We present a deep ( \sim 85 ksec ) ASCA observation of the prototype Broad Absorption Line Quasar ( BALQSO ) PHL 5200 .
This is the best X-ray spectrum of a BALQSO yet .
We find that ( 1 ) the source is not intrinsically X-ray weak , ( 2 ) the line of sight absorption is very strong with N _ { H } = 5 \times 10 ^ { 23 } cm ^ { -2 } , ( 3 ) the absorber does not cover the source completely ; the covering fraction is \approx 90 % .
This is consistent with the large optical polarization observed in this source , implying multiple lines of sight .
The most surprising result of this observation is that ( 4 ) the spectrum of this BALQSO is not exactly similar to other radio-quiet quasars .
The hard X-ray spectrum of PHL 5200 is steep with the power-law spectral index \alpha \approx 1.5 .
This is similar to the steepest hard X-ray slopes observed so far .
At low redshifts , such steep slopes are observed in narrow line Seyfert 1 galaxies , believed to be accreting at a high Eddington rate .
This observation strengthens the analogy between BALQSOs and NLS1 galaxies and supports the hypothesis that BALQSOs represent an early evolutionary state of quasars ( Mathur 2000 ) .
It is well accepted that the orientation to the line of sight determines the appearance of a quasar ; age seems to play a significant role as well .