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Material expelled from binary neutron star (BNS) mergers can harbour r-process nucleosynthesis and power a kilonova (KN), both intimately related to the astrophysical conditions of the ejection. In turn such conditions indirectly depend on the equation of state (EOS) describing matter inside the neutron star. Therefore, in principle the above observables can hold valuable information on nuclear matter, as the merger gravitational wave signal already does. In this work, we consider the outcome of a set of BNS merger simulations employing different finite-temperature nuclear EOSs. The latter are obtained from a Skyrme-type interaction model where nuclear properties, such as the incompressibility and the nucleon effective mass at saturation density, are systematically varied. We post-process the ejecta using a reaction network coupled with a semi-analytic KN model, to assess the sensitivity on the input EOS of the final yields and the KN light curves. Both of them are found to be non-trivially influenced by the EOS, with the overall outcome being dominated by the heterogeneous outflows from the remnant disc, hosting a variable degree of neutron-rich material. The dynamical ejecta can be more directly related to the EOS parameters considered; however, we find their role in the yields production and the KN emission too entangled with the other ejecta components, in order to infer solid correlations. This result highlights the strong degeneracy that intervenes between the merger outcome and the behaviour of the intrinsic nuclear matter, and places itself as a limit to the employment of EOS-constraining approaches of such kind. [ABSTRACT FROM AUTHOR]

The behaviour of a short gamma-ray burst (sGRB) afterglow light curve can reveal the angular structure of the relativistic jet and constrain the observer's viewing angle |$\theta _\textrm {obs}$|⁠. The observed deceleration time of the jet, and, therefore, the time of the afterglow peak, depends on the observer's viewing angle. A larger viewing angle leads to a later peak of the afterglow and a lower flux at peak. We utilize the earliest afterglow detections of 58 sGRBs detected with the Neil Gehrels Swift Observatory X-ray Telescope to constrain the ratio of the viewing angle |$\theta _\textrm {obs}$| to the jet's core |$\theta _\textrm {c}$|⁠. We adopt a power-law angular jet structure in both energy |$E(\theta)\propto \theta ^{-a}$| and Lorentz factor |$\Gamma (\theta)\propto \theta ^{-b}$| beyond the core. We find that either sGRBs are viewed within |$\theta _\textrm {obs}/\theta _\textrm {c}\lt 1$| or the initial Lorentz factor of material in their jet's core is extremely high (⁠|$\Gamma _0\gt 500$|⁠). If we consider tophat jets, we constrain 90 per cent of our sample to be viewed within |$\theta _\textrm {obs}/\theta _\textrm {c}\lt 1.06$| and 1.15 for our canonical and conservative afterglow scenarios. For a subset of events with measurements of the jet break, we can constrain |$\Gamma _0\theta _\textrm {c}\gtrsim 30$|⁠. This confirmation that cosmological sGRBs are viewed either on-axis or very close to their jet's core has significant implications for the nature of the prompt gamma-ray production mechanism and for the rate of future sGRB detections coincident with gravitational waves, implying that they are extremely rare. [ABSTRACT FROM AUTHOR]

XTE J1701−462 is a neutron star low-mass X-ray binary (NS LMXB) discovered in 2006 as the first system to demonstrate unambiguously that the 'Atoll' and 'Z' classes of accreting neutron stars are separated by accretion rate. Radio observations during the 2006/7 outburst provided evidence for the formation of a relativistic jet, as now expected for all accreting neutron star and black hole X-ray binaries at high-accretion rates. The source entered a new outburst in 2022, and we report 29 observations made with the MeerKAT radio telescope. The first radio detection was on the 16th September 2022, we continued detecting the source until mid-December 2022. Thereafter, establishing radio upper limits till 25 March 2023. We present the radio analysis alongside analysis of contemporaneous X-ray observations from MAXI. The radio light curve shows evidence for at least three flare-like events over the first hundred days, the most luminous of which has an associated minimum energy of |$1\times 10^{38}$|  erg. We provide a detailed comparison with the 2006/7 outburst, and demonstrate that we detected radio emission from the source for considerably longer in the more recent outburst, although this is probably a function of sampling. We further constrain the radio emission from the source to have a polarization of less than 9 per cent at the time of 2022 IXPE detection of X-ray polarization. Finally, we place the source in the radio–X-ray plane, demonstrating that when detected in radio it sits in a comparable region of parameter space to the other Z-sources. [ABSTRACT FROM AUTHOR]

Motivated by the recent detection of ultralong-period radio transients, we investigate new models of coherent radio emission via low-altitude electron–positron pair production in neutron stars (NSs) beyond rotationally powered curvature radiation deathlines. We find that plastic motion (akin to 'continental drift') and qualitatively similar thermoelectric action by temperature gradients in the crusts of slowly rotating, highly magnetized NSs could impart mild local magnetospheric twists. Regardless of which mechanism drives twists, we find that particle acceleration initiates pair cascades across charge-starved gaps above a mild critical twist. Cascades are initiated via resonant inverse-Compton scattered photons or curvature radiation, and may produce broad-band coherent radio emission. We compute the pair luminosity (maximum allowed radio luminosity) for these two channels, and derive deathlines and 'active zones' in |$P-\dot{P}$| space from a variety of considerations. We find these twist-initiated pair cascades only occur for magnetar-like field strengths |$B \gtrsim 10^{14}$|  G and long periods: |$P_{\rm RICS} \gtrsim 120 \,\, (T/10^{6.5} {\rm K})^{-5} \, {\rm s}$| and |$P_{\rm curv} \gtrsim 150 \,\, ({\rm v_{\rm pl}}/10^{3} {\, \rm cm \, yr^{-1}})^{-7/6} \, {\rm s}$|⁠. Using a simplified geometric model, we find that plastic motion or thermoelectrically driven twists might naturally reproduce the observed luminosities, time-scales, and timing signatures. We further derive 'active zones' in which rotationally powered pair creation occurs via resonantly scattered photons, beyond standard curvature deathlines for pulsars. All cascades are generically accompanied by simultaneous (non-)thermal X-ray/UV counterparts which might be detectable with current instrumentation. [ABSTRACT FROM AUTHOR]

In this manuscript, we present a novel approach to constructing a distinct anisotropic solution for spherically symmetric spacetime. Our investigation focuses on the Buchdahl metric potential to solved Einstein’s field equations, and studied it for the cases of Buchdahl parameter K, when K ∉ [ 0 , 1 ] . We have obtained six different solutions and to show that our models fit with observational data, these solutions are analyzed for some known compact stars like EXO 1785-248, SMC X-1, LMC X-4, Her X-1, SAX J1808.4-3658, 4U 1538-52 and PSR B0941+10. The model satisfies all the physical as well as stability conditions, which verify the validity of the model. We have also explored the hydrostatic equilibrium for an uncharged case using the TOV equation. As strong evidence for more realistic and viable models, we have also provided graphical representations wherever required. [ABSTRACT FROM AUTHOR]

