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The millisecond pulsar J1713+0747 underwent a sudden and significant pulse shape change between 2021 April 16 and 17 (MJDs 59320 and 59321). Subsequently, the pulse shape gradually recovered over the course of several months. We report the results of continued multifrequency radio observations of the pulsar made using the Canadian Hydrogen Intensity Mapping Experiment and the 100 m Green Bank Telescope in a 3 yr period encompassing the shape change event, between 2020 February and 2023 February. As of 2023 February, the pulse shape had returned to a state similar to that seen before the event, but with measurable changes remaining. The amplitude of the shape change and the accompanying time-of-arrival residuals display a strong nonmonotonic dependence on radio frequency, demonstrating that the event is neither a glitch (the effects of which should be independent of radio frequency, ν ) nor a change in dispersion measure alone (which would produce a delay proportional to ν ^−2 ). However, it does bear some resemblance to the two previous “chromatic timing events” observed in J1713+0747, as well as to a similar event observed in PSR J1643−1224 in 2015.

We analyzed the globular cluster M5 (NGC 5904) using 15 yr of gamma-ray data from the Fermi Large Area Telescope (LAT). Using rotation ephemerides generated from Arecibo and FAST radio telescope observations, we searched for gamma-ray pulsations from the seven millisecond pulsars (MSPs) identified in M5. We detected no significant pulsations from any of the individual pulsars. In addition, we searched for possible variations of the gamma-ray emission as a function of orbital phase for all six MSPs in binary systems, but we did not detect any significant modulations. The gamma-ray emission from the direction of M5 is well described by an exponentially cutoff power-law spectral model, although other models cannot be excluded. The phase-averaged emission is consistent with being steady on a timescale of a few months. We estimate the number of MSPs in M5 to be between 1 and 10, using the gamma-ray conversion efficiencies for well-characterized gamma-ray MSPs in the Third Fermi-LAT Catalog of Gamma-ray Pulsars, suggesting that the sample of known MSPs in M5 is (nearly) complete, even if it is not currently possible to rule out a diffuse component of the observed gamma rays from the cluster.

Pulsar timing is a powerful tool that, by accounting for every rotation of a pulsar, precisely measures the spin frequency, spin frequency derivatives, astrometric position, binary parameters when applicable, properties of the interstellar medium, and potentially general relativistic effects. Typically, this process demands fairly stringent scheduling requirements for monitoring observations as well as deep domain knowledge to “phase connect” the timing data. We present an algorithm that automates the pulsar-timing process for binary pulsars, whose timing solutions have an additional level of complexity, although the algorithm works for isolated pulsars as well. Using the statistical F -test and the quadratic dependence of the reduced χ ^2 near a minimum, the global rotation count of a pulsar can be determined efficiently and systematically. We have used our algorithm to establish timing solutions for two newly discovered binary pulsars, PSRs J1748−2446aq and J1748−2446at, in the globular cluster Terzan 5, using ∼70 Green Bank Telescope observations from the last 13 yr.

We investigated the multiband emission from the pulsar binaries XSS J12270−4859, PSR J2039−5617, and PSR J2339−0533, which exhibit orbital modulation in the X-ray and gamma-ray bands. We constructed the sources’ broadband spectral energy distributions and multiband orbital light curves by supplementing our X-ray measurements with published gamma-ray results, and we modeled the data using intrabinary shock (IBS) scenarios. While the X-ray data were well explained by synchrotron emission from electrons/positrons in the IBS, the gamma-ray data were difficult to explain with the IBS components alone. Therefore, we explored other scenarios that had been suggested for gamma-ray emission from pulsar binaries: (1) inverse-Compton emission in the upstream unshocked wind zone and (2) synchrotron radiation from electrons/positrons interacting with the kilogauss magnetic field of the companion. Scenario (1) requires that the bulk motion of the wind substantially decelerates to ∼1000 km s ^−1 before reaching the IBS for increased residence time, in which case the formation of a strong shock is untenable, inconsistent with the X-ray phenomenology. Scenario (2) can explain the data if we assume the presence of electrons/positrons with a Lorentz factor ∼ 10 ^8 (∼0.1 PeV) that pass through the IBS and tap a substantial portion of the pulsar voltage drop. These findings raise the possibility that the orbitally modulating gamma-ray signals from pulsar binaries can provide insights into the flow structure and energy conversion within pulsar winds and particle acceleration nearing PeV energies in pulsars. These signals may also yield greater understanding of kilogauss magnetic fields potentially hosted by the low-mass stars in these systems.

Understanding the jitter noise resulting from single-pulse phase and shape variations is important for the detection of gravitational waves using pulsar timing arrays. We present measurements of the jitter noise and single-pulse variability of 12 millisecond pulsars that are part of the International Pulsar Timing Array sample using the Five-hundred-meter Aperture Spherical radio Telescope. We find that the levels of jitter noise can vary dramatically among pulsars. A moderate correlation with a correlation coefficient of 0.57 between jitter noise and pulse width is detected. To mitigate jitter noise, we perform matrix template matching using all four Stokes parameters. Our results reveal a reduction in jitter noise ranging from 6.7% to 39.6%. By performing longitude-resolved fluctuation spectrum analysis, we identify periodic intensity modulations in 10 pulsars. In PSR J0030+0451, we detect single pulses with energies more than 10 times the average pulse energy, suggesting the presence of giant pulses. We also observe a periodic mode-changing phenomenon in PSR J0030+0451. We examine the achievable timing precision by selecting a subset of pulses with a specific range of peak intensity, but no significant improvement in timing precision is achievable.

The radio galaxy 3C 66B has been hypothesized to host a supermassive black hole binary (SMBHB) at its center based on electromagnetic observations. Its apparent 1.05 yr period and low redshift (∼0.02) make it an interesting testbed to search for low-frequency gravitational waves (GWs) using pulsar timing array (PTA) experiments. This source has been subjected to multiple searches for continuous GWs from a circular SMBHB, resulting in progressively more stringent constraints on its GW amplitude and chirp mass. In this paper, we develop a pipeline for performing Bayesian targeted searches for eccentric SMBHBs in PTA data sets, and test its efficacy by applying it to simulated data sets with varying injected signal strengths. We also search for a realistic eccentric SMBHB source in 3C 66B using the NANOGrav 12.5 yr data set employing PTA signal models containing Earth term-only as well as Earth+pulsar term contributions using this pipeline. Due to limitations in our PTA signal model, we get meaningful results only when the initial eccentricity e _0 < 0.5 and the symmetric mass ratio η > 0.1. We find no evidence for an eccentric SMBHB signal in our data, and therefore place 95% upper limits on the PTA signal amplitude of 88.1 ± 3.7 ns for the Earth term-only and 81.74 ± 0.86 ns for the Earth+pulsar term searches for e _0 < 0.5 and η > 0.1. Similar 95% upper limits on the chirp mass are (1.98 ± 0.05) × 10 ^9 and (1.81 ± 0.01) × 10 ^9 M _☉ . These upper limits, while less stringent than those calculated from a circular binary search in the NANOGrav 12.5 yr data set, are consistent with the SMBHB model of 3C 66B developed from electromagnetic observations.

