OPTICAL PHOTOMETRY OF THE BL LAC OBJECT 1ES 1959+650

Abstract

Using the 1.56 m telescope at Shanghai Observatory, China, we present the photometric results of 1ES 1959+650, which cover from 2006 June 11 to 2014 July 31. The maximum variabilities are mag in the V band, mag in the R band, and mag in the I band. During the monitoring period, we obtain intraday variabilities on 2009 September 2 (JD 2455077) and 2009 September 3 (JD 2455078). On 2009 September 2, the intraday variabilities are mag within 1.56 hr, mag within 23 minutes, and mag within 45 minutes. On 2009 September 3, the intraday variabilities are mag within 27 minutes, mag within 3.24 hr, and mag within 3.72 hr. The two intraday variabilities occur in 24 hr, which may occur in the same variable phase. Other results show that (1) no quasi-periodicity is found in the long-term light curve and (2) the correlations between the brightness and the spectrum show obvious anti-correlation, , with the correlation coefficient r = −0.74 and the chance probability p < 0.01%.