Pulsar PSR J1023 Research Articles

Exploring Pulsar Timing Precision: A Comparative Study of Polarization Calibration Methods for NANOGrav Data from the Green Bank Telescope

Pulsar timing array experiments have recently uncovered evidence for a nanohertz gravitational wave background by precisely timing an ensemble of millisecond pulsars. The next significant milestones for these experiments include characterizing the detected background with greater precision, identifying its source(s), and detecting continuous gravitational waves from individual supermassive black hole binaries. To achieve these objectives, generating accurate and precise times of arrival of pulses from pulsar observations is crucial. Incorrect polarization calibration of the observed pulsar profiles may introduce errors in the measured times of arrival. Further, previous studies have demonstrated that robust polarization calibration of pulsar profiles can reduce noise in the pulsar timing data and improve timing solutions. In this paper, we investigate and compare the impact of different polarization calibration methods on pulsar timing precision using three distinct calibration techniques: the Ideal Feed Assumption (IFA), Measurement Equation Modeling (MEM), and Measurement Equation Template Matching (METM). Three NANOGrav pulsars—PSRs J1643−1224, J1744−1134, and J1909−3744—observed with the 800 MHz and 1.5 GHz receivers at the Green Bank Telescope (GBT) are utilized for our analysis. Our findings reveal that all three calibration methods enhance timing precision compared to scenarios where no polarization calibration is performed. Additionally, among the three calibration methods, the IFA approach generally provides the best results for timing analysis of pulsars observed with the GBT receiver system. We attribute the comparatively poorer performance of the MEM and METM methods to potential instabilities in the reference noise diode coupled to the receiver and temporal variations in the profile of the reference pulsar, respectively.

Constraining the Dense Matter Equation of State with New NICER Mass–Radius Measurements and New Chiral Effective Field Theory Inputs

Pulse profile modeling of X-ray data from the Neutron Star Interior Composition Explorer is now enabling precision inference of neutron star mass and radius. Combined with nuclear physics constraints from chiral effective field theory (χEFT), and masses and tidal deformabilities inferred from gravitational-wave detections of binary neutron star mergers, this has led to a steady improvement in our understanding of the dense matter equation of state (EOS). Here, we consider the impact of several new results: the radius measurement for the 1.42 M ⊙ pulsar PSR J0437−4715 presented by Choudhury et al., updates to the masses and radii of PSR J0740+6620 and PSR J0030+0451, and new χEFT results for neutron star matter up to 1.5 times nuclear saturation density. Using two different high-density EOS extensions—a piecewise-polytropic (PP) model and a model based on the speed of sound in a neutron star (CS)—we find the radius of a 1.4 M ⊙ (2.0 M ⊙) neutron star to be constrained to the 95% credible ranges 12.28−0.76+0.50 km ( 12.33−1.34+0.70 km) for the PP model and 12.01−0.75+0.56 km ( 11.55−1.09+0.94 km) for the CS model. The maximum neutron star mass is predicted to be 2.15−0.16+0.14 M ⊙ and 2.08−0.16+0.28 M ⊙ for the PP and CS models, respectively. We explore the sensitivity of our results to different orders and different densities up to which χEFT is used, and show how the astrophysical observations provide constraints for the pressure at intermediate densities. Moreover, we investigate the difference R 2.0 − R 1.4 of the radius of 2 M ⊙ and 1.4 M ⊙ neutron stars within our EOS inference.

