So far detached compact binaries containing neutron stars have been observed either at intermediate stages of the evolution by radio telescopes or at merger by ground-based gravitational wave detectors. Sensitive to gravitational waves from binaries millions to thousands years prior to the merger, the future Laser Interferometer Space Antenna (LISA) will be crucial for bridging the gap between the currently accessible regimes. Depending on the binary type, LISA could potentially discover from a few to several hundreds in the entirely new regime throughout the Milky Way. Here we provide a concise summary of the current expectation for the detection of Galactic binaries containing neutron stars with LISA, focusing on double neutron stars and neutron star - white dwarf binaries. We outline a few examples of science investigations that LISA data will enable for these binaries.

We report on our observing campaign of the compact binary merger GW190814, detected by the Advanced LIGO and Advanced Virgo detectors on August 14th, 2019. This signal has the best localisation of any observed gravitational wave (GW) source, with a 90% probability area of 18.5 deg2, and an estimated distance of ≈240 Mpc. We obtained wide-field observations with the Deca-Degree Optical Transient Imager (DDOTI) covering 88% of the probability area down to a limiting magnitude of w = 19.9 AB. Nearby galaxies within the high probability region were targeted with the Lowell Discovery Telescope (LDT), whereas promising candidate counterparts were characterized through multi-colour photometry with the Reionization and Transients InfraRed (RATIR) and spectroscopy with the Gran Telescopio de Canarias (GTC). We use our optical and near-infrared limits in conjunction with the upper limits obtained by the community to constrain the possible electromagnetic counterparts associated with the merger. A gamma-ray burst seen along its jet’s axis is disfavoured by the multi-wavelength dataset, whereas the presence of a burst seen at larger viewing angles is not well constrained. Although our observations are not sensitive to a kilonova similar to AT2017gfo, we can rule out high-mass (> 0.1 M⊙) fast-moving (mean velocity ≥ 0.3c) wind ejecta for a possible kilonova associated with this merger.

To form stars in hydrodynamical simulations, we introduce the grouped star formation prescription to convert the grouped sink particles into stars that follow the IMF. We show that this method is robust in different physical scales. Such methods to form stars are likely to become more important as galactic or even cosmological scale simulations begin to probe sub-parsec scales.

In this poster we present the structure of an axisymmetric, force-free magnetosphere of a twisted, aligned rotating dipole within a corotating plasma-filled magnetosphere. We explore various profiles for the twist. We find that as the current increases more field lines cross the light cylinder leading to more efficient spin-down. Moreover, we notice that the twist cannot be increased indefinitely and after a finite twist of about π/2 the field becomes approximately radial. This could have implications for torque variations of magnetars related to outbursts.

The late-time effect of primordial non-Gaussianity offers a window into the physics of inflation and the very early Universe. In this work we study the consequences of a particular class of primordial non-Gaussianity that is fully characterized by initial density fluctuations drawn from a non-Gaussian probability density function, rather than by construction of a particular form for the primordial bispectrum. We numerically generate multiple realisations of cosmological structure and use the late-time matter polyspectra to determine the effect of these modified initial conditions. In this non-Gaussianity has only a small imprint on the first polyspectra, when compared to a standard Gaussian cosmology. Furthermore, some of our models present an interesting scale-dependent deviation from the Gaussian case in the bispectrum and trispectrum, although the signal is at most at the percent level.

Continuous gravitational Waves (CWs) are a very promising, not yet detected, and interesting class of persistent and semi-periodic signals. They are emitted mainly by rapidly rotating asymmetric neutron stars, with frequencies that are well covered by the [10-3 000] Hz range of the advanced LIGO-Virgo detectors. Due to the expected small degree of asymmetry of a neutron star, the search for this kind of signals is extremely challenging, and can be very computationally expensive when the source parameters are not known or not well constrained. CW detection from a spinning neutron star will allow us to characterize its structure and properties, making this source an unparalleled laboratory for studying several key issues in fundamental physics and relativistic astrophysics, in conditions that cannot be reproduced on Earth. The most recent methodologies used in CW searches will be discussed, and the latest results from the third advanced LIGO-Virgo observational run will be presented. A summary of future prospects to feasibly detect such feeble signals as the detector performance improves, and ever-more-sensitive and robust data-analysis algorithms are implemented, will be also outlined.

