11 research outputs found
MeerKAT Pulsar Timing Array parallaxes and proper motions
We have determined positions, proper motions, and parallaxes of
millisecond pulsars (MSPs) from years of MeerKAT radio telescope
observations. Our timing and noise analyses enable us to measure
significant parallaxes ( of them for the first time) and significant
proper motions. Eight pulsars near the ecliptic have an accurate proper motion
in ecliptic longitude only. PSR~J09556150 has a good upper limit on its very
small proper motion (0.4 mas yr). We used pulsars with accurate
parallaxes to study the MSP velocities. This yields MSP transverse
velocities, and combined with MSPs in the literature (excluding those in
Globular Clusters) we analyse MSPs in total. We find that MSPs have, on
average, much lower velocities than normal pulsars, with a mean transverse
velocity of only km s (MSPs) compared with km s
(normal pulsars). We found no statistical differences between the velocity
distributions of isolated and binary millisecond pulsars. From Galactocentric
cylindrical velocities of the MSPs, we derive 3-D velocity dispersions of
, , = , , km
s. We measure a mean asymmetric drift with amplitude km
s, consistent with expectation for MSPs, given their velocity
dispersions and ages. The MSP velocity distribution is consistent with binary
evolution models that predict very few MSPs with velocities km s
and a mild anticorrelation of transverse velocity with orbital period
Lava Bubble-wall Fragments Formed by Submarine Hydrovolcanic Explosions on LĆ\u27ihi Seamount and KÄ«lauea Volcano
Glassy bubble-wall fragments, morphologically similar to littoral limu o Pele, have been found in volcanic sands erupted on LĆ\u27ihi Seamount and along the submarine east rift zone of KÄ«lauea Volcano. The limu o Pele fragments are undegassed with respect to H2O and S and formed by mild steam explosions. Angular glass sand fragments apparently form at similar, and greater, depths by cooling-contraction granulation. The limu o Pele fragments from LĆ\u27ihi Seamount are dominantly tholeiitic basalt containing 6.25â7.25% MgO. None of the limu o Pele samples from LĆ\u27ihi Seamount contains less than 5.57% MgO, suggesting that higher viscosity magmas do not form lava bubbles. The dissolved CO2 and H2O contents of 7 of the limu o Pele fragments indicate eruption at 1200±300âm depth (120±30âbar). These pressures exceed that generally thought to limit steam explosions. We conclude that hydrovolcanic eruptions are possible, with appropriate pre-mixing conditions, at pressures as great as 120âbar
The MeerKAT Pulsar Timing Array: First Data Release
International audienceWe present the first 2.5 years of data from the MeerKAT Pulsar Timing Array (MPTA), part of MeerTime, a MeerKAT Large Survey Project. The MPTA aims to precisely measure pulse arrival times from an ensemble of 88 pulsars visible from the Southern Hemisphere, with the goal of contributing to the search, detection and study of nanohertz-frequency gravitational waves as part of the International Pulsar Timing Array. This project makes use of the MeerKAT telescope, and operates with a typical observing cadence of two weeks using the L-band receiver that records data from 856-1712 MHz. We provide a comprehensive description of the observing system, software, and pipelines used and developed for the MeerTime project. The data products made available as part of this data release are from the 78 pulsars that had at least observations between the start of the MeerTime programme in February 2019 and October 2021. These include both sub-banded and band-averaged arrival times, as well as the initial timing ephemerides, noise models, and the frequency-dependent standard templates (portraits) used to derive pulse arrival times. After accounting for detected noise processes in the data, the frequency-averaged residuals of of the pulsars achieved a root-mean-square residual precision of . We also present a novel recovery of the clock correction waveform solely from pulsar timing residuals, and an exploration into preliminary findings of interest to the international pulsar timing community. The arrival times, standards and full Stokes parameter calibrated pulsar timing archives are publicly available
Immunoglobulin diversity gene usage predicts unfavorable outcome in a subset of chronic lymphocytic leukemia patients
Survival of patients with B cell chronic lymphocytic leukemia (B-CLL) can be predicted by analysis of mutations in the immunoglobulin heavy chain variable gene (IGHV). Patients without mutations (unmutated [UM]) are at greater risk for disease progression and death than patients with mutations (M). Despite this broad prognostic difference, there remains wide intragroup variation in the clinical outcome of UM patients, especially those with low/intermediate Rai risk disease. We evaluated UM B-CLL patients with low/intermediate Rai risk to determine the relationship between IGHV, IGH diversity (IGHD), and IGH joining (IGHJ) gene usage and time to treatment (TTT). Irrespective of IGHV usage, UM patients whose B-CLL cells expressed the IGHD3-3 gene had a significantly shorter TTT than other UM B-CLL patients, and specifically, use of the IGHD3-3 gene in reading frame 2 (RF2) predicted shorter TTT. As expected, Rai risk was the best single prognostic factor for TTT; however, IGHD usage was also a significant variable for TTT. Therefore, both IGHD gene and IGHD RF usage have prognostic relevance in UM B-CLL patients with low/intermediate Rai risk disease. In addition, these data support the concept that antigen-driven selection of specific Ig receptors plays a role in the clinical course of B-CLL