2015/07/09 by Sébastien Guillot, Guillot, Sebastien, Rosalba Perna +8 · 2 citations
Earth and Planetary Sciences · Physics and Astronomy · #FOS: Physical sciences #Gamma-ray bursts and supernovae #High Energy Astrophysical Phenomena (astro-ph.HE) #High-pressure geophysics and materials #Pulsars and Gravitational Waves Research
paper · pdf · doi:10.48550/arxiv.1507.02689
openalex publication_date 2015/07/09 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
We perform a detailed modelling of the post-outburst surface emission of the\nlow magnetic field magnetar SGR 0418+5729. The dipolar magnetic field of this\nsource, B=6x1012 G estimated from its spin-down rate, is in the observed range\nof magnetic fields for normal pulsars. The source is further characterized by a\nhigh pulse fraction and a single-peak profile. Using synthetic temperature\ndistribution profiles, and fully accounting for the general-relativistic\neffects of light deflection and gravitational redshift, we generate synthetic\nX-ray spectra and pulse profiles that we fit to the observations. We find that\nasymmetric and symmetric surface temperature distributions can reproduce\nequally well the observed pulse profiles and spectra of SGR 0418. Nonetheless,\nthe modelling allows us to place constraints on the system geometry (i.e. the\nangles \ψ and \ξ that the rotation axis makes with the line of sight and\nthe dipolar axis, respectively), as well as on the spot size and temperature\ncontrast on the neutron star surface. After performing an analysis iterating\nbetween the pulse profile and spectra, as done in similar previous works, we\nfurther employed, for the first time in this context, a Markov-Chain\nMonte-Carlo approach to extract constraints on the model parameters from the\npulse profiles and spectra, simultaneously. We find that, to reproduce the\nobserved spectrum and flux modulation: (a) the angles must be restricted to\n65\deg < \ψ+\ξ < 125\deg or 235\deg < \ψ+\ξ <295\deg; (b) the\ntemperature contrast between the poles and the equator must be at least a\nfactor of \∼6, and (c) the size of the hottest region ranges between\n0.2-0.7 km (including uncertainties on the source distance). Last, we interpret\nour findings within the context of internal and external heating models.\n