Search

The eclipses seen in the radio emission of some pulsars can be invaluable to study the properties of the material from the companion stripped away by the pulsar. We present a study of six consecutive eclipses of PSR J0024–7204O in the globular cluster 47 Tucanae as seen by the MeerKAT radio telescope in the UHF (544–1088 MHz) band. A high scintillation state boosted the signal during one of the orbits and allowed a detailed study of the eclipse properties. We measure significant dispersion measure (DM) variations and detect strong scattering that seems to be the dominating mechanism of the eclipses at these frequencies. A complete drop in the linear polarization together with a small increase in the rotation measure suggests the presence of a magnetic field of |$\sim 2$|  mG. The study of multiple eclipses allowed us to measure difference in the lengths of the eclipses and DM differences of |$\sim 0.01$|  pc cm |$^{-3}$| in consecutive orbits. One orbit, in particular, shows a delay in recovery of the linear polarization and a visible delay in the arrival of the pulses caused by a stronger scattering event. We suggest that these are caused by a higher variance of density fluctuations during the event. [ABSTRACT FROM AUTHOR]

Using MeerKAT , we have discovered three new millisecond pulsars (MSPs) in the bulge globular cluster M62: M62H, M62I, and M62J. All three are in binary systems, which means all ten known pulsars in the cluster are in binaries. M62H has a planetary-mass companion with a median mass M c, med ∼ 3 MJ and a mean density of ρ ∼ 11 g cm−3. M62I has an orbital period of 0.51 d and a M c, med ∼ 0.15 M⊙. Neither of these low-mass systems exhibit eclipses. M62J has only been detected in the two Ultra High Frequency band (816 MHz) observations with a flux density S 816 = 0.08 mJy. The non-detection in the L-band (1284 MHz) indicates it has a relatively steep spectrum (β < −3.1). We also present 23-yr-long timing solutions obtained using data from the Parkes 'Murriyang', Effelsberg , and MeerKAT telescopes for the six previously known pulsars. For all these pulsars, we measured the second spin-period derivatives and the rate of change of orbital period caused by the gravitational field of the cluster, and their proper motions. From these measurements, we conclude that the pulsars' maximum accelerations are consistent with the maximum cluster acceleration assuming a core-collapsed mass distribution. Studies of the eclipses of the redback M62B and the black widow M62E at four and two different frequency bands, respectively, reveal a frequency dependence with longer and asymmetric eclipses at lower frequencies. The presence of only binary MSPs in this cluster challenges models which suggest that the MSP population of core-collapsed clusters should be dominated by isolated MSPs. [ABSTRACT FROM AUTHOR]

The most massive globular cluster in our Galaxy, Omega Centauri, is an interesting target for pulsar searches, because of its multiple stellar populations and the intriguing possibility that it was once the nucleus of a galaxy that was absorbed into the Milky Way. The recent discoveries of pulsars in this globular cluster and their association with known X-ray sources was a hint that, given the large number of known X-ray sources, there is a much larger undiscovered pulsar population. We used the superior sensitivity of the MeerKAT radio telescope to search for pulsars in Omega Centauri. In this paper, we present some of the first results of this survey, including the discovery of 13 new pulsars; the total number of known pulsars in this cluster currently stands at 18. At least half of them are in binary systems and preliminary orbital constraints suggest that most of the binaries have light companions. We also discuss the ratio between isolated and binaries pulsars, and how they were formed in this cluster. [ABSTRACT FROM AUTHOR]

