ONS in molecular clouds

A different approach for the search of ONSs was suggested by Blaes & Madau (1993) and Colpi, Campana & Treves (1993), who indicate as a very promising environment for their detection nearby giant molecular clouds, where the density of the ISM is sufficiently high for a single neutron star to emit a considerable amount of radiation. However, in this case also the absorption of the ISM will be enhanced and the detectability will crucially rely on the delicate balance between the emitted luminosity and the absorbed flux. As shown by Blaes & Madau (1993), Colpi, Campana & Treves (1993) and Zane et al. (1995a), some molecular clouds in the vicinity of the Sun are expected to contain a large number of ONSs emitting at relatively high rates and then representing the most favourable sites for the observability of these sources. A search has been carried out in the two most promising clouds by Belloni et al. (1996), leading to 4 (weak) ONS candidates.