The Green Bank 820 MHz Pulsar Survey. I. Survey Overview and Initial Results

The Green Bank 820 MHz pulsar survey covers ≃173 deg2 in the Cygnus X region of the Galaxy, centered on l = 84.°5 and b = 1.°5. Significant star formation is present in this region, and lines of sight pass through three arms of the Galaxy (Orion–Cygnus, Perseus, and an outer arm). Using the Green Bank Telescope, we recorded 200 MHz of bandwidth for 4.5 minutes at 81.92 μs resolution for each of 3457 observed survey pointings during 2016 and 2017, covering about two-thirds of the total area. We searched these data for pulsars and report the discovery of six new pulsars—PSRs J2016+3820, J2016+4231, J2019+3810, J2035+3538, J2035+3655, and J2041+4551—and the codiscovery of PSR J2057+4701. PSR J2035+3655 is in a short (4.5 hr) binary orbit; we report the full binary solution and weakly constrain the mass of the pulsar via a marginal (2σ) detection of the Shapiro delay. We also searched the survey data for known pulsars to estimate the survey’s sensitivity and measured 820 MHz pulse widths and flux density for 20 detected sources. For sources that were also detected in the Green Bank North Celestial Cap survey at 350 MHz, we measure scattering parameters and compare to expectations for the region. With these results, we revisit the population estimates that motivated this survey and consider the impact of the survey’s yield on their underlying models. We note an apparent underestimate in dispersion measure predictions from typical Galactic electron density models in the survey region, and discuss future observation strategies.

A phase-resolvedFermi-LAT analysis of the mode-changing pulsar PSR J2021+4026 shows hints of a multipolar magnetosphere

Context.The radio-quietγ-ray pulsar PSR J2021+4026 is a peculiarFermi-LAT pulsar showing repeated and quasi-periodic mode changes. Itsγ-ray flux shows repeated variations between two states at intervals of ∼3.5 years. These events occur over timescales < 100 days and are correlated with sudden changes in the spin-down rate. Multiwavelength observations also revealed an X-ray phase shift relative to theγ-ray profile for one of the events. PSR J2021+4026 is currently the only known isolatedγ-ray pulsar showing significant variability, and thus it has been the object of thorough investigations.Aims.The goal of our work is to study the mode changes of PSR J2021+4026 with improved detail. By accurately characterizing variations in theγ-ray spectrum and pulse profile, we aim to relate theFermi-LAT observations to theoretical models. We also aim to interpret the mode changes in terms of variations in the structure of a multipolar dissipative magnetosphere.Methods.We continually monitored the rotational evolution and theγ-ray flux of PSR J2021+4026 using more than 13 years ofFermi-LAT data with a binned likelihood approach. We investigated the features of the phase-resolved spectrum and pulse profile, and from these we inferred the macroscopic conductivity, the electric field parallel to the magnetic field, and the curvature radiation cutoff energy. These physical quantities are related to the spin-down rate and theγ-ray flux and therefore are relevant to the theoretical interpretation of the mode changes. We introduced a simple magnetosphere model that combines a dipole field with a strong quadrupole component. We simulated magnetic field configurations to determine the positions of the polar caps for different sets of parameters.Results.We clearly detect the previous mode changes and confirm a more recent mode change that occurred around June 2020. We provide a full set of best-fit parameters for the phase-resolvedγ-ray spectrum and the pulse profile obtained in five distinct time intervals. We computed the relative variations in the best-fit parameters, finding typical flux changes between 13% and 20%. Correlations appear between theγ-ray flux and the spectral parameters, as the peak of the spectrum shifts by ∼10% toward lower energies when the flux decreases. The analysis of the pulse profile reveals that the pulsed fraction of the light curve is larger when the flux is low. Finally, the magnetosphere simulations show that some configurations could explain the observed multiwavelength variability. However, self-consistent models are required to reproduce the observed magnitudes of the mode changes.

Properties of PSR J1023+0038 Based on Kepler, TESS, and FAST

The pulsar system PSR J1023+0038 is a very interesting binary with radio millisecond pulsar and low-mass X-ray binary transitions, which depend on the stellar accretion process. We have used Kepler light curves with 1 minute cadence and TESS light curves with 2 minute cadence to study the flare properties of PSR J1023+0038. We detected 516 flare events in the K2 data and 84 flare events in the TESS survey data. We determined the flare rise and delay times, the flare durations and amplitudes, and flare energies. We obtained a value of the power-law index of 0.359 ± 0.023 between the flare energies and decay times, which is similar to the theoretically predicted value of 1/3. This in turn indicates that PSR J1023+0038 might be exhibiting physical mechanisms described by magnetic reconnection theory. Using the maximum likelihood estimation method, we also calculated the power-law index of the cumulative flare frequency distribution, finding 1.87 ± 0.27 for the Kepler data and 1.74 ± 0.29 for the TESS data. Meanwhile, we reduced six FAST observations of PSR J1023+0038 from 2019–2021 using a standard pulsar search procedure. We report that we detected a prompt signal with a period compatible with that found in previous observations of PSR J1023+0038. However, there are several reasons (statistical, excess DM, pulse shape, etc.) as to why the association is not likely.

