VLBI astrometry of PSR J2222-0137: a pulsar distance measured to 0.4% accuracy

The binary pulsar J2222-0137 is an enigmatic system containing a partially recycled millisecond pulsar and a companion of unknown nature. Whilst the low eccentricity of the system favors a white dwarf companion, an unusual double neutron star system is also a possibility, and optical observations will be able to distinguish between these possibilities. In order to allow the absolute luminosity (or upper limit) of the companion object to be properly calibrated, we undertook astrometric observations with the Very Long Baseline Array to constrain the system distance via a measurement of annual geometric parallax. With these observations, we measure the parallax of the J2222-0137 system to be 3.742 +0.013 -0.016 milliarcseconds, yielding a distance of 267.3 +1.2 -0.9 pc, and measure the transverse velocity to be 57.1 +0.3 -0.2 km/s. Fixing these parameters in the pulsar timing model made it possible to obtain a measurement of Shapiro delay and hence the system inclination, which shows that the system is nearly edge-on (sin i = 0.9985 +/- 0.0005). Furthermore, we were able to detect the orbital motion of J2222-0137 in our VLBI observations and measure the longitude of ascending node. The VLBI astrometry yields the most accurate distance obtained for a radio pulsar to date, and is furthermore the most accurate parallax for any radio source obtained at "low" radio frequencies (below ~5 GHz, where the ionosphere dominates the error budget). Using the astrometric results, we show the companion to J2222-0137 will be easily detectable in deep optical observations if it is a white dwarf. Finally, we discuss the implications of this measurement for future ultra-high-precision astrometry, in particular in support of pulsar timing arrays.Comment: 22 pages, 7 figures, accepted for publication in 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

Eight new MSPs in NGC 6440 and NGC 6441

We report the discovery of five new millisecond pulsars in the globular cluster NGC 6440 and three new ones in NGC 6441; each cluster has one previously known pulsar. Four of the new pulsars are found in binary systems. One of the new pulsars, PSR J1748-2021B in NGC 6440, is notable for its eccentric (e = 0.57) and wide (P_b = 20.5 days) orbit. If the rate of advance of periastron is due solely to general relativity, we can estimate of the total mass of this binary system: 2.92 +/- 0.20 solar masses. This would imply an anomalously large mass for this pulsar, which could introduce important constraints in the study of the equation of state for cold neutron matter.Comment: 3 pages, 3 figures. To appear in the proceedings of "40 Years of Pulsars: Millisecond Pulsars, Magnetars, and More", August 12-17, 2007, McGill University, Montreal, Canad

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

LOFAR discovery of the fastest-spinning millisecond pulsar in the Galactic field

We report the discovery of PSR J0952$-$0607, a 707-Hz binary millisecond pulsar which is now the fastest-spinning neutron star known in the Galactic field (i.e., outside of a globular cluster). PSR J0952$-$0607 was found using LOFAR at a central observing frequency of 135 MHz, well below the 300 MHz to 3 GHz frequencies typically used in pulsar searches. The discovery is part of an ongoing LOFAR survey targeting unassociated Fermi Large Area Telescope $\gamma$-ray sources. PSR J0952$-$0607 is in a 6.42-hr orbit around a very low-mass companion ($M_\mathrm{c}\gtrsim0.02$ M$_\odot$) and we identify a strongly variable optical source, modulated at the orbital period of the pulsar, as the binary companion. The light curve of the companion varies by 1.6 mag from $r^\prime=22.2$ at maximum to $r^\prime>23.8$, indicating that it is irradiated by the pulsar wind. Swift observations place a 3-$\sigma$ upper limit on the $0.3-10$ keV X-ray luminosity of $L_X < 1.1 \times 10^{31}$ erg s$^{-1}$ (using the 0.97 kpc distance inferred from the dispersion measure). Though no eclipses of the radio pulsar are observed, the properties of the system classify it as a black widow binary. The radio pulsed spectrum of PSR J0952$-$0607, as determined through flux density measurements at 150 and 350 MHz, is extremely steep with $\alpha\sim-3$ (where $S \propto \nu^{\alpha}$). We discuss the growing evidence that the fastest-spinning radio pulsars have exceptionally steep radio spectra, as well as the prospects for finding more sources like PSR J0952$-$0607.Comment: 9 pages, 3 figures, 1 table, published in ApJ letter

