A. K. Harding
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View article: New and updated timing models for seven young energetic X-ray pulsars, including the Big Glitcher PSR J0537−6910
New and updated timing models for seven young energetic X-ray pulsars, including the Big Glitcher PSR J0537−6910 Open
We present new timing models and update our previous ones for the rotational evolution of seven young energetic pulsars, including four of the top five in spin-down luminosity $\dot{E}$ among all known pulsars. For each of the six pulsars …
View article: Magnetosphere Evolution and Precursor-driven Electromagnetic Signals in Merging Binary Neutron Stars
Magnetosphere Evolution and Precursor-driven Electromagnetic Signals in Merging Binary Neutron Stars Open
We detail new force-free simulations to investigate magnetosphere evolution and precursor electromagnetic (EM) signals from binary neutron stars. Our simulations fully follow a representative inspiral motion, capturing the intricate magnet…
View article: Monte Carlo Simulations of Polarized Radiative Transfer in Neutron Star Atmospheres
Monte Carlo Simulations of Polarized Radiative Transfer in Neutron Star Atmospheres Open
Soft X-ray emission from neutron stars affords powerful diagnostic tools for uncovering their surface and interior properties, as well as their geometric configurations. In the atmospheres of neutron stars, the presence of magnetic fields …
View article: Pair Cascades in Magnetar Magnetospheres
Pair Cascades in Magnetar Magnetospheres Open
Resonant inverse Compton scattering (RICS) of soft thermal photons by relativistic particles on closed magnetic field loops has been proposed to explain the hard emission observed up to and beyond 200 keV from magnetars. If particles injec…
View article: Pioneering High-speed Pulsar Parameter Estimation Using Convolutional Neural Networks
Pioneering High-speed Pulsar Parameter Estimation Using Convolutional Neural Networks Open
Accurate thermal emission models of neutron stars are essential for constraining the dense matter equation of state. However, incorporating realistic magnetic field structures is computationally prohibitive, severely constraining feasible …
View article: A Systematic Search for MeV–GeV Pulsar Wind Nebulae without Gamma-Ray Detected Pulsars
A Systematic Search for MeV–GeV Pulsar Wind Nebulae without Gamma-Ray Detected Pulsars Open
An increasing number of pulsar wind nebulae (PWNe) are being identified in the TeV band by ground-based Imaging Air Cherenkov Telescopes such that they constitute the dominant source class of Galactic TeV emitters. However, MeV–GeV PWN cou…
View article: Timing and Spectral Evolution of the Magnetar 1E 1841-045 in Outburst
Timing and Spectral Evolution of the Magnetar 1E 1841-045 in Outburst Open
We present timing and spectral analyses of Neutron star Interior Composition Explorer (NICER), Nuclear Spectroscopic Telescope Array (NuSTAR), and IXPE observations of the magnetar 1E 1841−045 covering 82 days following its 2024 August bur…
View article: Towards modelling AR Sco: calibration – reproducing high-energy pulsar emission and testing convergence to Aristotelian electrodynamics
Towards modelling AR Sco: calibration – reproducing high-energy pulsar emission and testing convergence to Aristotelian electrodynamics Open
In recent years, kinetic simulations have been crucial to further our understanding of pulsar electrodynamics. Yet, due to the large-scale separation between the gyro-period and the stellar rotation period, resolving the particle gyration …
View article: X-Ray Polarization of the Magnetar 1E 1841−045
X-Ray Polarization of the Magnetar 1E 1841−045 Open
We report on IXPE and NuSTAR observations beginning 40 days after the 2024 outburst onset of magnetar 1E 1841−045, marking the first IXPE observation of a magnetar in an enhanced state. Our spectropolarimetric analysis indicates that both …
View article: Pioneering High-Speed Pulsar Parameter Estimation Using Convolutional Neural Networks
Pioneering High-Speed Pulsar Parameter Estimation Using Convolutional Neural Networks Open
Accurate thermal emission models of neutron stars are essential for constraining the dense matter equation of state. However, incorporating realistic magnetic field structures is computationally prohibitive, severely constraining feasible …
View article: X-ray polarization of the magnetar 1E 1841-045
X-ray polarization of the magnetar 1E 1841-045 Open
We report on IXPE and NuSTAR observations beginning forty days after the 2024 outburst onset of magnetar 1E 1841-045, marking the first IXPE observation of a magnetar in an enhanced state. Our spectropolarimetric analysis indicates that bo…
View article: Towards modelling AR Sco: generalized particle dynamics and strong radiation-reaction regimes
Towards modelling AR Sco: generalized particle dynamics and strong radiation-reaction regimes Open
Numerical simulations of relativistic plasmas have become more feasible, popular, and crucial for various astrophysical sources with the availability of computational resources. The necessity for high-accuracy particle dynamics is especial…
View article: A phase-resolved Fermi-LAT analysis of the mode-changing pulsar PSR J2021+4026 shows hints of a multipolar magnetosphere
A phase-resolved Fermi-LAT analysis of the mode-changing pulsar PSR J2021+4026 shows hints of a multipolar magnetosphere Open
The goal of our work is to study the mode changes of the radio-quiet gamma-ray pulsar PSR J2021+4026 with improved detail. By accurately characterizing variations in the gamma-ray spectrum and pulse profile, we aim to relate the Fermi-LAT …
View article: A phase-resolved<i>Fermi</i>-LAT analysis of the mode-changing pulsar PSR J2021+4026 shows hints of a multipolar magnetosphere
A phase-resolved<i>Fermi</i>-LAT analysis of the mode-changing pulsar PSR J2021+4026 shows hints of a multipolar magnetosphere Open
