Resumen:

Pulsars have exceptionally stable rotation. However, their high rotational stability can be disturbed by glitches, a phenomenon that involves a sudden increase in their rotation frequency, the cause of which is not fully understood. Since 2018, the PuMA collaboration has been using the antennas of the Argentine Institute of Radio Astronomy (IAR) to monitor a group of bright pulsars with high cadence in the southern hemisphere that have previously exhibited glitches. In this work, we report the detection and characterization, through the pulsar timing technique, of: i) two glitches in PSR J1048-5832, which turned out to be the smallest among the 7 glitches previously reported for this pulsar; ii) the most recent glitch in the Vela pulsar; iii) a glitch in PSR J0742-2822, the largest observed in this pulsar to date, and iv) a glitch in PSR J1740-3015.

Resumen:

The internal composition of neutron stars, one of the densest astronomical objects in the universe, is still unknown. Although in the last decade, with the onset of multi-messenger gravitational wave astronomy, several astrophysical observations placed strong constraints on these compact objects, there is still a lack of understanding of the dense matter equation of state. In this work, we model neutron stars as hybrid stars -composed of an inner core of quark matter and a mantle of hadronic matter-, considering an abrupt and slow first-order hadron-quark phase transition in their core. We model the hadronic phase with a piecewise polytropic fit, and the inner quark core through a Color Flavor Locked superconducting equation of state, with corrections due to the strong coupling constant, within the framework of the MIT Bag model. In the framework of this abrupt and slow scenario, it is possible to obtain an extended branch of stable stellar configurations. It has been shown that the appearance of such branches could resolve the existing tension between current astrophysical observations. We analyze the behavior of this extended stability branch by quantifying and systematically studying, for the first time, its length, relating this quantity to fundamental properties of the hybrid equation of state. This study allows not only a deeper understanding of the extended stability scenario with slow hadron-quark conversions but could reveal the mystery of the composition of neutron stars and, consequently, clarify the uncertainty about the equation of state of dense matter.

Resumen:

In this work, we show that, within the slow hadron-quark conversion regime where extended branches of hybrid stars (SSHS) appear, all universal relationships for wI-modes available in the literature do not hold. Moreover, we show newly discovered universal relationships that include SSHS, and present potential astronomical applications of such relationships, showing that, if the frequency and damping time of the fundamental mode are measured, its mass, radius, and dimensionless tidal deformability can be inferred. The errors of such estimates are smaller than a few per cent for the mass and the radius. For the dimensionless tidal deformability, the errors for compact objects with masses greater than 1.4 solar masses are typically less than 100%.

Resumen:

Cosmic rays are charged particles that permeate astrophysical environments and possess energies much higher than those of particles in thermal equilibrium in these media. Their origin is one of the key unresolved questions in high-energy astrophysics. It is believed that the majority of galactic cosmic rays (with energies up to ~PeV) are accelerated in shocks produced by the expansion of supernova remnants (SNRs), although this process is not yet fully understood. On the other hand, in the interplanetary medium, particles accelerated to tens of MeV are directly detected in correlation with the presence of shocks. This research aims to develop a one-dimensional model of confinement and injection of energized particles into the heliosphere and apply it to supernova shocks. In this initial stage, we employ modified magnetohydrodynamic (MHD) simulations to include the influence of cosmic rays through diffusion approximation. We simulate the evolution of the spatial distribution of particles injected in the vicinity of shocks based on events detected in the heliosphere. We will also present the evolution of the energy distribution of particles in Particle-In-Cell-MHD simulations. We compare our results with direct particle observations and also with previous models. Additionally, we outline how we intend to apply this model to SNR shocks. The developing model has the potential to contribute to the understanding of the cosmic ray acceleration process, as certain open questions, such as the development of instabilities and turbulence near the shock - and their impact on particle confinement - can be tested in the interplanetary medium, where direct observations are available. In the future, we plan to extend its application to the construction of non-thermal emission models for SNRs.

Resumen:

The smooth rotation of the Vela pulsar was interrupted 17 times during the last 50 years by very rapid and significant increments. These events, known as glitches, are thought to be caused by a dynamic interplay between the outer crust of the star and its superfluid interior. Glitch sizes distribute narrowly around two millionths of the rotation rate. Glitch-like events of smaller sizes can be observed but are considerably less frequent. However, very small events, 100 to 1000 times smaller than the glitches, are ubiquitous but exhibit noise-like properties. We present a complete study of the rotational irregularities of the Vela pulsar using observations carried out at the Mount Pleasant Radio Observatory (Hobart, Australia) for over 20 yr. Preliminary results suggest that the small noise-like events correspond to recurrent small variations of the torque acting on the pulsar and not to rapid increments in the rotation rate, thereby implying an exterior origin.

Resumen:

Gravitational waves detected from the inspiral stage of a binary neutron star merger give information about the nature of the initial components such as their masses, spins, radii and tidal deformabilities. Similarly, observations of the post-merger stage would give hints on the characteristics and the evolution of the remnant of these coalescences. Since post-merger observations by earth-based detectors are not available yet, only numerical simulations are used to study this stage. Therefore, we will review the main characteristics of this kind of merger, as well as the results given by the numerical simulations in order to better understand the different outcomes that are produced in these systems and how the final fate is related to the initial components.