PSR J1614-2230 Research Articles

Stability of a realistic astrophysical pulsar and its mass–radius relation in higher-order curvature gravity

The objective of this research is to explore compact celestial objects while considering the framework of an extended gravitational theory known as R+f(G) gravity. The notations R and G denote the Ricci scalar and the Gauss–Bonnet invariant, respectively. Radio pulsars, which are neutron stars with masses greater than 1.8 times that of the Sun (M⊙), provide exceptional opportunities for delving into fundamental physics in extraordinary environments unparalleled in the observable universe and surpassing the capabilities of experiments conducted on Earth. Through the utilization of both the linear and quadratic expressions of the function f(G)=α1G2, where α1 (with dimensional units of [length6]) are incorporated, we have achieved an accurate analytical solution for anisotropic perfect-fluid spheres in a state of hydrostatic equilibrium. By integrating the dimensional parameters α1 and the compactness factor, defined as C=2GMRc2, we showcase our capacity to encompass and depict all physical characteristics within the stellar structure. We illustrate that the model is capable of producing a stable arrangement for the pulsar PSR J0740+6620, encompassing its geometric and physical properties. We illustrate that by utilizing the quadratic form of G in the R+f(G) framework, the Krori-Barua ansatz establishes semi-analytical relationships between radial pressure (pr), tangential pressure (pt), and density (ρ). Remarkably, in the context of the positive/negative α1 quadratic R+f(G) gravity framework, the maximum compactness is inherently restricted to values fail below the Buchdahl limit when the surface density exceeds 4×1014 g/cm3. This differs from General Relativity (GR) in which the compactness is unlikely to approach the black hole limit. The model predicts a core density that is multiple times greater than the saturation nuclear density, represented as ρnuc=4×1014 g/cm3, and a surface density ρs that surpasses the nuclear saturation density. We offer the mass–radius diagram associated with the boundary density we have determined, and this diagram has been shown to be consistent with other observational discoveries.

Radio Polarization of Millisecond Pulsars with Multipolar Magnetic Fields

NICER has observed a few millisecond pulsars where the geometry of the X-ray-emitting hotspots on the neutron star have been analyzed in order to constrain the mass and radius from X-ray light-curve modeling. One example, PSR J0030 + 0451, has been shown to possibly have significant multipolar magnetic fields at the stellar surface. Using force-free simulations of the magnetosphere structure, it has been shown that the radio, X-ray, and γ-ray light curves can be modeled simultaneously with an appropriate field configuration. An even more stringent test is to compare predictions of the force-free magnetosphere model with observations of radio polarization. This paper attempts to reproduce the radio polarization of PSR J0030 + 0451 using a force-free magnetospheric solution. As a result of our modeling, we can reproduce certain features of the polarization well.

Revision of the GeV γ-Ray Emission in the Region of HESS J1813-178 with Fermi-LAT

HESS J1813-178 is one of the brightest and most compact TeV γ-ray sources, and whether its γ-ray emission is associated with supernova remnant (SNR), pulsar wind nebula (PWN), or young stellar cluster (YSC) is still under debate. By analyzing the GeV γ-ray data in the field of HESS J1813-178 using 14 yr of PASS 8 data recorded by the Fermi Large Area Telescope (Fermi-LAT), we report the discovery of three different sources with different spectra in this region. The hard source with a PL spectral index of 2.11 ± 0.08 has a small size extension, which is spatially and spectrally coincident with the TeV γ-ray emission from HESS J1813-178. CO observations display the dense molecular clouds surrounding HESS J1813-178 in the velocity range of 45–60 km s−1. The possible origins of the γ-ray emission from HESS J1813-178 are discussed, including SNR G12.820.02, the PWN driven by the energetic X-ray pulsar PSR J1813-1749 and YSC Cl 1813-178. However, none of them can be ruled out clearly. Note that the maximum energy of protons in the hadronic model should exceed a few hundred TeV, which makes HESS J1813-178 a promising PeVatron. A detailed LHAASO data analysis about the morphology and spectrum would be helpful to investigate the origin of the γ-ray emission in this region and test its PeVatron nature.

An Unusual Pulse Shape Change Event in PSR J1713+0747 Observed with the Green Bank Telescope and CHIME

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.

