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

An X-ray observation of a famous Lyman-limit quasar PKS 2145+067 at z_em= 0.990 was carried out with ASCA. The source showed a 2-10 keV flux of 1.3times 10^-11 erg cm^-2 s^-1 (L_X = 2.5 x 10⁴⁶ erg s^-1 for H₀= 50 km s^-1 Mpc^-1) described by a power-law spectrum with a photon index of the Gamma = 1.63 +/- 0.04. In the ASCA energy band, no excess absorption was detected, implying that absorption column density at z_ab = 0.791 was less than 1.6times 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.