The challenges of detecting and localising Fast Radio Bursts in real time can be met with the use of Phased Array Feeds. One such system, capable of creating up to 36 simultaneous beams, is currently ...being commissioned at the Effelsberg radio telescope in Germany following testing at the 64 m Parkes radio telescope. The PAFINDER (Phased Array Feed FRB Finder) pipeline will be used with this receiver to enable real–time single–pulse detection and localisation.
Large-scale beamforming with radio interferometers has the potential to revolutionize the science done with pulsars and fast radio bursts by improving the survey efficiency for these sources. We ...describe a wide-field beamformer for the MeerKAT radio telescope and outline strategies to optimally design such surveys. A software implementation of these techniques, \({\rm M{\small OSAIC}}\) is introduced and its application in the MeerKAT telescope is presented. We show initial results using the beamformer by observing a globular cluster to track several pulsars simultaneously and demonstrate the source localization capability of this observation.
Magnetars are highly-magnetised rotating neutron stars that are predominantly observed as high-energy sources. Six of this class of neutron star are known to also emit radio emission, and magnetars ...are, thus, a favoured model for the origin for at least some of the Fast Radio Bursts (FRBs). If magnetars, or neutron stars in general, are indeed responsible, sharp empirical constraints on the mechanism producing radio emission are required. Here we report on the detection of polarised quasi-periodic sub-structure in the emission of all well-studied radio-detected magnetars. A correlation previously seen, relating sub-structure in pulsed emission of radio emitting neutron stars to their rotational period, is extended, and shown to now span more than six of orders of magnitude in pulse period. This behaviour is not only seen in magnetars but in members of all classes of radio-emitting rotating neutron stars, regardless of their evolutionary history, their power source or their inferred magnetic field strength. If magnetars are responsible for FRBs, it supports the idea of being able to infer underlying periods from sub-burst timescales in FRBs.
The shape and polarisation properties of the radio pulse profiles of radio-loud magnetars provide a unique opportunity to investigate their magnetospheric properties. Gaussian Process Regression ...analysis was used to investigate the variation in the total intensity shape of the radio pulse profiles of the magnetar Swift J1818.0-1607. The observed profile shape was found to evolve through three modes between MJDs 59104 and 59365. The times at which these transitions occurred coincided with changes in the amplitude of modulations in the spin-down rate. The amount of linear and circular polarisation was also found to vary significantly with time. Lomb-Scargle periodogram analysis of the spin-down rate revealed three possibly harmonically related frequencies. This could point to the magnetar experiencing seismic activity. However, no profile features exhibited significant periodicity, suggesting no simple correlations between the profile variability and fluctuations of the spin-down on shorter timescales within the modes. Overall, this implies the mode changes seen are a result of local magnetospheric changes, with other theories, such as precession, less able to explain these observations.
BlackHoleCam is a project funded by a European Research Council Synergy Grant to build a complete astrophysical description of nearby supermassive black holes by using a combination of radio imaging, ...pulsar observations, stellar astrometry and general relativistic magneto-hydrodynamic models. BlackHoleCam scientists are active partners of the Event Horizon Telescope Consortium. In this talk I will discuss the use of pulsars orbiting Sagittarius A* for tests of General Relativity, the current difficulties in detecting such sources, recent results from the Galactic Centre magnetar PSR J1745-2900 and how BlackHoleCam aims to search for undiscovered pulsars in the Galactic Centre.
Propagation effects are one of the main sources of noise in high-precision
pulsar timing. For pulsars below an ecliptic latitude of $5^\circ$, the ionised
plasma in the solar wind can introduce ...dispersive delays of order 100
microseconds around solar conjunction at an observing frequency of 300 MHz. A
common approach to mitigate this assumes a spherical solar wind with a
time-constant amplitude. However, this has been shown to be insufficient to
describe the solar wind. We present a linear, Gaussian-process piecewise
Bayesian approach to fit a spherical solar wind of time-variable amplitude,
which has been implemented in the pulsar software run_enterprise. Through
simulations, we find that the current EPTA+InPTA data combination is not
sensitive to such variations; however, solar wind variations will become
important in the near future with the addition of new InPTA data and data
collected with the low-frequency LOFAR telescope. We also compare our results
for different high-precision timing datasets (EPTA+InPTA, PPTA, and LOFAR) of
three millisecond pulsars (J0030$+$0451, J1022$+$1001, J2145$-$0450), and find
that the solar-wind amplitudes are generally consistent for any individual
pulsar, but they can vary from pulsar to pulsar. Finally, we compare our
results with those of an independent method on the same LOFAR data of the three
millisecond pulsars. We find that differences between the results of the two
methods can be mainly attributed to the modelling of dispersion variations in
the interstellar medium, rather than the solar wind modelling.
