Magnetar structure in non-linear electrodynamics with mixed poloidal-toroidal fields
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arXiv
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| Format: | Preprint |
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2025
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| _version_ | 1866918014078681088 |
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| author | Suvorov, Arthur G. Pons, José A. |
| author_facet | Suvorov, Arthur G. Pons, José A. |
| contents | Magnetars have inferred polar field strengths in excess of the Schwinger limit, where non-linear electromagnetic effects can be significant. Their internal fields may be even stronger, suggesting that Maxwellian characterizations of hydromagnetic structure may require revision. A generalized Grad-Shafranov equation, describing static and axisymmetric fluid stars with mixed poloidal-toroidal fields, is introduced and subsequently solved in a perturbative scheme to calculate quadrupolar deformations. In the Born-Infeld theory, we show that the toroidal field has a maximum strength set by the scale parameter, $b$, implying an upper limit to the stellar prolateness, $|ε_{\rm max}| \sim 10^{-5} \left(b/10^{16}\text{ G}\right)^2$, that is independent of field specifics. Observations of magnetar phenomena that are interpreted as evidence for ellipticity, such as precession, can thus implicitly constrain post-Maxwellian parameters in a way that complements terrestrial experiments. Toroidal ceilings also have implications for dynamo theory and gravitational waves, which we revisit together with field evolution in crusts abiding by beyond-Maxwell physics. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2503_01409 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Magnetar structure in non-linear electrodynamics with mixed poloidal-toroidal fields Suvorov, Arthur G. Pons, José A. High Energy Astrophysical Phenomena General Relativity and Quantum Cosmology High Energy Physics - Phenomenology High Energy Physics - Theory Magnetars have inferred polar field strengths in excess of the Schwinger limit, where non-linear electromagnetic effects can be significant. Their internal fields may be even stronger, suggesting that Maxwellian characterizations of hydromagnetic structure may require revision. A generalized Grad-Shafranov equation, describing static and axisymmetric fluid stars with mixed poloidal-toroidal fields, is introduced and subsequently solved in a perturbative scheme to calculate quadrupolar deformations. In the Born-Infeld theory, we show that the toroidal field has a maximum strength set by the scale parameter, $b$, implying an upper limit to the stellar prolateness, $|ε_{\rm max}| \sim 10^{-5} \left(b/10^{16}\text{ G}\right)^2$, that is independent of field specifics. Observations of magnetar phenomena that are interpreted as evidence for ellipticity, such as precession, can thus implicitly constrain post-Maxwellian parameters in a way that complements terrestrial experiments. Toroidal ceilings also have implications for dynamo theory and gravitational waves, which we revisit together with field evolution in crusts abiding by beyond-Maxwell physics. |
| title | Magnetar structure in non-linear electrodynamics with mixed poloidal-toroidal fields |
| topic | High Energy Astrophysical Phenomena General Relativity and Quantum Cosmology High Energy Physics - Phenomenology High Energy Physics - Theory |
| url | https://arxiv.org/abs/2503.01409 |