Constraining the magnetic field geometry of the millisecond pulsar PSR J0030+0451 from joint radio, thermal X-ray, andγ-ray emission

Context.With the advent of multi-wavelength electromagnetic observations of neutron stars – spanning many decades in photon energies – from radio wavelengths up to X-rays andγ-rays, it has become possible to significantly constrain the geometry and the location of the associated emission regions.Aims.In this work, we use results from the modelling of thermal X-ray observations of PSR J0030+0451 from the Neutron Star Interior Composition Explorer (NICER) mission and phase-aligned radio andγ-ray pulse profiles to constrain the geometry of an off-centred dipole that is able to reproduce the light curves in these respective bands simultaneously.Methods.To this aim, we deduced a configuration with a simple dipole off-centred from the location of the centre of the thermal X-ray hot spots. We show that the geometry is compatible with independent constraints from radio andγ-ray pulsations only, leading to a fixed magnetic obliquity ofα ≈ 75° and a line-of-sight inclination angle ofζ ≈ 54°.Results.We demonstrate that an off-centred dipole cannot be rejected by accounting for the thermal X-ray pulse profiles. Moreover, the crescent shape of one spot is interpreted as the consequence of a small-scale surface dipole on top of the large-scale off-centred dipole.

New Insights on 30 Dor B Revealed by High-quality Multiwavelength Observations

The supernova remnant (SNR) 30 Dor B is associated with the H ii region ionized by the OB association LH99. The complex interstellar environment has made it difficult to study the physical structure of this SNR. We have used Hubble Space Telescope Hα images to identify SNR shocks and deep Chandra X-ray observations to detect faint diffuse emission. We find that 30 Dor B hosts three zones with very different X-ray surface brightnesses and nebular kinematics that are characteristic of SNRs in different interstellar environments and/or evolutionary stages. The ASKAP 888 MHz map of 30 Dor B shows counterparts to all X-ray emission features except the faint halo. The ASKAP 888 and 1420 MHz observations are used to produce a spectral index map, but its interpretation is complicated by the background thermal emission and the pulsar PSR J0537−6910's flat spectral index. The stellar population in the vicinity of 30 Dor B indicates a continuous star formation in the past 8–10 Myr. The observed very massive stars in LH99 cannot be coeval with the progenitor of 30 Dor B’s pulsar. Adopting the pulsar’s spin-down timescale, 5000 yr, as the age of the SNR, the X-ray shell would be expanding at ∼4000 km s−1 and the post-shock temperature would be 1–2 orders of magnitude higher than that indicated by the X-ray spectra. Thus, the bright central region of 30 Dor B and the X-ray shell requires two separate SN events, and the faint diffuse X-ray halo perhaps other older SN events.

Matter ejections behind the highs and lows of the transitional millisecond pulsar PSR J1023+0038

Transitional millisecond pulsars are an emerging class of sources that link low-mass X-ray binaries to millisecond radio pulsars in binary systems. These pulsars alternate between a radio pulsar state and an active low-luminosity X-ray disc state. During the active state, these sources exhibit two distinct emission modes (high and low) that alternate unpredictably, abruptly, and incessantly. X-ray to optical pulsations are observed only during the high mode. The root cause of this puzzling behaviour remains elusive. This paper presents the results of the most extensive multi-wavelength campaign ever conducted on the transitional pulsar prototype, PSR J1023+0038, covering from the radio to X-rays. The campaign was carried out over two nights in June 2021 and involved 12 different telescopes and instruments, including XMM-Newton, HST, VLT/FORS2 (in polarimetric mode), ALMA, VLA, and FAST. By modelling the broadband spectral energy distributions in both emission modes, we show that the mode switches are caused by changes in the innermost region of the accretion disc. These changes trigger the emission of discrete mass ejections, which occur on top of a compact jet, as testified by the detection of at least one short-duration millimetre flare with ALMA at the high-to-low mode switch. The pulsar is subsequently re-enshrouded, completing our picture of the mode switches.

