Narrow C iv Absorption Lines with Multi-epoch Observations

Using the quasar spectra from the Sloan Digital Sky Survey, all with two-epoch to six-epoch observations, we search for C IV λλ1548,1551 narrow absorption doublets in spectral data from the blue wing r = 30,000 km s−1 until the red wing of C IV λ1549 emission lines. We have obtained 21,239 C IV narrow absorption line (NAL) systems, of which 647 systems were significantly changed on timescales from ΔMJD = 0.24 to 1842.38 days at rest-frame. Both samples of the C IV NAL systems with multi-epoch observations and the variable C IV NAL systems are the largest ones to date. The offset velocity distribution of the variable C IV NALs from quasars has a peak at r 2000 km s−1 and gently extends to a larger offset velocity. There are 110 variable C IV NALs with r > 12,000 km s−1. In addition, about 10% intrinsic C IV NALs show time variability on a timescale of