arXiv subjects

Manoel F. Sousa

Publications and source records attributed to Manoel F. Sousa.

7 recordsLinked to original sources

arXiv2026

Magnetically Confined Mountains on Accreting White Dwarfs

The hydromagnetic structure of magnetically confined mountains on accreting white dwarfs is computed, alongside the effects of accretion on the reduction of the star's magnetic field. The equilibrium structure of the mountain is obtained by numerically solving the Grad-Shafranov equation with a self-consistent scheme that enforces magnetic flux freezing. For characteristic system parameters, it is shown that magnetic field lines are significantly deformed and dragged equatorwards by mountains with masses $\sim10^{-3}M_\odot$ that have a characteristic height of $\sim10^5\,\mathrm{cm}$. A mathematical relation is obtained for the maximum mass that a white dwarf can confine magnetically given the star's magnetic field and temperature. It is found that the accretion buries the star's magnetic field by reducing it by up to $10\%$ of its pre-accretion value. The star's magnetic field remains dominantly dipolar, but with added multipolar components.

astro-ph.SR↗

arXiv2026

Non-thermal emission from the vicinity of the magnetar CXOU J171405.7-381031

Magnetars are neutron stars with ultra-strong magnetic fields ($B \sim 10^{14}$-$10^{15}$ G) and are promising candidates for high-energy particle acceleration. We present a multiwavelength analysis of the region surrounding CXOU J171405.7-381031, a magnetar associated with the supernova remnant (SNR) CTB 37B. The broadband spectral energy distribution spanning radio to TeV energies is modeled using leptonic and lepto-hadronic scenarios, with particle populations constrained using Markov Chain Monte Carlo techniques. Within an SNR framework, both scenarios provide acceptable descriptions of the gamma-ray data. The purely leptonic model reproduces the overall spectral shape but slightly underestimates the highest-energy flux measured by H.E.S.S., whereas a lepto-hadronic interpretation offers an improved description above $\sim 10$ TeV, with inverse-Compton scattering dominating the GeV emission and neutral-pion decay contributing at the highest energies. The required proton energy ($W_{\rm p} \gtrsim 10^{51}$ erg) can be substantially reduced if the remnant interacts with a dense ambient medium. A magnetar wind nebula scenario can reproduce the broadband spectrum but is strongly disfavored by the observed source morphology. Simulated Cherenkov Telescope Array Observatory (CTAO) observations indicate that exposures of $\sim 50$ h will constrain the proton cut-off energy, enabling a decisive test of hadronic emission in this region.

astro-ph.HE↗

arXiv2026

Multiwavelength study of non-thermal emission in the Swift J1834.9-0846/W41 region

We investigate the origin of non-thermal emission from the Swift J1834-0846/W41 region by modeling its broadband spectral energy distribution from radio to TeV energies within leptonic and lepto-hadronic frameworks using Markov Chain Monte Carlo sampling. Motivated by morphological studies of HESS J1834-087 suggesting a two-component TeV structure, we explore a single extended source scenario and a configuration comprising a central point-like component embedded within extended emission. Purely leptonic models are disfavored in both scenarios by unrealistically low magnetic field strengths, whereas lepto-hadronic solutions yield field intensities and non-thermal energy budgets consistent with an evolved supernova remnant undergoing efficient cosmic-ray acceleration. In the two-component scenario, hadronic interactions dominate the extended TeV emission from W41, while the central excess is well described by a leptonic magnetar wind nebula powered by Swift J1834-0846, implying a short initial spin period of $P_0 \lesssim 0.2$ s. Simulated observations with the Cherenkov Telescope Array Observatory show that 30 h exposures will discriminate between the two morphological configurations and extend spectral measurements beyond $\sim$10 TeV.

astro-ph.HE↗

arXiv2026

Double White Dwarf Mergers as Progenitors of Long-Period Transients

There is an ongoing discussion in the literature on the nature of long-period transients (LPTs), radio-emitting sources with periods ranging from hundreds to tens of thousands of seconds. Although some of these objects have been identified as white dwarf (WD) + M-dwarf binaries, this description currently does not fit the entire class. An example is GLEAM-X J162759.5-523504.3 (hereafter GLEAM-X J1627-5235), with a period of 1091 s, for which the lack of an optical counterpart disfavors the presence of such a binary system. In this case, GLEAM-X J1627-5235 could be interpreted as an isolated, massive, fast-rotating, and highly magnetized (~ 1e+9 G) WD pulsar. Its properties are consistent with a carbon-oxygen WD of mass ~1.3 Msun and radius ~2500 km, possibly supported by small-scale multipolar magnetosphere structures that keep it above the death line for WD-pulsars. We assess a double WD merger origin, modeling the post-merger rotational evolution under accretion, propeller, and magnetic braking torques. We find rotational age of ~572 Myr for GLEAM-X J1627-5235, i.e., the post-merger time required to reach its observed period. This result is consistent with current optical upper limits for GLEAM-X J1627-5235 and support the WD pulsar interpretation for this source. We also discuss how the same model can apply to other LPTs.

