz genome (9,284 bp). Phylogenetic analyses revealed that SIVcpzCAM13 fell well within the radiation of the SIVcpzPtt group of viruses, as part of a clade including all other SIVcpzPtt strains as well as HIV-1 groups M and N. However, SIVcpzCAM13 clustered most closely with SIVcpzGAB1 from Gabon rather than with SIVcpzCAM3 and SIVcpzCAM5 from Cameroon, indicating the existence of divergent SIVcpzPtt lineages within the same geographic region. These data, together with evidence of recombination among ancestral SIVcpzPtt lineages, indicate long-standing endemic infection of central chimpanzees and reaffirm a west central African origin of HIV-1. Whether P. t. vellerosus apes are naturally infected with SIVcpz requires further study
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