PICA, AJ, WEBB, JR, SMITH, AG
et al. (1987). OPTICAL VARIABILITY OF X-RAY-SELECTED QSOS
.
ASTRONOMICAL JOURNAL, 94(2), 289-296. 10.1086/114469
PICA, AJ, WEBB, JR, SMITH, AG et al. (1987). OPTICAL VARIABILITY OF X-RAY-SELECTED QSOS
. ASTRONOMICAL JOURNAL, 94(2), 289-296. 10.1086/114469