arXiv subjects

B. Posselt

Publications and source records attributed to B. Posselt.

At least 19 recordsLinked to original sources

arXiv2026

Understanding the Neutron Star Population with the SKAO Telescopes

The known population of non-accreting neutron stars is ever growing and currently consists of more than 3500 sources. Pulsar surveys with the SKAO telescopes will greatly increase the known population, adding radio pulsars to every subgroup in the radio-loud neutron star family. These discoveries will not only add to the current understanding of neutron star physics by increasing the known sample, but will undoubtedly also uncover new types of sources that will challenge our theories of a wide range of physical phenomena. A broad variety of scientific studies will be made possible by a significantly increased population of neutron stars, unravelling questions such as: How do isolated pulsars evolve with time; What is the connection between magnetars, high B-field pulsars, and the newly discovered long-period pulsars; How is a pulsar's spin-down related to its radio emission; What is the nuclear equation of state? Increasing the numbers of pulsars in binary systems enables both larger numbers and higher precision tests of gravitational theories and general relativity, as well as probing the neutron star mass distribution. The excellent sensitivity of the SKAO telescopes combined with the wide field of view, large numbers of simultaneous tied-array beams that will be searched in real time, wide range of observing frequencies, and the ability to form multiple sub-arrays will make the SKAO an excellent facility for neutron star research. This chapter presents an overview of different types of neutron stars and discusses how the SKAO will aid in our understanding of the neutron star population.

astro-ph.HE↗

arXiv2026

Understanding Pulsar Wind Nebulae with the SKA

Produced by the interaction between the ``pulsar wind'' powered by the rotational energy of a neutron star and its surroundings, the study of pulsar wind nebulae (PWNe) provides vital insight into the physics of neutron star magnetospheres and ultra-relativistic outflows. Spatially-resolved studies of the continuum and polarized radio emission of these sources are vital for understanding the production of $e^\pm$ in the magnetospheres of neutron stars, the acceleration of these particles (and potentially baryons) to $\gtrsim10^{15}~{\rm eV}$ energies, and their propagation within the PWN and in the surrounding interstellar medium. The significant improvements in sensitivity, dynamic range, timing capabilities offered by the Square Kilometer Array have the potential to greatly improve our understanding of the origin of some of the highest energy particles produced in the Milky Way.

astro-ph.HE↗

arXiv2025

Understanding Pulsar Wind Nebulae with the SKA

Produced by the interaction between the ``pulsar wind'' powered by the rotational energy of a neutron star and its surroundings, the study of pulsar wind nebulae (PWNe) provides vital insight into the physics of neutron star magnetospheres and ultra-relativistic outflows. Spatially-resolved studies of the continuum and polarized radio emission of these sources are vital for understanding the production of $e^\pm$ in the magnetospheres of neutron stars, the acceleration of these particles to $\gtrsim10^{15}~{\rm eV}$ energies, and the propagation of these particles within the PWN as well as the surrounding interstellar medium. The significant improvements in sensitivity, dynamic range, timing capabilities offered by the Square Kilometer Array have the potential to significantly improve our understanding of the origin of some of the highest energy particles produced in the Milky Way.

astro-ph.HE↗

arXiv2025

Understanding the Neutron Star Population with the SKAO telescopes

The known population of non-accreting neutron stars is ever growing and currently consists of more than 3500 sources. Pulsar surveys with the SKAO telescopes will greatly increase the known population, adding radio pulsars to every subgroup in the radio-loud neutron star family. These discoveries will not only add to the current understanding of neutron star physics by increasing the sample of sources that can be studied, but will undoubtedly also uncover previously unknown types of sources that will challenge our theories of a wide range of physical phenomena. A broad variety of scientific studies will be made possible by a significantly increased known population of neutron stars, unravelling questions such as: How do isolated pulsars evolve with time; What is the connection between magnetars, high B-field pulsars, and the newly discovered long-period pulsars; How is a pulsar's spin-down related to its radio emission; What is the nuclear equation of state? Increasing the known numbers of pulsars in binary or triple systems may enable both larger numbers and higher precision tests of gravitational theories and general relativity, as well as probing the neutron star mass distribution. The excellent sensitivity of the SKAO telescopes combined with the wide field of view, large numbers of simultaneous tied-array beams that will be searched in real time, wide range of observing frequencies, and the ability to form multiple sub-arrays will make the SKAO an excellent facility to undertake a wide range of neutron star research. In this paper, we give an overview of different types of neutron stars and discuss how the SKAO telescopes will aid in our understanding of the neutron star population.