astro-ph.HE↗

arXiv2021

Gravitational Wave Emission by Accretion of Matter and Magnetic Deformation in Fast Rotating White Dwarfs

We discuss some aspects of Sousa et al.(2020a, 2020b) concerning two mechanisms of gravitational wave (GW) emission in fast-spinning white dwarfs (WDs): accretion of matter and magnetic deformation. In both cases, the GW emission is generated by an asymmetry around the rotation axis of the star. However, in the first case, the asymmetry is due to the amount of accreted matter in the magnetic poles, while in the second case it is due to the intense magnetic field. We have estimated the GW amplitude and luminosity for three binary systems that have a fast-spinning magnetized WD, namely, AE Aquarii, AR Scorpii and RX J0648.0-4418. In addition, we applied the magnetic deformation mechanism for SGRs/AXPs described as WD pulsars. We found that, for the first mechanism, the systems AE Aquarii and RX J0648.0-4418 can be observed by the space detectors BBO and DECIGO if they have an amount of accreted mass of $δm \geq 10^{-5}M_{\odot }$. For the second mechanism, the three systems studied require that the WD has a magnetic field above $\sim 10^{9}$ G to emit GWs that can be detected by BBO. Furthermore, we found that some SGRs/AXPs as WD pulsars can be detected by BBO and DECIGO, whereas SGRs/AXPs as highly magnetized neutron stars are far below the sensitivity curves of these detectors.

astro-ph.SR↗

arXiv2020

Gravitational waves from SGRs and AXPs as fast-spinning white dwarfs

Gravitational waves (GWs) emission due to magnetic deformation mechanism is applied for Soft Gamma Repeaters (SGRs) and Anomalous X-Ray Pulsars(AXPs), described as fast-spinning and magnetized white dwarfs (WDs). The emission is caused by the asymmetry around the rotation axis of the star generated by its own intense magnetic field. Thus, for the first time in the literature, it is estimated the GWs counterpart for SGRs/AXPs described as WD pulsars. We find that some SGRs/AXPs can be observed by the space detectors BBO and DECIGO. In particular, 1E 1547.0-5408 and SGR 1806-20 could be detected in 1 year of observation, whereas SGR 1900+14, CXOU J171405.7-381031, Swift J1834.9-0846 and SGR 1627-41 could be observed with a 5-year observation time. We also found that SGRs/AXPs as highly magnetized neutron stars are far below the sensitivity curves of BBO and DECIGO. This result indicates that a possible detection of continuous GWs originated from these objects would corroborate the WD pulsar model.

astro-ph.SR↗

arXiv2020

Gravitational waves from fast-spinning white dwarfs

Two mechanisms of gravitational waves (GWs) emission in fast-spinning white dwarfs (WDs) are investigated: accretion of matter and magnetic deformation. In both cases, the GW emission is generated by an asymmetry around the rotation axis of the star. However, in the first case, the asymmetry is due to the amount of accreted matter on the magnetic poles, while in the second case it is due to the intense magnetic field. We have estimated the GW amplitude and luminosity for three binary systems that have a fast-spinning magnetized WD, namely, AE Aquarii, AR Scorpii and RX J0648.0-4418. We find that, for the first mechanism, the systems AE Aquarii and RX J0648.0-4418 can be observed by the space detectors BBO and DECIGO if they have an amount of accreted mass of $δm \geq 10^{-5}M_{\odot }$. For the second mechanism, the three systems studied require that the WD have a magnetic field above $\sim 10^{9}$ G to emit GWs that can be detected by BBO. We also verified that, in both mechanisms, the gravitational luminosity has an irrelevant contribution to the spindown luminosity of these three systems. Therefore, other mechanisms of energy emission are needed to explain the spindown of these objects.

astro-ph.SR↗