The C 3 approach is an invariant formalism that utilizes the eigenvalues of the Riemann curvature tensor to match spacetimes across a specific matching surface. We apply this approach to match an anisotropic fluid with an exterior vacuum solution, including the case in which discontinuities appear on the matching surface. As a particular example, a class of analytic solutions, which describe the gravitational field of realistic neutron stars, is matched to the exterior Schwarzschild spacetime. [ABSTRACT FROM AUTHOR]

The Rapid Burster is a unique neutron star low-mass X-ray binary system, showing both thermonuclear v-I and accretion-driven Type-II X-ray bursts. Recent studies have demonstrated how coordinated observations of X-ray and radio variability can constrain jet properties of accreting neutron stars – particularly when the X-ray variability is dominated by discrete changes. We present a simultaneous very large array, Swift , and INTErnational Gamma-Ray Astrophysics Laboratory observing campaign of the Rapid Burster to investigate whether its jet responds to Type-II bursts. We observe the radio counterpart of the X-ray binary at its faintest-detected radio luminosity, while the X-ray observations reveal prolific, fast X-ray bursting. A time-resolved analysis reveals that the radio counterpart varies significantly between observing scans, displaying a fractional variability of |$38 \pm 5$|  per cent. The radio faintness of the system prevents the robust identification of a causal relation between individual Type-II bursts and the evolution of the radio jet. However, based on a comparison of its low-radio luminosity with archival Rapid Burster observations and other accreting neutron stars, and on a qualitative assessment of the X-ray and radio light curves, we explore the presence of a tentative connection between bursts and jet: i.e. the Type-II bursts may weaken or strengthen the jet. The former of those two scenarios would fit with magnetorotational jet models; we discuss three lines of future research to establish this potential relation between Type-II bursts and jets more confidently. [ABSTRACT FROM AUTHOR]

4U 1954 |$+$| 31 is a high-mass X-ray binary (HMXB) that contains a neutron star (NS) and an M supergiant companion. The NS has a spin period of |$\sim 5.4$| h. The traditional wind-accreting model requires an ultra-strong magnetic field for the NS to explain its extremely long spin period, which seems problematic for the NS with age of a few |$10^7$| yr. In this work, we take into account the unsteady feature of wind accretion, which results in alternation of the direction of the wind matter's angular momentum. Accordingly, the torque exerted by the accreted wind matter varies between positive and negative from time to time, and largely cancels out over long time. In such a scenario, NSs can naturally attain long spin periods without the requirement of a very strong magnetic field. This may also provide a reasonable explanation for the spin period distribution of long-period NSs in HMXBs. [ABSTRACT FROM AUTHOR]

A semi-analytic approximation is derived for the time-dependent fraction |$f_\gamma (t)$| of the energy deposited by radioactive decay |$\gamma$| -rays in a homologously expanding plasma of general structure. An analytic approximation is given for spherically symmetric plasma distributions. Applied to Kilonovae (KNe) associated with neutron stars mergers and Type Ia supernovae, our semi-analytic and analytic approximations reproduce, with a few per cent and 10 per cent accuracy, respectively, the energy deposition rates, |$\dot{Q}_{\rm dep}$|⁠ , obtained in numeric Monte Carlo calculations. The time |$t_\gamma$| beyond which |$\gamma$| -ray deposition is inefficient is determined by an effective frequency-independent |$\gamma$| -ray opacity |$\kappa _{\gamma ,\text{eff}}$|⁠ , |$t_\gamma = \sqrt{\kappa _{\gamma ,\text{eff}}\langle \Sigma \rangle t^2}$|⁠ , where |$\langle \Sigma \rangle \propto t^{-2}$| is the average plasma column density. For |$\beta$| -decay dominated energy release, |$\kappa _{\gamma ,\text{eff}}$| is typically close to the effective Compton scattering opacity, |$\kappa _{\gamma ,\text{eff}} \approx 0.025$| cm |$^{2}$|  g |$^{-1}$| with a weak dependence on composition. For KNe, |$\kappa _{\gamma ,\text{eff}}$| depends mainly on the initial electron fraction |$Y_e$|⁠ , |$\kappa _{\gamma ,\text{eff}} \approx 0.03(0.05)$| cm |$^{2}$|  g |$^{-1}$| for |$Y_e \gtrsim (\lesssim) 0.25$| (in contrast with earlier work that found |$\kappa _{\gamma ,\text{eff}}$| larger by 1–2 orders of magnitude for low |$Y_e$|⁠), and is insensitive to the (large) nuclear physics uncertainties. Determining |$t_\gamma$| from observations will therefore measure the ejecta |$\langle \Sigma \rangle t^2$|⁠ , providing a stringent test of models. For |$\langle \Sigma \rangle t^2=2\times 10^{11}~{\rm g\, {cm}^{-2}\, s^2}$|⁠ , a typical value expected for KNe, |$t_\gamma \approx 1$| d. [ABSTRACT FROM AUTHOR]

The thermal evolution of isolated neutron stars is a key element in unravelling their internal structure and composition and establishing evolutionary connections among different observational subclasses. Previous studies have predominantly focused on one-dimensional or axisymmetric two-dimensional models. In this study, we present the thermal evolution component of the novel three-dimensional magnetothermal code MATINS (MAgneto-Thermal evolution of Isolated Neutron Star). MATINS employs a finite volume scheme and integrates a realistic background structure, along with state-of-the-art microphysical calculations for the conductivities, neutrino emissivities, heat capacity, and superfluid gap models. This paper outlines the methodology employed to solve the thermal evolution equations in MATINS , along with the microphysical implementation that is essential for the thermal component. We test the accuracy of the code and present simulations with non-evolving magnetic fields of different configurations (all with electrical currents confined to the crust and a magnetic field that does not thread the core), to produce temperature maps of the neutron star surface. Additionally, for a specific magnetic field configuration, we show one fully coupled evolution of magnetic field and temperature. Subsequently, we use a ray-tracing code to link the neutron star surface temperature maps obtained by MATINS with the phase-resolved spectra and pulsed profiles that would be detected by distant observers. This study, together with our previous article focused on the magnetic formalism, presents in detail the most advanced evolutionary code for isolated neutron stars, with the aim of comparison with their timing properties, thermal luminosities and the associated X-ray light curves. [ABSTRACT FROM AUTHOR]

