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F. Camilo

Publications and source records attributed to F. Camilo.

At least 55 records · Page 3Linked to original sources

Statistical Properties of the Population of the Galactic Center Filaments: The Spectral Index and Equipartition Magnetic Field

We present high-pass filtered continuum images of the inner $3.5^\circ\times2.5^\circ$ of the Galactic center at 20 cm with $6.4''$ resolution. These mosaic images are taken with MeerKAT and reveal a large number of narrow filaments, roughly an order of magnitude increase in their numbers compared to past measurements. For the first time, we carry out population studies of the spectral index and magnetic field of the entire region. The mean spectral indices of the filaments are steeper than supernova remnants (SNRs) (-0.62) with a value of $α\sim-0.83$. The variation in $α$ is much larger than for the SNRs, suggesting that these characteristics have a different origin. A large-scale cosmic-ray driven wind has recently been proposed to explain the origin of filaments and the large-scale 430 pc bipolar radio and X-ray structure. This favors the possibility that the large-scale bipolar radio/X-ray structure is produced by past activity of Sgr A* rather than coordinated burst of supernovae. A trend of steeper indices is also noted with increasing distance from the Galactic plane. This could be explained either by synchrotron cooling or weak shocks accelerating cosmic-ray particles in the context of the cosmic-ray driven wind. The mean magnetic field strengths along the filaments ranges from $\sim100$ to 400 $μ$G depending on the assumed ratio of cosmic-ray protons to electrons. Given that there is a high cosmic ray pressure in the Galactic center, the large equipartition magnetic field implies that the magnetic field is weak in most of the interstellar volume of the Galactic center.

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Strong-field Gravity Tests with the Double Pulsar

Continued observations of the Double Pulsar, PSR J0737-3039A/B, consisting of two radio pulsars (A and B) that orbit each other with a period of 2.45hr in a mildly eccentric (e=0.088) binary system, have led to large improvements in the measurement of relativistic effects in this system. With a 16-yr data span, the results enable precision tests of theories of gravity for strongly self-gravitating bodies and also reveal new relativistic effects that have been expected but are now observed for the first time. These include effects of light propagation in strong gravitational fields which are currently not testable by any other method. We observe retardation and aberrational light-bending that allow determination of the pulsar's spin direction. In total, we have detected seven post-Keplerian (PK) parameters, more than for any other binary pulsar. For some of these effects, the measurement precision is so high that for the first time we have to take higher-order contributions into account. These include contributions of A's effective mass loss (due to spin-down) to the observed orbital period decay, a relativistic deformation of the orbit, and effects of the equation of state of super-dense matter on the observed PK parameters via relativistic spin-orbit coupling. We discuss the implications of our findings, including those for the moment of inertia of neutron stars. We present the currently most precise test of general relativity's (GR's) quadrupolar description of gravitational waves, validating GR's prediction at a level of $1.3 \times 10^{-4}$ (95% conf.). We demonstrate the utility of the Double Pulsar for tests of alternative theories by focusing on two specific examples and discuss some implications for studies of the interstellar medium and models for the formation of the Double Pulsar. Finally, we provide context to other types of related experiments and prospects for the future.

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Study of 72 pulsars discovered in the PALFA survey: Timing analysis, glitch activity, emission variability, and a pulsar in an eccentric binary

We present new discoveries and results from long-term timing of 72 pulsars discovered in the Arecibo PALFA survey, including precise determination of astrometric and spin parameters, and flux density and scatter broadening measurements at 1.4 GHz. Notable discoveries include two young pulsars (characteristic ages $\sim$30 kyr) with no apparent supernova remnant associations, three mode changing, 12 nulling and two intermittent pulsars. We detected eight glitches in five pulsars. Among them is PSR J1939+2609, an apparently old pulsar (characteristic age $\sim$1 Gy), and PSR J1954+2529, which likely belongs to a newly-emerging class of binary pulsars. The latter is the only pulsar among the 72 that is clearly not isolated: a non-recycled neutron star with a 931-ms spin period in an eccentric ($e\,=\,0.114$) wide ($P_b\,=\,82.7\,$d) orbit with a companion of undetermined nature having a minimum mass of $\sim0.6\,M_{\odot}$. Since operations at Arecibo ceased in 2020 August, we give a final tally of PALFA sky coverage, and compare its 207 pulsar discoveries to the known population. On average, they are 50% more distant than other Galactic plane radio pulsars; PALFA millisecond pulsars (MSP) have twice the dispersion measure per unit spin period than the known population of MSP in the Plane. The four intermittent pulsars discovered by PALFA more than double the population of such objects, which should help to improve our understanding of pulsar magnetosphere physics. The statistics for these, RRATS, and nulling pulsars suggest that there are many more of these objects in the Galaxy than was previously thought.

