25 research outputs found
Trapum discovery of 13 new pulsars in ngc 1851 using meerkat
We report the discovery of 13 new pulsars in the globular cluster NGC 1851 by the TRAPUM Large Survey Project using the
MeerKAT radio telescope. The discoveries consist of six isolated millisecond pulsars (MSPs) and seven binary pulsars, of which
six are MSPs and one is mildly recycled. For all the pulsars, we present the basic kinematic, astrometric, and orbital parameters,
where applicable, as well as their polarimetric properties, when these are measurable. Two of the binary MSPs (PSR J0514â4002D
and PSR J0514â4002E) are in wide and extremely eccentric (e > 0.7) orbits with a heavy white dwarf and a neutron star as their
companion, respectively. With these discoveries, NGC 1851 is now tied with M28 as the cluster with the third largest number of
known pulsars (14). Its pulsar population shows remarkable similarities with that of M28, Terzan 5, and other clusters with comparable
structural parameters. The newly found pulsars are all located in the innermost regions of NGC 1851 and will likely enable, among
other things, detailed studies of the cluster structure and dynamics
Gravitational signal propagation in the double pulsar studied with the MeerKAT telescope
The double pulsar PSR J0737â3039A/B has offered a wealth of gravitational experiments in the strong-field regime, all of which
general relativity has passed with flying colours. In particular, among current gravity experiments that test photon propagation, the
double pulsar probes the strongest spacetime curvature. Observations with MeerKAT and, in the future, the Square Kilometre Array
(SKA) can greatly improve the accuracy of current tests and facilitate tests of next-to-leading-order (NLO) contributions in both
orbital motion and signal propagation. We present our timing analysis of new observations of PSR J0737â3039A, made using the
MeerKAT telescope over the last three years. The increased timing precision offered by MeerKAT yields a measurement of Shapiro
delay parameter s that it twice as good, and an improved mass measurements compared to previous studies. In addition, our results
provide an independent confirmation of the NLO signal propagation effects and already surpass the previous measurement from 16 yr
data by a factor of 1.65. These effects include the retardation effect due to the movement of the companion and the deflection of
the signal by the gravitational field of the companion. We also investigate the novel effects that have been expected. For instance, we
search for potential profile variations near superior conjunctions caused by shifts of the line of sight due to latitudinal signal deflection,
and we find insignificant evidence with our current data. With simulations, we find that the latitudinal deflection delay is unlikely to
be measured with timing because of its correlation with Shapiro delay. Furthermore, although it is currently not possible to detect the
expected lensing correction to the Shapiro delay, our simulations suggest that this effect may be measured with the full SKA. Finally,
we provide an improved analytical description for the signal propagation in the double pulsar system that meets the timing precision
expected from future instruments such as the full SKA
The MeerKAT pulsar timing array: First data release
We 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 30 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 67
of the pulsars achieved a root-mean-square residual precision of 1s.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
Pulsar scintillation studies with LOFAR I. The census
Interstellar scintillation (ISS) of pulsar emission can be used both as a probe of the ionized interstellar medium (IISM) and
cause corruptions in pulsar timing experiments. Of particular interest are so-called scintillation arcs which can be used to measure
time-variable interstellar scattering delays directly, potentially allowing high-precision improvements to timing precision.The primary aim of this study is to carry out the first sizeable and self-consistent census of diffractive pulsar scintillation and
scintillation-arc detectability at low frequencies, as a primer for larger-scale IISM studies and pulsar-timing related propagation studies
with the LOw-Frequency ARray (LOFAR) High Band Antennae (HBA)
The lofar tied-array all-sky survey: Timing of 35 radio pulsars and an overview of the properties of the lofar pulsar discoveries
The LOFAR Tied-Array All-Sky Survey (LOTAAS) is the most sensitive untargeted radio pulsar survey performed at low radio
frequencies (119â151 MHz) to date and has discovered 76 new radio pulsars, including the 23.5-s pulsar J0250+5854, which up until
recently was the slowest spinning radio pulsar known. In this paper, we report on the timing solutions of 35 pulsars discovered by
LOTAAS, which include a nulling pulsar and a mildly recycled pulsar, and thereby complete the full timing analysis of the LOTAAS
pulsar discoveries. We give an overview of the findings from the full LOTAAS sample of 76 pulsars, discussing their pulse profiles,
radio spectra, and timing parameters. We found that the pulse profiles of some of the pulsars show profile variations in time or
frequency, and while some pulsars show signs of scattering, a large majority display no pulse broadening. The LOTAAS discoveries
have on average steeper radio spectra and longer spin periods (1.4Ă), as well as lower spin-down rates (3.1Ă) compared to the known
pulsar population. We discuss the cause of these differences and attribute them to a combination of selection effects of the LOTAAS
survey as well as previous pulsar surveys, though we cannot rule out that older pulsars tend to have steeper radio spectra