To date GW170817, produced by a binary neutron star (BNS) merger, is the only gravitational wave (GW) event with an electromagnetic counterpart. It was associated with a prompt short gamma-ray burst (GRB), an optical kilonova, and the afterglow of a structured off-axis relativistic jet. We model the prospects for future mergers discovered in gravitational waves to produce detectable afterglows. Using a model fit to GW170817, we assume all BNS mergers produce jets with the same parameters, and model the afterglow luminosity for a full distribution of observer angles, ISM densities, and distances. We find that in the LIGO/Virgo/KAGRA O4 run, 30 per cent–45 per cent of BNS mergers with a well-localized counterpart will have an afterglow detectable with current instrumentation in the X-ray, radio and optical. Without a previously detected counterpart, 10 per cent–15 per cent will have an afterglow detectable by wide-area radio and optical surveys, compared to only about 5 per cent–12 per cent of events expected to have bright (on-axis) gamma-ray emission. Most afterglows that are detected will be from off-axis jets. Further in the future, in the A + era (O5), 40 per cent–50 per cent of mergers will have afterglows detectable with next-generation X-ray and radio instruments. Future wide-area radio survey instruments, particularly DSA-2000, could detect 40 per cent of afterglows, even without a kilonova counterpart. Finding and monitoring these afterglows will provide valuable insight into the structure and diversity of relativistic jets, the rate at which mergers produce jets, and constrain the angle of the mergers relative to our line of sight. [ABSTRACT FROM AUTHOR]

Utilizing four archival X-ray data sets taken with the Hard X-ray Detector onboard Suzaku , timing studies were performed on three magnetars, 1E 1841−045 (observed in 2006), SGR 0501+4516 (2008), and 1RXS J170849.0−400910 (2009 and 2010). Their pulsations were reconfirmed, typically in an energy range of 12–50 keV. The 11.783 s pulses of 1E 1841−045 and those of SGR 0501+4516 at 5.762 s were periodically phase modulated, with a long period of |$\approx 23.4$| and |$\approx 16.4$|  ks, respectively. The pulse-phase modulation was also observed, at |$\approx 46.5$|  ks, from two data sets of 1RXS J170849.0−400910. In all these cases, the modulation amplitude was 6 per cent to 16 per cent of the pulse cycle. Including previously confirmed four objects, this characteristic timing behaviour is now detected from seven magnetars in total, and interpreted as a result of free precession of neutron stars that are deformed to an asphericity of |$\sim 10^{-4}$|⁠. Assuming that the deformation is due to magnetic stress, these magnetars are inferred to harbour toroidal magnetic fields of |$B_{\rm t}\sim 10^{16}$|  G. By comparing the estimated |$B_{\rm t}$| of these objects with their poloidal dipole field |$B_{\rm d}$|⁠ , the |$B_{\rm t}/B_{\rm d}$| ratio is found to increase with their characteristic age. Therefore, the toroidal fields of magnetars are likely to last longer than their poloidal fields. This explains the presence of some classes of neutron stars that have relatively weak |$B_{\rm d}$| but are suspected to hide strong |$B_{\rm t}$| inside them. [ABSTRACT FROM AUTHOR]

A number of pulsar timing arrays have recently reported preliminary evidence for the existence of a nanohertz frequency gravitational wave background. These analyses rely on noise analyses, which are inherently complex due to the many astrophysical and instrumental factors. We investigate whether realistic systematic errors, stemming from misspecified noise models that fail to capture salient features of the pulsar timing noise, could bias the evidence for gravitational waves. We consider two plausible forms of misspecification: small instrumental pulse arrival time offsets and radio-frequency-dependent time-correlated noise. Using simulated data, we calculate the distribution of the commonly used optimal statistic with no signal present and using plausibly misspecified noise models. By comparing the optimal statistic distribution with the distribution created using "quasi-resampling" techniques (such as sky scrambles and phase shifts), we endeavour to determine the extent to which plausible misspecification might lead to a false positive. The results are reassuring: we find that quasi-resampling techniques tend to underestimate the significance of pure-noise data sets. We conclude that recent reported evidence for a nanohertz gravitational wave background is likely robust to the most obvious sources of systematic errors; if anything, the significance of the signal is potentially underestimated. [ABSTRACT FROM AUTHOR]

Glitching pulsars are expected to be important sources of gravitational waves (GWs). In this paper, we explore six different models that propose the emission of transient continuous waves, lasting days to months, coincident with glitches. The maximal GW energy is calculated for each model, which is then used to determine whether associated GWs could be detectable with LIGO-Virgo-KAGRA's O4 detectors. We provide an analytical approximation to calculate the signal-to-noise ratio (SNR) which includes information about the source's sky position, improving on previous estimates that assume isotropic or sky and orientation averaged sensitivities. By analysing the entire glitching population, we find that certain models predict detectable signals in O4, whereas others do not. We also rank glitching pulsars by SNR, based on archival data, and we find that for all models, the Vela pulsar (PSR J0835 |$-$| 4510) would provide the strongest signal. Moreover, PSR J0537 |$-$| 6910 is not expected to yield a detectable signal in O4, but will start becoming relevant for next-generation detectors. Our analysis also extends to the entire pulsar population, regardless of whether they have glitched, and we provide a list of pulsars that would present a significant signal, if they were to glitch. Finally, we apply our analysis to the 2024 April Vela glitch and find that a signal should be detectable under certain models. The non-detection of a supposedly detectable signal would provide an efficiency factor that quantifies a model's contribution to GW emission, eventually leading to a differentiation of models and independent constraints on physical parameters. [ABSTRACT FROM AUTHOR]

Localization of fast radio bursts (FRBs) to arcsecond and subarcsecond precision maximizes their potential as cosmological probes. To that end, FRB detection instruments are deploying triggered complex-voltage capture systems to localize FRBs, identify their host galaxy, and measure a redshift. Here, we report the discovery and localization of two FRBs (20220717A and 20220905A) that were captured by the transient buffer system deployed by the MeerTRAP instrument at the MeerKAT telescope in South Africa. We were able to localize the FRBs to precision of |$\sim$| 1 arcsecond that allowed us to unambiguously identify the host galaxy for FRB 20220717A (posterior probability |$\sim$| 0.97). FRB 20220905A lies in a crowded region of the sky with a tentative identification of a host galaxy but the faintness and the difficulty in obtaining an optical spectrum preclude a conclusive association. The bursts show low linear polarization fractions (10–17 per cent) that conform to the large diversity in the polarization fraction observed in apparently non-repeating FRBs akin to single pulses from neutron stars. We also show that the host galaxy of FRB 20220717A contributes roughly 15 per cent of the total dispersion measure (DM), indicating that it is located in a plasma-rich part of the host galaxy which can explain the large rotation measure. The scattering in FRB 20220717A can be mostly attributed to the host galaxy and the intervening medium and is consistent with what is seen in the wider FRB population. [ABSTRACT FROM AUTHOR]

X-ray observations of neutron star (NS) low-mass X-ray binaries (LMXBs) are useful for probing the physical processes close to the NS and for constraining source parameters. Aql X-1 is a transient NS LMXB that frequently undergoes outbursts and provides an excellent opportunity to study source properties and accretion mechanisms in a strong-gravity regime over a wide range of accretion rates. In this work, we systematically investigate the spectral evolution of Aql X-1 using NICER observations during the source outbursts in 2019 and 2020. The NICER observations cover the complete transition of the source from its canonical hard state to a soft state and back. The spectra extracted from most observations can be explained by a partially Comptonized accretion disc. We find that the system can be described by an accretion disc with an inner temperature of |$\sim 0.7$| keV and a Comptonizing medium of thermal electrons at |$\sim 2$| keV, while the photon index is strongly degenerate with the covering fraction of the medium. We also find evidence of Fe K |$\alpha$| fluorescence emission in the spectra, indicating reprocessing of the Comptonized photons. We observe an absorption column density higher than the Galactic column density for most of the observations, indicating a significant local absorption. For some of the observations in the 2020 outburst, however, the local absorption is negligible. [ABSTRACT FROM AUTHOR]