Spin period distribution provides important clues to understand the formation of millisecond pulsars (MSPs). To uncover the intrinsic period distribution, we analyze three samples of radio MSPs in the Galactic field and globular clusters. The selection bias due to pulse broadening has been corrected but turns out to be negligible. We find that all the samples can be well described by a Weibull distribution of spin frequencies. Considering MSPs in the Galactic field or globular clusters and in isolation or binary systems, we find no significant difference in the spin distribution among these subpopulations. Based on the current known population of MSPs, we find that submillisecond pulsars are unlikely to be discovered by the Square Kilometre Array, although up to ∼10 discoveries of pulsars that spin faster than the current record holder of P = 1.4 ms are expected.

We present results from long-term monitoring of frequency-dependent eclipses of the radio emission from PSR J1544+4937, which is a black widow spider millisecond pulsar (MSP) in a compact binary system. The majority of such systems often exhibit relatively long-duration radio eclipses caused by ablated material from their companion stars. With the wide spectral bandwidth of the upgraded Giant Metrewave Radio Telescope, we present the first systematic study of temporal variation of eclipse cutoff frequency. With decade-long monitoring of 39 eclipses for PSR J1544+4937, we notice significant changes in the observed cutoff frequency ranging from 343 ± 7 to ≥740 MHz. We also monitored changes in eclipse cutoff frequency on timescales of tens of days and observed a maximum change of ≥315 MHz between observations that were separated by 22 days. In addition, we observed a change of ∼47 MHz in eclipse cutoff frequency between adjacent orbits, i.e., on timescales of ∼2.9 hr. We infer that such changes in the eclipse cutoff frequency depict an eclipse environment for the PSR J1544+4937 system that is dynamically evolving, where, along with the change in electron density, the magnetic field could also be varying. We also report a significant correlation between the eclipse cutoff frequency and the mass-loss rate of the companion. This study provides the first direct evidence of mass-loss rate affecting the frequency-dependent eclipsing in a spider MSP.

Globular clusters (GCs) are particularly efficient at forming millisecond pulsars. Among these pulsars, about half lack a companion star, a significantly higher fraction than in the Galactic field. This fraction increases further in some of the densest GCs, especially those that have undergone core collapse, suggesting that dynamical interaction processes play a key role. For the first time, we create N -body models that reproduce the ratio of single-to-binary pulsars in Milky Way–like GCs. We focus especially on NGC 6752, a typical core-collapsed cluster with many observed millisecond pulsars. Previous studies suggested that an increased rate of neutron star binary disruption in the densest clusters could explain the overabundance of single pulsars in these systems. Here, we demonstrate that binary disruption is ineffective and instead we propose that two additional dynamical processes play dominant roles: (1) tidal disruption of main-sequence stars by neutron stars and (2) gravitational collapse of heavy white dwarf binary merger remnants. Neutron stars formed through these processes may also be associated with fast radio bursts similar to those observed recently in an extragalactic GC.

The discovery and timing follow up of millisecond pulsars (MSPs) are necessary not just for their usefulness in pulsar timing arrays (PTAs) but also for investigating their own intriguing properties. In this work, we provide the findings of the decade-long timing of four MSPs discovered by the Giant Meterwave Radio Telescope (GMRT), including their timing precision, model parameters, and newly detected proper motions. We compare the timing results for these MSPs before and after the GMRT upgrade in 2017 and characterize the improvement in timing precision due to the bandwidth upgrade. We discuss the suitability of these four GMRT MSPs as well as the usefulness of the decade-long timing data for PTA experiments. These data may aid in the global effort to improve the signal-to-noise ratios of recently detected signature of gravitational waves in cross-correlation statistics of residuals of MSPs.

We present the results of an ultradeep radio continuum survey, containing ∼480 hr of observations, of the Galactic globular cluster 47 Tucanae with the Australia Telescope Compact Array. This comprehensive coverage of the cluster allows us to reach rms noise levels of 1.19 μ Jy beam ^−1 at 5.5 GHz, 940 nJy beam ^−1 at 9 GHz, and 790 nJy beam ^−1 in a stacked 7.25 GHz image. This is the deepest radio image of a globular cluster and the deepest image ever made with the Australia Telescope Compact Array. We identify ATCA J002405.702-720452.361, a faint (6.3 ± 1.2 μ Jy at 5.5 GHz, 5.4 ± 0.9 μ Jy at 9 GHz), flat-spectrum ( α = −0.31 ± 0.54) radio source that is positionally coincident with the cluster center and potentially associated with a faint X-ray source. No convincing optical counterpart was identified. We use radio, X-ray, optical, and UV data to show that explanations involving a background active galactic nucleus, a chromospherically active binary, or a binary involving a white dwarf are unlikely. The most plausible explanations are that the source is an undiscovered millisecond pulsar or a weakly accreting black hole. If the X-ray source is associated with the radio source, the fundamental plane of black-hole activity suggests a black hole mass of ∼54–6000 M _⊙ , indicating an intermediate-mass black hole or a heavy stellar-mass black hole.

We report detection results of nine millisecond pulsars (MSPs) at 8600 MHz using simultaneous 2250 and 8600 MHz observations conducted with the Shanghai Tian Ma Radio Telescope. Mainly benefiting from updated ephemerids with 2250 MHz observations, integrated profiles of all nine MSPs at 8600 MHz are successfully obtained by coherently adding multi-epoch (3–83 epochs) observation data spanning from 19–1210 days, which significantly increases the number of MSPs with published profiles (from 4 to 11) above 8000 MHz, as seven of our target MPSs had no related results previously. Combining our new flux density and pulse width measurements with previous low-frequency results, we study their integrated profile evolution and spectral behaviors in a wider frequency range. We find their component separations and pulse widths remain almost constant, which is consistent with previous findings. While dramatic evolution of integrated profiles exists at low frequencies, we observe a potential end of the related evolution around 5 GHz in eight MSPs. The spectra of four MSPs are found to deviate from a single power law, and we fit them with a broken power law. The change in the profile of PSR J1713+0747, which started around MJD 59320−59321, seems to be more prominent as the observation frequency increases. Compared with the effects of the interstellar medium, we prefer to explain this event as some changes in the magnetosphere. We also find its integrated profile possibly had not recovered to the pre-event state until MJD 59842–59857.

There is growing evidence that the Galactic Center Excess identified in the Fermi-LAT gamma-ray data arises from a population of faint astrophysical sources. We provide compelling supporting evidence by showing that the morphology of the excess traces the stellar over-density of the Galactic bulge. By adopting a template of the bulge stars obtained from a triaxial 3D fit to the diffuse near-infrared emission, we show that it is detected at high significance. The significance deteriorates when either the position or the orientation of the template is artificially shifted, supporting the correlation of the gamma-ray data with the Galactic bulge. In deriving these results, we have used more sophisticated templates at low-latitudes for the Fermi bubbles compared to previous work and the three-dimensional Inverse Compton (IC) maps recently released by the GALPROP team. Our results provide strong constraints on Millisecond Pulsar (MSP) formation scenarios proposed to explain the excess. We find that an admixture formation scenario, in which some of the relevant binaries are primordial and the rest are formed dynamically, is preferred over a primordial-only formation scenario at 7.6σ confidence level. Our detailed morphological analysis also disfavors models of the disrupted globular clusters scenario that predict a spherically symmetric distribution of MSPs in the Galactic bulge. For the first time, we report evidence of a high energy tail in the nuclear bulge spectrum that could be the result of IC emission from electrons and positrons injected by a population of MSPs and star formation activity from the same site.

