Paper detail

Surprises from a deep ASCA spectrum of a Broad Absorption Line Quasar PHL 5200

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 x 10^{23} cm^{-2}, (3) the absorber does not cover the source completely; the covering fraction is about 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 ~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.