Understanding the explosion mechanism and hydrodynamic evolution of core-collapse supernovae (SNe) is a long-standing quest in astronomy. The asymmetries caused by the explosion are encoded into the line profiles which appear in the nebular phase of the SN evolution – with particularly clean imprints in He star explosions. Here, we carry out nine different supernova simulations of He-core progenitors, exploding them in 3D with parametrically varied neutrino luminosities using the prometheus-hotb code, hydrodynamically evolving the models to the homologous phase. We then compute nebular phase spectra with the 3D Non-Local Thermodynamic Equilibrium spectral synthesis code extrass (EXplosive TRAnsient Spectral Simulator). We study how line widths and shifts depend on progenitor mass, explosion energy, and viewing angle. We compare the predicted line profile properties against a large set of Type Ib observations, and discuss the degree to which current neutrino-driven explosions can match observationally inferred asymmetries. With self-consistent 3D modelling – circumventing the difficulties of representing |$^{56}$| Ni mixing and clumping accurately in 1D models – we find that neither low-mass He cores exploding with high energies nor high-mass cores exploding with low energies contribute to the Type Ib SN population. Models which have line profile widths in agreement with this population give sufficiently large centroid shifts for calcium emission lines. Calcium is more strongly affected by explosion asymmetries connected to the neutron star kicks than oxygen and magnesium. Lastly, we turn to the near-infrared spectra from our models to investigate the potential of using this regime to look for the presence of He in the nebular phase. [ABSTRACT FROM AUTHOR]

XB 1254−690 is a neutron star low-mass X-ray binary with an orbital period of 3.88 h, and it exhibits energy-dependent intensity dips, thermonuclear bursts, and flares. We present the results of an analysis of a long observation of this source using the AstroSat satellite. The X-ray light curve gradually changed from a high-intensity flaring state to a low-intensity one with a few dips. The hardness–intensity diagram showed that the source is in a high-intensity banana state with a gradually changing flux. Based on this, we divide the observation into four flux levels for a flux-resolved spectral study. The X-ray spectra can be explained by a model consisting of absorption, thermal emission from the disc, and non-thermal emission from the corona. From our studies, we detect a correlation between the temperature of the thermal component and the flux and we examine the implications of our results for the accretion disc geometry of this source. [ABSTRACT FROM AUTHOR]

It is believed that the core of a neutron star can be host to various novel phases of matter, from nucleon superfluid phase to exotic high baryon density quantum chromodynamics (QCD) phases. Different observational signals for such phase transitions have been discussed in the literature. Here, we point out a unique phenomenon associated with phase transition to a superfluid phase, which may be the nucleon superfluid phase or a phase like the colour-flavour locked phase, allowing for superfluid vortices. In any superfluid phase transition, a random network of vortices forms via the so-called Kibble–Zurek mechanism, which eventually mostly decays away, finally leaving primarily vortices arising from the initial angular momentum of the core. This transient, random vortex network can have a non-zero net angular momentum for the superfluid component, which will generally be oriented in an arbitrary direction. This is in contrast to the final vortices, which arise from initial rotation and hence have the initial angular momentum of the neutron star. The angular momentum of the random vortex network is balanced by an equal and opposite angular momentum in the normal fluid due to the conservation of angular momentum, thereby imparting an arbitrarily oriented angular momentum component to the outer shell of the neutron star. This will affect the pulse timing and pulse profile of a pulsar. These changes in the pulses will decay away in a characteristic manner that this as the random vortex network decays, obeying specific scaling laws leading to universal features for the detection of superfluid transitions occurring in a pulsar core. [ABSTRACT FROM AUTHOR]

We propose a simplified 2D effective scalar electrodynamics model of relativistic type-II superconductivity. Within this framework, we discuss possible electromagnetic (EM) behaviors of superconductivity along the lines of the nonrelativistic Ginzburg–Landau (GL) theory. This model may be of significance to study very diverse physical phenomena such as a nonlinear version of the electron–hole conversion by a superconductor and electron-positron dynamics around neutron stars. We briefly comment on extending the model to study the 3D dynamics of vortex–vortex interactions and Abrikosov fluxonics. [ABSTRACT FROM AUTHOR]

Employing the Korea-IBS-Daegu-SKKU (KIDS) density functional for the hadron phase and the MIT bag model with vector (vBag) model for the quark phase, we obtain hadron-quark phase transition in neutron stars considering Maxwell construction. The structural properties of the resultant hybrid stars are computed for three different values of bag constant (B) in the range B1/4 = (145-160 MeV). We study the effects of symmetry energy (J) on the hybrid star properties with the different KIDS model and found that J has important influence not only on the transition properties like the transition mass, transition radius and jump in density due to phase transition, but also on the stability of the hybrid stars. The vector repulsion of the quark phase via the parameter GV has profound influence in obtaining reasonable hybrid star configurations, consistent with the recent astrophysical constraints on the structural properties of compact stars. Within the aforesaid range of B, the value of GV is constrained to be 0.3 < GV < 0.4 in order to obtain reasonable hybrid star configurations. [ABSTRACT FROM AUTHOR]

In this study, the geometrically deformed compact objects in the f(Q, T) gravity theory under an electric field through gravitational decoupling via minimal geometric deformation (MGD) technique are developed for the first time. The decoupled field equations are solved via two different mimic approaches Θ00=ρ${\Theta}_{0}^{0}=\rho $ and Θ11=pr${\Theta}_{1}^{1}={p}_{r}$ through the Karmarkar condition. Physical viability tests are conducted on our models and examine how decoupling parameters affect the physical qualities of objects. The obtained models are compared with the observational constraints for neutron stars PSR J1810+174, PSR J1959+2048, and PSR J2215+5135, including GW190814. Particularly, by modifying parameters α and n, the occurrence of a “mass gap” component is accomplished. The resulting models exhibit stable, well‐behaved mass profiles, regular behavior and no gravitational collapse, as verified by the Buchdahl–Andréasson's limit. Furthermore, a thorough physical analysis that is based on two parameters: n (f(Q, T)–coupling parameter) and α (decoupling parameter) is provided. This work extends our current understanding of compact star configurations and sheds light on the behavior of compact objects in the f(Q, T) gravity. [ABSTRACT FROM AUTHOR]