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The MeerKAT Galaxy Cluster Legacy Survey I. Survey Overview and Highlights

MeerKAT's large number of antennas, spanning 8 km with a densely packed 1 km core, create a powerful instrument for wide-area surveys, with high sensitivity over a wide range of angular scales. The MeerKAT Galaxy Cluster Legacy Survey (MGCLS) is a programme of long-track MeerKAT L-band (900-1670 MHz) observations of 115 galaxy clusters, observed for $\sim$6-10 hours each in full polarisation. The first legacy product data release (DR1), made available with this paper, includes the MeerKAT visibilities, basic image cubes at $\sim$8" resolution, and enhanced spectral and polarisation image cubes at $\sim$8" and 15" resolutions. Typical sensitivities for the full-resolution MGCLS image products are $\sim$3-5 μJy/beam. The basic cubes are full-field and span 4 deg^2. The enhanced products consist of the inner 1.44 deg^2 field of view, corrected for the primary beam. The survey is fully sensitive to structures up to $\sim$10' scales and the wide bandwidth allows spectral and Faraday rotation mapping. HI mapping at 209 kHz resolution can be done at $0<z<0.09$ and $0.19<z<0.48$. In this paper, we provide an overview of the survey and DR1 products, including caveats for usage. We present some initial results from the survey, both for their intrinsic scientific value and to highlight the capabilities for further exploration with these data. These include a primary beam-corrected compact source catalogue of $\sim$626,000 sources for the full survey, and an optical/infrared cross-matched catalogue for compact sources in Abell 209 and Abell S295. We examine dust unbiased star-formation rates as a function of clustercentric radius in Abell 209 and present a catalogue of 99 diffuse cluster sources (56 are new), some of which have no suitable characterisation. We also highlight some of the radio galaxies which challenge current paradigms and present first results from HI studies of four targets.

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Timing observations of three Galactic millisecond pulsars

We report observed and derived timing parameters for three millisecond pulsars (MSPs) from observations collected with the Parkes 64-m telescope, Murriyang. The pulsars were found during re-processing of archival survey data by Mickaliger et al. One of the new pulsars (PSR J1546-5925) has a spin period $P=7.8$ ms and is isolated. The other two (PSR J0921-5202 with $P=9.7$ ms and PSR J1146-6610 with $P=3.7$ ms) are in binary systems around low-mass ($>0.2 M_{\odot}$) companions. Their respective orbital periods are $38$.2 d and $62.8$ d. While PSR J0921-5202 has a low orbital eccentricity $e=1.3 \times 10^{-5}$, in keeping with many other Galactic MSPs, PSR J1146-6610 has a significantly larger eccentricity, $e = 7.4 \times 10^{-3}$. This makes it a likely member of a group of eccentric MSP-He white dwarf binary systems in the Galactic disk whose formation is poorly understood. Two of the pulsars are co-located with previously unidentified point sources discovered with the Fermi satellite's Large Area Telescope, but no $γ$-ray pulsations have been detected, likely due to their low spin-down powers. We also show that, particularly in terms of orbital diversity, the current sample of MSPs is far from complete and is subject to a number of selection biases.

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Threads, Ribbons, and Rings in the Radio Galaxy IC 4296

The nearby elliptical galaxy IC4296 has produced a large (510 kpc) low-luminosity radio source with typical FR I core/jet/lobe morphology. The unprecedented combination of brightness sensitivity, dynamic range, and angular resolution of a new 1.28 GHz MeerKAT continuum image reveals striking new morphological features which we call threads, ribbons, and rings. The threads are faint narrow emission features originating where helical Kelvin-Helmholtz instabilities disrupt the main radio jets. The ribbons are smooth regions between the jets and the lobes, and they appear to be relics of jets powered by earlier activity that have since come into pressure equilibrium. Vortex rings in the outer portions of the lobes and their backflows indicate that the straight outer jets and ribbons are inclined by $i = 60 \pm 5^\circ$ from the line-of-sight, in agreement with photometric, geometric, and gas-dynamical estimates of inclination angles near the nucleus.