In 2018 an ultra–wide-bandwidth low-frequency (UWL) receiver was installed on the 64 m Parkes Radio Telescope, enabling observations with an instantaneous frequency coverage from 704 to 4032 MHz. Here we present the analysis of a 3 yr data set of 35 ms pulsars observed with the UWL by the Parkes Pulsar Timing Array, using wide-band timing methods. The two key differences compared to typical narrowband methods are (1) generation of two-dimensional templates accounting for pulse shape evolution with frequency and (2) simultaneous measurements of the pulse time of arrival (TOA) and dispersion measure (DM). This is the first time that wide-band timing has been applied to a uniform data set collected with a single large fractional bandwidth receiver, for which such techniques were originally developed. As a result of our study, we present a set of profile evolution models and new timing solutions, including initial noise analysis. Precision of our TOA and DM measurements is in the range of 0.005–2.08 μ s and (0.043–14.24) × 10−4 cm−3 pc, respectively, with 94% of the pulsars achieving a median TOA uncertainty of less than 1 μ s. [ABSTRACT FROM AUTHOR]

We present ab initio global general-relativistic Particle-in-cell (GR-PIC) simulations of compact millisecond neutron star magnetospheres in the axisymmetric aligned rotator configuration. We investigate the role of GR and plasma supply on the polar cap particle acceleration efficiency – the precursor of coherent radio emission – employing a new module for the PIC code OSIRIS, designed to model plasma dynamics around compact objects with fully self-consistent GR effects. We provide a detailed description of the main sub-algorithms of the novel PIC algorithm, including a charge-conserving current deposit scheme for curvilinear coordinates. We demonstrate efficient particle acceleration in the polar caps of compact neutron stars with denser magnetospheres, numerically validating the spacelike current extension provided by force-free models. We show that GR relaxes the minimum required poloidal magnetospheric current for the transition of the polar cap to the accelerator regime, thus justifying the observation of weak pulsars beyond the expected death line. We denote that spin-down luminosity intermittency and radio pulse nullings for older pulsars might arise from the interplay between the polar and outer gaps. Also, narrower radio beams are expected for weaker low-obliquity pulsars. • We present an axisymmetric general-relativistic Particle-in-cell code, OSIRIS-GR. • Charge-conserving GR-PIC code designed to model compact object magnetospheres. • GR-PIC simulations of compact neutron star magnetospheres are presented. • We show that spacelike polar angle deviates from GR-FF estimates for weak pulsars. • Older pulsars may be observable beyond the expected death line due to GR. [ABSTRACT FROM AUTHOR]

A millisecond pulsar (MSP) is an old neutron star (NS) that has accreted material from its companion star, causing it to spin up, which is known as the recycling scenario. During the mass transfer phase, the system manifests itself as an X-ray binary. PSR J1402+13 is an MSP with a spin period of 5.89 ms and a spin period derivative of $\mathrm{log}{\dot{P}}_{\mathrm{spin}}=-16.32$ . These properties make it a notable object within the pulsar population, as MSPs typically exhibit low spin period derivatives. In this paper, we aim to explain how an MSP can possess a high spin period derivative by binary evolution. By utilizing the stellar evolution code MESA , we examine the effects of irradiation on the companion star and the propeller effect on the NS during binary evolution. We demonstrate that irradiation can modify the spin period and mass of an MSP, resulting in a higher spin period derivative. These results suggest that the irradiation effect may serve as a key factor in explaining MSPs with high spin period derivatives.

The most distant globular cluster (GC) with known pulsars is NGC 5024 (M53). In this paper, we report the discovery of a new binary millisecond pulsar, PSR J1312+1810E (M53E), and present the new timing solutions for M53B–E based on 22 observations from the Five-hundred-meter Aperture Spherical radio Telescope (FAST). These discoveries and timing work benefit from FAST’s high sensitivity. We find that M53C is the only isolated millisecond pulsar known in this distant GC, with a spin period of 12.53 ms and spin period derivative of 5.26 × 10 ^−20 s s ^−1 . Our results reveal orbital periods of 47.7, 5.8, and 2.4 days for M53B, D, and E, respectively. The companions, with masses of 0.25, 0.27, and 0.18 M _⊙ , respectively, are likely to be white dwarf stars; if they are extended objects, they do not eclipse the pulsars. We find no X-ray counterparts for these millisecond pulsars in archival Chandra images in the band of 0.3–8 keV. The characteristics of this pulsar population are similar to the population of millisecond pulsars in the Galactic disk, as expected from the low stellar density of M53.

Pulsar timing array collaborations, such as the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), are seeking to detect nanohertz gravitational waves emitted by supermassive black hole binaries formed in the aftermath of galaxy mergers. We have searched for continuous waves from individual circular supermassive black hole binaries using NANOGrav’s recent 12.5 yr data set. We created new methods to accurately model the uncertainties on pulsar distances in our analysis, and we implemented new techniques to account for a common red-noise process in pulsar timing array data sets while searching for deterministic gravitational wave signals, including continuous waves. As we found no evidence for continuous waves in our data, we placed 95% upper limits on the strain amplitude of continuous waves emitted by these sources. At our most sensitive frequency of 7.65 nHz, we placed a sky-averaged limit of h _0 < (6.82 ± 0.35) × 10 ^−15 , and h _0 < (2.66 ± 0.15) × 10 ^−15 in our most sensitive sky location. Finally, we placed a multimessenger limit of ${ \mathcal M }\lt (1.41\pm 0.02)\times {10}^{9}\,{M}_{\odot }$ on the chirp mass of the supermassive black hole binary candidate 3C 66B.

We report multiple lines of evidence for a stochastic signal that is correlated among 67 pulsars from the 15 yr pulsar timing data set collected by the North American Nanohertz Observatory for Gravitational Waves. The correlations follow the Hellings–Downs pattern expected for a stochastic gravitational-wave background. The presence of such a gravitational-wave background with a power-law spectrum is favored over a model with only independent pulsar noises with a Bayes factor in excess of 10 ^14 , and this same model is favored over an uncorrelated common power-law spectrum model with Bayes factors of 200–1000, depending on spectral modeling choices. We have built a statistical background distribution for the latter Bayes factors using a method that removes interpulsar correlations from our data set, finding p = 10 ^−3 (≈3 σ ) for the observed Bayes factors in the null no-correlation scenario. A frequentist test statistic built directly as a weighted sum of interpulsar correlations yields p = 5 × 10 ^−5 to 1.9 × 10 ^−4 (≈3.5 σ –4 σ ). Assuming a fiducial f ^−2/3 characteristic strain spectrum, as appropriate for an ensemble of binary supermassive black hole inspirals, the strain amplitude is ${2.4}_{-0.6}^{+0.7}\times {10}^{-15}$ (median + 90% credible interval) at a reference frequency of 1 yr ^−1 . The inferred gravitational-wave background amplitude and spectrum are consistent with astrophysical expectations for a signal from a population of supermassive black hole binaries, although more exotic cosmological and astrophysical sources cannot be excluded. The observation of Hellings–Downs correlations points to the gravitational-wave origin of this signal.