astro-ph.HE↗

arXiv2025

UVOIR spectrum, X-ray emission, and proper motion of the isolated neutron star RX J2143.0+0654

We observed the isolated neutron star RX J2143.0+0654 with the Hubble Space Telescope (HST) in the UVOIR wavelength range (0.14-1.7 $\mu$m). The UV part is consistent with a Rayleigh-Jeans tail of a thermal spectrum, $f_\nu\propto \nu^2$, while a power-law spectrum, $f_\nu \propto \nu^\alpha$ with $\alpha \sim -0.8$, dominates in the NIR-optical. A joint fit of the UVOIR and contemporaneous X-ray spectra with a two-component blackbody with possible absorption features + power-law optical spectrum yields the following temperature and apparent radius of the colder component (which gives the main contribution in the UV): $kT_{\rm cold}\approx 45$ eV, $R_{\rm cold}\approx 6 d_{260}$ km, where $d_{260}$ is the distance in units of 260 pc. The temperature and radius of the hotter component, $kT_{\rm hot}\approx 106$ eV and $R_{\rm hot} \approx 1.5d_{260}$ km, the parameters of an absorption feature at 0.74 keV, and the properties of X-ray pulsations, are the same as found in previous X-ray observations. In the NIR images the neutron star is possibly surrounded by extended emission with a characteristic size of $\sim 2''$ and flux densities of about 1.7 and 0.9 $\mu$Jy at 1.54 and 1.15 $\mu$m, respectively. Comparison with a previous HST observation in the optical 14 years ago shows a proper motion $\mu\approx 6$ mas yr$^{-1}$, which corresponds to a small transverse velocity of $7d_{260}$ km s$^{-1}$. It is consistent with the hypothesis that the neutron star was born in the vicinity of the solar system about 0.5 Myr ago.

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arXiv2025

A coherent radio burst from an X-ray neutron star in the Carina Nebula

The neutron star zoo comprises several sub-populations that range from energetic magnetars and thermally emitting X-ray neutron stars to radio-emitting pulsars. Despite studies over the last five decades, it has been challenging to obtain a clear physical link between the various populations of neutron stars, vital to constrain their formation and evolutionary pathways. Here we report the detection of a burst of coherent radio emission from a known radio-quiet, thermally emitting neutron star 2XMM J104608.7$-$594306in the Carina Nebula. The burst has a distinctive sharp rise followed by a decay made up of multiple components, which is unlike anything seen from other radio-emitting neutron stars. It suggests an episodic event from the neutron star surface, akin to transient radio emission seen from magnetars. The radio burst confirms that the X-ray source is a neutron star and suggests a new link between these apparently radio-quiet X-ray emitting sources and other transient or persistent radio-emitting neutron stars. It also suggests that a common physical mechanism for emission might operate over a range of magnetic field strengths and neutron star ages. We propose that 2XMM J104608.7$-$594306 straddles the boundary between young, energetic neutron stars and their evolved radio-emitting cousins and may bridge these two populations. The detection of such a radio burst also shows that other radio-quiet neutron stars may also emit such sporadic radio emission that has been missed by previous radio surveys and highlights the need for regular monitoring of this unique sub-population of neutron stars.

astro-ph.HE↗

arXiv2025

The Thousand-Pulsar-Array programme on MeerKAT -- XVI. Mapping the Galactic magnetic field with pulsar observations