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Radio Detection of PSR J1813-1749 in HESS J1813-178: The Most Scattered Pulsar Known

The 44.7 ms X-ray pulsar in the supernova remnant G12.82-0.02/HESS J1813-178 has the second highest spin-down luminosity of known pulsars in the Galaxy, with E-dot=5.6e37 erg/s. Using the Green Bank Telescope, we have detected radio pulsations from PSR J1813-1749 at 4.4-10.2 GHz. The pulse is highly scattered, with an exponential decay timescale τlonger than that of any other pulsar at these frequencies. A point source detected at this position by Dzib et al. in several observations with the Jansky Very Large Array can be attributed to the pulsed emission. The steep dependence of τon observing frequency explains why all previous pulsation searches at lower frequencies failed (τ~0.25 s at 2 GHz). The large dispersion measure, DM=1087 pc/cc, indicates a distance of either 6.2 or 12 kpc according to two widely used models of the electron density distribution in the Galaxy. These disfavor a previously suggested association with a young stellar cluster at the closer distance of 4.8 kpc. The high X-ray measured column density of ~1e23/cm^2 also supports a large distance. If at d~12 kpc, HESS J1813-178 would be one of the most luminous TeV sources in the Galaxy.

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The Relativistic Binary Programme on MeerKAT: Science objectives and first results

We describe the ongoing Relativistic Binary programme (RelBin), a part of the MeerTime large survey project with the MeerKAT radio telescope. RelBin is primarily focused on observations of relativistic effects in binary pulsars to enable measurements of neutron star masses and tests of theories of gravity. We selected 25 pulsars as an initial high priority list of targets based on their characteristics and observational history with other telescopes. In this paper, we provide an outline of the programme, present polarisation calibrated pulse profiles for all selected pulsars as a reference catalogue along with updated dispersion measures. We report Faraday rotation measures for 24 pulsars, twelve of which have been measured for the first time. More than a third of our selected pulsars show a flat position angle swing confirming earlier observations. We demonstrate the ability of the Rotating Vector Model (RVM), fitted here to seven binary pulsars, including the Double Pulsar (PSR J0737$-$3039A), to obtain information about the orbital inclination angle. We present a high time resolution light curve of the eclipse of PSR J0737$-$3039A by the companion's magnetosphere, a high-phase resolution position angle swing for PSR J1141$-$6545, an improved detection of the Shapiro delay of PSR J1811$-$2405, and pulse scattering measurements for PSRs J1227$-$6208, J1757$-$1854, and J1811$-$1736. Finally, we demonstrate that timing observations with MeerKAT improve on existing data sets by a factor of, typically, 2-3, sometimes by an order of magnitude.

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Eight new millisecond pulsars from the first MeerKAT globular cluster census

We have used the central 44 antennas of the new 64-dish MeerKAT radio telescope array to conduct a deep search for new pulsars in the core of nine globular clusters. This has led to the discovery of eight new millisecond pulsars in six different clusters. Two new binaries, 47 Tuc ac and 47 Tuc ad, are eclipsing "spiders", featuring compact orbits ($\lesssim 0.32$ days), very low-mass companions and regular occultations of their pulsed emission. The other three new binary pulsars (NGC 6624G, M62G, and Ter 5 an) are in wider ($> 0.7$ days) orbits, with companions that are likely to be white dwarfs or neutron stars. NGC 6624G has a large eccentricity of $e\simeq 0.38$, which enabled us to detect the rate of advance of periastron. This suggests that the system is massive, with a total mass of $M{\rm tot} = 2.65 \pm 0.07$ M$_{\odot}$. Likewise, for Ter 5 an, with $e \simeq 0.0066$, we obtain $M{\rm tot}= 2.97 \pm 0.52$ M$_{\odot}$. The other three new discoveries (NGC 6522D, NGC 6624H and NGC 6752F) are faint isolated pulsars. Finally, we have used the whole MeerKAT array and synthesized 288 beams, covering an area of $\sim2$ arcmin in radius around the center of NGC 6624. This has allowed us to localize many of the pulsars in the cluster, demonstrating the beamforming capabilities of the TRAPUM software backend and paving the way for the upcoming MeerKAT globular cluster pulsar survey.