We present observations and timing analyses of 68 millisecond pulsars (MSPs) comprising the 15 yr data set of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). NANOGrav is a pulsar timing array (PTA) experiment that is sensitive to low-frequency gravitational waves (GWs). This is NANOGrav’s fifth public data release, including both “narrowband” and “wideband” time-of-arrival (TOA) measurements and corresponding pulsar timing models. We have added 21 MSPs and extended our timing baselines by 3 yr, now spanning nearly 16 yr for some of our sources. The data were collected using the Arecibo Observatory, the Green Bank Telescope, and the Very Large Array between frequencies of 327 MHz and 3 GHz, with most sources observed approximately monthly. A number of notable methodological and procedural changes were made compared to our previous data sets. These improve the overall quality of the TOA data set and are part of the transition to new pulsar timing and PTA analysis software packages. For the first time, our data products are accompanied by a full suite of software to reproduce data reduction, analysis, and results. Our timing models include a variety of newly detected astrometric and binary pulsar parameters, including several significant improvements to pulsar mass constraints. We find that the time series of 23 pulsars contain detectable levels of red noise, 10 of which are new measurements. In this data set, we find evidence for a stochastic GW background.

Pulsar timing arrays (PTAs) are galactic-scale gravitational wave (GW) detectors. Each individual arm, composed of a millisecond pulsar, a radio telescope, and a kiloparsecs-long path, differs in its properties but, in aggregate, can be used to extract low-frequency GW signals. We present a noise and sensitivity analysis to accompany the NANOGrav 15 yr data release and associated papers, along with an in-depth introduction to PTA noise models. As a first step in our analysis, we characterize each individual pulsar data set with three types of white-noise parameters and two red-noise parameters. These parameters, along with the timing model and, particularly, a piecewise-constant model for the time-variable dispersion measure, determine the sensitivity curve over the low-frequency GW band we are searching. We tabulate information for all of the pulsars in this data release and present some representative sensitivity curves. We then combine the individual pulsar sensitivities using a signal-to-noise ratio statistic to calculate the global sensitivity of the PTA to a stochastic background of GWs, obtaining a minimum noise characteristic strain of 7 × 10 ^−15 at 5 nHz. A power-law-integrated analysis shows rough agreement with the amplitudes recovered in NANOGrav’s 15 yr GW background analysis. While our phenomenological noise model does not model all known physical effects explicitly, it provides an accurate characterization of the noise in the data while preserving sensitivity to multiple classes of GW signals.

Pulsar timing arrays aim to detect nanohertz-frequency gravitational waves (GWs). A background of GWs modulates pulsar arrival times and manifests as a stochastic process, common to all pulsars, with a signature spatial correlation. Here we describe a search for an isotropic stochastic gravitational-wave background (GWB) using observations of 30 millisecond pulsars from the third data release of the Parkes Pulsar Timing Array (PPTA), which spans 18 yr. Using current Bayesian inference techniques we recover and characterize a common-spectrum noise process. Represented as a strain spectrum ${h}_{c}=A{(f/1{\mathrm{yr}}^{-1})}^{\alpha }$ , we measure $A={3.1}_{-0.9}^{+1.3}\times {10}^{-15}$ and α = −0.45 ± 0.20, respectively (median and 68% credible interval). For a spectral index of α = −2/3, corresponding to an isotropic background of GWs radiated by inspiraling supermassive black hole binaries, we recover an amplitude of $A={2.04}_{-0.22}^{+0.25}\times {10}^{-15}$ . However, we demonstrate that the apparent signal strength is time-dependent, as the first half of our data set can be used to place an upper limit on A that is in tension with the inferred common-spectrum amplitude using the complete data set. We search for spatial correlations in the observations by hierarchically analyzing individual pulsar pairs, which also allows for significance validation through randomizing pulsar positions on the sky. For a process with α = −2/3, we measure spatial correlations consistent with a GWB, with an estimated false-alarm probability of p ≲ 0.02 (approx. 2 σ ). The long timing baselines of the PPTA and the access to southern pulsars will continue to play an important role in the International Pulsar Timing Array.

The noise in millisecond pulsar (MSP) timing data can include contributions from observing instruments, the interstellar medium, the solar wind, solar system ephemeris errors, and the pulsars themselves. The noise environment must be accurately characterized in order to form the null hypothesis from which signal models can be compared, including the signature induced by nanohertz-frequency gravitational waves (GWs). Here we describe the noise models developed for each of the MSPs in the Parkes Pulsar Timing Array (PPTA) third data release, which have been used as the basis of a search for the isotropic stochastic GW background. We model pulsar spin noise, dispersion measure variations, scattering variations, events in the pulsar magnetospheres, solar wind variability, and instrumental effects. We also search for new timing model parameters and detected Shapiro delays in PSR J0614−3329 and PSR J1902−5105. The noise and timing models are validated by testing the normalized and whitened timing residuals for Gaussianity and residual correlations with time. We demonstrate that the choice of noise models significantly affects the inferred properties of a common-spectrum process. Using our detailed models, the recovered common-spectrum noise in the PPTA is consistent with a power law with a spectral index of γ = 13/3, the value predicted for a stochastic GW background from a population of supermassive black hole binaries driven solely by GW emission.

We present a pulse timing analysis of NICER observations of the accreting millisecond X-ray pulsar SAX J1808.4−3658 during the outburst that started on 2022 August 19. Similar to previous outbursts, after decaying from a peak luminosity of ≃1 × 10 ^36 erg s ^−1 in about a week, the pulsar entered a ∼1 month long reflaring stage. Comparison of the average pulsar spin frequency during the outburst with those previously measured confirmed the long-term spin derivative of ${\dot{\nu }}_{\mathrm{SD}}=-(1.15\,\pm \,0.06)\times \,{10}^{-15}$ Hz s ^−1 , compatible with the spin-down torque of a ≈10 ^26 G cm ^3 rotating magnetic dipole. For the first time in the last twenty years, the orbital phase evolution shows evidence for a decrease of the orbital period. The long-term behavior of the orbit is dominated by an ∼11 s modulation of the orbital phase epoch consistent with a ∼21 yr period. We discuss the observed evolution in terms of a coupling between the orbit and variations in the mass quadrupole of the companion star.

