An observation was considered to be pointed at dark Earth if the angle between the vector Sun-Earth and the vector directed from the center of Earth towards the point on its surface observed by RXTE/PCA is larger than $90^\circ$ and the RXTE/PCA field of view is directed more than $10^\circ$ below the Earth's limb.

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Note that we here take into account a recently realized correction for flux ``leakage'' due to the fast motion of the PCA field of view during RXTE slews: the fluxes of point sources reported by Revnivtsev et al. (2004) were underestimated by a factor of 1/0.7 (Sazonov et al. 2008).

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