Context. The radio-quiet γ -ray pulsar PSR J2021+4026 is a peculiar Fermi -LAT pulsar showing repeated and quasi-periodic mode changes. Its γ -ray flux shows repeated variations between two states at intervals of ∼3.5 years. These events o…
View article: The invisible black widow PSR J1720−0534: implications for the electron density towards the North Polar Spur
The invisible black widow PSR J1720−0534: implications for the electron density towards the North Polar Spur Open
Radio emission from pulsars can be used to map out their distances through dispersion measure (DM), which quantifies the amount of radio pulse dispersion. However, this method relies on accurately modelling the free electron density in the…
View article: The invisible black widow PSR J1720-0534: implications for the electron density towards the North Polar Spur
The invisible black widow PSR J1720-0534: implications for the electron density towards the North Polar Spur Open
Radio emission from pulsars can be used to map out their distances through dispersion measure (DM), which quantifies the amount of radio pulse dispersion. However, this method relies on accurately modelling the free electron density in the…
View article: The high energy X-ray probe (HEX-P): magnetars and other isolated neutron stars
The high energy X-ray probe (HEX-P): magnetars and other isolated neutron stars Open
The hard X-ray emission from magnetars and other isolated neutron stars remains under-explored. An instrument with higher sensitivity to hard X-rays is critical to understanding the physics of neutron star magnetospheres and also the relat…
View article: The Third Fermi Large Area Telescope Catalog of Gamma-Ray Pulsars
The Third Fermi Large Area Telescope Catalog of Gamma-Ray Pulsars Open
We present 294 pulsars found in GeV data from the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope. Another 33 millisecond pulsars (MSPs) discovered in deep radio searches of LAT sources will likely reveal pulsations once …
View article: The High Energy X-ray Probe (HEX-P): Magnetars and Other Isolated Neutron Stars
The High Energy X-ray Probe (HEX-P): Magnetars and Other Isolated Neutron Stars Open
The hard X-ray emission from magnetars and other isolated neutron stars remains under-explored. An instrument with higher sensitivity to hard X-rays is critical to understanding the physics of neutron star magnetospheres and also the relat…
View article: Modelling the Multi-Wavelength Non-thermal Emission of AR Sco.
Modelling the Multi-Wavelength Non-thermal Emission of AR Sco. Open
AR Scorpii (AR Sco) is an intriguing binary system that contains both a white and red dwarf. The spin rate of the white dwarf has been observed to slow down with time, analogous to the case of rotation-powered radio pulsars; it has thus be…
View article: Broadband Spectral Modelling of the Galactic Globular Cluster 47 Tucanae
Broadband Spectral Modelling of the Galactic Globular Cluster 47 Tucanae Open
Terzan 5 is the only Galactic globular cluster that has plausibly been detected at very-high energies (VHEs; E > 100 GeV) by H.E.S.S., with 47 Tucanae (47 Tuc) being the densest and a very promising source in the Southern hemisphere for po…
View article: The Gamma-Ray Pulsar Phenomenology in View of 3D Kinetic Global Magnetosphere Models
The Gamma-Ray Pulsar Phenomenology in View of 3D Kinetic Global Magnetosphere Models Open
We develop kinetic plasma models of pulsar magnetospheres with magnetic-field-line-dependent plasma injection that reveal the importance of various magnetosphere regions in regulating the γ -ray emission. We set different particle injectio…
View article: Erratum: “Probing the Pulsar Population of Terzan 5 via Spectral Modeling” (2019, ApJ, 880, 53)
Erratum: “Probing the Pulsar Population of Terzan 5 via Spectral Modeling” (2019, ApJ, 880, 53) Open
Erratum: "Probing the Pulsar Population of Terzan 5 via Spectral Modeling" (2019, ApJ, 880, 53), H. Ndiyavala, C. Venter, T. J. Johnson, A. K. Harding, D. A. Smith, (Fermi Large Area Telescope (LAT)), P. Eger, A. Kopp, D. J. van der Walt
View article: Multiwavelength observations of PSR J2021+4026 across a mode change reveal a phase shift in its X-ray emission
Multiwavelength observations of PSR J2021+4026 across a mode change reveal a phase shift in its X-ray emission Open
Context. We have investigated the multiwavelength emission of PSR J2021+4026, the only isolated gamma-ray pulsar known to be variable, which in October 2011 underwent a simultaneous change in gamma-ray flux and spin-down rate, followed by …
View article: A NICER View on the 2020 Magnetar-like Outburst of PSR J1846−0258
A NICER View on the 2020 Magnetar-like Outburst of PSR J1846−0258 Open
We report on our monitoring of the strong-field magnetar-like pulsar PSR J1846−0258 with the Neutron Star Interior Composition Explorer (NICER) and the timing and spectral evolution during its outburst in 2020 August. Phase-coherent timing…
View article: Multiwavelength observations of PSR J2021+4026 across a mode change reveal a phase shift in its X-ray emission
Multiwavelength observations of PSR J2021+4026 across a mode change reveal a phase shift in its X-ray emission Open
Context. We have investigated the multiwavelength emission of PSR J2021+4026, the only isolated γ -ray pulsar known to be variable, which in October 2011 underwent a simultaneous change in γ -ray flux and spin-down rate, followed by a seco…
View article: Pulsar timing for the <i><b>Fermi</b></i> gamma-ray space telescope
Pulsar timing for the <i><b>Fermi</b></i> gamma-ray space telescope Open
Here, we describe a comprehensive pulsar monitoring campaign for the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope (formerly GLAST). The detection and study of pulsars in gamma rays give insights into the populations of…