The standard technique for very low-frequency gravitational wave detection is mainly based on searching for a specific spatial correlation in the variation of the times of arrival of the radio pulses emitted by millisecond pulsars with respect to a timing model. This spatial correlation, which in the case of the gravitational wave background must have the form described by the Hellings and Downs function, has not yet been observed. Therefore, despite the numerous hints of a common red noise in the timing residuals of many millisecond pulsars compatible with that expected for the gravitational wave background, its detection has not yet been achieved. By now, the reason is not completely clear and, from some recent works, the urgency to adopt new detection techniques, possibly complementary to the standard one, is emerging clearly. Of course, this demand also applies to the detection of continuous gravitational waves emitted by supermassive black hole binaries populating the Universe. In the latter case, important information could, in principle, emerge from the millisecond pulsars considered individually in a single-pulsar search of continuous GWs. In this context, the surfing effect can then be exploited, helping to select the best pulsars to carry out such analysis. This paper aims to clarify when the surfing effect occurs and describe it exhaustively. A possible application to the case of the supermassive black hole binary candidate PKS 2131–021 and millisecond pulsar J2145–0750 is also analyzed. [ABSTRACT FROM AUTHOR]

We perform a composite likelihood analysis of subdivided regions within the central 26° × 20° of the Milky Way, with the aim of characterizing the spectrum of the gamma-ray galactic center excess in regions of varying galactocentric distance. Outside of the innermost few degrees, we find that the radial profile of the excess is background-model dependent and poorly constrained. The spectrum of the excess emission is observed to extend upwards of 10 GeV outside ∼5° in radius, but cuts off steeply between 10-20 GeV only in the innermost few degrees. If interpreted as a real feature of the excess, this radial variation in the spectrum has important implications for both astrophysical and dark matter interpretations of the galactic center excess. Single-component dark matter annihilation models face challenges in reproducing this variation; on the other hand, a population of unresolved millisecond pulsars contributing both prompt and secondary inverse Compton emission may be able to explain the spectrum as well as its spatial dependency. We show that the expected differences in the photon-count distributions of a smooth dark matter annihilation signal and an unresolved point source population are an order of magnitude smaller than the fluctuations in residuals after fitting the data, which implies that mismodeling is an important systematic effect in point source analyses aimed at resolving the gamma-ray excess.

We report on a comprehensive multiwavelength study of the pulsars in the globular cluster (GC) M5, including the discovery of M5G, a new compact noneclipsing “black widow” pulsar. Thanks to the analysis of 34 yr of radio data taken with the Five-hundred-meter Aperture Spherical radio Telescope and Arecibo telescopes, we obtained new phase-connected timing solutions for four pulsars and improved those of the other three. These have resulted in, among other things, (a) much improved proper motions for five pulsars, with transverse velocities (relative to the cluster) that are smaller than their respective escape velocities; (b) 3 σ and 1.5 σ detections of Shapiro delays in M5F and M5D, respectively; and (c) greatly improved measurement of the periastron advance in M5B, whose value of $\dot{\omega }=0\buildrel{\circ}\over{.} 01361(6)$ implies that M5B is still likely to be a heavy ( ${m}_{p}={1.981}_{-0.088}^{+0.038}\,{M}_{\odot }$ ) neutron star. The binary pulsars M5D, M5E, and M5F are confirmed to be in low-eccentricity binary systems, the low-mass companions of which are newly identified to be He white dwarfs using Hubble Space Telescope data. Four pulsars are also found to be associated with X-ray sources. Similarly to the eclipsing pulsar M5C, M5G shows little or no nonthermal X-ray emission, indicative of weak synchrotron radiation produced by intrabinary shocks. All seven pulsars known in M5 have short spin periods (

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 phase-connected rotation ephemerides are achieved. A further dozen optical and/or X-ray binary systems colocated with LAT sources also likely harbor gamma-ray MSPs. This catalog thus reports roughly 340 gamma-ray pulsars and candidates, 10% of all known pulsars, compared to ≤11 known before Fermi. Half of the gamma-ray pulsars are young. Of these, the half that are undetected in radio have a broader Galactic latitude distribution than the young radio-loud pulsars. The others are MSPs, with six undetected in radio. Overall, ≥236 are bright enough above 50 MeV to fit the pulse profile, the energy spectrum, or both. For the common two-peaked profiles, the gamma-ray peak closest to the magnetic pole crossing generally has a softer spectrum. The spectral energy distributions tend to narrow as the spindown power $\dot{E}$ decreases to its observed minimum near 10 ^33 erg s ^−1 , approaching the shape for synchrotron radiation from monoenergetic electrons. We calculate gamma-ray luminosities when distances are available. Our all-sky gamma-ray sensitivity map is useful for population syntheses. The electronic catalog version provides gamma-ray pulsar ephemerides, properties, and fit results to guide and be compared with modeling results.

We studied the broadband X-ray timing and spectral behaviors of the newly confirmed accreting millisecond X-ray pulsar MAXI J1816−195 during its 2022 outburst. We used data from the Insight-HXMT Medium Energy (ME) and High Energy (HE) telescopes, NICER, and NuSTAR that cover the energy range between 0.8 and 210 keV. A coherent timing analysis of solely the Insight-HXMT HE data across the full outburst revealed a complex behavior of the timing residuals, also prominently visible in the independent Insight-HXMT ME and NICER data, particularly at the rising part of the outburst and at the very end in the NICER data. Therefore, we broke down the full outburst into a (noisy) rising part, covering only about five days, from MJD 59737.0 to 59741.9, and a decaying part, lasting for 19 days across MJD 59741.9–59760.6. Fitting for the decaying part, a timing model including a frequency ν and frequency time derivative $\dot{\nu }$ component yielded a value of (+9.0 ± 2.1) × 10 ^−14 Hz s ^−1 for $\dot{\nu }$ , which could be interpreted as a spinup under our model assumptions. We detected X-ray pulsations up to ∼95 keV in a combination of Insight-HXMT HE observations. The pulse profiles were quite stable over the whole outburst and could be well described by a truncated Fourier series using two harmonics, the fundamental and the first overtone. Both components kept alignment in the range 0.8–64 keV. The joint and time-averaged NICER and Insight-HXMT spectra in the energy range 1–150 keV were well fitted by the absorbed Comptonization model compps plus disk blackbody with two additional Gaussian components. Using the bolometric flux and spinup values both evaluated during the decay phase, we determined a magnetic field strength of (0.2–2) × 10 ^8 G for MAXI J1816−195.

We present the discovery and timing solutions of four millisecond pulsars (MSPs) discovered in the Arecibo 327 MHz Drift-Scan Pulsar Survey. Three of these pulsars are in binary systems, consisting of a redback (PSR J2055+1545), a black widow (PSR J1630+3550), and a neutron star–white dwarf binary (PSR J2116+1345). The fourth MSP, PSR J2212+2450, is isolated. We present the multiyear timing solutions as well as polarization properties across a range of radio frequencies for each pulsar. We perform a multiwavelength search for emission from these systems and find an optical counterpart for PSR J2055+1545 in Gaia DR3, as well as a gamma-ray counterpart for PSR J2116+1345 with the Fermi-LAT telescope. Despite the close colocation of PSR J2055+1545 with a Fermi source, we are unable to detect gamma-ray pulsations, likely due to the large orbital variability of the system. This work presents the first two binaries found by this survey with orbital periods shorter than a day; we expect to find more in the 40% of the survey data that have yet to be searched.