Millisecond pulsars in timing arrays can act as probes for gravitational wave detection and improving the solar system ephemerides among several other applications. However, the stability of the ...integrated pulse profiles can limit the precision of the ephemeris parameters and in turn the applications derived from it. It is thus crucial for the pulsars in the array to have stable integrated pulse profiles. Here we present evidence for long-term profile instability in PSR J1022+1001 which is currently included in the European and Parkes pulsar timing arrays. We apply a new evaluation method to an expanded data set ranging from the Effelsberg Pulsar Observing System back-end used in the 1990s to that of data from the current PSRIX backend at the Effelsberg Radio Telescope. We show that this intrinsic variability in the pulse shape persists over time scales of years. We investigate if systematic instrumental effects like polarisation calibration or signal propagation effects in the interstellar medium causes the observed profile instability. We find that the total variation cannot be fully accounted for by instrumental and propagation effects. This suggests additional intrinsic effects as the origin for the variation. We finally discuss several factors that could lead to the observed behaviour and comment on the consequent implications.
Interstellar scintillation analysis of pulsars allows us to probe the small-scale distribution and inhomogeneities of the ionized interstellar medium. Our priority is to present the data set and the ...basic measurements of scintillation parameters of pulsars employing long-term scintillation observations carried out from 2011 January to 2020 August by the European Pulsar Timing Array radio telescopes in the 21-cm and 11-cm bands. Additionally, we aim to identify future possible lines of study using this long-term scintillation dataset. We present the long-term time series of \(\nu_{\rm d}\) and \(\tau_{\rm d}\) for 13 pulsars. Sanity-checks and comparisons indicate that the scintillation parameters of our work and previously published works are mostly consistent. For two pulsars, PSRs~J1857+0943 and J1939+2134, we were able to obtain measurements of the \(\nu_{\rm d}\) at both bands, which allows us to derive the time series of frequency scaling indices with a mean and a standard deviation of 2.82\(\pm\)1.95 and 3.18\(\pm\)0.60, respectively. We found some interesting features which will be studied in more detail in subsequent papers in this series: (i) in the time series of PSR~J1939+2134, where the scintillation bandwidth sharply increases or decreases associated with a sharp change of dispersion measure; (ii) PSR~J0613\(-\)0200 and PSR~J0636+5126 show a strong annual variation in the time series of the \(\tau_{\rm d}\); (iii) PSR~J1939+2134 shows a weak anti-correlation between scintillation timescale and dispersion in WSRT data.
Pulsars in the Galactic centre promise to enable unparalleled tests of gravity theories and black hole physics and to serve as probes of the stellar formation history and evolution and the ...interstellar medium in the complex central region of the Milky Way. The community has surveyed the innermost region of the galaxy for decades without detecting a population of pulsars, which is puzzling. A strong scattering of the pulsed signals in this particular direction has been argued to be a potential reason for the non-detections. Scattering has a strong inverse dependence on observing frequency, therefore an effective way to alleviate its effect is to use higher frequencies in a survey for pulsars in the Galactic centre, in particular, close to the supermassive black hole Sagittarius A*. We present the first pulsar survey at short millimetre wavelengths, using several frequency bands between 84 and 156 GHz (3.57-1.92 mm), targeted to the Galactic centre. The observations were made with the Institut de Radioastronomie Millimetrique (IRAM) 30m Telescope in 28 epochs between 2016 December and 2018 May. This survey is the first that is essentially unaffected by scattering and therefore unbiased in population coverage, including fast-spinning pulsars that might be out of reach of lower-frequency Galactic centre surveys. We discovered no new pulsars and relate this result mainly to the decreased flux density of pulsars at high frequencies, combined with our current sensitivity. However, we demonstrate that surveys at these extremely high radio frequencies are capable of discovering new pulsars, analyse their sensitivity limits with respect to a simulated Galactic centre pulsar population, and discuss the main challenges and possible improvements for similar surveys in the future.
We report the discovery of two Black Widow millisecond pulsars in the globular cluster M28 with the MeerKAT telescope. PSR J1824\(-\)2452M (M28M) is a 4.78-ms pulsar in a \(5.82\,\)hour orbit and PSR ...J1824\(-\)2452N (M28N) is a 3.35-ms pulsar in a \(4.76\,\)hour orbit. Both pulsars have dispersion measures near \(119.30\,\)pc\(\,\)cm\(^{-3}\) and have low mass companion stars ($\sim$$0.01-0.03\,\(M\)_\odot$), which do not cause strong radio eclipses or orbital variations. Including these systems, there are now five known black widow pulsars in M28. The pulsar searches were conducted as a part of an initial phase of MeerKAT's globular cluster census (within the TRAPUM Large Survey Project). These faint discoveries demonstrate the advantages of MeerKAT's survey sensitivity over previous searches and we expect to find additional pulsars in continued searches of this cluster.
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