purpose — to set an upper limit to the value $T_{bb}$, to set later, using our own optical observations of the GRB790613 [$\gamma$]{}–ray box, a limit on $T_{bb}$ and a lower limit on the distance to the supposed potential candidates. Thus, that is a kind of development of the method of Pizzichini et al. (1986) for single objects, which has already become almost standard.

In Fig.1 are presented corresponding bounds on $T_{bb}$ temperature of emission from the surface of the compact object with $R=10\rm \ km$ as a function of distance to it. The source of black body emission with $R=10\rm \ km$ can be detected in the X–rays or/and in the optical if at a given temperature and distance it is found to the left or/and above the corresponding curve in Fig.1.

For the all–sky survey in the energy range of $0.1-2.4\rm \ keV$ with the help of the ROSAT satellite (ROSAT All-Sky Survey = ROSAT ASS) we will use the flux $F_{x}\approx 4.2 \cdot 10^{-13}\,{\rm erg\cdot cm^{-
2}\cdot s^{-1}}$, averaged over the whole survey (with an average exposure time of 500 s), which corresponds approximately to a level of $4\sigma$. (5 X-ray sources found near or inside small 