A renewed search for radio emission from the variable γ-ray pulsar PSR J2021+4026

ABSTRACT We undertake the first targeted search at 1.5 GHz for radio emission from the variable γ-ray pulsar PSR J2021+4026. This radio-quiet pulsar assumes one of two stable γ-ray emission states, between which it transitions on a time-scale of years. These transitions, in both γ-ray flux and pulse profile shape, are accompanied by contemporaneous changes to the pulsar’s spin-down rate. A number of radio pulsars are known to exhibit similar correlated variability, which in some cases involves an emission state in which the radio emission ceases to be detectable. In this paper, we perform a search for radio emission from PSR J2021+4026, using archival radio observations recorded when the pulsar was in each of its emission/spin-down states. Using improved techniques, we search for periodic radio emission as well as single pulse phenomena such as giant radio pulses and RRAT-like emission. Our search reveals no evidence of radio emission from PSR J2021+4026. We estimate that the flux density for periodic emission from PSR J2021+4026 does not exceed 0.2 mJy at this frequency. We also estimate single-pulse flux limits for RRAT-like bursts and giant radio pulses to be 0.3 and 100 Jy, respectively. We discuss the transitioning behaviour of PSR J2021+4026 in the context of pulsar glitches, intermittent pulsars and the increasingly common emission-rotation correlation observed in radio pulsars.

Investigating the origin of optical and X-ray pulsations of the transitional millisecond pulsar PSR J1023+0038

Context. PSR J1023+0038 is the first millisecond pulsar that was ever observed as an optical and UV pulsar. So far, it is the only optical transitional millisecond pulsar. The rotation- and accretion-powered emission mechanisms hardly individually explain the observed characteristics of optical pulsations. A synergistic model, combining these standard emission processes, was proposed to explain the origin of the X-ray/UV/optical pulsations. Aims. We study the phase lag between the pulses in the optical and X-ray bands to gain insight into the physical mechanisms that cause it. Methods. We performed a detailed timing analysis of simultaneous or quasi-simultaneous observations in the X-ray band, acquired with the XMM-Newton and NICER satellites, and in the optical band, with the fast photometers SiFAP2 (mounted at the 3.6 m Telescopio Nazionale Galileo) and Aqueye+ (mounted at the 1.8 m Copernicus Telescope). We estimated the time lag of the optical pulsation with respect to that in the X-rays by modeling the folded pulse profiles with two harmonic components. Results. Optical pulses lag the X-ray pulses by ∼150 μs in observations acquired with instruments (NICER and Aqueye+) whose absolute timing uncertainty is much smaller than the measured lag. We also show that the phase lag between optical and X-ray pulsations lies in a limited range of values, δϕ ∈ (0 − 0.15), which is maintained over timescales of about five years. This indicates that both pulsations originate from the same region, and it supports the hypothesis of a common emission mechanism. Our results are interpreted in the shock-driven mini pulsar nebula scenario. This scenario suggests that optical and X-ray pulses are produced by synchrotron emission from the shock that formed within a few light cylinder radii away (∼100 km) from the pulsar, where its striped wind encounters the accretion disk inflow.

Compact star coupled with dark energy in the background of Tolman–Kuchowicz spacetime

This paper provides a simplified description for simulating the coupling of dark energy with baryonic matter by considering a super-dense pulsar PSRJ1614-2230 as the model star. The starting equation of state for modeling the dark energy is motivated by the MIT Bag model for spherically confined hadrons and the observational evidences of its repulsive nature. Einstein field equations are solved in the stellar interior using the generalized framework of Tolman–Kuchowicz spacetime metric. The solutions are then analyzed for various physical parameters such as metric potential, pressure, density, energy conditions, etc. The physical analysis of multiple parameters indicates stable star formation. The proposed stellar model is free from all singularities and also meets the requisite stability criteria. The numerical results obtained for relativistic adiabatic index indicate that the model star is stiff and stable against radially induced adiabatic perturbations.