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Measurements of pulse jitter and single-pulse variability in millisecond pulsars using MeerKAT

Using the state-of-the-art SKA precursor, the MeerKAT radio telescope, we explore the limits to precision pulsar timing of millisecond pulsars achievable due to pulse stochasticity (jitter). We report new jitter measurements in 15 of the 29 pulsars in our sample and find that the levels of jitter can vary dramatically between them. For some, like the 2.2~ms pulsar PSR J2241--5236, we measure an implied jitter of just $\sim$ 4~ns/hr, while others like the 3.9~ms PSR J0636--3044 are limited to $\sim$ 100 ns/hr. While it is well known that jitter plays a central role to limiting the precision measurements of arrival times for high signal-to-noise ratio observations, its role in the measurement of dispersion measure (DM) has not been reported, particularly in broad-band observations. Using the exceptional sensitivity of MeerKAT, we explored this on the bright millisecond pulsar PSR J0437--4715 by exploring the DM of literally every pulse. We found that the derived single pulse DMs vary by typically 0.0085 cm$^{-3}$ pc from the mean, and that the best DM estimate is limited by the differential pulse jitter across the band. We postulate that all millisecond pulsars will have their own limit on DM precision which can only be overcome with longer integrations. Using high-time resolution filterbank data of 9 $μ$s, we also present a statistical analysis of single pulse phenomenology. Finally, we discuss optimization strategies for the MeerKAT pulsar timing program and its role in the context of the International Pulsar Timing Array (IPTA).

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Timing of Eight Binary Millisecond Pulsars Found with Arecibo in Fermi-LAT Unidentified Sources

We present timing solutions for eight binary millisecond pulsars (MSPs) discovered by searching unidentified Fermi-LAT source positions with the 327 MHz receiver of the Arecibo 305-m radio telescope. Five of the pulsars are "spiders" with orbital periods shorter than 8.1 h. Three of these are in "black widow" systems (with degenerate companions of 0.02-0.03 solar masses), one is in a "redback" system (with a non-degenerate companion of $\gtrsim 0.3$ solar masses), and one (J1908+2105) is an apparent middle-ground case between the two observational classes. The remaining three pulsars have white dwarf companions and longer orbital periods. With the initially derived radio timing solutions, we detected gamma-ray pulsations from all MSPs and extended the timing solutions using photons from the full Fermi mission, thus confirming the identification of these MSPs with the Fermi-LAT sources. The radio emission of the redback is eclipsed during 50% of its orbital period, which is typical for this kind of system. Two of the black widows exhibit radio eclipses lasting for 10-20% of the orbit, while J1908+2105 eclipses for 40% of the orbit. We investigate an apparent link between gamma-ray emission and a short orbital period among known binary MSPs in the Galactic disk, and conclude that selection effects cannot be ruled out as the cause. Based on this analysis we outline how the likelihood of new MSP discoveries can be improved in ongoing and future pulsar searches.

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Discovery of a Gamma-ray Black Widow Pulsar by GPU-accelerated Einstein@Home

We report the discovery of 1.97 ms period gamma-ray pulsations from the 75 minute orbital-period binary pulsar now named PSR J1653-0158. The associated Fermi Large Area Telescope gamma-ray source 4FGL J1653.6-0158 has long been expected to harbor a binary millisecond pulsar. Despite the pulsar-like gamma-ray spectrum and candidate optical/X-ray associations -- whose periodic brightness modulations suggested an orbit -- no radio pulsations had been found in many searches. The pulsar was discovered by directly searching the gamma-ray data using the GPU-accelerated Einstein@Home distributed volunteer computing system. The multi-dimensional parameter space was bounded by positional and orbital constraints obtained from the optical counterpart. More sensitive analyses of archival and new radio data using knowledge of the pulsar timing solution yield very stringent upper limits on radio emission. Any radio emission is thus either exceptionally weak, or eclipsed for a large fraction of the time. The pulsar has one of the three lowest inferred surface magnetic-field strengths of any known pulsar with $B_{\rm surf} \approx 4 \times 10^{7}\,$G. The resulting mass function, combined with models of the companion star's optical light curve and spectra, suggests a pulsar mass $\gtrsim 2\,M_{\odot}$. The companion is light-weight with mass $\sim 0.01\,M_{\odot}$, and the orbital period is the shortest known for any rotation-powered binary pulsar. This discovery demonstrates the Fermi Large Area Telescope's potential to discover extreme pulsars that would otherwise remain undetected.