Measuring the magnetic field of the Milky Way reveals the structure and evolution of the galaxy. Pulsar rotation measures (RMs) provide a means to probe this Galactic magnetic field (GMF) in three dimensions. We use the largest single-origin data set of pulsar measurements, from the MeerKAT Thousand-Pulsar-Array, to map out GMF components parallel to pulsar lines of sight. We also present these measurements for easy integration into the consolidated RM catalogue, RMTable. Focusing on the Galactic disk, we investigate competing theories of how the GMF relates to the spiral arms, comparing our observational map with five analytic models of magnetic field structure. We also analyse RMs to extragalactic radio sources, to help build up a three-dimensional picture of the magnetic structure of the galaxy. In particular, our large number of measurements allows us to investigate differing magnetic field behaviour in the upper and lower halves of the Galactic plane. We find that the GMF is best explained as following the spiral arms in a roughly bisymmetric structure, with antisymmetric parity with respect to the Galactic plane. This picture is complicated by variations in parity on different spiral arms, and the parity change location appears to be shifted by a distance of 0.15 kpc perpendicular to the Galactic plane. This indicates a complex relationship between the large-scale distributions of matter and magnetic fields in our galaxy. Future pulsar discoveries will help reveal the origins of this relationship with greater precision, as well as probing the locations of local magnetic field inhomogenities.

astro-ph.GA↗

arXiv2025

The middle-aged pulsar PSR J1741-2054 and its bow-shock nebula in far ultraviolet

Context. The nearby middle-aged gamma-ray pulsar J1741-2054 and its pulsar wind nebula (PWN) have been studied in X-rays, and its bow-shock nebula (BSN) has been investigated in the Balmer lines, but they have never been observed in far ultraviolet (FUV). Aims. To further study the thermal and magnetospheric emission from PSR J1741-2054 and the BSN properties, we observed them in the FUV range with the Hubble Space Telescope (HST). Methods. We imaged the target in two FUV filters of the HST's ACS/SBC detector. We also re-analyzed previous optical observations of the pulsar and its BSN. We fit the pulsar's FUV-optical spectrum separately and together with its X-ray spectrum. Results. We found that the pulsar's FUV-optical spectrum consists of a thermal and nonthermal components. A joint fit of the FUV-optical and X-ray spectra with combinations of a nonthermal and thermal components showed a hard optical nonthermal spectrum with a photon index $\Gamma_{opt} \approx 1.0-1.2$ and a softer X-ray component, $\Gamma_X \approx 2.6-2.7$. The thermal emission is dominated by the cold component with the temperature $kT_{cold}\approx 40-50$ eV and emitting sphere radius $R_{cold}\approx 8-15$ km, at $d=270$ pc. An additional hot thermal component, with $kT_{hot}\sim 80$ eV and $R_{hot}\sim 1$ km, is also possible. Such a spectrum resembles the spectra of other middle-aged pulsars, but it shows a harder (softer) optical (X-ray) nonthermal spectrum. We detected the FUV BSN, the first one associated with a middle-aged pulsar. Its closed-shell morphology is similar to the H$\alpha$ BSN morphology, while its FUV flux, $\sim10^{-13}$ erg cm$^{-2}$ s$^{-1}$, is a factor of $\sim 4$ higher than the H$\alpha$ flux. This FUV BSN has a higher surface brightness than the two previously known ones.

astro-ph.HE↗

arXiv2024

The Thousand-Pulsar-Array programme on MeerKAT XV: A comparison of the radio emission properties of slow and millisecond pulsars

We use data from the MeerTime project on the MeerKAT telescope to ask whether the radio emission properties of millisecond pulsars (MSPs) and slowly rotating, younger pulsars (SPs) are similar or different. We show that the flux density spectra of both populations are similarly steep, and the widths of MSP pulsar profiles obey the same dependence on the rotational period as slow pulsars. We also show that the polarization of MSPs has similar properties to slow pulsars. The commonly used pseudo-luminosity of pulsars, defined as the product of the flux density and the distance squared, is not appropriate for drawing conclusions about the relative intrinsic radio luminosity of SPs and MSPs. We show that it is possible to scale the pseudo-luminosity to account for the pulse duty cycle and the solid angle of the radio beam, in such a way that MSPs and SPs do not show clear differences in intrinsic luminosity. The data, therefore, support common emission physics between the two populations in spite of orders of magnitude difference in their period derivatives and inferred, surface, dipole magnetic field strengths.

