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Astron. Astrophys. 341, L51-L54 (1999)

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Letter to the Editor

The isolated neutron star candidate RBS1223 (1RXS J130848.6+212708)

A.D. Schwope 1, G. Hasinger 1, R. Schwarz 1, F. Haberl 2 and M. Schmidt 3

1 Astrophysikalisches Institut Potsdam, An der Sternwarte 16, D-14482 Potsdam, Germany
2 Max-Planck-Institut für Extraterrestrische Physik, Karl-Schwarzschild-Strasse 2, D-85740 Garching bei München, Germany
3 California Institute of Technology, Pasadena, CA 91125, USA

Received 25 August 1998 / Accepted 18 November 1998


In the ROSAT Bright Survey (RBS) we have almost completely optically identified the brightest [FORMULA]2000 high-galactic latitude sources from the ROSAT All-Sky Survey Bright Source Catalogue (1RXS). A small number of sources has empty X-ray error circles on optical images. ROSAT HRI follow-up observations of RBS1223 (=1RXS J130848.6+212708), a soft object with extreme X-ray to optical flux ratio, have confirmed a relatively bright X-ray source, whose position could be determined to an accuracy of 1.6 arcsec (90%) due to the presence of a nearby, X-ray detected bright star. Deep Keck R- and B-band images of the field were taken, but the refined X-ray error circle remains empty to a limiting magnitude [FORMULA]. With an X-ray to optical flux ratio of [FORMULA] this object is almost certainly an isolated neutron star, similar to the two so far best-known examples RX J1856.4-3754 and RX J0720.4-3125. We discuss limits on the number of similar objects in the RBS catalogue.

Key words: accretion, accretion disks – stars: neutron – X-rays: stars – stars: individual: RBS 1223

Send offprint requests to: A. Schwope

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© European Southern Observatory (ESO) 1999

Online publication: December 4, 1998