M71E is a spider pulsar (i.e., a millisecond pulsar with a tight binary companion) with the shortest known orbital period of P = 53.3 minutes, which was discovered by Pan et al. Their favored evolutionary model suggests that it bridges between two types of spider pulsars, namely, it descended from a “redback” and will become a “black widow.” Using Hubble Space Telescope (HST) archival imaging data, we report the first optical identification of its companion COM-M71E. The HST and pulsar timing coordinates are in excellent agreement (within ∼10 mas). If M71E is associated with the globular cluster M71, our measured brightness of COM-M71E ( m _F606W ≈ 25.3) is broadly consistent with the expectation from Pan et al.'s preferred binary evolutionary model of a stripped dwarf companion, while it is also compatible with an ultralow-mass degenerate companion. Future multiwavelength photometric and spectroscopic observations can characterize the companion and test the evolutionary scenarios.

We present timing solutions for 21 pulsars discovered in 350 MHz surveys using the Green Bank Telescope (GBT). All were discovered in the Green Bank North Celestial Cap pulsar survey, with the exception of PSR J0957−0619, which was found in the GBT 350 MHz Drift-scan pulsar survey. The majority of our timing observations were made with the GBT at 820 MHz. With a spin period of 37 ms and a 528 days orbit, PSR J0032+6946 joins a small group of five other mildly recycled wide binary pulsars, for which the duration of recycling through accretion is limited by the length of the companion’s giant phase. PSRs J0141+6303 and J1327+3423 are new disrupted recycled pulsars. We incorporate Arecibo observations from the NANOGrav pulsar timing array into our analysis of the latter. We also observed PSR J1327+3423 with the Long Wavelength Array, and our data suggest a frequency-dependent dispersion measure. PSR J0957−0619 was discovered as a rotating radio transient, but is a nulling pulsar at 820 MHz. PSR J1239+3239 is a new millisecond pulsar (MSP) in a 4 days orbit with a low-mass companion. Four of our pulsars already have published timing solutions, which we update in this work: the recycled wide binary PSR J0214+5222, the noneclipsing black widow PSR J0636+5128, the disrupted recycled pulsar J1434+7257, and the eclipsing binary MSP J1816+4510, which is in an 8.7 hr orbit with a redback-mass companion.

The recent observation of a common red-noise process in pulsar timing arrays (PTAs) suggests that the detection of nanohertz gravitational waves might be around the corner. However, in order to confidently attribute this red process to gravitational waves, one must observe the Hellings–Downs curve—the telltale angular correlation function associated with a gravitational-wave background. This effort is complicated by the complex modeling of pulsar noise. Without proper care, misspecified noise models can lead to false-positive detections. Background estimation using “quasi-resampling” methods such as sky scrambles and phase shifts, which use the data to characterize the noise, are therefore important tools for assessing significance. We investigate the ability of current PTA experiments to estimate their background with “quasi-independent” scrambles—characterized by a statistical “match” below the fiducial value: ∣ M ∣ < 0.1. We show that sky scrambling is affected by “saturation” after ${ \mathcal O }(10)$ quasi-independent realizations; subsequent scrambles are no longer quasi-independent. We show that phase scrambling saturates after ${ \mathcal O }(100)$ quasi-independent realizations. With so few independent scrambles, it is difficult to make reliable statements about the ≳5 σ tail of the null distribution of the detection statistic. We sketch out various methods by which one may increase the number of independent scrambles. We also consider an alternative approach, wherein one reframes the background estimation problem so that the significance is calculated using statistically dependent scrambles. The resulting p -value is in principle well defined, but may be susceptible to failure if assumptions about the data are incorrect.

Black widows are millisecond pulsars ablating their companions. The material blown from the companion blocks the radio emission, resulting in radio eclipses. The properties of the eclipse medium are poorly understood. Here, we present direct evidence of the existence of magnetic fields in the eclipse medium of the black widow PSR J2051−0827 using observations made with the Five-hundred-meter Aperture Spherical radio Telescope. We detect a regular decrease in rotation measure (RM) in the egress of the eclipse, changing from 60 to −28.7 rad m ^−2 . The RM gradually changes back to normal when the line of sight moves away from the eclipse. The estimated line-of-sight magnetic field strength in the eclipse medium is ∼0.1 G. The RM reversal could be caused by a change in the magnetic field strength along the line of sight due to binary orbital motion. The RM reversal phenomenon has also been observed in some repeating fast radio bursts (FRBs), and the study of spider pulsars may provide additional information about the origin of FRBs.

We report optical observations of the millisecond pulsar binary system PSR J1622–0315 with the Lulin 1 m telescope in Taiwan and the Lijiang 2.4 m telescope in China between 2019 and 2021. The companion of the pulsar, which is of V ∼ 19 mag, showed ellipsoidal-distorted orbital variations in its light curves. The best-fit model to the light curves, with the binary code PHOEBE , gives a companion mass of 0.122 ± 0.006 M _⊙ . This places PSR J1622–0315 in the spider-system subclass. We compared the properties of PSR J1622–0315 with other spider pulsar binaries for the scalings between the spin-down luminosity derived for the pulsar, irradiation luminosity of the companion, and X-ray luminosity of the binary. We find that pulsar irradiation in PSR J1622–0315 is insignificant and the irradiation luminosity of the transitional millisecond pulsars PSR J1023+0038 and PSR J1227–4853 are the highest among the redback systems.

Pulsar distances are notoriously difficult to measure, and play an important role in many fundamental physics experiments, such as pulsar timing arrays. Here, we perform a cross-match between International PTA pulsars (IPTA) and Gaia's Data Release 2 (DR2) and Data Release 3 (DR3). We then combine the IPTA pulsar’s parallax with its binary companion’s parallax, found in Gaia, to improve the distance measurement to the binary. We find seven cross-matched IPTA pulsars in Gaia DR2, and when using Gaia DR3 we find six IPTA pulsar cross-matches but with seven Gaia objects. Moving from Gaia DR2 to Gaia DR3, we find that the Gaia parallaxes for the successfully cross-matched pulsars improved by 53%, and pulsar distances improved by 29%. Finally, we find that binary companions with a

We report the discovery of a 2.11 ms binary millisecond pulsar during a targeted search of the redback optical candidate coincident with the γ -ray source 3FGL J0212.5+5320 using the Robert C. Byrd Green Bank Telescope (GBT) with the Breakthrough Listen backend at L band. Over a seven month period, five pointings were made near inferior conjunction of the pulsar in its 20.9 hr orbit, resulting in two detections, lasting 12 and 42 minutes. The pulsar dispersion measure (DM) of 25.7 pc cm ^−3 corresponds to a distance of 1.15 kpc in the NE2001 Galactic electron density model, consistent with the Gaia parallax distance of 1.16 ± 0.03 kpc for the companion star. We suspect the pulsar experiences wide orbital eclipses, similar to other redbacks, as well as scintillation and DM delays caused by its interaction with its companion and surroundings. Although the pulsar was only detected over ≈3.7% of the orbit, its measured acceleration is consistent with published binary parameters from optical radial velocity spectroscopy and light-curve modeling of the companion star, and it provides a more precise mass ratio and a projected semimajor axis for the pulsar orbit. We also obtained a refined optical photometric orbit ephemeris, and observed variability of the tidally distorted companion over 7 yr. A hard X-ray light curve from NuSTAR shows expected orbit-modulated emission from the intrabinary shock. The pulsar parameters and photometric ephemeris greatly restrict the parameter space required to search for a coherent timing solution including pulsar spin-down rate, either using Fermi γ -rays or further radio pulse detections.

