X-Ray Spectrum and Variability of the Quasar PG 1211+143

Abstract We present preliminary results of an ASCA observation of the classic soft-excess quasar PG 1211 + 143. The overall ASCA spectrum can be characterized by a blackbody with a temperature of ~ 125 eV (quasar frame) and a power law with photon index ~ 2. Simultaneous ROSAT data are suggestive of further steepening of the spectrum just below the ASCA band. Comparison with previous observations shows that the soft flux in the 0.1–2 keV band varies by at least a factor of ~ 16, scaling roughly as the square of the hard flux in the 2–10 keV band over a timescale of ~ 13.5 yr. We also find evidence of short-term amplitude variability of up to a factor ~ 2 on a timescale of ~ 2 × 104 s, in both the soft and hard flux so that the soft and hard photons are likely to originate from the same, compact, region. The data rule out variable absorption (cold or ionized) as the origin of the soft excess, favoring an intrinsic emission component. However, we argue against optically thin emission for the ‘blue bump’ in PG 1211+143. The large amplitude soft X-ray variability may be indicative of variations in the effective temperature, or peak, of the soft component. There is only marginal evidence for Fe K line emission between 6–7 keV in the quasar frame.