astro-ph.HE↗

arXiv2024

NICER timing of the X-ray thermal isolated neutron star RX J0806.4--4123

The X-ray thermal isolated neutron star (XTINS) RX J0806.4--4123 shows interesting multiwavelength properties that seemingly deviate from those of similar neutron stars. An accurate determination of the spin frequency change over time can assist in interpreting RX J0806.4-4123's properties in comparison to those of other XTINSs and the wider pulsar population. From 2019 to 2023 we carried out a tailored X-ray timing campaign of RX J0806.4-4123 with the NICER instrument. We used statistical properties of the Fourier coefficients and the $Z_K^2$ test for phase-connecting separate observations and finding a timing solution for the entire dataset. We also developed a simple and universal method for estimating the uncertainties of frequency $\nu$ and its derivative $\dot{\nu}$ from the empirical dependencies of $Z_K^2$ on trial values of these parameters, with account of all significant harmonics of the frequency. Applying this method, we determined a spin-down rate $\dot{\nu} = -7.3(1.2)\times 10^{-17}\,{\rm Hz\, s}^{-1}$. The resulting spin-down power $\dot{E}=2.6\times 10^{29}$ erg s$^{-1}$ is the lowest among the XTINSs, and it is a factor of 60 lower than the X-ray luminosity of this neutron star. RX J0806.4-4123 is also among the pulsars with the lowest measured $\dot{E}$ in general.

astro-ph.HE↗

arXiv2024

Shockingly Bright Warm Carbon Monoxide Molecular Features in the Supernova Remnant Cassiopeia A Revealed by JWST

We present JWST NIRCam (F356W and F444W filters) and MIRI (F770W) images and NIRSpec- IFU spectroscopy of the young supernova remnant Cassiopeia A (Cas A). We obtained the data as part of a JWST survey of Cas A. The NIRCam and MIRI images map the spatial distributions of synchrotron radiation, Ar-rich ejecta, and CO on both large and small scales, revealing remarkably complex structures. The CO emission is stronger at the outer layers than the Ar ejecta, which indicates the reformation of CO molecules behind the reverse shock. NIRSpec-IFU spectra (3 - 5.5 microns) were obtained toward two representative knots in the NE and S fields. Both regions are dominated by the bright fundamental rovibrational band of CO in the two R and P branches, with strong [Ar VI] and relatively weaker, variable strength ejecta lines of [Si IX], [Ca IV], [Ca V] and [Mg IV]. The NIRSpec-IFU data resolve individual ejecta knots and filaments spatially and in velocity space. The fundamental CO band in the JWST spectra reveals unique shapes of CO, showing a few tens of sinusoidal patterns of rovibrational lines with pseudo-continuum underneath, which is attributed to the high-velocity widths of CO lines. The CO also shows high J lines at different vibrational transitions. Our results with LTE modeling of CO emission indicate a temperature of 1080 K and provide unique insight into the correlations between dust, molecules, and highly ionized ejecta in supernovae, and have strong ramifications for modeling dust formation that is led by CO cooling in the early Universe.

astro-ph.GA↗

arXiv2024

The Thousand-Pulsar-Array programme on MeerKAT XIII: Timing, flux density, rotation measure and dispersion measure timeseries of 597 pulsars

We report here on the timing of 597 pulsars over the last four years with the MeerKAT telescope. We provide Times-of-Arrival, pulsar ephemeris files and per-epoch measurements of the flux density, dispersion measure (DM) and rotation measure (RM) for each pulsar. In addition we use a Gaussian process to model the timing residuals to measure the spin frequency derivative at each epoch. We also report the detection of 11 glitches in 9 individual pulsars. We find significant DM and RM variations in 87 and 76 pulsars respectively. We find that the DM variations scale approximately linearly with DM, which is broadly in agreement with models of the ionised interstellar medium. The observed RM variations seem largely independent of DM, which may suggest that the RM variations are dominated by variations in the interstellar magnetic field on the line of sight, rather than varying electron density. We also find that normal pulsars have around 5 times greater amplitude of DM variability compared to millisecond pulsars, and surmise that this is due to the known difference in their velocity distributions.

astro-ph.HE↗

arXiv2024

The Thousand-Pulsar-Array programme on MeerKAT -- XII. Discovery of long-term pulse profile evolution in 7 young pulsars