It has been shown that the nonminimal coupling between geometry and matter can provide models for massive compact stars that are consistent with the conformal bound on the sound speed, $0\leqslant {c}_{s}^{2}\leqslant {c}^{2}/3$ , where the core density approaches a few times the nuclear saturation density. We impose the conformal upper bound on the sound speed on Rastall’s field equations of gravity, with Krori–Barua potentials in the presence of an anisotropic fluid as a matter source, to estimate the radius of the most massive pulsar ever observed, PSR J0952–0607. For its measured mass M = 2.35 ± 0.17 M _⊙ , we obtain a radius R = 14.087 ± 1.0186 km as inferred by the model. We investigate a possible connection between Rastall gravity and the MIT bag model with an equation of state, ${p}_{r}(\rho )\approx {c}_{s}^{2}\left(\rho -{\rho }_{{\rm{s}}}\right)$ , in the radial direction, with ${c}_{s}=c/\sqrt{3}$ and a surface density ρ _s slightly above the nuclear saturation density ρ _nuc = 2.7 × 10 ^14 g cm ^–3 . The corresponding mass–radius diagram is in agreement with our estimated value of the radius and with astrophysical observations of other pulsars at 68% confidence level.

We report on the discovery of the companion star to the millisecond pulsar PSR J1835−3259B in the Galactic globular cluster NGC 6652. Taking advantage of deep photometric archival observations acquired through the Hubble Space Telescope in near-UV and optical bands, we identified a bright and blue object at a position compatible with that of the radio pulsar. The companion is located along the helium-core white dwarf cooling sequence, and the comparison with binary evolution models provides a mass of 0.17 ± 0.02 M _⊙ , a surface temperature of 11,500 ± 1900 K, and a very young cooling age of only 200 ± 100 Myr. The mass and the age of the companion are compatible with a progenitor star of about 0.87 M _⊙ , which started transferring mass to the primary during its evolution along the subgiant branch and stopped during the early red giant branch phase. Combining together the pulsar mass function and the companion mass, we found that this system is observed at an almost edge-on orbit and hosts a neutron star with a mass of 1.44 ± 0.06 M _⊙ , thus suggesting a highly nonconservative mass accretion phase. The young age of the WD companion is consistent with the scenario of a powerful, relatively young MSP indicated by the earlier detection of gamma-rays from this system.

The timing follow-up of newly discovered millisecond pulsars (MSPs) is hindered by the larger positional uncertainty (a few tens of arcminutes) associated with the discovery. In this paper, we present the localization of two MSPs, discovered by the GMRT High Resolution Southern Sky survey, up to arcsecond accuracy using a 33 MHz offline coherently dedispersed gated correlator. This gated correlator is an upgraded version of the earlier 16 MHz design. This new development with a factor of 2 enhancement in the observing bandwidth offers better sensitivity in the image domain, leading to more precise localization. Aided by the precise position, we followed up these two MSPs with sensitive phased-array (PA) beams of upgraded GMRT from 300 to 1460 MHz. More sensitive observations in the PA mode for these two MSPs yield precise (∼sub- μ s) time-of-arrivals, with dispersion measure uncertainties in the range of 10 ^−4 –10 ^−5 pc cm ^−3 . We also report the profile evolution of the two MSPs over 300–1460 MHz. Finally, we discuss the suitability of these MSPs for the pulsar timing array experiments aimed to detect low-frequency gravitational waves.

In 2018 an ultra–wide-bandwidth low-frequency (UWL) receiver was installed on the 64 m Parkes Radio Telescope, enabling observations with an instantaneous frequency coverage from 704 to 4032 MHz. Here we present the analysis of a 3 yr data set of 35 ms pulsars observed with the UWL by the Parkes Pulsar Timing Array, using wide-band timing methods. The two key differences compared to typical narrowband methods are (1) generation of two-dimensional templates accounting for pulse shape evolution with frequency and (2) simultaneous measurements of the pulse time of arrival (TOA) and dispersion measure (DM). This is the first time that wide-band timing has been applied to a uniform data set collected with a single large fractional bandwidth receiver, for which such techniques were originally developed. As a result of our study, we present a set of profile evolution models and new timing solutions, including initial noise analysis. Precision of our TOA and DM measurements is in the range of 0.005–2.08 μ s and (0.043–14.24) × 10 ^−4 cm ^−3 pc, respectively, with 94% of the pulsars achieving a median TOA uncertainty of less than 1 μ s.

Results from 11 yr of radio timing for the eclipsing black widow millisecond pulsar (MSP) binary J1544+4937 is presented in this paper. We report a phase-connected timing model for this MSP, using observations with the Giant Metrewave Radio Telescope (GMRT) at multiple frequencies and with the Green Bank Telescope. This is the longest-duration timing study of any galactic-field MSP with the GMRT. While extending the timing baseline from the existing 1.5 yr to about a decade we report the first detection for a significant value of proper motion ( μ _T ∼ 10.14(5) mas yr ^−1 ) for this pulsar. Temporal variations of dispersion measure (ΔDM ∼ 10 ^−3 pc cm ^−3 ) manifested by significant determination of first-, second-, and third-order dispersion measure (DM) derivatives are observed along the line of sight to the pulsar. We also noticed frequency-dependent DM variations of the order of 10 ^−3 pc cm ^−3 , which could arise due to spatial electron density variations in the interstellar medium. This study has revealed a secular variation of the orbital period for this MSP for the first time. We investigated possible causes and propose that variation in the gravitational quadrupole moment of the companion could be responsible for the observed temporal changes in the orbital period.

