Magnetic hydrogen atmosphere models and the neutron star RX J1856.5–3754 |
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| Authors: | Wynn C G Ho † David L Kaplan ‡ Philip Chang Matthew van Adelsberg Alexander Y Potekhin |
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| Institution: | Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA;Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, PO Box 20450, Mail Stop 29, Stanford, CA 94309, USA;Department of Astronomy, 601 Campbell Hall, University of California, Berkeley, CA 94720, USA;Department of Physics, Broida Hall, University of California, Santa Barbara, CA 93106, USA;Center for Radiophysics and Space Research, Department of Astronomy, Cornell University, Ithaca, NY 14853, USA;Ioffe Physico-Technical Institute, Politekhnicheskaya 26, 194021 St Petersburg, Russia |
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| Abstract: | RX J1856.5?3754 is one of the brightest nearby isolated neutron stars (INSs), and considerable observational resources have been devoted to it. However, current models are unable to satisfactorily explain the data. We show that our latest models of a thin, magnetic, partially ionized hydrogen atmosphere on top of a condensed surface can fit the entire spectrum, from X-rays to optical, of RX J1856.5?3754, within the uncertainties. In our simplest model, the best-fitting parameters are an interstellar column density N H≈ 1 × 1020 cm?2 and an emitting area with R ∞≈ 17 km (assuming a distance to RX J1856.5?3754 of 140 pc), temperature T ∞≈ 4.3 × 105 K , gravitational redshift z g ～ 0.22 , atmospheric hydrogen column y H≈ 1 g cm?2 , and magnetic field B ≈ (3–4) × 1012 G ; the values for the temperature and magnetic field indicate an effective average over the surface. We also calculate a more realistic model, which accounts for magnetic field and temperature variations over the NS surface as well as general relativistic effects, to determine pulsations; we find that there exist viewing geometries that produce pulsations near the currently observed limits. The origin of the thin atmospheres required to fit the data is an important question, and we briefly discuss mechanisms for producing these atmospheres. Our model thus represents the most self-consistent picture to date for explaining all the observations of RX J1856.5?3754. |
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| Keywords: | stars: atmospheres stars: individual: RX J1856 5?3754 stars: neutron X-rays: stars |
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