|ROSAT Home Page||ROSAT
Consider a distant AGN with a power law spectrum of energy slope 0.5 which is at a luminosity distance of 1000 Mpc and is viewed through an absorption column of cm (log(N ). The AGN luminosity in the ROSAT band is L ergs s . We want to determine how long an observation is required for a detection. The unabsorbed flux is ergs cm s . The ECF for this spectral model is taken from Table 11.3 or Figure 11.5, it is , which gives a count rate counts s . Using the sensitivity formula from section 11.2, we calculate that the observation time needed to detect this source at the level (50% in detect cell) is about 12,600 seconds.