The spectacular detection of the first electromagnetic counterpart of a gravitational wave event detected by the LIGO/Virgo interferometers and originated by the coalescence of a double neutron star (NS) system (GW 170817) marked the dawn of a new era for astronomy. The short GRB 170817A associated to the gravitational wave event provided the long-sought evidence that at least a fraction of short GRBs are originated by NS-NS merging and suggested the intriguing possibility that relativistic jets can be launched in the process of a NS-NS merger. The wealth of data collected provided the first compelling observational evidence for the existence of kilonovae, i.e. the emission due to radioactive decay of heavy nuclei produced through rapid neutron capture. Besides the remarkable event associated to GW 170817, kilonova signatures have been identified in a few short GRBs light curves, supporting a scenario where kilonovae are ubiquitous and can probe neutron star mergers well beyond the horizon of the gravitational wave detectors. In this paper I will review the situation and perspectives of our understanding of short GRBs progenitors and kilonovae in the multi-messenger era.

We use hydrodynamical simulations to study the evolution of baryonic gas in a cosmologically evolving dark matter halo. We model both the inner and outer regions of the halo using a density profile that transitions from an inner NFW profile to a flat profile far from the halo. Metallicity-dependent radiative cooling and AGN jet feedback are implemented, which lead to heating and cooling cycles in the core. We analyze the evolution of gas and the central supermassive black hole (SMBH) across cosmological time. We find that the properties of the gas and the SMBH are correlated across halo masses and feedback efficiencies.

Most stars form in clumpy and sub-structured clusters. These properties also emerge in hydro-dynamical simulations of star-forming clouds, which provide a way to generate realistic initial conditions for N-body runs of young stellar clusters. However, producing large sets of initial conditions by hydro-dynamical simulations is prohibitively expensive in terms of computational time. We introduce a novel technique for generating new initial conditions from a given sample of hydro-dynamical simulations, at a tiny computational cost. In particular, we apply a hierarchical clustering algorithm to learn a tree representation of the spatial and kinematic relations between stars, where the leaves represent the single stars and the nodes describe the structure of the cluster at larger and larger scales. This procedure can be used as a basis for the random generation of new sets of stars, by simply modifying the global structure of the stellar cluster, while leaving the small-scale properties unaltered.

The dynamics of massless planetesimals in the gravitational field of a star with a planet in a circular orbit is considered. The invariant of this problem is the Jacobi integral. Preserving the value of the Jacobi integral can be a test for numerical algorithms solving the equation of motion. The invariant changes for particles in the planetary chaotic zone due to numerical errors that occur during close encounters with the planet. The limiting distances from the planet, upon reaching which the value of the Jacobi integral changes, are determined for Bulirsch-Stoer algorithm. It is shown that violation of the Jacobi integral can be used to define the boundaries of the planetary chaotic zone.

The combination of strong magnetic fields and fast rotation is often invoked as a characteristic of the central engine for outstanding sources such as GRBs, hypernovae, and superluminous supernovae. However, the actual properties of the magnetic field during the collapse of the stellar progenitor are very uncertain, since they depend on the evolution of the star and can be affected by complex dynamo processes occurring in the central proto-neutron star. Using 3D relativistic MHD models we show that higher-order multipolar fields can lead to the onset of a supernova, although they tend to produce less energetic explosions and less collimated outflows. Quadrupolar fields efficiently extract angular momentum from the central core, but the rotational energy is partly stored in the equatorial regions, rather than powering up the polar outflows. Finally, our results show a strong magnetic quenching of the hydrodynamic non-axisymmetric instabilities that are associated to the emission of GWs.

The binary neutron star merger gravitational-wave event GW170817 and observations of the subsequent electromagnetic signals at different wavelengths have helped better understand the outflows that follow these mergers. In particular, the off-axis afterglow of the jetted ejecta has allowed to probe the lateral structure of such jets, especially thanks to VLBI imagery of the source. In this work, we model this afterglow including a decelerating jet with lateral structure, while synchrotron emission and synchrotron self-Compton scatterings power the jet radiation. In particular, we extend our analysis to very high energies and predict the light curve in the energy range of H.E.S.S. and the CTA. We finally discuss how future detections of afterglows by these observatories can help break the degeneracies in some key physical parameter measurements, and allow to probe efficiently a sub-population of fast-merging binaries.

We present the results of global three-dimensional radiation magnetohydrodynamic simulations of the formation of soft X-ray emitting regions in active galactic nuclei by applying a radiation magnetohydrodynamic code based on the M1-closure scheme. The effect of Compton cooling is taken into account. When the surface density of the accretion flow exceeds the upper limit of the radiatively inefficient accretion flow (RIAF), the optically thin, hot accretion flow near the black hole co-exists with the soft X-ray emitting, warm (T = 106 – 107 K) Comptonized region around r = 20 – 40rs, where rs is the Schwarzschild radius. Numerical results indicate that when the accretion rate approaches the Eddington accretion rate, the warm Comptonized region stays in optically thin for effective optical depth, Thomson thick, and radiation pressure dominant state. This region is found to oscillate between a geometrically thin, cool state and a geometrically thick state inflated by radiation pressure. The time variability of the accretion flow is consistent with that of the narrow-line Seyfert 1 galaxies.