A millisecond pulsar in a stellar triple system

Gravitationally bound three-body systems have been studied for hundreds of years and are common in our Galaxy. They show complex orbital interactions, which can constrain the compositions, masses, and interior structures of the bodies and test theories of gravity, if sufficiently precise measurements are available. A triple system containing a radio pulsar could provide such measurements, but the only previously known such system, B1620-26 (with a millisecond pulsar, a white dwarf, and a planetary-mass object in an orbit of several decades), shows only weak interactions. Here we report precision timing and multi-wavelength observations of PSR J0337+1715, a millisecond pulsar in a hierarchical triple system with two other stars. Strong gravitational interactions are apparent and provide the masses of the pulsar (1.4378(13) Msun, where Msun is the solar mass and the parentheses contain the uncertainty in the final decimal places) and the two white dwarf companions (0.19751(15) Msun and 0.4101(3) Msun), as well as the inclinations of the orbits (both approximately 39.2 degrees). The unexpectedly coplanar and nearly circular orbits indicate a complex and exotic evolutionary past that differs from those of known stellar systems. The gravitational field of the outer white dwarf strongly accelerates the inner binary containing the neutron star, and the system will thus provide an ideal laboratory in which to test the strong equivalence principle of general relativity.Comment: 17 pages, 3 figures, 1 table. Published online by Nature on 5 Jan 2014. Extremely minor differences with published version may exis

Discovery and Follow-up of Rotating Radio Transients with the Green Bank and LOFAR Telescopes

We have discovered 21 Rotating Radio Transients (RRATs) in data from the Green Bank Telescope (GBT) 350-MHz Drift-scan and the Green Bank North Celestial Cap pulsar surveys using a new candidate sifting algorithm. RRATs are pulsars with sporadic emission that are detected through their bright single pulses rather than Fourier domain searches. We have developed {\tt RRATtrap}, a single-pulse sifting algorithm that can be integrated into pulsar survey data analysis pipelines in order to find RRATs and Fast Radio Bursts. We have conducted follow-up observations of our newly discovered sources at several radio frequencies using the GBT and Low Frequency Array (LOFAR), yielding improved positions and measurements of their periods, dispersion measures, and burst rates, as well as phase-coherent timing solutions for four of them. The new RRATs have dispersion measures (DMs) ranging from 15 to 97 pc cm$^{-3}$, periods of 240 ms to 3.4 s, and estimated burst rates of 20 to 400 pulses hr$^{-1}$ at 350 MHz. We use this new sample of RRATs to perform statistical comparisons between RRATs and canonical pulsars in order to shed light on the relationship between the two populations. We find that the DM and spatial distributions of the RRATs agree with those of the pulsars found in the same survey. We find evidence that slower pulsars (i.e. $P>200$ ms) are preferentially more likely to emit bright single pulses than are faster pulsars ($P<200$ ms), although this conclusion is tentative. Our results are consistent with the proposed link between RRATs, transient pulsars, and canonical pulsars as sources in various parts of the pulse activity spectrum.Comment: 18 pages, 13 figures, 5 tables, published in Ap

Predictors of Patient Satisfaction in Spine Surgery: A Systematic Review

Background: Recently, there has been increased interest in patient satisfaction measures such as Press Ganey and Hospital Consumer Assessment of Healthcare Providers and Systems (HCAHPS) surveys. In this systematic review, the spine surgery literature is analyzed to evaluate factors predictive of patient satisfaction as measured by these surveys. Methods: A thorough literature search was performed in PubMed/MEDLINE, Google Scholar, and Cochrane databases. All English-language articles from database inception to July 2020 were screened for study inclusion according to PRISMA guidelines. Results: Twenty-four of the 1899 published studies were included for qualitative analysis. There has been a statistically significant increase in the number of publications across years (P = 0.04). Overall, the studies evaluated the relationship between patient satisfaction and patient demographics (71%), preoperative and intraoperative clinical factors (21%), and postoperative factors (33%). Top positive predictors of patient satisfaction were patient and nursing/medical staff relationship (n = 4; 17%), physician–patient relationship (n = 4; 17%), managerial oversight of received care (n = 3; 13%), same sex/ethnicity between patient and physician (n = 2; 8%), and older age (n = 2; 8%). Top negative predictors of patient satisfaction were high Charlson Comorbidity Index/high disability/worse overall health functioning (n = 7; 29%), increased length of hospital stay (n = 4; 17%), high rating for pain/complications/readmissions (n = 4; 17%), and psychosocial factors (n = 3; 13%). Conclusions: There is heterogeneity in terms of different factors, both clinical and nonclinically related, that affect patient satisfaction ratings. More research is warranted to investigate the role of hospital consumer surveys in the spine surgical patient population