174 research outputs found
Twenty-One Millisecond Pulsars in Terzan 5 Using the Green Bank Telescope
We have discovered 21 millisecond pulsars (MSPs) in the globular cluster
Terzan 5 using the Green Bank Telescope, bringing the total of known MSPs in
Terzan 5 to 24. These discoveries confirm fundamental predictions of globular
cluster and binary system evolution. Thirteen of the new MSPs are in binaries,
of which two show eclipses and two have highly eccentric orbits. The
relativistic periastron advance for the two eccentric systems indicates that at
least one of these pulsars has a mass >1.68 Msun at 95% confidence. Such large
neutron star masses constrain the equation of state of matter at or beyond the
nuclear equilibrium density.Comment: 12 pages, 2 figures. Accepted by Science. Published electronically
via Science Express 13 Jan 200
The Millisecond Pulsars in NGC 6760
We present the results of recent Arecibo and Green Bank observations of the
globular cluster NGC 6760. Using Arecibo, a phase-coherent timing solution has
been obtained for the previously known binary pulsar in this cluster, PSR
J1911+0102A. We have also discovered a new millisecond pulsar in NGC 6760, PSR
J1911+0101B, an isolated object with a rotational period of 5.38 ms and a
dispersion measure DM = 196.7 cm-3 pc. Both pulsars are located within 1.3 core
radii of the cluster center and have negative period derivatives. The resulting
lower limits for the accelerations of the pulsars are within the range expected
given a simple model of the cluster. A search for eclipses in the PSR
J1911+0102A binary system using both telescopes yielded negative results. The
corresponding limits on the extra gas column density at superior conjunction
are consistent with the hypothesis that the observational properties of
ultra-low-mass binary pulsars like PSR J1911+0102A are strongly affected by the
inclination of the orbital plane of the system. Among globular cluster pulsar
populations, that of NGC 6760 exhibits one of the largest known spreads in DM.
This quantity seems to be roughly proportional to a cluster's central DM; this
suggests that the observed spread is caused by a turbulent interstellar medium
at spatial scales of 1 pc.Comment: 10 pages in referee format, 4 figures, one table, re-submitted to the
Astrophysical Journa
Spectroscopy of the inner companion of the pulsar PSR J0337+1715
The hierarchical triple system PSR J0337+1715 offers an unprecedented
laboratory to study secular evolution of interacting systems and to explore the
complicated mass-transfer history that forms millisecond pulsars and
helium-core white dwarfs. The latter in particular, however, requires knowledge
of the properties of the individual components of the system. Here we present
precise optical spectroscopy of the inner companion in the PSR J0337+1715
system. We confirm it as a hot, low-gravity DA white dwarf with
Teff=15,800+/-100 K and log(g)=5.82+/-0.05. We also measure an inner mass ratio
of 0.1364+/-0.0015, entirely consistent with that inferred from pulsar timing,
and a systemic radial velocity of 29.7+/-0.3 km/s. Combined with the mass
(0.19751 Msun) determined from pulsar timing, our measurement of the surface
gravity implies a radius of 0.091+/-0.005 Rsun; combined further with the
effective temperature and extinction, the photometry implies a distance of
1300+/-80 pc. The high temperature of the companion is somewhat puzzling: with
current models, it likely requires a recent period of unstable hydrogen
burning, and suggests a surprisingly short lifetime for objects at this phase
in their evolution. We discuss the implications of these measurements in the
context of understanding the PSR J0337+1715 system, as well as of low-mass
white dwarfs in general.Comment: ApJ Letters, in press. 6 pages, two figures. v2 fixes typ
A Radio Pulsar/X-ray Binary Link
Radio pulsars with millisecond spin periods are thought to have been spun up
by transfer of matter and angular momentum from a low-mass companion star
during an X-ray-emitting phase. The spin periods of the neutron stars in
several such low-mass X-ray binary (LMXB) systems have been shown to be in the
millisecond regime, but no radio pulsations have been detected. Here we report
on detection and follow-up observations of a nearby radio millisecond pulsar
(MSP) in a circular binary orbit with an optically identified companion star.
Optical observations indicate that an accretion disk was present in this system
within the last decade. Our optical data show no evidence that one exists
today, suggesting that the radio MSP has turned on after a recent LMXB phase.Comment: published in Scienc
Irinotecan or FOLFIRI for 2nd line colorectal
Background Second-line treatment with irinotecan for advanced or metastatic colorectal cancer prolongs survival. It is uncertain whether irinotecan is better administered with 5- fluorouracil or alone in patients previously treated with a fluoropyrimidine. We compared toxicity (particularly diarrhoea), quality of life, and efficacy of combination chemotherapy and irinotecan in these patients. Methods In DaVINCI, a randomised phase II trial, patients with advanced colorectal cancer were randomly allocated to: combination therapy (FOLFIRI), irinotecan (180 mg/m2 IV over 90 min, day 1), 5-fluorouracil (400 mg/m2 IV bolus and 2400 mg/m2 by 46-hour infusion from day 1) and folinic acid (20 mg/m2 IV bolus, day 1), 2-weekly; or single-agent, irinotecan (350 mg/m2 IV over 90 min), 3-weekly. Toxicity was evaluated every treatment cycle; QOL and response 6 weekly. Analysis was by intention to treat. Results were also combined with those of other trials. Findings We randomised 44 patients to combination and 45 to single-agent. The most common toxicity was complete alopecia (single-agent 37%, combination 14%, P<0.02). Eight patients in the irinotecan arm and 4 in the combination arm had grade 3–4 diarrhoea (P=0.24). The treatment groups did not differ significantly in overall QOL changes, response rate, or progression free or overall survival. In a systematic review of 29 trials of second-line irinotecan-based treatment, single-agent irinotecan was associated with more diarrhoea and alopecia than the combination, but efficacy was similar. Interpretation Combination treatment compared with single-agent irinotecan appears to reduce the rateof complete alopecia and diarrhoea without compromising efficacy on clinical outcomes.Australasian Gastro-Intestinal Trials Grou
Multi-Messenger Gravitational Wave Searches with Pulsar Timing Arrays: Application to 3C66B Using the NANOGrav 11-year Data Set
When galaxies merge, the supermassive black holes in their centers may form
binaries and, during the process of merger, emit low-frequency gravitational
radiation in the process. In this paper we consider the galaxy 3C66B, which was
used as the target of the first multi-messenger search for gravitational waves.
