A new analysis of Keck/HIRES observations of the broad absorption line QSO APM 0827+5255 indicates that a number of intervening C iv absorbers give rise to absorption lines for which the observed optical depths for 1548 , 1550 Å doublet components are not in the expected 2 : 1 ratio .
To compensate for the effect , a local adjustment of the zero-level is required .
We model this effect as coverage of one line of sight to this gravitationally lensed QSO and perform a set of simulations to select a sample of lines for which our model provides an explanation for the effect .
We use lines in this sample to obtain estimates for minimum C iv absorber sizes from total coverage and the separations of the lines of sight for a range of lens redshifts , z _ { l } , and two cosmologies .
We also obtain best estimates for overall sizes from a statistical ‘ hit and miss ’ approach .
For z _ { l } = 0.7 our results set a lower limit to sizes of C iv absorbers of \sim 0.3 h ^ { -1 } _ { 72 } kpc ( \sim 0.5 h ^ { -1 } _ { 72 } kpc ) for \Omega _ { M } = 1 , \Omega _ { \Lambda } = 0 ( \Omega _ { M } = 0.3 , \Omega _ { \Lambda } = 0.7 ) , in agreement with other results from similar work but are limited by sample size and the uncertainty in z _ { l } .
Our method can be used to detect lensed QSOs and to probe absorber sizes when separate spectra can not be obtained for each line of sight .