The Optical Counterpart of the Isolated Neutron Star
RX J185635-3754

F. M. Walter, L. D. Matthews, P. An, J. Lattimer, and M. Prakash
Department of Physics and Astronomy
SUNY Stony Brook

R. Neuhaeuser
Max-Planck-Institut fuer Extraterrestrische Physik

Presented at 1997 HEAD meeting, Nov 4-7 1997


We have identified the optical counterpart of the isolated, non-pulsing, radio-quiet neutron star RXJ185635-3754 in HST/WFPC2 images as a faint blue object with V=25.6 and U-V = -1.2. The 3000 and 6060A fluxes lie above the extrapolation of the X-ray black body, by factors of 2.4 and 3.7, respectively. The optical points are not consistent with a black body continuum unless the reddening greatly exceeds that suggested by the X-rays. We interpret the spectrum in terms of a latitudinal temperature gradient plus excess emission in the red. If the object lies in front of the CrA molecular cloud, the radius R_infinity < 14 km.

We report on the current status of the investigation. We have obtained a spectrum near 100 A from the EUVE, and further broadband photometry. Planned HST observations will yield the proper motion and parallax. Knowledge of the distance will permit us to investigate the interior equation of state: we will discuss the observational constraints on conventional and kaon-condensate equations of state.


  1. Introduction
  2. The X-Ray Data
  3. Distance
  4. X-Ray Astrometry
  5. Searches for Counterparts at Other Wavelengths
  6. The Hubble Space Telescope Observation
  7. Recent Ground-based Observations
  8. The EUVE Observation
  9. What is it?
  10. What are we doing about it?
  11. Spectral Modelling Efforts
  12. References

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