MeerKAT radio observations of the neutron star low-mass X-ray binary Cen X–4 at low accretion rates

ABSTRACT Centaurus X–4 (Cen X–4) is a relatively nearby neutron star low-mass X-ray binary that showed outbursts in 1969 and 1979, but has not shown a full outburst since. Due to its proximity and sustained period of quiescence, it is a prime target to study the coupling between accretion and jet ejection in quiescent neutron star low-mass X-ray binaries. Here, we present four MeerKAT radio observations at 1.3 GHz of Cen X–4, combined with NICER and Swift X-ray monitoring. During the first and most sensitive observation, Cen X–4 was in a fully quiescent X-ray state. The three later and shorter observations targeted a brief period of faint X-ray activity in 2021 January, which has been referred to as a ‘mis-fired’ outburst. Cen X–4 is not detected in any of the four MeerKAT observations. We place these radio non-detections on the X-ray–radio luminosity diagram, improving the constraints on the correlation between the two luminosities from earlier quiescent radio studies. We confirm that Cen X–4 is radio fainter than the transitional millisecond pulsar PSR J1023+0038 at the same X-ray luminosity. We discuss the radio behaviour of accreting neutron stars at low X-ray luminosity more generally and finally comment on future observing campaigns.

UV and X-ray pulse amplitude variability in the transitional millisecond pulsar PSR J1023+0038

The transitional millisecond pulsar PSR J1023+0038 is the first millisecond pulsar discovered to emit UV and optical pulses. Here we present the results of the UV and X-ray phase-resolved timing analysis of observations performed with the Hubble Space Telescope, XMM-Newton, and NuSTAR satellites between 2014 and 2021. Ultraviolet pulsations are detected in the high luminosity mode and disappear during low and flaring modes, similar to what is observed in the X-ray band. In the high mode, we find variability in both the UV and X-ray pulse amplitudes. The root mean square pulsed amplitude in the UV band ranges from ~2.1% down to ~0.7%, while it oscillates in the interval 5.5–12% in the X-ray band. As also observed in the optical band, this variability is not correlated with the orbital phase. Notwithstanding the rather low statistics, we have marginal evidence that variations in the pulse amplitude do not occur simultaneously in the UV and X-ray bands. When the UV pulsed amplitude decreases below the detection threshold, no significant variation in the X-ray pulsed amplitude is observed. These oscillations in the pulse amplitude could be caused by small random variations in the mass accretion rate leading to a variation in the size of the intra-binary shock region. Finally, we find that the pulsed flux spectral distribution from the X-ray to the UV band is well fitted using a power-law relation of the form νFνpulsed∼ν0.4. This supports the hypothesis of a common physical mechanism underlying the X-ray, UV, and optical pulsed emissions in PSR J1023+0038.

The peculiar chemical abundance of the transitional millisecond pulsar PSR J1023+0038 – Li enhancement

ABSTRACT Using high-resolution optical spectroscopy we determine the chemical abundance of the secondary star in the binary millisecond pulsar PSR J1023+0038. We measure a metallicity of [Fe/H] = 0.48 ± 0.04 which is higher than the Solar value and in general find that the element abundances are different compared to the secondary stars in X-ray binaries and stars in the solar neighbourhood of similar Fe content. Our results suggest that the pulsar was formed in a supernova explosion. We find that supernova models, where matter that has been processed in the supernova is captured by the secondary star leading to abundance anomalies, qualitatively agree with the observations. We measure Li abundance of A(Li) = 3.66 ± 0.20, which is anomalously high compared to the Li abundance of stars with the same effective temperature, irrespective of the age of the system. Furthermore, the Li abundance in PSR J1023+0038 is higher than the Cosmic value and what is observed in young Population I stars and so provides unambiguous evidence for fresh Li production. The most likely explanation is the interaction of high-energy gamma-rays or relativistic protons from the pulsar wind or intrabinary shock with the CNO nuclei in the secondary star’s atmosphere via spallation which leads to substantial Li enrichment in the secondary star’s atmosphere.