Context. PSR J1910−5959A is a binary millisecond pulsar in a 0.837 day circular orbit around a helium white dwarf (HeWD) companion. The position of this pulsar is 6.3 arcmin (∼74 core radii) away from the optical centre of the globular cluster (GC) NGC 6752. Given the large offset, the association of the pulsar with the GC has been debated. Aims. We aim to obtain precise measurements of the masses of the stars in the system along with secular orbital parameters, which will help identify if the system belongs to the GC. Methods. We have made use of archival Parkes 64 m 'Murriyang' telescope data and carried out observations with the MeerKAT telescope with different backends and receivers over the last two decades. Pulse times of arrival were obtained from these using standard pulsar data reduction techniques and analysed using state-of-the-art Bayesian pulsar timing techniques. We also performed an analysis of the pulsar's total intensity and polarisation profile to understand the interstellar scattering along the line of sight, and we determined the pulsar's geometry by fitting the rotating vector model to the polarisation data. Results. We obtain precise measurements of several post-Keplerian parameters: the range, r = 0.202(6) T⊙, and shape, s = 0.999823(4), of the Shapiro delay, from which we infer: the orbital inclination to be 88.9−0.14+0.15 deg; the masses of the pulsar and the companion to be 1.55(7) M⊙ and 0.202(6) M⊙, respectively; a secular change in the orbital period Ṗb = −53−6.0+7.4 × 10−15 s s−1 that proves the GC association; and a secular change in the projected semi-major axis of the pulsar, ẋ = −40.7−8.2+7.3 × 10−16 s s−1, likely caused by the spin–orbit interaction from a misaligned HeWD spin, at odds with the likely isolated binary evolution of the system. We also discuss some theoretical models for the structure and evolution of white dwarfs in neutron star–white dwarf binaries, using PSR J1910−5959A's companion as a test bed. Conclusions. PSR J1910−5959A is a rare system for which several parameters of both the pulsar and the HeWD companion can be accurately measured. As such, it is a test bed for discriminating between alternative models of HeWD structure and cooling. [ABSTRACT FROM AUTHOR]

We present the polarization profiles of 22 pulsars in the globular cluster 47 Tucanae using observations from the MeerKAT radio telescope at UHF band (544–1088 MHz) and report precise values of dispersion measure (DM) and rotation measure (RM). We use these measurements to investigate the presence of turbulence in electron density and magnetic fields. The structure function of DM shows a break at ∼30 arcsec (∼0.6 pc at the distance of 47 Tucanae) that suggests the presence of turbulence in the gas in the cluster driven by the motion of wind-shedding stars. On the other hand, the structure function of RM does not show evidence of a break. This non-detection could be explained either by the limited number of pulsars or by the effects of the intervening gas in the Galaxy along the line of sight. Future pulsar discoveries in the cluster could help confirm the presence and localize the turbulence. [ABSTRACT FROM AUTHOR]

We report four new pulsars discovered in the core-collapsed globular cluster (GC) NGC 6624 by the TRAPUM Large Survey Project with the MeerKAT telescope. All of the new pulsars found are isolated. PSR J1823−3021I and PSR J1823−3021K are millisecond pulsars with period of respectively 4.319 and 2.768 ms. PSR J1823−3021J is mildly recycled with a period of 20.899 ms, and PSR J1823−3022 is a long period pulsar with a period of 2.497 s. The pulsars J1823−3021I, J1823−3021J, and J1823−3021K have position and dispersion measure (DM) compatible with being members of the GC and are therefore associated with NGC 6624. Pulsar J1823−3022 is the only pulsar bright enough to be re-detected in archival observations of the cluster. This allowed the determination of a timing solution that spans over two decades. It is not possible at the moment to claim the association of pulsar J1823−3022 with the GC given the long period and large offset in position (∼3 arcmin) and DM (with a fractional difference of 11 percent compared the average of the pulsars in NGC 6624). The discoveries made use of the beamforming capability of the TRAPUM backend to generate multiple beams in the same field of view which allows sensitive searches to be performed over a few half-light radii from the cluster centre and can simultaneously localize the discoveries. The discoveries reflect the properties expected for pulsars in core-collapsed GCs. [ABSTRACT FROM AUTHOR]

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 h of integration time, with an average wait time of about 1 s 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 ± 0.02, and contribute 4 per cent of the total integrated flux. The spectral index of the giant pulses follows a Gaussian distribution centred 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 ± 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 per cent level and circular polarization at the 3 per cent level, similar to the polarization percentages of the total integrated emission. In four cases, it was possible to measure the RM of the GPs that are highly variable and, in two cases, is inconsistent with the mean RM of the total integrated pulsar signal. [ABSTRACT FROM AUTHOR]