We search for possible correlations between neutron star observables and thermodynamic quantities that characterize high density nuclear matter. We generate a set of model-independent equations of state describing stellar matter from a Taylor expansion around saturation density. We found that the neutron star tidal deformability and radius are strongly correlated with the pressure, the energy...
Astrophysical observations of neutron stars (NS) allow us to study the physics of matter at extreme conditions which are beyond the scope of any terrestrial experiments. In this work, we perform a Bayesian analysis putting together the available knowledge from the nuclear physics experiments,
observations of different x-ray sources and the gravitational wave event GW170817 to constrain the...
We have studied the thermal properties of a recently formulated nuclear energy density functional. The functional is known as BCPM (Barcelona-Catania-Paris-Madrid) and it is based on Brueckner calculations using the realistic Argonne $v_{18}$ potential plus three-body forces of Urbana type. This functional has been successfully used to describe finite nuclei and cold neutron stars....
With the advent of gravitational wave (GW) astronomy, neutron star (NS) properties, such as its equation of state, could be better constrained. This is possible thanks to measurements of their tidal deformations, which modify gravitational waveforms of the early inspiral phase of binary NSs. Our main goal here is to show that, differently from usually believed, tidal deformations of hybrid...
We explore the connection between the stiffness of an hadronic equation of state with a sharp phase transition to quark matter to its tidal deformability. To this end we employ a hadronic relativistic mean field model with a parameterized effective nucleons mass to vary the stiffness in conjunction with a constant speed of sound EoS for quark matter. We compute multiple scenarios with phase...
It is believed that the main dissipative agents in oscillating neutron stars are bulk and shear viscosities (the effect of thermal conductivity is known to be weak and can be disregarded). But the internal layers of neutron stars are composed of a mixture of various particle species (neutrons, protons, electrons,...). Then additional, usually ignored, dissipation mechanism can arise, related...
The Fermi data imply that the gamma-ray observables, i.e., the gamma-ray luminosity, spectral cut-off energy, stellar surface magnetic field, and spin-down power obey a relation that represents a 3D plane in the 4D log-space. This observed fundamental plane (FP) is remarkably close to the theoretical relation that is obtained, assuming that the pulsar gamma-ray emission is due to curvature...
In this talk, I shall present recent works on the spectral characterization of the non-thermal X-ray emission and its subsequent modelling using synchro-curvature radiation. I shall introduce the use of the differential geometry Frenet-Serret equations to describe a magnetic line in a pulsar magnetosphere. These equations, which need to be solved numerically, fix the magnetic line in terms of...
Multi-wavelength observations of pulsar emission properties are powerful means to constrain their magnetospheric activity and magnetic topology. Usually a star centred magnetic dipole model is invoked to explain the main characteristics of this radiation. However in some particular pulsars where observational constraints exist, such simplified models are unable to predict salient features of...
The frequency widening of pulsar profiles is commonly attributed to lower frequencies being produced at greater heights above the surface of the pulsar; so-called radius-to-frequency mapping. Our understanding of the structures of pulsar radio beams is limited by the fact that we can only observe that emission which points along our line of sight. However, single pulses give us a population of...
The gamma pulsar J1957 + 5033 has a period of 375 ms, a characteristic age of 840 thousand years, and a rotation energy loss rate of 5e33 erg / s. According to the age, this pulsar can be at the beginning of the photon stage of the neutron star cooling process when according to standard cooling scenarios the surface temperature and thermal luminosity of a star, begin to drop exponentially...
Although there are copious amount of theory and observation dedicated to pulsar radio emission, very few have investigated the exact nature of emission mechanism and power spectra of radio pulsars. Some recent literature have tried to make out consensus with observed brightness temperature of radio pulsars by incorporating bunch, plasma physics along with suitably chosen emission beam...
Extended near-infrared emission was recently discovered with the Hubble Space Telescope at the position of RX J0806.4-4123, an X-ray thermal isolated neutron star and member of the so-called Magnificent Seven. The nature of this infrared source is still a matter of debate. Both a pulsar wind nebula or a circumpulsar disk could be explanations. We will present a summary of the multiwavelength...
