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Astron. Astrophys. 351, 177-184 (1999)

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The isolated neutron star candidate RX J1605.3+3249

C. Motch *  1, F. Haberl 2, F.-J. Zickgraf 1, G. Hasinger 3 and A.D. Schwope 3

1 Observatoire Astronomique, UA 1280 CNRS, 11 rue de l'Université, 67000 Strasbourg, France
2 Max-Planck-Institut für Extraterrestrische Physik, 85740 Garching bei München, Germany
3 Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany

Received 10 May 1999 / Accepted 23 July 1999


We report on X-ray and optical observations of a ROSAT X-ray source, RX J1605.3+3249, selected from the all-sky survey on the basis of its spectral softness and lack of bright optical counterpart. The ROSAT PSPC energy distribution is well fitted by a blackbody with kT = 92[FORMULA]6 eV and [FORMULA] = 1.1[FORMULA]0.4[FORMULA]1020 cm-2. X-ray observations spanning 6.5 years fail to reveal any flux or spectral variability on any time scales. The ROSAT HRI error circle only contains a R = 23.25 M star which is unlikely to be associated with the X-ray source. We conclude that RX J1605.3+3249 is a probable nearby isolated neutron star detected from its thermal emission. The present data do not allow to unambiguously determine the X-ray powering mechanism, cooling from a young neutron star or heating by accretion from the interstellar medium onto an old neutron star. However, the long term stability of the X-ray flux favours the young neutron star hypothesis.

Key words: stars: individual: RX J1605.3+3249 – stars: neutron – X-rays: general

* Visiting Astronomer, Canada-France-Hawaii Telescope operated by the National Research Council of Canada, the Centre National de la Recherche Scientifique de France and the University of Hawaii.

Send offprint requests to: C. Motch

© European Southern Observatory (ESO) 1999

Online publication: November 2, 1999