We study a model of the neutron star in κ -deformed space-time in the presence of the cosmological constant (Λ ). The Einstein tensor and the energy-momentum tensor are generalized to κ -deformed space-time and we construct the field equations with the cosmological constant. Considering the interior of the star to be a perfect fluid as in the commutative case, we find the Tolman–Oppenheimer–Volkoff equations with the inclusion of the cosmological constant in κ -deformed space-time. The behavior of the maximum allowed mass of the star and its radius are studied with the variation in the cosmological constant as well as the deformation parameter. We see that the non-commutativity enhances the mass of the star and its maximum mass increases with a decrease in the cosmological constant. The maximum mass varies from 3.44 to 3.68 M ⊙ as Λ varies from 10 - 10 to 10 - 15 m - 2 . We also obtain the compactness factor and surface redshift of the star. We observe that the compactness of the star increases as the cosmological constant decreases, whereas the surface redshift of the star decreases with a decrease in the cosmological constant. The compactness factor and surface redshift corresponding to the maximum mass of the neutron star remains almost constant as Λ decreases. [ABSTRACT FROM AUTHOR]

Neutron stars (NSs) are observed with high space velocities and elliptical orbits in binaries. The magnitude of these effects points to natal kicks that originate from asymmetries during the supernova (SN) explosions. Using a growing set of long-time 3D SN simulations with the Prometheus-Vertex code, we explore the interplay of NS kicks that are induced by asymmetric neutrino emission and by asymmetric mass ejection. Anisotropic neutrino emission can arise from a large-amplitude dipolar convection asymmetry inside the proto-NS (PNS) termed LESA (Lepton-number Emission Self-sustained Asymmetry) and from aspherical accretion downflows around the PNS, which can lead to anisotropic neutrino emission (absorption/scattering) with a neutrino-induced NS kick roughly opposite to (aligned with) the kick by asymmetric mass ejection. In massive progenitors, hydrodynamic kicks can reach up to more than 1300 km s−1, whereas our calculated neutrino kicks reach (55–140) km s−1 (estimated upper bounds of (170–265) km s−1) and only ∼(10–50) km s−1, if LESA is the main cause of asymmetric neutrino emission. Therefore, hydrodynamic NS kicks dominate in explosions of high-mass progenitors, whereas LESA-induced neutrino kicks dominate for NSs born in low-energy SNe of the lowest-mass progenitors, when these explode nearly spherically. Our models suggest that the Crab pulsar with its velocity of ∼160 km s−1, if born in the low-energy explosion of a low-mass, single-star progenitor, should have received a hydrodynamic kick in a considerably asymmetric explosion. Black holes, if formed by the collapse of short-lived PNSs and solely kicked by anisotropic neutrino emission, obtain velocities of only some km s−1. [ABSTRACT FROM AUTHOR]

This study is an overview of the atomic data and opacity computations performed by the Atomic Physics and Astrophysics Unit of Mons University in the context of kilonova emission following neutron star mergers, in both the photospheric and nebular phases. In this work, as a sample case, we focus on a specific lanthanide ion, namely Er III. As far as the LTE photospheric phase of the kilonova ejecta is concerned, we present our calculations using both a theoretical method (the pseudo-relativistic Hartree-Fock method, HFR) and a statistical approach (the Resolved Transition Array approach, RTA) to obtain the atomic data required to estimate the Er III expansion opacity for typical conditions expected in kilonova ejecta one day after the merger. In order to draw the limitations of both of our strategies, the results obtained using the latter are compared, and a calibration procedure of the HFR atomic data in this context is also discussed. Concerning the kilonova ejecta nebular phase, atomic parameters that characterize forbidden lines in Er III are calculated using HFR as well as another computational approach, namely the Multiconfiguration Dirac–Hartree–Fock (MCDHF) method. The potential detection of such lines in late-phase kilonova spectra is then discussed. [ABSTRACT FROM AUTHOR]

We investigate solutions to the Tolman-Oppenheimer-Volkoff equations and their implications, deriving an equation of state for the star’s surface as a function of two geometric parameters, λ (r) and ν (r) . We find that the parameter λ (r) is essential for explaining fluctuations in the baryon number density and baryonic chemical potential within and outside a neutron star, enabling simulations of regions with varying neutron matter densities. We also highlight the significant role of the ν (r) parameter for describing the explosive transition of a neutron star to a black hole, establishing a direct connection between the neutron star’s radius and the event horizon’s radius. The parameter λ (r) is crucial for understanding how the baryon number density and baryonic chemical potential fluctuate inside and outside a neutron star. The core is characterized by λ > 0 , and the outer crust is defined by λ < 0 . Finally, by analyzing the polytropic equation of state, we find that the neutron stars are composed of two distinct regions: a low-density outer crust and a very high-density core, separated by a sharp boundary. The mixing region between the two layers is known as the inner crust and outer core. [ABSTRACT FROM AUTHOR]

When a neutron star is spun-up or spun-down, the changing strains in its solid elastic crust can give rise to sudden fractures known as starquakes. Early interest in starquakes focused on their possible connection to pulsar glitches. While modern glitch models rely on pinned superfluid vorticity rather than crustal fracture, starquakes may nevertheless play a role in the glitch mechanism. Recently, there has been interest in the issue of starquakes resulting in non-axisymmetric shape changes, potentially linking the quake phenomenon to the building of neutron star mountains, which would then produce continuous gravitational waves. Motivated by this issue, we present a simple model that extends the energy minimization-based calculations, originally developed to model axisymmetric glitches, to also include non-axisymmetric shape changes. We show that the creation of a mountain in a quake necessarily requires a change in the axisymmetric shape too. We apply our model to the specific problem of the spin-up of an initially non-rotating star, and estimate the maximum mountain that can be built in such a process, subject only to the constraints of energy and angular momentum conservation. [ABSTRACT FROM AUTHOR]

Millisecond pulsars (MSPs) are a kind of radio pulsars with short spin periods, playing a key role in many aspects of stellar astrophysics. In recent years, some more MSPs with wide orbits (⁠|$\gt 30\, \rm d$|⁠) have been discovered, but their origin is still highly unclear. In this work, according to an adiabatic power-law assumption for the mass-transfer process, we carried out a large number of complete binary evolution computations for the formation of MSPs with wide orbits through the iron core-collapse supernova (CCSN) channel, in which a neutron star originating from a CCSN accretes matter from a red-giant star and spun up to millisecond periods. We found that this channel can form the observed MSPs with wide orbits in the range of |$30\!-\!1200\, {\rm d}$|⁠ , in which the white dwarf (WD) companions have masses in the range of |$0.28\!-\!0.55\, \rm M_{\odot }$|⁠. We also found that almost all the observed MSPs can be reproduced by this channel in the WD companion mass versus orbital period diagram. We estimate that the Galactic numbers of the resulting MSPs from the CCSN channel are in the range of |$\sim 4.8\!-\!8.5\times 10^{5}$|⁠. Compared with the accretion-induced collapse channel, the CCSN channel provides a main way to produce MSPs with wide orbits. [ABSTRACT FROM AUTHOR]

