Jaziel G. Coelho

Jaziel G. Coelho
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Jaziel G. Coelho

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High Energy Astrophysical Phenomena (8)
Solar and Stellar Astrophysics (7)
General Relativity and Quantum Cosmology (5)
Nuclear Theory (3)
High Energy Physics - Phenomenology (1)
High Energy Physics - Theory (1)

Publications Authored By Jaziel G. Coelho

The sources of ultra-high-energy cosmic rays ($E\gtrsim10^{19}$ eV) is still an open question in astroparticle physics and in the last years some efforts were made to understand its origin. In this work we consider white dwarf pulsars (WDPs) as possible sources of these ultra energetic particles. If some Soft Gamma Repeaters (SGRs) and Anomalous X-ray Pulsars (AXPs) are considered as white dwarf pulsars, these sources can achieve large electromagnetic potentials on its surface and possibly accelerate particle almost of speed of light and with energies $E \sim 10^{20-21}$ eV. Read More

We investigate the possibility that some SGRs/AXPs could be canonical rotation-powered pulsars using realistic NS structure parameters instead of fiducial values. We show that realistic NS parameters lowers the estimated value of the magnetic field and radiation efficiency, $L_X/\dot{E}_{\rm rot}$, with respect to estimates based on fiducial NS parameters. We show that nine SGRs/AXPs can be described as canonical pulsars driven by the NS rotational energy, for $L_X$ computed in the soft (2--10~keV) X-ray band. Read More

In one of our previous articles we have considered the role of a time dependent magnetic ellipticity on pulsars' braking indices and on the putative gravitational waves these objects can emit. Since only nine of more than 2000 known pulsars have accurately measured braking indices, it is of interest to extend this study to all known pulsars, in particular to what concerns the gravitational waves generation. To do so, as shown in our previous article, we need to know some pulsars' observable quantities such as: periods and their time derivatives, and estimated distances to the Earth. Read More

We study the role of time dependent magnetic ellipticities ($\epsilon_{B}$) on the calculation of the braking index of pulsars. Moreover, we study the consequences of such a $\epsilon_{B}$ on the amplitude of gravitational waves (GWs) generated by pulsars with measured braking indices. We show that, since the ellipticity generated by the magnetic dipole is extremely small, the corresponding amplitude of GWs is much smaller than the amplitude obtained via the spindown limit. Read More

We study the putative emission of gravitational waves (GWs) in particular for pulsars with measured braking index. We show that the appropriate combination of both GW emission and magnetic dipole brakes can naturally explain the measured braking index, when the surface magnetic field and the angle between the magnetic dipole and rotation axes are time dependent. Then we discuss the detectability of these very pulsars by aLIGO and the Einstein Telescope. Read More

We firstly revisit the energy loss mechanism known as quantum vacuum friction (QVF), clarifying some of its subtleties. Then we investigate the observables that could easily differentiate QVF from the classical magnetic dipole radiation for pulsars with braking indices (n) measured accurately. We show this is specially the case for the time evolution of a pulsar's magnetic dipole direction ($\dot{\phi}$) and surface magnetic field ($\dot{B}_0$). Read More

The Anomalous X-ray Pulsars (AXPs) and Soft Gamma-ray Repeaters (SGRs) are a class of pulsars understood as neutron stars (NSs) with super strong surface magnetic fields, namely $B\gtrsim10^{14}$ G, and for that reason are known as Magnetars. However, in the last years some SGRs/AXPs with low surface magnetic fields $B\sim(10^{12}-10^{13})$ G have been detected, challenging the Magnetar description. Moreover, some fast and very magnetic white dwarfs (WDs) have also been observed, and at least one showed X-Ray energy emission as an ordinary pulsar. Read More

We use the thin-shell Darmois-Israel formalism to model and assess the stability of the interfaces separating phases, e.g. the core and the crust, within compact stars. Read More