A number of pulsars are known to have profile evolution on timescales of months, often correlated with spin-down rate changes. Here, we present the first result from 3 years of monitoring observations from MeerKAT as part of the Thousand Pulsar Array programme. This programme obtains high-fidelity pulse profiles for $\sim$ 500 pulsars, which enabled the detection of subtle changes in seven sources not previously known to exhibit long-term profile evolution. A 2D Gaussian convolution is used to highlight correlated emission variability in both the pulse phase and observing epoch direction. Simulations show that for one additional source the observed profile variability is likely to originate from stochastic single-pulse shape variability (jitter). We find that it is common for long-term profile variability to be associated with changes in polarization fractions, but not with polarisation position angle (PA) changes. PA changes are expected if emission height changes or precession is responsible for the profile variability. PSR J1741$-$3927 is the only pulsar in our sample that shows correlated PA variability, and this is associated with orthogonal polarization mode activity. For the six %the rest, without correlated PA variability, other pulsars limits on possible emission height changes and impact angle changes are derived. These limits are consistent with the small changes in the total intensity profile shape. None of the sources show detectable spin-down variability correlated with the emission changes, which are thought to be driven by magnetospheric current fluctuations. Therefore the absence of correlated spin-down rate variability allows upper limits to be placed on changes in the magnetospheric charge density.

astro-ph.HE↗

arXiv2023

X-ray and near-infrared observations of the middle-aged pulsar B1055-52, its multiwavelength spectrum, and proper motion

Previous observations of the middle-aged $\gamma$-ray, X-ray, and radio pulsar B1055-52 indicated some peculiarities, such as a suspected changing of the X-ray flux and spectral parameters, a large excess of the alleged thermal component of the ultraviolet (UV) spectrum over the Rayleigh-Jeans extension of the X-ray thermal spectrum, and a possible double break in the nonthermal spectral component between the optical and X-ray bands. We observed PSR B1055-52 with the XMM-Newton observatory in X-rays and the Hubble Space Telescope in near-infrared (NIR). The analysis of the XMM-Newton observations does not support the notion of long-term changes in the X-ray flux and broad-band X-ray spectrum of the pulsar. Using an observing mode less affected by background noise than the previous XMM-Newton observations, we constrain the power-law (PL) spectral index as $\alpha_X=-0.57^{+0.26}_{-0.25} $ ($F_{\nu} \propto \nu^{\alpha}$) in the energy band 3-10 keV. From the NIR-optical data we obtain a PL slope $\alpha_O= -0.24 \pm 0.10$ for the color index $E(B-V)=0.03$ mag. The slopes and fluxes of the NIR-optical and X-ray nonthermal spectra suggest that the NIR through X-ray emission can be described by the same PL and is generated by the same mechanism, unlike the pulsar's $\gamma$-ray emission. The excess of the UV thermal component over the extension of the X-ray thermal component became smaller but did not disappear, indicating a non-uniformity of the bulk surface temperature. The NIR data also enable us to accurately measure the proper motion with values $\mu_\alpha =47.5\pm 0.7\,{\rm mas\,yr}^{-1}$ and $\mu_\delta = -8.7 \pm 0.7 \,{\rm mas\,yr}^{-1}$.

astro-ph.HE↗

arXiv2023

The Thousand-Pulsar-Array programme on MeerKAT -- VIII. The subpulse modulation of 1198 pulsars

We report on the subpulse modulation properties of 1198 pulsars using the Thousand-Pulsar-Array programme on MeerKAT. About 35% of the analysed pulsars exhibit drifting subpulses which are more pronounced towards the deathline, consistent with previous studies. We estimate that this common phenomenon is detectable in 60% of the overall pulsar population if high quality data were available for all. This large study reveals the evolution of drifting subpulses across the pulsar population in unprecedented detail. In particular, we find that the modulation period $P_3$ follows a V-shaped evolution with respect to the characteristic age $\tau_c$, such that the smallest $P_3$ values, corresponding to the Nyquist period $P_3>\sim2$, are found at $\tau_c>\sim10^{7.5}$ yr. The V-shaped evolution can be interpreted and reproduced if young pulsars possess aliased fast intrinsic $P_3$, which monotonically increase, ultimately achieving a slow unaliased $P_3$. Enhancement of irregularities in intrinsic subpulse modulation by aliasing in small $\tau_c$ pulsars would explain their observed less well defined $P_3$'s and weaker spectral features. Modelling these results as rotating subbeams, their circulation must slow down as the pulsar evolves. This is the opposite to that expected if circulation is driven by ExB drift. This can be resolved if the observed $P_3$ periodicity is due to a beat between an ExB system and the pulsar period. As a by-product, we identify the correct periods and spin-down rates for 12 pulsars, for which harmonically related values were reported in the literature.

