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 x 10" 11 erg cm"2 s _1 (L x = 2.5 x 10 46 erg s"1 for Ho = 50 km s _1 Mpc -1 ) described by a power-law spectrum with a photon index of the r = 1.63 ± 0.04. In the ASCA energy band, no excess absorption was detected, implying that absorption column density at ^ab = 0.791 was less than 1.6 x 10 21 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.