Astronomy and Astrophysics – Astrophysics
Scientific paper
Sep 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001cnoc.conf....6c&link_type=abstract
The Second National Conference on Astrophysics of Compact Objects, held in Bologna (Italy), September 19 - 21, 2001, p. 6
Astronomy and Astrophysics
Astrophysics
Scientific paper
Over the last years ROSAT observations led to the discovery of six very soft X-ray sources with quite peculiar characteristics. Among these are (i) blackbody-like spectrum with T~ 100 eV; (ii) exceedingly large X-ray to optical flux ratio, fX/fV > 103; (iii) low X-ray luminosity, LX≈ 1030-1031 erg s-1; (iv) low column density, NH~ 1020 cm-2; (v) no evidence for a binary companion; (vi) absence of large flux variations on timescales from months to years. All these points, in particular the extreme values of fX/fV together with the small distances implied by the low column density, qualify these sources as potential, close-by Isolated Neutron Stars. The discovery of new INS candidates is of paramount importance to shed light on the properties of these sources and to constrain their distribution in the Galaxy. We report the identification of a new INS candidate in archival ROSAT observations. The source, RBS 1774, is very soft, exhibits a thermal spectrum well fitted by a blackbody at T~ 90 eV and has low column density, NH~ 4× 1020 cm-2. No plausible optical counterpart was found on DSS2 blue and red plates to a limiting magnitude ~ 22, implying a X-ray to optical flux ratio ≈ 100. Catalogue searches revealed no known sources in other energy bands within the X-ray error box of RBS 1774. Follow-up optical observations with NTT show no peculiar object close to the X-ray source position down to a magnitude mR&sim ;25. Comparison with a previous RASS observation do not show variability on a timescale of months. All these points are at the basis of our claim that RBS 1774 is the seventh isolated neutron star discovered so far.
Campana Sergio
Chieregato L.
Falomo Renato
Fugazza Dino
Moretti Alberto
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