Stability analysis of anisotropic stellar structures in Rastall theory of gravity utilizing cracking technique

In this manuscript, we employ the cracking technique in the Rastall gravity framework to assess how local density perturbations affect the stability of anisotropic stellar structures. To achieve this, we developed field equations for spherically symmetric spacetime with the charge inclusion in the context of Rastall gravity and then employed the krori Barua approach and barotropic equation of state while considering Reissner–Nordstrom metric as exterior spacetime, to develop the solution of the field equations. Further, we formulated the Tolman–Oppenheimer–Volkoff (TOV) equation by considering the non-conservation of energy–momentum tensor in the context of Rastall gravity. The stability of configuration is then disrupted by incorporating local density perturbations. Subsequently, our proposed approach is employed on the following compact stars: Her X-1, SAX J1808.4-3658, 4U 1820-30, PSR J1614-2230, Vela X-1, Cen X-3, and RXJ1856-37 to demonstrate its viability. The findings demonstrate that all stars under consideration experience cracking. This work particularly emphasizes the crucial role of cracking method in offering insightful information on the stability analysis of anisotropic stellar structures.

A comprehensive study of massive compact star admitting conformal motion under bardeen geometry

This article primarily investigates the existence of the charged compact star under the conformal motion treatment within the context of f(Q) gravity. We have developed two models by implementing the power-law and linear form of conformal factor, enabling an in-depth comparison in our study. We have selected the MIT Bag model equation of state to describe the connection between pressure and energy density and matched the interior spherically symmetric space-time with the Bardeen space-time. In addition, the present research examines various physically valid characteristics of realistic stars, such as PSR J1614−2230, PSR J1903+327, Vela X-1, Cen X-3, and SMC X-1. We compare two constructed models by attributing the behavior of density, pressure, equilibrium conditions, and the adiabatic index. We have additionally included a brief analysis of the scenario involving Reissner-Nordstrom spacetime as an external geometry for the matching condition. In contrast to the Reissner-Nordstrom instance, the Bardeen model with the extra term in the asymptotic representations yields a more intriguing and viable result. The current analysis reveals that the resulting compact star solutions are physically acceptable and authentic when considering the presence of charge with conformal motion in f(Q) gravity.

Extracting the hyperon-nucleon interaction via collective flows in heavy-ion collisions

The 2-body hyperon-nucleon interaction softens the equation of state of neutron star matter and leads to the maximum mass of neutron star to be 1.3-1.6M⊙, which deviates from the recent observation with the masses of PSR J0348+0432 (2.01±0.04M⊙) and J0740+6620 (2.14−0.09+0.10M⊙). One attempt is to introduce the more repulsive hyperon-nucleon interaction above the saturation density. A phenomenological Λ potential by fitting the 3-body ΛNN results of chiral effective field theory is implemented into the quantum molecular dynamics transport model to solve the ‘hyperon puzzle’ in neutron stars. It is found that the directed and elliptic flows are sensitive to the high-density hyperon-nucleon potentials in collisions of 197Au + 197Au and 124Sn + 124Sn. The influence of the phenomenological potential on the Λ yields, rapidity distributions and transverse momentum spectra is negligible in comparison with the ones calculated by the well-known relativistic mean-field model. The inclusion of the ΛN, ΣN and ΞN potentials leads to the reduction of hyperon production in the midrapidity region. The Λ directed flows and the slope in the midrapidity region are enhanced with the phenomenological potential and more consistent with the STAR data in collisions of 197Au + 197Au at sNN=3 GeV.

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This work investigates static and dynamical quark star properties within a D3-D7\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$D_3{-}D_7$$\\end{document} holographic model. We solve the Tolman–Oppenheimer–Volkoff equations for the quark matter equation of state obtained from the brane configuration. We determine the mass-radius diagram for a range of model parameters and compare with recent NICER observational data for the pulsars PSR J0030+0451\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$0030+0451$$\\end{document} and PSR J0740+6620.\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$0740+6620.$$\\end{document} Motivated by the GW170817 event detected by the LIGO-Virgo collaboration, we also calculate the tidal deformability parameter obtained for each component of the binary star system. We show that quark stars composed of flavor-independent quark matter derived from the D3-D7\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$D_3{-}D_7$$\\end{document} holographic model are not able to satisfy simultaneously the LIGO-Virgo and NICER astrophysical bounds.

Pulse Jitter and Single-pulse Variability in Millisecond Pulsars

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.

