2009AJ....138.1428F

The quasar 3C 273 is one of the widely studied quasars that is also a selected target in our monitoring program. In this paper, we present the optical V, R, and I photometric observations done with the 1.56 m telescope at the Shanghai Astronomical Observatory from 2000 to 2008. Our monitoring results show 1118 sets of observations (258 sets for the V band, 414 sets for the R band, and 446 sets for the I band). The observations indicate that (1) the variations in the three bands are ΔV = 1.363±0.088 mag from V = 12.204±0.062 to V = 13.567±0.062, ΔR = 1.299±0.023 mag from R = 12.014±0.014 to R = 13.313±0.013, and ΔI = 1.041±0.088 mag from I = 11.628±0.046 to I = 12.669±0.075. Compared with the result by Toone, who presented the yearly averaged light curve during the period of 1980-2004 and found that the source shows a slow brightening with <V≥12.95 in 1996-1997 to <V≥12.5 in 2003-2004, our observations show that it is variable and both a state brighter than the yearly averaged brightness of <V≥12.5 and a state fainter than the yearly averaged brightness of <V≥12.95 were detected in our observing period. Intra-day variation timescales are from 13 minutes to 245 minutes. (2) The color indices are variable with V-R from -0.27 to 0.68, V - I from 0.11 to 1.14, and R - I from 0.14 to 0.86. The average values are <V-R≥0.18±0.10, <V-I≥0.64±0.14, and <R-I≥0.46±0.11.