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A LOFAR observation of ionospheric scintillation from two simultaneous travelling ionospheric disturbances
This paper presents the results from one of the first observations of ionospheric scintillation taken using the Low-Frequency Array (LOFAR). The observation was of the strong natural radio source Cassiopeia A, taken overnight on 18â19 August 2013, and exhibited moderately strong scattering effects in dynamic spectra of intensity received across an observing bandwidth of 10â80 MHz. Delay-Doppler spectra (the 2-D FFT of the dynamic spectrum) from the first hour of observation showed two discrete parabolic arcs, one with a steep curvature and the other shallow, which can be used to provide estimates of the distance to, and velocity of, the scattering plasma. A cross-correlation analysis of data received by the dense array of stations in the LOFAR âcoreâ reveals two different velocities in the scintillation pattern: a primary velocity of ~20â40 msâ1 with a north-west to south-east direction, associated with the steep parabolic arc and a scattering altitude in the F-region or higher, and a secondary velocity of ~110 msâ1 with a north-east to south-west direction, associated with the shallow arc and a scattering altitude in the D-region. Geomagnetic activity was low in the mid-latitudes at the time, but a weak sub-storm at high latitudes reached its peak at the start of the observation. An analysis of Global Navigation Satellite Systems (GNSS) and ionosonde data from the time reveals a larger-scale travelling ionospheric disturbance (TID), possibly the result of the high-latitude activity, travelling in the north-west to south-east direction, and, simultaneously, a smaller-scale TID travelling in a north-east to south-west direction, which could be associated with atmospheric gravity wave activity. The LOFAR observation shows scattering from both TIDs, at different altitudes and propagating in different directions. To the best of our knowledge this is the first time that such a phenomenon has been reported
Anomalous gas in ESO 149-G003 : a MeerKAT-16 view
ESO 149-G003 is a close-by, isolated dwarf irregular galaxy. Previous observations with the ATCA indicated the presence of anomalous neutral hydrogen (â HIâ ) deviating from the kinematics of a regularly rotating disc. We conducted follow-up observations with the MeerKAT radio telescope during the 16-dish Early Science programme as well as with the MeerLICHT optical telescope. Our more sensitive radio observations confirm the presence of anomalous gas in ESO 149-G003, and further confirm the formerly tentative detection of an extraplanar HI component in the galaxy. Employing a simple tilted-ring model, in which the kinematics is determined with only four parameters but including morphological asymmetries, we reproduce the galaxyâs morphology, which shows a high degree of asymmetry. By comparing our model with the observed HIâ , we find that in our model, we cannot account for a significant (but not dominant) fraction of the gas. From the differences between our model and the observed data cube, we estimate that at least 7â8 perâcent of the HI in the galaxy exhibits anomalous kinematics, while we estimate a minimum mass fraction of less than 1 perâcent for the morphologically confirmed extraplanar component. We investigate a number of global scaling relations and find that, besides being gas-dominated with a neutral gas-to-stellar mass ratio of 1.7, the galaxy does not show any obvious global peculiarities. Given its isolation, as confirmed by optical observations, we conclude that the galaxy is likely currently acquiring neutral gas. It is either re-accreting gas expelled from the galaxy or accreting pristine intergalactic material.http://mnras.oxfordjournals.orghj2022Physic
Anomalous gas in ESO 149-G003: A MeerKAT-16 view
ESO 149-G003 is a close-by, isolated dwarf irregular galaxy. Previous observations with the ATCA indicated the presence of anomalous neutral hydrogen (H I) deviating from the kinematics of a regularly rotating disc. We conducted follow-up observations with the MeerKAT radio telescope during the 16-dish Early Science programme as well as with the MeerLICHT optical telescope. Our more sensitive radio observations confirm the presence of anomalous gas in ESO 149-G003, and further confirm the formerly tentative detection of an extraplanar H I component in the galaxy. Employing a simple tilted-ring model, in which the kinematics is determined with only four parameters but including morphological asymmetries, we reproduce the galaxy's morphology, which shows a high degree of asymmetry. By comparing our model with the observed H I, we find that in our model, we cannot account for a significant (but not dominant) fraction of the gas. From the differences between our model and the observed data cube, we estimate that at least 7-8 per cent of the H I in the galaxy exhibits anomalous kinematics, while we estimate a minimum mass fraction of less than 1 per cent for the morphologically confirmed extraplanar component
Interstellar medium studies below 200 MHz: LOFAR single stations and NenuFAR
International audienceInternational LOFAR stations, equipped with powerful backends, can be used as individual telescopes, and provide data sets complementary to those obtained with the LOFAR Core. Such ``local mode'' observations are particularly adapted to monitoring observations, where the advantage of having a high observing cadence (one observation per week) outweighs the reduced sensitivity of a single station when compared to the full array. With such observations, it is possible to monitor the temporal evolution of the pulsars' behaviour via its dispersion, scattering, intensity, and profile shape. We present recent studies performed in the LOFAR low band (10-90 MHz)