Upper Limits on the Radio Pulses from Magnetars and a Central Compact Object with FAST

Magnetars and central compact objects (CCOs) are subgroups of neutron stars that show a number of properties distinguished from canonical radio pulsars. We performed radio observations of three magnetars, SGR 0418+5729, 1E 2259+586, and 4U 0142+61, and a CCO, PSR J1852+0040, with the Five-hundred-meter Aperture Spherical radio Telescope at 1.25 GHz, aiming to search for radio pulsations in their quiescent states. During two observation epochs, no radio pulses have been detected toward any target above a significance of signal-to-noise ratio = 7 from either the direct folding or blind search. We provided the most stringent upper limit of radio flux (≲2–4 μJy) for the magnetars and the CCO. For the magnetars with long periods, the real upper limits are likely 1 order of magnitude larger due to the red noise. The deep radio observations suggest that these magnetars and the CCO are indeed radio-quiet sources or unfavorably beamed.

Correction to: Investigation of states switch properties of PSR J1946 + 1805 with the FAST

Correction to: Investigation of states switch properties of PSR J1946 + 1805 with the FAST

Formation of PSR J1012+5307 with an Extremely Low-mass White Dwarf: Testing Magnetic Braking Models

PSR J1012+5307 is a millisecond pulsar with an extremely low-mass white dwarf (WD) companion in an orbit of 14.5 hr. Magnetic braking (MB) plays an important role in influencing the orbital evolution of binary systems with a low-mass (≲1–2 M ⊙) donor star. At present, there exist several different MB descriptions. In this paper, we investigate the formation of PSR J1012+5307 as a probe to test plausible MB models. Employing a detailed stellar evolution model with the MESA code, we find that the convection- and rotation-boosted MB and “Intermediate” MB models can reproduce the WD mass, WD radius, WD surface gravity, neutron star mass, and orbital period observed in PSR J1012+5307. However, our simulated WD has a higher effective temperature than the observations. Three other MB mechanisms, including the standard MB model, are too weak to account for the observed orbital period in the Hubble time. A long cooling timescale caused by H-shell flashes of the WD may alleviate the discrepancy between the simulated effective temperature and the observed value.

A MeerKAT view of the double pulsar eclipses

The double pulsar system, PSR J0737−3039A/B, consists of two neutron stars bound together in a highly relativistic orbit that is viewed nearly edge-on from the Earth. This alignment results in brief radio eclipses of the fast-rotating pulsar A when it passes behind the toroidal magnetosphere of the slow-rotating pulsar B. The morphology of these eclipses is strongly dependent on the geometric orientation and rotation phase of pulsar B, and their time evolution can be used to constrain the geodetic precession rate of the pulsar. We demonstrate a Bayesian inference framework for modelling high-sensitivity eclipse light curves obtained with MeerKAT between 2019 and 2023. Using a hierarchical inference approach, we obtained a precession rate of ΩSOB = 5.16°−0.34°+0.32° yr−1 (68% confidence intervals) for pulsar B, consistent with predictions from general relativity to a relative uncertainty of 6.5%. This updated measurement provides a 6.1% test of relativistic spin-orbit coupling in the strong-field regime. We show that a simultaneous fit to all of our observed eclipses can in principle return a ∼1.5% test of spin-orbit coupling. However, systematic effects introduced by the current geometric orientation of pulsar B along with inconsistencies between the observed and predicted eclipse light curves result in difficult to quantify uncertainties when using this approach. Assuming the validity of general relativity, we definitively show that the spin axis of pulsar B is misaligned from the total angular momentum vector by 40.6° ±0.1° and that the orbit of the system is inclined by approximately 90.5° from the direction of our line of sight. Our measured geometry for pulsar B suggests the largely empty emission cone contains an elongated horseshoe-shaped beam centred on the magnetic axis, and that it may not be re-detected as a radio pulsar until early 2035.

Towards Uncovering Dark Matter Effects on Neutron Star Properties: A Machine Learning Approach