Due to the observed periodicities present in the photometric and astrometric
data of the source of the source, it has been theorized to contain a
supermassive black hole binary. Its apparent 1.05-year orbital period would
place the gravitational wave emission directly in the pulsar timing band. Since
the first pulsar timing array study of 3C66B, revised models of the source have
been published, and timing array sensitivities and techniques have improved
dramatically. With these advances, we further constrain the chirp mass of the
potential supermassive black hole binary in 3C66B to less than using data from the NANOGrav 11-year data set. This
upper limit provides a factor of 1.6 improvement over previous limits, and a
factor of 4.3 over the first search done. Nevertheless, the most recent orbital
model for the source is still consistent with our limit from pulsar timing
array data. In addition, we are able to quantify the improvement made by the
inclusion of source properties gleaned from electromagnetic data to `blind'
pulsar timing array searches. With these methods, it is apparent that it is not
necessary to obtain exact a priori knowledge of the period of a binary to gain
meaningful astrophysical inferences.Comment: 14 pages, 6 figures. Accepted by Ap
Properties and Evolution of the Redback Millisecond Pulsar Binary PSR J2129-0429
PSR J2129−0429 is a "redback" eclipsing millisecond pulsar binary with an unusually long 15.2 hr orbit. It was discovered by the Green Bank Telescope in a targeted search of unidentified Fermi gamma-ray sources. The pulsar companion is optically bright (mean m_R = 16.6 mag), allowing us to construct the longest baseline photometric data set available for such a system. We present 10 years of archival and new photometry of the companion from the Lincoln Near-Earth Asteroid Research Survey, the Catalina Real-time Transient Survey, the Palomar Transient Factory, the Palomar 60 inch, and the Las Cumbres Observatory Global Telescope. Radial velocity spectroscopy using the Double-Beam Spectrograph on the Palomar 200 inch indicates that the pulsar is massive: 1.74 ± 0.18 M_☉. The G-type pulsar companion has mass 0.44 ± 0.04 M_☉, one of the heaviest known redback companions. It is currently 95 ± 1% Roche-lobe filling and only mildly irradiated by the pulsar. We identify a clear 13.1 mmag yr^(−1) secular decline in the mean magnitude of the companion as well as smaller-scale variations in the optical light curve shape. This behavior may indicate that the companion is cooling. Binary evolution calculations indicate that PSR J2129−0429 has an orbital period almost exactly at the bifurcation period between systems that converge into tighter orbits as black widows and redbacks and those that diverge into wider pulsar–white dwarf binaries. Its eventual fate may depend on whether it undergoes future episodes of mass transfer and increased irradiation
A 1.05 M_☉ Companion to PSR J2222–0137: The Coolest Known White Dwarf?
The recycled pulsar PSR J2222–0137 is one of the closest known neutron stars (NSs) with a parallax distance of 267_(-0.9)^(+1.2) pc and an edge-on orbit. We measure the Shapiro delay in the system through pulsar timing with the Green Bank Telescope, deriving a low pulsar mass (1.20 ± 0.14 M_☉) and a high companion mass (1.05 ± 0.06 M_☉) consistent with either a low-mass NS or a high-mass white dwarf. We can largely reject the NS hypothesis on the basis of the system's extremely low eccentricity (3 × 10^(–4))—too low to have been the product of two supernovae under normal circumstances. However, despite deep optical and near-infrared searches with Southern Astrophysical Research and the Keck telescopes we have not discovered the optical counterpart of the system. This is consistent with the white dwarf hypothesis only if the effective temperature is <3000 K, a limit that is robust to distance, mass, and atmosphere uncertainties. This would make the companion to PSR J2222–0137 one of the coolest white dwarfs ever observed. For the implied age to be consistent with the age of the Milky Way requires the white dwarf to have already crystallized and entered the faster Debye-cooling regime
The NANOGrav 11-Year Data Set: Arecibo Observatory Polarimetry And Pulse Microcomponents
We present the polarization pulse profiles for 28 pulsars observed with the
Arecibo Observatory by the North American Nanohertz Observatory for
Gravitational Waves (NANOGrav) timing project at 2.1 GHz, 1.4 GHz, and 430 MHz.
These profiles represent some of the most sensitive polarimetric millisecond
pulsar profiles to date, revealing the existence of microcomponents (that is,
pulse components with peak intensities much lower than the total pulse peak
intensity). Although microcomponents have been detected in some pulsars
previously, we present microcomponents for PSRs B1937+21, J1713+0747, and
J2234+0944 for the first time. These microcomponents can have an impact on
pulsar timing, geometry, and flux density determination. We present rotation
measures for all 28 pulsars, determined independently at different observation
frequencies and epochs, and find the Galactic magnetic fields derived from
these rotation measures to be consistent with current models. These
polarization profiles were made using measurement equation template matching,
which allows us to generate the polarimetric response of the Arecibo
Observatory on an epoch-by-epoch basis. We use this method to describe its time
variability, and find that the polarimetric responses of the Arecibo
Observatory's 1.4 and 2.1 GHz receivers vary significantly with time.Comment: 41 pages, 20 figure
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