The Orion Nebula Cluster (ONC) is one of the nearest open clusters, which we can directly compare to numerical simulations. We performed a simulation of star cluster formation similar to the ONC using our new N-body/smoothed particle hydrodynamics code, ASURA+BRIDGE. We found that the hierarchical formation of star clusters via clump mergers can explain the observed three peaks in the stellar age distribution as well as the dynamically anisotropic structures of the ONC.

Auroral events are the prominent manifestation of solar/stellar forcing on planetary atmospheres and are closely related to the energy deposition by and evolution of planetary atmospheres. Observations of auroras are widely used to analyze the composition, structure, and chemistry of the atmosphere under study, as well as charged particle and energy fluxes that affect the atmosphere. Numerical kinetic Monte Carlo models had been developed allowing us to study the processes of precipitation of high-energy electrons, protons and hydrogen atoms into the planetary atmospheres on molecular level of description, taking into account the stochastic nature of collisional scattering at high kinetic energies. Such models are used to study auroras at both magnetized and non-magnetized planets in the Solar and extrasolar planetary systems. The current status of the kinetic model is illustrated in application to the auroral events at Mars.

The LIGO-Virgo gravitational wave detectors have confidently observed 4 events involving neutron stars: two binary neutron star (BNS) mergers (GW170817 and GW190425), and two neutron star-black hole mergers (GW200105 and GW200115). However, our theoretical understanding of the remnant properties of such systems is incomplete due to the complexities related to the modeling of matter effects and the very high computational cost of corresponding numerical relativity simulations. An important such property is the recoil velocity, which is imparted onto the remnant due to the anisotropic emission of gravitational radiation and the dynamical ejection of matter in the kilonova. In this work, we combine gravitational radiation as well as dynamical ejecta distributions, computed by the Computational Relativity numerical simulations, to get accurate estimates for BNS remnant recoil velocities. We find that recoils due to ejection of matter dominate those caused by gravitational wave emission. Knowledge of BNS remnant recoil velocities is important in determining if the remnant is retained by its environment for future hierarchical mergers which, in turn, can form binaries with black holes in the so-called lower mass gap of ∼ 3 – 5M⊙.

Triggered by the MGF detected from the Sculptor galaxy on April 2020, the study described in this proceeding reports the unambiguous identification of a distinct population of 4 local (< 5 Mpc) short GRBs, whose rise time and isotropic energy release are independently inconsistent with the larger short GRB population at >99.9% confidence. These properties, the host galaxies, and non-detection in gravitational waves all point to an extragalactic MGF origin. The inferred volumetric rates for events above 4 × 1044 erg of $$R{\rm{ = }}3.8_{ - 3.1}^{ + 4.0} \times {10^5}Gp{c^{ - 3}}y{r^{ - 1}}$$. These rates imply that some magnetars produce multiple MGFs, providing a source of repeating GRBs. The rates and host galaxies favor common core-collapse supernova as key progenitors of magnetars.

Boasting supreme magnetic strengths, magnetars are among the prime candidates to generate fast radio bursts. Several theories have been proposed for the formation mechanism of magnetars, but have not yet been fully tested. As different magnetar formation theories expect distinct magnetar space velocity distributions, high-precision astrometry of Galactic magnetars can serve as a probe for the formation theories. In addition, magnetar astrometry can refine the understanding of the distribution of Galactic magnetars. This distribution can be compared against fast radio bursts (FRBs) localized in spiral galaxies, in order to test the link between FRBs and magnetars. Swift J1818.0–1607 is the hitherto fastest-spinning magnetar and the fifth discovered radio magnetar. In an ongoing astrometric campaign, we have observed Swift J1818.0–1607 for one year using the Very Long Baseline Array, and have determined a precise proper motion as well as a tentative parallax for the magnetar.

Magnetars are neutron stars with exceptionally strong dipole magnetic fields which are observed to display a range of x-ray flaring behavior, but the flaring mechanism is not well understood. The third observing run of Advanced LIGO and Virgo extended from April 1, 2019 to March 27, 2020, and contained x-ray flares from known magnetar SGR 1935+2154, as well as the newly-discovered magnetar, Swift J1818-1607. We search for gravitational waves coincident with these magnetar flares with minimally modeled, coherent searches which specifically target both short-duration gravitational waves produced by excited f-modes in the magnetar’s core, as well as long-duration gravitational waves motivated by the Quasi-Periodic Oscillations observed in the tails of giant flares. In this talk, we report on the methods and sensitivity estimates of there searches, and the astrophysical implications.