Over the last few years, researchers have become increasingly interested in understanding how dark matter affects neutron stars, helping them to better understand complex astrophysical phenomena. In this paper, we delve deeper into this problem by using advanced machine learning techniques to find potential connections between dark matter and various neutron star characteristics. We employ Random Forest classifiers to analyze neutron star (NS) properties and investigate whether these stars exhibit characteristics indicative of dark matter admixture. Our dataset includes 32,000 sequences of simulated NS properties, each described by mass, radius, and tidal deformability, inferred using recent observations and theoretical models. We explore a two-fluid model for the NS, incorporating separate equations of state for nucleonic and dark matter, with the latter considering a fermionic dark matter scenario. Our classifiers are trained and validated in a variety of feature sets, including the tidal deformability for various masses. The performance of these classifiers is rigorously assessed using confusion matrices, which reveal that NS with admixed dark matter can be identified with approximately 17% probability of misclassification as nuclear matter NS. In particular, we find that additional tidal deformability data do not significantly improve the precision of our predictions. This article also delves into the potential of specific NS properties as indicators of the presence of dark matter. Radius measurements, especially at extreme mass values, emerge as particularly promising features. The insights gained from our study are pivotal for guiding future observational strategies and enhancing the detection capabilities of dark matter in NS. This study is the first to show that the radii of neutron stars at 1.4 and 2.07 solar masses, measured using NICER data from pulsars PSR J0030+0451 and PSR J0740+6620, strongly suggest that the presence of dark matter in a neutron star is more likely than only hadronic composition.

Post-Newtonian binary dynamics in the effective field theory of Horndeski gravity* *Supported by National Key Research and Development Program of China (2021YFC2201901) and National Natural Science Foundation of China (12147103, 11851302)

General relativity has been very successful since its proposal more than a century ago. However, various cosmological observations and theoretical consistency still motivate us to explore extended gravity theories. Horndeski gravity stands out as one attractive theory by introducing only one scalar field. Here we formulate the post-Newtonian effective field theory of Horndeski gravity and investigate the conservative dynamics of inspiral compact binary systems. We calculate the leading effective Lagrangian for a compact binary and obtain the periastron advance per period. In particular, we apply our analytical calculation to two binary systems, PSR B 1534+12 and PSR J0737-3039, and constrain the relevant model parameters. This theoretical framework can also be systematically extended to higher orders.

An Updated Mass–Radius Analysis of the 2017–2018 NICER Data Set of PSR J0030+0451

In 2019 the NICER collaboration published the first mass and radius inferred for PSR J0030+0451, thanks to NICER observations, and consequent constraints on the equation of state characterizing dense matter. Two independent analyses found a mass of ∼1.3–1.4 M ⊙ and a radius of ∼13 km. They also both found that the hot spots were all located on the same hemisphere, opposite to the observer, and that at least one of them had a significantly elongated shape. Here we reanalyze, in greater detail, the same NICER data set, incorporating the effects of an updated NICER response matrix and using an upgraded analysis framework. We expand the adopted models and also jointly analyze XMM-Newton data, which enables us to better constrain the fraction of observed counts coming from PSR J0030+0451. Adopting the same models used in previous publications, we find consistent results, although with more stringent inference requirements. We also find a multimodal structure in the posterior surface. This becomes crucial when XMM-Newton data is accounted for. Including the corresponding constraints disfavors the main solutions found previously, in favor of the new and more complex models. These have inferred masses and radii of ∼[1.4 M ⊙, 11.5 km] and ∼[1.7 M ⊙, 14.5 km], depending on the assumed model. They display configurations that do not require the two hot spots generating the observed X-rays to be on the same hemisphere, nor to show very elongated features, and point instead to the presence of temperature gradients and the need to account for them.

A Possible γ-Ray Pulsation from PSR J1740−5340B in the Globular Cluster NGC 6397

Recently, a new radio millisecond pulsar (MSP) J1740−5340B, hosted in the globular cluster (GC) NGC 6397, was reported with a 5.78 ms spin period in an eclipsing binary system with a 1.97 days orbital period. Based on a modified radio ephemeris updated by tool tempo2, we analyze the ∼15 yr γ-ray data obtained from the Large Area Telescope on board the Fermi Gamma-ray Space Telescope and detect PSR J1740−5340B’s γ-ray pulsation at a confidence level of ∼4σ with a weighted H-test value of ∼26. By performing a phase-resolved analysis, the γ-ray luminosity in on-pulse interval of PSR J1740−5340B is L γ ∼ 3.8 × 1033 erg s−1 using NGC 6397's distance of 2.48 kpc. And γ-rays from the on-pulse part of PSR J1740−5340B contribute ∼90% of the total observed γ-ray emissions from NGC 6397. No significant γ-ray pulsation of another MSP J1740−5340A in the GC is detected. Considering that the previous four cases of MSPs in GCs, more data in γ-ray, X-ray, and radio are encouraged to finally confirm the γ-ray emissions from MSP J1740−5340B, especially starving for a precise ephemeris.