We have investigated whether the lack of X-ray pulsations from most neutron star (NS) low-mass X-ray binaries (LMXBs) could be due to the extension of their inner disc to the NS surface. To estimate the inner disc radii, we have employed the model, recently proposed to account for the torque reversals of LMXBs. In this model, the inner disc radius depends on the spin period as well as the dipole moment and the mass inflow rate of the disc. Our model results indicate that most LMXBs have mass accretion rates above the minimum critical rates required for the inner disc to reach down to the NS surface and thereby quench the pulsed X-ray emission. For most sources X-ray pulsations are allowed when the period decreases below a certain critical value. For the same parameters, the model is also consistent with the observed X-ray luminosity ranges of the individual accreting millisecond X-ray pulsars (AMXPs). The paucity of AMXPs compared to the majority population of non-pulsing LMXBs is explained, as well as the fact that AMXPs are transient sources. [ABSTRACT FROM AUTHOR]

This paper investigates the accretion of neutron stars (NSs) in active galactic nucleus (AGN) accretion discs. We classify potential accretion modes of NSs in AGN discs, proposing a hierarchical model of NS accretion: accretion flow from the Bondi sphere to accretion columns. The accretion of NSs in AGN discs differs from that of BHs, especially within the scale of the NS's magnetosphere due to its hard surface and magnetic field. As the accretion flow approaches the magnetosphere, the magnetic fields guide the accretion flow to form accretion columns, primarily dominated by neutrinos. While neutrinos generated from single NS accretion may not have observable effects, considering the all-sky background, they contribute to the neutrino background in the sub-MeV energy range comparable to that of supernova explosions. NS accretion may also lead to the generation of mass quadrupole moments, consequently generating gravitational waves (GWs). The GWs, which exhibit characteristic effects like periodic modulations and echoes, could be observed by third-generation GW detectors. The emission of neutrinos and GWs carries away energy and angular momentum brought by accretion, reducing the feedback effect on the AGN disc. This results in an exceptionally high NS accretion rate, leading to a collapse time-scale shorter than the migration-merge time-scale, making it less likely that binary NS mergers originate from AGN discs. [ABSTRACT FROM AUTHOR]

The concept of symmetry under various transformations of quantities describing basic natural phenomena is one of the fundamental principles in the mathematical formulation of physical laws. Starting with Noether's theorems, we highlight some well–known examples of global symmetries and symmetry breaking on the particle level, such as the separation of strong and electroweak interactions and the Higgs mechanism, which gives mass to leptons and quarks. The relation between symmetry energy and charge symmetry breaking at both the nuclear level (under the interchange of protons and neutrons) and the particle level (under the interchange of u and d quarks) forms the main subject of this work. We trace the concept of symmetry energy from its introduction in the simple semi-empirical mass formula and liquid drop models to the most sophisticated non-relativistic, relativistic, and ab initio models. Methods used to extract symmetry energy attributes, utilizing the most significant combined terrestrial and astrophysical data and theoretical predictions, are reviewed. This includes properties of finite nuclei, heavy-ion collisions, neutron stars, gravitational waves, and parity–violating electron scattering experiments such as CREX and PREX, for which selected examples are provided. Finally, future approaches to investigation of the symmetry energy and its properties are discussed. [ABSTRACT FROM AUTHOR]

The properties of isospin-asymmetric cold nuclear matter are studied in terms of the relativistic mean-field theory in which, besides the fields of σ, ω, and ρ mesons, and the isovector, Lorentz-scalar field of the δ-meson is also taken into account. The properties of purely nucleonic np matter are studied as a function of the baryon density nB and the asymmetry parameter α, as well as the properties of electrically neutral β-equilibrium npe μ matter as a function of the baryon density nB. For different values of nB and a, such characteristics of np matter as the energy per baryon, the specific energy owing to isospin asymmetry, the effective proton and neutron masses, and the specific binding energy, are determined. It is shown that the energy owing to the asymmetry for a fixed value of α is a monotonically increasing function of the baryon density nB. For npem matter, the effective proton and neutron masses M p e f f , M n e f f , the specific binding energy Ebind, the symmetry energy Esym, the quantitative fraction of protons Yp = np/nB are studied, as well as the average meson fields σ ~ , ω ~ , δ ~ , and ρ ~ as functions of the baryon density nB. [ABSTRACT FROM AUTHOR]

A new type of cosmological transient, dubbed fast radio bursts (FRBs), was recently discovered. The source of FRBs is still unknown. One possible scenario of an FRB is the collapse of a spinning supra-massive neutron star. Zhang (2014 , ApJ, 780, L21) suggests that the collapse can happen shortly (hundreds to thousands of seconds) after the birth of supra-massive neutron stars. The signatures can be visible in X-ray afterglows of long and short gamma-ray bursts (GRBs). For instance, a sudden drop (decay index steeper than |$-3$| to |$-9$|⁠) from a shallow decay (decay index shallower than |$-1$|⁠) in the X-ray afterglow flux can indicate such an event. We selected the X-ray afterglow light curves with a steep decay after the shallow decay phase from the Swift/XRT GRB catalog. We analyzed when the decay index changed suddenly by fitting these light curves to double power-law functions and compared them with the onset of FRBs. We found that none of our GRB samples match the onset of FRBs. [ABSTRACT FROM AUTHOR]

Strongly magnetized, rapidly rotating massive white dwarfs (WDs) emerge as potential outcomes of double degenerate mergers. These WDs can act as sources of non-thermal emission and cosmic rays, gethering attention as WD pulsars. In this context, we studied the X-ray emissions from ZTF J190132.9+145808.7 (hereafter ZTF J1901+14), a notable massive isolated WD in the Galaxy, using the Chandra X-ray observatory. Our results showed 3.5σ level evidence of X-ray signals, although it is marginal. Under the assumption of a photon index of 2, we derived its intrinsic flux to be 2.3 (0.9–4.7) × 10−15 erg cm−2 s−1 and luminosity 4.6 (2.0–9.5) × 1026 erg s−1 for a 0.5–7 keV band in the |$90\%$| confidence range, given its distance of 41 pc. We derived the X-ray efficiency (η) concerning the spin-down luminosity to be 0.012 (0.0022–0.074), a value comparable to that of ordinary neutron star pulsars. The inferred X-ray luminosity may be compatible with curvature radiation from sub-TeV electrons accelerated within open magnetic fields in the magnetosphere of ZTF J1901+14. Conducting more extensive X-ray observations is crucial to confirm whether ZTF J1901+14-like isolated WDs are also significant sources of X-rays and sub-TeV electron cosmic rays, similar to other WD pulsars in accreting systems. [ABSTRACT FROM AUTHOR]