We present the study of multiwavelength observations of an unidentified Fermi Large Area Telescope (LAT) source, 4FGL J1910.7−5320, a new candidate redback millisecond pulsar binary. In the 4FGL 95% error region of 4FGL J1910.7−5320, we find a possible binary with a 8.36 hr orbital period from the Catalina Real-Time Transient Survey, confirmed by optical spectroscopy using the SOAR telescope. This optical source was recently independently discovered as a redback pulsar by the TRAPUM project, confirming our prediction. We fit the optical spectral energy distributions of 4FGL J1910.7−5320 with a blackbody model, inferring a maximum distance of 4.1 kpc by assuming that the companion fills its Roche lobe with a radius of R = 0.7 R _☉ . Using a 12.6 ks Chandra X-ray observation, we identified an X-ray counterpart for 4FGL J1910.7−5320, with a spectrum that can be described by an absorbed power law with a photon index of 1.0 ± 0.4. The spectrally hard X-ray emission shows tentative evidence for orbital variability. Using more than 12 yr of Fermi-LAT data, we refined the position of the γ -ray source, and the optical candidate still lies within the 68% positional error circle. In addition to 4FGL J1910.7−5320, we find a variable optical source with a periodic signal of 4.28 hr inside the 4FGL catalog 95% error region of another unidentified Fermi source, 4FGL J2029.5−4237. However, the γ -ray source does not have a significant X-ray counterpart in an 11.7 ks Chandra observation, with a 3 σ flux upper limit of 2.4 × 10 ^−14 erg cm ^−2 s ^−1 (0.3–7 keV). Moreover, the optical source is outside our updated Fermi-LAT 95% error circle. These observational facts all suggest that this new redback millisecond pulsar powers the gamma-ray source 4FGL J1910.7−5320 while 4FGL J2029.5−4237 is unlikely the γ -ray counterpart to the 4.28 hr variable.

We present timing solutions for 12 pulsars discovered in the Green Bank North Celestial Cap 350 MHz pulsar survey, including six millisecond pulsars (MSPs), a double neutron star (DNS) system, and a pulsar orbiting a massive white dwarf companion. Timing solutions presented here include 350 and 820 MHz Green Bank Telescope data from initial confirmation and follow-up, as well as a dedicated timing campaign spanning 1 ryr PSR J1122−3546 is an isolated MSP, PSRs J1221−0633 and J1317−0157 are MSPs in black widow systems and regularly exhibit eclipses, and PSRs J2022+2534 and J2039−3616 are MSPs that can be timed with high precision and have been included in pulsar timing array experiments seeking to detect low-frequency gravitational waves. PSRs J1221−0633 and J2039−3616 have Fermi Large Area Telescope gamma-ray counterparts and also exhibit significant gamma-ray pulsations. We measure proper motions for three of the MSPs in this sample and estimate their space velocities, which are typical compared to those of other MSPs. We have detected the advance of periastron for PSR J1018−1523 and therefore measure the total mass of the DNS system, m _tot = 2.3 ± 0.3 M _⊙ . Long-term pulsar timing with data spanning more than 1 yr is critical for classifying recycled pulsars, carrying out detailed astrometry studies, and shedding light on the wealth of information in these systems post-discovery.

We have performed a systematic study of the rotational, orbital, and X-ray properties of millisecond pulsars (MSPs) in globular clusters (GCs) and compared their nature with those of the MSPs in the Galactic field (GF). We found that GC MSPs generally rotate slower than their counterparts in the GF. Different from the expectation of a simple recycling scenario, no evidence for the correlation between the orbital period and the rotation period can be found in the MSP binaries in GCs. There is also an indication that the surface magnetic field of GC MSPs is stronger than those in the GF. All these suggest dynamical interactions in GCs can alter the evolution of MSPs/their progenitors, which can leave an imprint on their X-ray emission properties. While the MSPs in both GF and GCs have similar distributions of X-ray luminosity and hardness, our sample supports the notion that these two populations follow different relations between the X-ray luminosity and spin-down power. We discuss this in terms of both the pulsar emission model and the observational bias.

Superluminous supernovae (SLSNe) are a rare class of stellar explosions with luminosities ∼ 10–100 times greater than ordinary core-collapse supernovae. One popular model to explain the enhanced optical output of hydrogen-poor (Type I) SLSNe invokes energy injection from a rapidly spinning magnetar. A prediction in this case is that high-energy gamma-rays, generated in the wind nebula of the magnetar, could escape through the expanding supernova ejecta at late times (months or more after optical peak). This paper presents a search for gamma-ray emission in the broad energy band from 100 MeV to 30 TeV from two Type I SLSNe, SN2015bn, and SN2017egm, using observations from Fermi-LAT and VERITAS. Although no gamma-ray emission was detected from either source, the derived upper limits approach the putative magnetar’s spin-down luminosity. Prospects are explored for detecting very-high-energy (VHE; 100 GeV–100 TeV) emission from SLSNe-I with existing and planned facilities such as VERITAS and CTA.

We present updated measurements of the X-ray properties of the pulsar wind nebula associated with the TeV γ -ray source HESS J1640-465 derived from Chandra and Nuclear Spectroscopic Telescope Array data. We report a high N _H value along the line of sight, consistent with previous work, which led us to incorporate the effects of dust scattering in our spectral analysis. Due to uncertainties in the dust scattering, we report a range of values for the PWN properties (photon index and unabsorbed flux). In addition, we fit the broadband spectrum of this source and found evidence for spectral softening and decreasing unasborbed flux as we go to higher photon energies. We then used a one-zone time-dependent evolutionary model to reproduce the dynamical and multiwavelength spectral properties of our source. Our model suggests a short spin-down timescale, a relatively higher than average magnetized pulsar wind, a strong pulsar wind nebula magnetic field and maximum electron energy up to PeV, suggesting HESS J1640-465 could be a PeVatron candidate.

Pulsar timing arrays (PTAs) are searching for nanohertz-frequency gravitational waves (GWs) through cross-correlation of pulse arrival times from a set of radio pulsars. PTAs have relied on a frequency-shift formula of the pulse, where planar GWs are usually assumed. Phase corrections due to the wave front curvature have been recently discussed. In this paper, frequency-shift and timing-residual formulae are derived for GWs with fully spherical wave fronts from a compact source such as a binary of supermassive black holes, where the differences in the GW amplitude and direction between Earth and the pulsar are examined in the quadrupole approximation. By using the new formulae, effects beyond the plane-wave approximation are discussed, and a galactic center PTA and nearby GW source candidates are also mentioned.

The standard technique for very low-frequency gravitational wave detection is mainly based on searching for a specific spatial correlation in the variation of the times of arrival of the radio pulses emitted by millisecond pulsars with respect to a timing model. This spatial correlation, which in the case of the gravitational wave background must have the form described by the Hellings and Downs function, has not yet been observed. Therefore, despite the numerous hints of a common red noise in the timing residuals of many millisecond pulsars compatible with that expected for the gravitational wave background, its detection has not yet been achieved. By now, the reason is not completely clear and, from some recent works, the urgency to adopt new detection techniques, possibly complementary to the standard one, is emerging clearly. Of course, this demand also applies to the detection of continuous gravitational waves emitted by supermassive black hole binaries populating the Universe. In the latter case, important information could, in principle, emerge from the millisecond pulsars considered individually in a single-pulsar search of continuous GWs. In this context, the surfing effect can then be exploited, helping to select the best pulsars to carry out such analysis. This paper aims to clarify when the surfing effect occurs and describe it exhaustively. A possible application to the case of the supermassive black hole binary candidate PKS 2131–021 and millisecond pulsar J2145–0750 is also analyzed.