Constraints from LIGO O3 Data on Gravitational-wave Emission Due to R-modes in the Glitching Pulsar PSR J0537–6910

Abstract We present a search for continuous gravitational-wave emission due to r-modes in the pulsar PSR J0537–6910 using data from the LIGO–Virgo Collaboration observing run O3. PSR J0537–6910 is a young energetic X-ray pulsar and is the most frequent glitcher known. The inter-glitch braking index of the pulsar suggests that gravitational-wave emission due to r-mode oscillations may play an important role in the spin evolution of this pulsar. Theoretical models confirm this possibility and predict emission at a level that can be probed by ground-based detectors. In order to explore this scenario, we search for r-mode emission in the epochs between glitches by using a contemporaneous timing ephemeris obtained from NICER data. We do not detect any signals in the theoretically expected band of 86–97 Hz, and report upper limits on the amplitude of the gravitational waves. Our results improve on previous amplitude upper limits from r-modes in J0537-6910 by a factor of up to 3 and place stringent constraints on theoretical models for r-mode-driven spin-down in PSR J0537–6910, especially for higher frequencies at which our results reach below the spin-down limit defined by energy conservation.

Non-Newtonian gravity in strange stars and constraints from the observations of compact stars

We study non-Newtonian gravity effects on the structure and the tidal deformability of strange stars using the standard MIT model, and compare the theory with the observations of compact stars following the approach of Yang et al. (2020). Different to Yang et al. (2020), in which the authors only employed the constraints from the mass of PSR J0740+6620 and the dimensionless tidal deformability of a 1.4M⊙ star of GW170817, here we also consider another constraint, namely, from the observations of the mass and radius of the isolated pulsar PSR J0030+0451 by NICER. We find that for the standard MIT model, strange stars can not agree with the observations of PSR J0740+6620, PSR J0030+0451 and GW170817 simultaneously. In other words, for the standard MIT model, the observations of PSR J0740+6620, PSR J0030+0451 and GW170817 rule out the possibility of the existence of strange stars even when we consider the effects of non-Newtonian gravity.

Diving below the Spin-down Limit: Constraints on Gravitational Waves from the Energetic Young Pulsar PSR J0537-6910

Abstract We present a search for quasi-monochromatic gravitational-wave signals from the young, energetic X-ray pulsar PSR J0537−6910 using data from the second and third observing runs of LIGO and Virgo. The search is enabled by a contemporaneous timing ephemeris obtained using Neutron star Interior Composition Explorer (NICER) data. The NICER ephemeris has also been extended through 2020 October and includes three new glitches. PSR J0537−6910 has the largest spin-down luminosity of any pulsar and exhibits fRequent and strong glitches. Analyses of its long-term and interglitch braking indices provide intriguing evidence that its spin-down energy budget may include gravitational-wave emission from a time-varying mass quadrupole moment. Its 62 Hz rotation frequency also puts its possible gravitational-wave emission in the most sensitive band of the LIGO/Virgo detectors. Motivated by these considerations, we search for gravitational-wave emission at both once and twice the rotation frequency from PSR J0537−6910. We find no signal, however, and report upper limits. Assuming a rigidly rotating triaxial star, our constraints reach below the gravitational-wave spin-down limit for this star for the first time by more than a factor of 2 and limit gravitational waves from the l = m = 2 mode to account for less than 14% of the spin-down energy budget. The fiducial equatorial ellipticity is constrained to less than about 3 ×10−5, which is the third best constraint for any young pulsar.

Probing the hadronic nature of the gamma-ray emission associated with Westerlund 2

ABSTRACT Star-forming regions have been proposed as potential Galactic cosmic ray accelerators for decades. Cosmic ray acceleration can be probed through observations of gamma-rays produced in inelastic proton–proton collisions at GeV and TeV energies. In this paper, we analyse more than 11 yr of Fermi–LAT data from the direction of Westerlund 2, one of the most massive and best-studied star-forming regions in our Galaxy. In particular, we investigate the characteristics of the bright pulsar PSR J1023–5746 that dominates the gamma-ray emission below a few GeV at the position of Westerlund 2 and the underlying extended source FGES J1023.3–5747. The analysis results in a clear identification of FGES J1023.3–5747 as the GeV counterpart of the TeV source HESS J1023-575, through its morphological and spectral properties. This identification provides new clues about the origin of the HESS J1023-575 gamma-ray emission, favouring a hadronic origin of the emission, powered by Westerlund 2, rather than a leptonic origin related to either the pulsar wind nebula associated with PSR J1023–5746 or the cluster itself. This result indirectly supports the hypothesis that star-forming regions can contribute to the cosmic ray sea observed in our Galaxy.

