RX J1856.5 - 3754 is one of the brightest nearby isolated neutron stars , 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-fit parameters are an interstellar column density N _ { H } \approx 1 \times 10 ^ { 20 } \mbox { cm$ { } ^ { -2 } $ } and an emitting area with R ^ { \infty } \approx 17 km ( assuming a distance to RX J1856.5 - 3754 of 140 pc ) , temperature T ^ { \infty } \approx 4.3 \times 10 ^ { 5 } K , gravitational redshift z _ { g } \sim 0.22 , atmospheric hydrogen column y _ { H } \approx 1 \mbox { g cm$ { } ^ { -2 } $ } , and magnetic field B \approx ( 3 - 4 ) \times 10 ^ { 12 } 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 neutron star surface as well as general relativistic effects , to determine pulsations ; we find 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 .