RX J185635-3754: Spectral Modelling Efforts

Neutron Star ATMosphere model (ATM):

model spectral energy distributions.

We show results for atmospheres made of pure H, He, and Fe in this figure. These represent the best fits to the X-ray data alone; the spectra are plotted with arbitrary normalizations for clarity.
Solid line: 57 eV blackbody spectrum.
Dotted line: hydrogen atmosphere (T=21 eV g=2 X 10^14 cgs).
Dashed line: helium atmosphere (T= 18 eV g=1 X 10^14 cgs).
Dash-dot line: Iron atmosphere (T= 35 eV g=4 X 10^14 cgs).

The first table gives the predicted distance for an assumed radius of 10 km. The blackbody prediction is 162 pc; the true distance is less than 130 pc. For comparison, we show the Pavlov et al [12] model atmosphere predictions.

Predicted distance of RX J185635-3754
Model Pavlov ATM
H Atmosphere 4.8 12.
He Atmosphere 3.8 12.
Fe Atmosphere 216. 38.


The second table gives the predicted V magnitudes from the model normalized to the X-ray flux. An extrapolation of the X-ray blackbody gives V=26.8; the observed V=25.7 +/- 0.2 For comparison, we show the Pavlov et al [12] model atmosphere predictions.

Predicted V magnitude of RX J1856.5-3754.
Model Pavlov ATM
H Atmosphere 21.8 24.0
He Atmosphere 20.8 23.3
Fe Atmosphere 27.5 25.3


The iron atmosphere is most consistent with the optical data, but we require a parallax to distinguish between the models.

References:
12: Pavlov, G.G., Zavlin, V., Truemper, J., & Neuhaeuser, R. 1996. ApJL, 472, L33.

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