A search for radio pulsars in five nearby supernova remnants

Context. Most neutron stars are expected to be born in supernovae, but only about half of supernova remnants (SNRs) are associated with a compact object. In many cases, a supernova progenitor may have resulted in a black hole. However, there are several possible reasons why true pulsar-SNR associations may have been missed in previous surveys: The pulsar’s radio beam may not be oriented towards us; the pulsar may be too faint to be detectable; or there may be an offset in the pulsar position caused by a kick. Aims. Our goal is to find new pulsars in SNRs and explore their possible association with the remnant. The search and selection of the remnants presented in this paper was inspired by the non-detection of any X-ray bright compact objects in these remnants when previously studied. Methods. Five SNRs were searched for radio pulsars with the Green Bank Telescope at 820 MHz with multiple pointings to cover the full spatial extent of the remnants. A periodicity search plus an acceleration search up to 500 m s−2 and a single pulse search were performed for each pointing in order to detect potential isolated binary pulsars and single pulses, respectively. Results. No new pulsars were detected in the survey. However, we were able to re-detect a known pulsar, PSR J2047+5029, near SNR G89.0+4.7. We were unable to detect the radio-quiet gamma-ray pulsar PSR J2021+4026, but we do find a flux density limit of 0.08 mJy. Our flux density limits make our survey two to 16 times more sensitive than previous surveys, while also covering the whole spatial extent of the same remnants. Conclusions. We discuss potential explanations for the non-detection of a pulsar in the studied SNRs and conclude that sensitivity is still the most likely factor responsible for the lack of pulsars in some remnants.

X-Ray Spectroscopy of the Highly Magnetized Pulsar PSR J1846-0258, Its Wind Nebula, and Hosting Supernova Remnant Kes 75

Abstract We present broadband X-ray spectroscopy of the energetic components that make up the supernova remnant (SNR) Kesteven 75 using concurrent 2017 August 17–20 XMM-Newton and NuSTAR observations, during which the pulsar PSR J1846−0258 is found to be in the quiescent state. The young remnant hosts a bright pulsar wind nebula powered by the highly energetic ( erg s−1) isolated, rotation-powered pulsar, with a spin-down age of only . Its inferred magnetic field (B s = 4.9 × 1013 G) is the largest known for these objects, and is likely responsible for intervals of flare and burst activity, suggesting a transition between/to a magnetar state. The pulsed emission from PSR J1846−0258 is well-characterized in the 2–50 keV range by a power-law model with photon index ΓPSR = 1.24 ± 0.09 and a 2–10 keV unabsorbed flux of (2.3 ± 0.4) × 10−12 erg s−1 cm−2. We find no evidence for an additional non-thermal component above 10 keV in the current state, as would be typical for a magnetar. Compared to the Chandra pulsar spectrum, the intrinsic pulsed fraction is 71 ± 16% in 2–10 keV band. A power-law spectrum for the pulsar wind nebulae (PWN) yields ΓPWN = 2.03 ± 0.02 in the 1–55 keV band, with no evidence of curvature in this range, and a 2–10 keV unabsorbed flux (2.13 ± 0.02) × 10−11 erg s−1 cm−2. The NuSTAR data reveal evidence for a hard X-ray component dominating the SNR spectrum above 10 keV that we attribute to a dust-scattered PWN component. We model the dynamical and radiative evolution of the Kes 75 system to estimate the birth properties of the neutron star, the energetics of its progenitor, and properties of the PWN. This suggests that the progenitor of Kes 75 was originally in a binary system which transferred most of its mass to a companion before exploding.