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G0.173-0.42: an X-ray and radio magnetized filament near the galactic center

The recent detection of an X-ray filament associated with the radio filament G0.173-0.42 adds to four other nonthermal radio filaments with X-ray counterparts, amongst the more than 100 elongated radio structures that have been identified as synchrotron-emitting radio filaments in the inner couple of degrees of the Galactic center. The synchrotron mechanism has also been proposed to explain the emission from X-ray filaments. However, the origin of radio filaments and the acceleration sites of energetic particles to produce synchrotron emission in radio and X-rays remain mysterious. Using MeerKAT, VLA, Chandra, WISE and Spitzer, we present structural details of G0.173-0.42 which consists of multiple radio filaments, one of which has an X-ray counterpart. A faint oblique radio filament crosses the radio and X-ray filaments. Based on the morphology, brightening of radio and X-ray intensities, and radio spectral index variation, we argue that a physical interaction is taking place between two magnetized filaments. We consider that the reconnection of the magnetic field lines at the interaction site leads to the acceleration of particles to GeV energies. We also argue against the synchrotron mechanism for the X-ray emission due to the short $\sim$30 year lifetime of TeV relativistic particles. Instead, we propose that the inverse Compton scattering mechanism is more likely to explain the X-ray emission by upscattering of seed photons emitted from a 10^6 solar luminosity star located at the northern tip of the X-ray filament.

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The Thousand-Pulsar-Array programme on MeerKAT IV: Polarisation properties of young, energetic pulsars

We present observations of 35 high spin-down energy radio pulsars using the MeerKAT telescope. Polarisation profiles and associated parameters are also presented. We derive the geometry for a selection of pulsars which show interpulse emission. We point out that, in several cases, these radio pulsars should also be seen in $γ$-rays but that improved radio timing is required to aid the high-energy detection. We discuss the relationship between the width of the radio profile and its high-energy detectability. Finally, we reflect on the correlation between the spin-down energy and the radio polarisation fraction and the implications this may have for $γ$-ray emission.

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Giant pulses from J1823-3021A observed with the MeerKAT telescope

The millisecond pulsar J1823-3021A is a very active giant pulse emitter in the globular cluster NGC 6624. New observations with the MeerKAT radio telescope have revealed 14350 giant pulses over 5 hours of integration time, with an average wait time of about 1 second between giant pulses. The giant pulses occur in phases compatible with the ordinary radio emission, follow a power-law distribution with an index of -2.63 $\pm$ 0.02 and contribute 4 percent of the total integrated flux. The spectral index of the giant pulses follows a Gaussian distribution centered around -1.9 with a standard deviation of 0.6 and is on average flatter than the integrated emission, which has a spectral index of -2.81 $\pm$ 0.02. The waiting times between the GPs are accurately described by a Poissonian distribution, suggesting that the time of occurrence of a GP is independent from the times of occurrence of other GPs. 76 GPs show multiple peaks within the same rotation, a rate that is also compatible with the mutual independence of the GP times of occurrence. We studied the polarization properties of the giant pulses finding, on average, linear polarization only at the 1 percent level and circular polarization at the 3 percent level, similar to the polarization percentages of the total integrated emission. In 4 cases it was possible to measure the RM of the GPs which are highly variable and, in two cases, is inconsistent with the mean RM of the total integrated pulsar signal.