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arXiv2022

The Thousand-Pulsar-Array program on MeerKAT -- IX. The time-averaged properties of the observed pulsar population

We present the largest single survey to date of average profiles of radio pulsars, observed and processed using the same telescope and data reduction software. Specifically, we present measurements for 1170 pulsars, observed by the Thousand Pulsar Array (TPA) programme at the 64-dish SARAO MeerKAT radio telescope, in a frequency band from 856 to 1712 MHz. We provide rotation measures (RM), dispersion measures, flux densities and polarization properties. The catalogue includes 254 new RMs that substantially increase the total number of known pulsar RMs. Our integration times typically span over 1000 individual rotations per source. We show that the radio (pseudo)luminosity has a strong, shallow dependence on the spin-down energy, proportional to $\dot{E}^{0.15\pm0.04}$, that contradicts some previous proposals of population synthesis studies. In addition, we find a significant correlation between the steepness of the observed flux density spectra and $\dot{E}$, and correlations of the fractional linear polarization with $\dot{E}$, the spectral index, and the pulse width, which we discuss in the context of what is known about pulsar radio emission and how pulsars evolve with time. On the whole, we do not see significant correlations with the estimated surface magnetic field strength, and the correlations with $\dot{E}$ are much stronger than those with the characteristic age. This finding lends support to the suggestion that magnetic dipole braking may not be the dominant factor for the evolution of pulsar rotation over the lifetimes of pulsars. A public data release of the high-fidelity time-averaged pulse profiles in full polarization accompanies our catalogue.

astro-ph.HE↗

arXiv2022

The Thousand-Pulsar-Array programme on MeerKAT -- X. Scintillation arcs of 107 pulsars

We present the detection of 107 pulsars with interstellar scintillation arcs at 856--1712\,MHz, observed with the MeerKAT Thousand Pulsar Array Programme. Scintillation arcs appear to be ubiquitous in clean, high S/N observations, their detection mainly limited by short observing durations and coarse frequency channel resolution. This led the survey to be sensitive to nearby, lightly scattered pulsars with high effective velocity -- from a large proper motion, a screen nearby the pulsar, or a screen near the Earth. We measure the arc curvatures in all of our sources, which can be used to give an estimate of screen distances in pulsars with known proper motion, or an estimate of the proper motion. The short scintillation timescale in J1731$-$4744 implies a scattering screen within 12\,pc of the source, strongly suggesting the association between this pulsar and the supernova remnant RCW 114. We measure multiple parabolic arcs of 5 pulsars, all of which are weakly scintillating with high proper motion. Additionally, several sources show hints of inverted arclets suggesting scattering from anisotropic screens. Building on this work, further targeted MeerKAT observations of many of these pulsars will improve understanding of our local scattering environment and the origins of scintillation; annual scintillation curves would lead to robust screen distance measurements, and the evolution of arclets in time and frequency can constrain models of scintillation.

astro-ph.HE↗

arXiv2022

The cooling of the Central Compact Object in Cas A from 2006 to 2020

We report on the study of six Chandra observations (four epochs) of the Central Compact Object (CCO) in the Cassiopeia A supernova remnant with the ACIS instrument in the subarray mode. This mode minimizes spectrum-distorting instrumental effects such as pileup. The data were taken over a time span ~ 14 years. If a non-magnetic carbon atmosphere is assumed for this youngest known CCO, then the temperature change is constrained to be $\dot{T}=-2900\pm 600$ K yr$^{-1}$ or $\dot{T}=-4500\pm 800 $ K yr$^{-1}$ ($1\sigma$ uncertainties) for constant or varying absorbing hydrogen column density. These values correspond to cooling rates of $-1.5 \pm 0.3$% per 10yr and $-2.3 \pm 0.4$% per 10yr, respectively. We discuss an apparent increase in the cooling rate in the last five years and the variations of the inferred absorbing hydrogen column densities between epochs. Considered together, these changes could indicate systematic effects such as caused by, e.g., an imperfect calibration of the increasing contamination of the ACIS filter.

astro-ph.HE↗