Quark matter and quark star in color-flavor-locked phase

In this work, we investigate the thermodynamical properties of strange quark matter (SQM) and color-flavor-locked (CFL) quark matter under strong magnetic fields by using a quasiparticle model. We calculate the energy density and the corresponding anisotropic pressure of both SQM and CFL quark matter. Our results indicate that CFL quark matter exhibits greater stability than the SQM, and the pressure of CFL quark matter increases with the energy gap constant <inline-formula><tex-math id="Z-20240223200049">\begin{document}$\varDelta $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231649_Z-20240223200049.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231649_Z-20240223200049.png"/></alternatives></inline-formula> increasing. We also observe that the oscillation effects coming from the lowest Landau level can be reduced by increasing the energy gap constant <inline-formula><tex-math id="Z-20240223200123">\begin{document}$ \varDelta $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231649_Z-20240223200123.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231649_Z-20240223200123.png"/></alternatives></inline-formula>, which cannot be observed in SQM under a similar strong magnetic field. The equivalent quark mass for u, d, and s quark and the chemical potential for each flavor of quarks decrease with the energy gap constant <inline-formula><tex-math id="Z-20240223200141">\begin{document}$ \varDelta $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231649_Z-20240223200141.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231649_Z-20240223200141.png"/></alternatives></inline-formula> increasing, which matches the conclusion that CFL quark matter is more stable than SQM. From the calculations of the magnetars with SQM and CFL quark matter, we find that the maximum mass of magnetars increases with the energy gap constant <inline-formula><tex-math id="Z-20240223200204">\begin{document}$\varDelta $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231649_Z-20240223200204.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231649_Z-20240223200204.png"/></alternatives></inline-formula> increasing for both the longitudinal and the transverse orientation distribution of magnetic field. Additionally, the tidal deformability of the magnetars increases with the <inline-formula><tex-math id="Z-20240223200231">\begin{document}$\varDelta $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231649_Z-20240223200231.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231649_Z-20240223200231.png"/></alternatives></inline-formula> increasing. On the other hand, the central baryon density of the maximum mass of the magnetars decreases with the <inline-formula><tex-math id="Z-20240223200245">\begin{document}$\varDelta $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231649_Z-20240223200245.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231649_Z-20240223200245.png"/></alternatives></inline-formula> increasing. The results also indicate that the mass-radius lines of the CFL quark star can also satisfy the new estimates of the mass-radius region from PSR J0740 + 6620, PSR J0030 + 0451, and HESS J1731-347.

Chandra X-Ray Observatory Observations of 13 Fermi LAT Sources

In the latest data release from the Fermi Gamma-ray Space Telescope (the 4th Fermi LAT 14 yr Catalog, or 4FGL), more than 50% of the Galactic sources are yet to be identified. We observed 13 unidentified Fermi LAT sources with the Chandra X-Ray Observatory to explore their nature. We report the results of the classification of X-ray sources in the fields of these γ-ray sources and discuss the implications for their nature. We use multiwavelength (MW) data for a machine-learning classification, accompanied by a more detailed spectral/variability analysis for brighter sources. Eight 4FGL sources have γ-ray pulsars within their position error ellipses. We consider three of these pulsars (PSR J1906+0722, PSR J1105–6037, and PSR J1358–6025) to be detected in X-rays, while PSR J1203–6242 shows a hint of X-ray emission. Within the positional uncertainties of three of the 4FGL sources, we detect X-ray sources that may be yet unknown pulsars, depending on the MW association. In addition to point sources, we discovered two extended sources, one of which is likely to be a bow-shock pulsar-wind nebula associated with PSR J1358–6025. Finally, we classify other X-ray sources detected in these observations and report the most interesting classifications.

Hybrid stars and the stiffness of the nuclear equation of state in light of the HESS J1731-347 remnant

The recent observation of the extremely compact neutron star in the HESS J1731-347 remnant has challenged our understanding concerning the nature of dense nuclear matter. In particular, the low radius of the aforementioned compact object favors soft nuclear equations of state. However, the neutron skin thickness of 208Pb extracted from the long-awaited PREX-II experiment favors stiff equations of state which may be associated with larger radii for low mass stellar configurations. In this contribution we present our recent work on the possible reconciliation of the HESS J1731-347 observation in the framework of hybrid stars, under the assumption of a stiff low-density phase which may be favored by the PREX-II results. In addition, we examine the compatibility of the resulting hybrid models with recent constraints based on the observation of PSR J0030+0451, PSR J0952-0607 and GW190814.