Four X-ray datasets of the soft gamma repeater SGR 1806−20, taken with the Gas Imaging Spectrometer (GIS) onboad ASCA, were analyzed. Three of them were acquired over 1993 October 9–20, the last one in 1995 October. Epoch-folding analysis of the 2.8–12 keV signals confirmed the ∼7.6 s pulses in these data, which Kouveliotou et al. (1998, Nature, 393, 235) reported as one of the earliest pulse detections from this object. In the 1995 observation, 3–12 keV pulses were phase modulated with a period of T  = 16.4 ± 0.4 ks, and an amplitude of ∼1 s. This makes a fourth example of the behavior observed from magnetars. As in the previous three sources, the pulse-phase modulation of SGR 1806−20 disappeared at ≲2.5 keV, where the soft X-ray component dominates. In the 1993 datasets, this periodic modulation was reconfirmed, and successfully phase-connected coherently across the 11 d interval. As a result, the modulation period was refined to T  = 16.435 ± 0.024 ks. The implied high stability of the phenomenon strengthens its interpretation in terms of free precession of the neutron star, which is deformed to an asphericity of ∼10−4, presumably by the stress of toroidal magnetic fields reaching ∼1016 G. Toroidal fields of this level can be common among magnetars. [ABSTRACT FROM AUTHOR]

In the present work, we investigate the bulk properties of nuclear matter and neutron stars with the newly proposed relativistic interaction NL-RS which provides an opportunity to readjust the coupling constants keeping in view the properties of finite nuclei, nuclear matter, PREX-II results for neutron skin thickness in 208Pb and astrophysical observations. The NL-RS model interaction has been proposed by fitting the ground state properties (binding energies and charge radii) of finite nuclei, bulk nuclear matter properties, and PREX-II results for neutron skin thickness of 208Pb. The relativistic interaction has been generated by including nonlinear self-interactions of σ and ω μ -mesons and mixed interactions of ω μ , and ρ μ -meson up to the quartic order. The proposed interaction harmonizes with the finite nuclei, bulk nuclear matter, and neutron star properties. A covariance analysis is performed to assess the statistical uncertainties on the model parameters and nuclear observables of interest along with correlations amongst them. The equation of state (EoS) composed of nucleons and leptons in β -equilibrium is computed with the proposed parameter set and used to study the neutron star structure. The maximum mass of the neutron star by employing the EoS computed with the NL-RS parameter set is 2.04 ± 0.03 M ⊙ and the radius of a canonical mass neutron star (R 1.4) comes out to be equal to 13.06 ± 0.16 Km. The value of dimensionless tidal deformability, for canonical mass, is 602.23 ± 33.13 which satisfies the constraints of waveform models analysis of GW170817 within 90% confidence level. [ABSTRACT FROM AUTHOR]

This work is dedicated to the study of interstellar medium (ISM) along the line of sight (LOS) of the transient low-mass X-ray binary, MXB 1659-298, capitalizing the high resolving power of XMM-Newton in the soft energy range. We emphasized the analysis of reflection grating spectrometer (RGS) data in the energy range 0.5–2.15 keV, suitable for the study of ISM. The paper includes an explanation of why, in the soft X-ray energy range, only two observations (out of seven) were deemed eligible for analysis. Three absorption lines associated with highly ionized Fe XX (1s22p2-2p2 (3p) 4d), Si XIV (1s2-1s2p), and Mg XI (1s2-1s6p) were identified in the observations, with IDs of 8620701(2001) and 748391601(2015). These new absorption lines and the absorption edge due to the neutral oxygen K edge seen in the spectra validate the multiphase structure of ISM. The predominance of interstellar medium over the ionized absorber is established along the direction of the source. The equivalent hydrogen column density measured is nearly equal to the galactic HI value derived previously. The small value of the ionic column density of Fe, Si, and Mg in the site of the high-temperature region resembles previous findings. [ABSTRACT FROM AUTHOR]

Radiation from X-ray pulsars (XRPs) was expected to be strongly linearly polarized owing to a large difference in their ordinary and extraordinary mode opacities. The launch of IXPE allowed us to check this prediction. IXPE observed a dozen X-ray pulsars, discovering pulse-phase dependent variation of the polarization degree (PD) and polarization angle (PA). Although the PD showed rather erratic profiles resembling flux pulse dependence, the PA in most cases showed smooth variations consistent with the rotating vector model (RVM), which can be interpreted as a combined effect of vacuum birefringence and dipole magnetic field structure at a polarization-limiting (adiabatic) radius. Application of the RVM allowed us to determine XRP geometry and to confirm the free precession of the NS in Her X-1. Deviations from RVM in two bright transients led to the discovery of an unpulsed polarized emission likely produced by scattering off the accretion disk wind. [ABSTRACT FROM AUTHOR]

Pulsars are neutron stars with high rotation speeds and have extraordinary long-term rotational stability. X-ray pulsar-based navigation (XNAV) is a navigation method that estimates the position and velocity of a spacecraft using the X-ray radiation from pulsars. Flight experiments on Insight-Hard X-ray Modulation Telescope (Insight-HXMT) and Neutron Star Interior Composition Explorer (NICER) have successfully verified the feasibility of using XNAV for a single spacecraft. For spacecraft in formation, a pulsar-based navigation method that uses the pulse phase delay between spacecraft is derived. Moreover, a direct estimation method for pulse phase delay, which is independent from the pulsar template, is proposed. The proposed method is verified with simulation data of the Crab pulsar and real data of the same pulsar obtained from Insight-HXMT and NICER. [ABSTRACT FROM AUTHOR]

For a selection of 35 pulsars with large spin-up glitches (⁠|$\Delta {\nu }/\nu \ge 10^{-6}$|⁠), which are monitored by the Jodrell Bank Observatory, we analyse 157 glitches and their recoveries. All parameters are measured consistently and we choose the best model to describe the post-glitch recovery based on Bayesian evidence. We present updated glitch epochs, sizes, changes of spin down rate, exponentially recovering components (amplitude and corresponding time-scale) when present, as well as pulsars' second frequency derivatives and their glitch-associated changes if detected. We discuss the different observed styles of post-glitch recovery as well as some particularly interesting sources. Several correlations are revealed between glitch parameters and pulsar spin parameters, including a very strong correlation between a pulsar's interglitch |$|\ddot{\nu }|$| and |$\dot{\nu }$|⁠ , as well as between the glitch-induced spin-down rate change |$\Delta \dot{\nu }_{\rm p}$| that does not relax exponentially and |$\dot{\nu }$|⁠. We find that the ratio |$\left|\Delta \dot{\nu }_{\mathrm{p}}/\ddot{\nu }\right|$| can be used as an estimate of glitch recurrence times, especially for those pulsars for which there are indications of a characteristic glitch size and interglitch waiting time. We calculate the interglitch braking index n and find that pulsars with large glitches typically have n greater than 3, suggesting that internal torques dominate the rotational evolution between glitches. The external torque, for example, from electromagnetic dipole radiation, could dominate the observed |$\ddot{\nu }$| for the youngest pulsars (⁠|$\lesssim 10^{4}\,\,\mathrm{yr}$|⁠), which may be expected to display |$n\sim 3$|⁠. [ABSTRACT FROM AUTHOR]