Pulsar Wind Nebulae (PWNe) are powered by the rotational energy lost by the central compact star. Thus they are the perfect place to look at to obtain information on the pulsar in case of a non-direct identification. Multidimensional MHD numerical models of Pulsar Wind Nebulae (PWNe) have been shown to be extremely successful at accounting for a large variety of properties of those sources,...
We present the discovery of sub-second X-ray/IR correlated variability in the accreting neutron star (NS) 4U 1728-34. The source was observed with simultaneous high time resolution XMM and HAWKI@VLT in February 2019. Data show a strongly correlated signal with a lag shorter than 0.125 s. Such behaviour is well known in black-hole transients, where fluctuations travel from the accretion inflow...
I will talk about dramatic spectral changes at very low luminosity state in accreting strongly magnetised neutron stars. These spectral changes were recently discovered in two X-ray pulsars - A 0535+262 and GX 304-1, - thanks to deep NuSTAR observations of these objects. This discovery can shed light on the process of spectra formation in accreting neutron stars under conditions of an...
1RXS J180408.9–342058 is a low mass X-ray binary (LMXB) hosting a neutron star, which shows X-ray activity at very different mass-accretion regimes, from ”very faint” outbursts to almost the Eddington luminosity.
In this work, we present a comprehensive X-ray study of this source using data from Swift, NuSTAR and INTEGRAL/JEM-X. In order to follow the spectral evolution, we analyzed the 2015...
Understanding the mechanism of outburst and modelling the corresponding detailed emission from compact objects in low mass X-ray binaries (LMXBs) is integral to probing the physics of strong gravity, ultra-dense degenerate matter and accretion dynamics. Broadband spectro-timing studies of these objects can put unique constraints on the evolution of the binary components in different spectral...
The superfluid in the interior of a mature neutron star plays a key role in many observational phenomena, with the most striking example being pulsar glitches.
Very few models, to date, have however considered the observational signature of turbulence in the superfluid, a phenomenon that is well known to develop in laboratory superfluids. In this talk will discuss the theoretical framework...
The spin down of many young pulsars are strongly affected by two distinct kinds of rotational irregularities: glitches and spin noise. In addition to allowing us to probe the interior dynamics of neutron stars, glitches introduce difficulties when attempting to model the long-term rotational evolution of pulsars. For instance, there is a long-standing question as to whether the anomalously...
Pulsar glitches are commonly interpreted as sudden transfers of angular momentum from a more rapidly rotating superfluid component to the rest of the neutron star, triggered by large-scale vortex unpinning events. However, large uncertainties remain concerning, e.g., the microscopic interactions between the neutron vortices and the proton flux tubes that are expected to be present in the outer...
In the superfluid interior of a neutron star the presence of quantized vortex lines defines an intermediate scale (in between the microscopic fermi-scale and the centimeter-scale) ranging from the radius of a vortex core to the typical separation between vortices. This complicates the hydrodynamic description of a neutron star interior. A classical treatment of a vortex moving through the...
Superfluidity is a generic feature of various quantum systems at low temperatures. It has been experimentally confirmed in many condensed matter systems, in 3He and 4He liquids, in nuclear systems including nuclei and neutron stars, in both fermionic and bosonic cold atoms in traps, and it is also predicted to show up in dense quark matter. Quantized vortices are regarded as hallmark of...
Despite 40 years of intensive study, the detailed mechanism for sudden increases in the spinning of neutron stars (known as glitches) remains a puzzle. It is believed that glitches are a direct manifestation of superfluidity in the stellar interior. One of the sources of the difficulty of modeling neutron stars is that the scales vary within many orders of magnitude. At the microscale one can...
Despite its importance in determining the interior structure of neutron stars has been universally acknowledged, Einstein's theory of General Relativity has been up to now mostly neglected in the study of pulsar glitches. Its inclusion into the existing Newtonian models seems to be too expensive, compared to the moderate qualitative gain in accuracy and comprehension it gives. However, as the...
