Evaluating the Evidence of Multipolar Surface Magnetic Field in PSR J0108$-$1431
| Autor: | Prakash Arumugasamy, Dipanjan Mitra |
|---|---|
| Jazyk: | angličtina |
| Rok vydání: | 2019 |
| Předmět: |
High Energy Astrophysical Phenomena (astro-ph.HE)
Physics Photon 010308 nuclear & particles physics Astrophysics::High Energy Astrophysical Phenomena FOS: Physical sciences Magnetosphere Astronomy and Astrophysics Astrophysics 01 natural sciences Spectral line Magnetic field Dipole Neutron star Pulsar Space and Planetary Science 0103 physical sciences Black-body radiation Astrophysics - High Energy Astrophysical Phenomena 010303 astronomy & astrophysics |
| Popis: | PSR J0108$-$1431 is an old pulsar where the X-ray emission is expected to have a thermal component from the polar cap and a non-thermal component from the magnetosphere. Although the phase-integrated spectra are fit best with a single non-thermal component modeled with a power-law (PL) of photon index $\Gamma=2.9$, the X-ray pulse profiles do show the presence of phase-separated thermal and non-thermal components. The spectrum extracted from half the rotational phase away from the X-ray peak fits well with either a single blackbody (BB) or a neutron star atmosphere (NA) model, whereas, the spectrum from the rest of the phase range is dominated by a PL. From Bayesian analysis, the estimated BB area is smaller than the expected polar cap area for a dipolar magnetic field with a probability of 86% whereas the area estimate from the NA model is larger with a probability of 80%. Due to the ambiguity in the thermal emission model, the polar cap area cannot be reliably estimated and hence cannot be used to understand the nature of the surface magnetic field. Instead, we can infer the presence of multipolar magnetic field from the misalignment between the pulsar's thermal X-ray peak and the radio emission peak. For J0108$-$1431, we estimated a phase-offset $\Delta\phi > 0.1$ between the thermal polar cap emission peak and the radio emission peak and argue that this is best explained by the presence of a multipolar surface magnetic field. Comment: 17 pages, 15 figures, accepted for publication in MNRAS |
| Databáze: | OpenAIRE |
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