With current and planned gravitational-wave (GW) observing runs, coincident multimessenger timing of resonant shattering flares (RSFs) and GWs may soon allow for neutron star (NS) asteroseismology to be used to constrain the nuclear symmetry energy, an important property of fundamental nuclear physics that influences the composition and equation of state of NSs. In this work, we examine the effects of combining multiple RSF detections on these symmetry energy constraints, and consider how realistic uncertainties in the masses of the progenitor NSs may weaken them. We show that the detection of subsequent multimessenger events has the potential to substantially improve constraints beyond those obtained from the first, and that this improvement is insensitive to the mass of the NSs that produce the RSFs and its uncertainty. This sets these asteroseismic constraints apart from bulk NS properties such as radius, for which the NS mass is highly important, meaning that any multimessenger RSF and GW events can equally improve our knowledge of fundamental physics. [ABSTRACT FROM AUTHOR]

We employ constrained path Auxiliary Field Quantum Monte Carlo (AFQMC) in the pursuit of studying physical nuclear systems using a lattice formalism. Since AFQMC has been widely used in the study of condensed-matter systems such as the Hubbard model, we benchmark our method against published results for both one- and two-dimensional Hubbard model calculations. We then turn our attention to cold atomic and nuclear systems. We use an onsite contact interaction that can be tuned in order to reproduce the known scattering length and effective range of a given interaction. Developing this machinery allows us to extend our calculations to study nuclear systems within a lattice formalism. We perform initial calculations for a range of nuclear systems from two- to few-body neutron systems. This article is part of the theme issue 'The liminal position of Nuclear Physics: from hadrons to neutron stars'. [ABSTRACT FROM AUTHOR]

Elucidating the role of strange baryons (hyperons) in neutron stars requires detailed knowledge of hyperon–nucleon interactions in the light (u,d,s) quark sector. The structure of the hyperons and their excitation spectra also directly impact, and are an input to, models of big-bang nucleosynthesis. The upcoming K-long Facility will provide a much-needed intense and clean neutral strange meson beam, from which hyperons can be produced at rates where hyperon structure, hyperon–nucleon interactions and higher-order interactions can be studied with a new level of accuracy and for hitherto unreachable measurements. The new facility has the potential to address long-standing questions surrounding the strange sector of the strong force and its relevance to the structure of atomic nuclei, neutron stars and the cosmos at large. This article is part of the theme issue 'The liminal position of Nuclear Physics: from hadrons to neutron stars'. [ABSTRACT FROM AUTHOR]

The pivotal role of nuclear physics in nucleosynthesis processes is being investigated, in particular the intricate influence of photon strength functions (PSFs) and nuclear level densities (NLDs) on shaping the outcomes of the i-, r- and p-processes. Exploring diverse NLD and PSF model combinations uncovers large uncertainties for (p, γ), (n, γ) and (α , γ) rates across many regions of the nuclear chart. These lead to potentially significant abundance variations of the nucleosynthesis processes and highlight the importance of accurate experimental nuclear data. Theoretical insights and advanced experimental techniques lay the ground work for profound understanding that can be gained of nucleosynthesis mechanisms and the origin of the elements. Recent results further underscore the effect of PSF and NLD data and its contribution to understanding abundance distributions and refining knowledge of the intricate nucleosynthesis processes. This article is part of the theme issue 'The liminal position of Nuclear Physics: from hadrons to neutron stars'. [ABSTRACT FROM AUTHOR]

One of the overarching goals in nuclear science is to understand how the nuclear chart emerges from the underlying fundamental interactions. The description of the structure of nuclei from first principles, using ab initio methods for the solution of the many-nucleon problem with inputs from chiral effective field theory, has advanced dramatically over the past two decades. We present an overview over the available ab initio tools with a specific emphasis on electromagnetic observables, such as multipole moments and transition strengths. These observables still pose a challenge for ab initio theory and are one of the most exciting domains to exploit synergies with modern experiments. Precise experimental data are vital for the validation of the theory predictions and the refinement of ab initio methods. We discuss some of the past and future experimental efforts highlighting these synergies. This article is part of the theme issue 'The liminal position of Nuclear Physics: from hadrons to neutron stars'. [ABSTRACT FROM AUTHOR]

Time-domain and multimessenger astronomy (TDAMM) involves the study of transient and time-variable phenomena across various wavelengths and messengers. The Astro2020 Decadal Survey has identified TDAMM as the top priority for NASA in this decade, emphasizing its crucial role in advancing our understanding of the universe and driving new discoveries in astrophysics. The TDAMM community has come together to provide further guidance to funding agencies, aiming to define a clear path toward optimizing scientific returns in this research domain. This encompasses not only astronomy but also fundamental physics, offering insights into properties of gravity, the formation of heavy elements, the equation of state of dense matter, and quantum effects associated with extreme magnetic fields. Magnetars, neutron stars with the strongest magnetic fields in the universe, play a critical role in this context. We aim to underscore the significance of magnetars in TDAMM, highlighting the necessity of ensuring observational continuity, addressing current limitations, and outlining essential requirements to expand our knowledge in this field. [ABSTRACT FROM AUTHOR]

The milestone discovery of GW170817-GRB 170817A-AT 2017gfo has shown that gravitational waves (GWs) could be produced during the merger of a neutron star–neutron star/black hole and that in electromagnetic (EM) waves, a gamma-ray burst (GRB) and a kilonova (KN) are generated in sequence after the merger. Observationally, however, EM properties before the merger phase are still unclear. Here we report a peculiar precursor in a KN-associated long-duration GRB 211211A, providing evidence of the EM before the merger. This precursor lasts ∼0.2 s, and the waiting time between the precursor and the main burst is ∼1 s, comparable to that between GW170817 and GRB 170817A. The spectrum of the precursor could be well fit with a nonthermal cutoff power-law model instead of a blackbody. In particular, a ∼22 Hz quasiperiodic oscillation candidate (∼3 σ) is detected in the precursor. These temporal and spectral properties indicate that this precursor is probably produced by a catastrophic flare accompanied with magnetoelastic or crustal oscillations of a magnetar in a binary compact merger. The strong magnetic field of the magnetar can also account for the prolonged duration of GRB 211211A. However, it poses a challenge to reconcile the rather short lifetime of a magnetar with the rather long spiraling time of a binary neutron star system only by the GW radiation before the merger. [ABSTRACT FROM AUTHOR]

The fallback disk model is widely accepted to explain long-period neutron stars (NSs) that cannot be simulated by magnetic dipole radiation. However, there was no confirmed detection of disks from the newly discovered long-period pulsars GLEAM-X 162759.5-523504.3 and GPM J1839-10 and the slowest known isolated NS 1E 161348-5055. This might be because the disks have either been in a noninteracting/inactive state where their emission is too weak to be detected or have been disrupted. In this work, we conduct simulations to examine the lifetime of supernova fallback disks around isolated NSs. We assume that the disks' mass varies in a self-similar way, and their interaction with the NS occurs only in an interacting/active state. Our results reveal that nearly all the interacting lifetimes for the disks are shorter than 105 yr, while the existence lifetimes are considerably longer. [ABSTRACT FROM AUTHOR]