ASCA Observation of the Lyman-Limit Quasar PKS 2145+067

An X-ray observation of a famous Lyman-limit quasar PKS 2145+067 at zem= 0.990 was carried out with ASCA. The source showed a 2–10 keV flux of 1.3 × 10⁻¹¹ erg cm⁻² s⁻¹ (LX = 2.5 ' 10⁴⁶ erg s⁻¹ for H0= 50 km s⁻¹ Mpc⁻¹) described by a power-law spectrum with a photon index of the Γ = 1.63 ± 0.04. In the ASCA energy band, no excess absorption was detected, implying that absorption column density at zab = 0.791 was less than 1.6 ' 10²¹ cm⁻² if the absorbing medium had a metal abundance of 0.5 solar. A comparison with previous Einstein Observatory and ROSAT observations shows that PKS 2145+067 has increased in luminosity by a factor of 2–3 between 1991 and 1998.