arXiv subjects

Celsa Pardo-Araujo

Publications and source records attributed to Celsa Pardo-Araujo.

4 recordsLinked to original sources

arXiv2026

Connecting radio pulsars, magnetars, and XDINSs in a unified evolutionary framework using simulation-based inference

Understanding the Galactic population of isolated neutron stars within a unified framework provides key insights into their birth properties, evolutionary pathways, and the connections between different neutron star classes. In this work, we aim to reproduce both the observed radio and quiescent X-ray emission from isolated neutron stars, including radio pulsars, magnetars and X-ray dim isolated neutron stars (XDINSs). We develop a comprehensive population synthesis framework that models neutron star birth properties, their dynamical, rotational, and magneto-thermal evolution, as well as radio and X-ray emission, and the selection effects of corresponding surveys. To simulate realistic X-ray spectra, we account for magnetospheric resonant cyclotron scattering and interstellar absorption. Additionally, we model the observational bias introduced by magnetar outbursts, by linking the outburst rate to magnetic stresses in the stellar crust. We then employ a simulation-based inference method, namely truncated sequential neural posterior estimation, to reconstruct the birth properties, such as the initial magnetic field distribution. We find that the Galactic neutron star population can be described by a two-component log-normal distribution of birth magnetic fields with peaks at $5 \times 10^{12}$ G and $10^{14}$ G, respectively. We further find that the Galactic neutron star birth rate is around 3-4 per century. Our results help establish the contribution of neutron stars as central engines of powerful astrophysical transient phenomena, such as fast radio bursts, super-luminous supernovae and gamma ray bursts.

astro-ph.HE↗

arXiv2026

Magnetar fraction in Core-Collapse Supernovae

Magnetars are extreme neutron stars powered by ultra-strong magnetic fields ($\sim10^{14}$ Gauss) and are compelling engines for some of the most powerful extragalactic transients such as Super Luminous Supernovae, Gamma-Ray Bursts, and Fast Radio Bursts. Yet their formation rate relative to ordinary neutron stars remains uncertain, often precluding direct comparisons with the rates of these extragalactic transients. Furthermore, magnetars have been recently shown to be evolutionarily related to other neutron star classes, complicating the estimate of the exact magnetar fraction within the neutron star population. We study the magnetar birth fraction in core-collapse supernovae using pulsar population synthesis of all isolated neutron star classes in our Galaxy, incorporating self-consistently the Galactic dynamical evolution, spin-down and magneto-thermal evolution. This approach allows us to derive strong constraints from small close-to-complete observational samples. In particular, looking at the age-limited young ($<$2 kyr) neutron star population in the Milky Way we find 24 detected young neutron stars, with only 10 of them (41%) being classical rotational powered pulsars, while the others (59%) are either magnetars or central compact objects, the latter believed to be equally magnetically powered. We further compare the results with the nearby volume-limited class ($<$500 pc) of X-ray Dim Isolated Neutron stars, old nearby magnetars. We conclude that the observed population of isolated neutron stars in the Galaxy can be reproduced only by assuming a core-collapse supernova rate larger than two, and a larger magnetar fraction than previously inferred. By assuming a bimodal initial magnetic field ($B_0$) distribution at birth, we find that the magnetar class peaks between $B_0\sim 1-2.5\times10^{14}$ Gauss and represents on average $\sim50$% of the entire neutron star population.

astro-ph.HE↗

arXiv2024

Isolated pulsar population synthesis with simulation-based inference

We combine pulsar population synthesis with simulation-based inference (SBI) to constrain the magnetorotational properties of isolated Galactic radio pulsars. We first develop a framework to model neutron star birth properties and their dynamical and magnetorotational evolution. We specifically sample initial magnetic field strengths, $B$, and spin periods, $P$, from lognormal distributions and capture the late-time magnetic field decay with a power law. Each lognormal is described by a mean, $μ_{\log B}, μ_{\log P}$, and standard deviation, $σ_{\log B}, σ_{\log P}$, while the power law is characterized by the index, $a_{\rm late}$. We subsequently model the stars' radio emission and observational biases to mimic detections with three radio surveys, and we produce a large database of synthetic $P$--$\dot{P}$ diagrams by varying our five magnetorotational input parameters. We then follow an SBI approach that focuses on neural posterior estimation and train deep neural networks to infer the parameters' posterior distributions. After successfully validating these individual neural density estimators on simulated data, we use an ensemble of networks to infer the posterior distributions for the observed pulsar population. We obtain $μ_{\log B} = 13.10^{+0.08}_{-0.10}$, $σ_{\log B} = 0.45^{+0.05}_{-0.05}$ and $μ_{\log P} = -1.00^{+0.26}_{-0.21}$, $σ_{\log P} = 0.38^{+0.33}_{-0.18}$ for the lognormal distributions and $a_{\rm late} = -1.80^{+0.65}_{-0.61}$ for the power law at the $95\%$ credible interval. We contrast our results with previous studies and highlight uncertainties of the inferred $a_{\rm late}$ value. Our approach represents a crucial step toward robust statistical inference for complex population synthesis frameworks and forms the basis for future multiwavelength analyses of Galactic pulsars.

astro-ph.HE↗

arXiv2023

Long-period radio pulsars: population study in the neutron star and white dwarf rotating dipole scenarios

The nature of two recently discovered radio emitters with unusually long periods of 18min (GLEAM-X J1627-52) and 21min (GPM J1839-10) is highly debated. Their bright radio emission resembles that of radio magnetars, but their long periodicities and lack of detection at other wavelengths challenge the neutron-star interpretation. In contrast, long rotational periods are common in white dwarfs but, although predicted, dipolar radio emission from isolated magnetic white dwarfs has never been unambiguously observed. In this work, we investigate these long-period objects as potential isolated neutron-star or white-dwarf dipolar radio emitters and find that both scenarios pose significant challenges to our understanding of radio emission via pair production in dipolar magnetospheres. We also perform population-synthesis simulations based on dipolar spin-down in both pictures, assuming different initial-period distributions, masses, radii, beaming fractions, and magnetic-field prescriptions, to assess their impact on the ultra-long pulsar population. In the neutron-star scenario, we do not expect a large number of ultra-long period pulsars under any physically motivated (or even extreme) assumptions for the period evolution. On the other hand, in the white-dwarf scenario, we can easily accommodate a large population of long-period radio emitters. However, no mechanism can easily explain the production of such bright coherent radio emission in either scenarios.

astro-ph.HE↗