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A magnetar parallax

XTE J1810-197 (J1810) was the first magnetar identified to emit radio pulses, and has been extensively studied during a radio-bright phase in 2003$-$2008. It is estimated to be relatively nearby compared to other Galactic magnetars, and provides a useful prototype for the physics of high magnetic fields, magnetar velocities, and the plausible connection to extragalactic fast radio bursts. Upon the re-brightening of the magnetar at radio wavelengths in late 2018, we resumed an astrometric campaign on J1810 with the Very Long Baseline Array, and sampled 14 new positions of J1810 over 1.3 years. The phase calibration for the new observations was performed with two phase calibrators that are quasi-colinear on the sky with J1810, enabling substantial improvement of the resultant astrometric precision. Combining our new observations with two archival observations from 2006, we have refined the proper motion and reference position of the magnetar and have measured its annual geometric parallax, the first such measurement for a magnetar. The parallax of $0.40\pm0.05\,$mas corresponds to a most probable distance $2.5^{+0.4}_{-0.3}\,$kpc for J1810. Our new astrometric results confirm an unremarkable transverse peculiar velocity of $\approx200\,\mathrm{km~s^{-1}}$ for J1810, which is only at the average level among the pulsar population. The magnetar proper motion vector points back to the central region of a supernova remnant (SNR) at a compatible distance at $\approx70\,$kyr ago, but a direct association is disfavored by the estimated SNR age of ~3 kyr.

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Asymmetric mass ratios for bright double neutron-star mergers

The discovery of a radioactively powered kilonova associated with the binary neutron star merger GW170817 was the first - and still only - confirmed electromagnetic counterpart to a gravitational-wave event. However, observations of late-time electromagnetic emission are in tension with the expectations from standard neutron-star merger models. Although the large measured ejecta mass is potentially explained by a progenitor system that is asymmetric in terms of the stellar component masses, i.e. with a mass ratio $q$ of 0.7-0.8, the known Galactic population of merging double neutron star (DNS) systems (i.e. those that will coalesce within billions of years or less) has, until now, only consisted of nearly equal-mass ($q > 0.9$) binaries. PSR J1913+1102 is a DNS system in a 5-hour, low-eccentricity ($e = 0.09$) orbit, implying an orbital separation of 1.8 solar radii, with the two neutron stars predicted to coalesce in 470 million years due to gravitational-wave emission. Here we report that the masses of the two neutron stars, as measured by a dedicated pulsar timing campaign, are $1.62 \pm 0.03$ and $1.27 \pm 0.03$ solar masses for the pulsar and companion neutron star, respectively; with a measured mass ratio $q = 0.78 \pm 0.03$, it is the most asymmetric DNS among known merging systems. Based on this detection, our population synthesis analysis implies that such asymmetric binaries represent between 2 and 30% (90% confidence) of the total population of merging DNS binaries. The coalescence of a member of this population offers a possible explanation for the anomalous properties of GW170817, including the observed kilonova emission from that event.

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The MeerKAT Telescope as a Pulsar Facility: System verification and early science results from MeerTime

We describe system verification tests and early science results from the pulsar processor (PTUSE) developed for the newly-commissioned 64-dish SARAO MeerKAT radio telescope in South Africa. MeerKAT is a high-gain (~2.8 K/Jy) low-system temperature (~18 K at 20cm) radio array that currently operates from 580-1670 MHz and can produce tied-array beams suitable for pulsar observations. This paper presents results from the MeerTime Large Survey Project and commissioning tests with PTUSE. Highlights include observations of the double pulsar J0737-3039A, pulse profiles from 34 millisecond pulsars from a single 2.5h observation of the Globular cluster Terzan 5, the rotation measure of Ter5O, a 420-sigma giant pulse from the Large Magellanic Cloud pulsar PSR J0540-6919, and nulling identified in the slow pulsar PSR J0633-2015. One of the key design specifications for MeerKAT was absolute timing errors of less than 5 ns using their novel precise time system. Our timing of two bright millisecond pulsars confirm that MeerKAT delivers exceptional timing. PSR J2241-5236 exhibits a jitter limit of <4 ns per hour whilst timing of PSR J1909-3744 over almost 11 months yields an rms residual of 66 ns with only 4 min integrations. Our results confirm that the MeerKAT is an exceptional pulsar telescope. The array can be split into four separate sub-arrays to time over 1000 pulsars per day and the future deployment of S-band (1750-3500 MHz) receivers will further enhance its capabilities.

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