CCD photometry and long-term optical variability of PKS 2155-304

¹ Yunnan Observatory, The Chinese Academy of Sciences, P.O. Box 110, Kunming 650011, P.R. China
² CCAST (World Laboratory) P.O. Box 8730, Beijing, 100080, P.R. China

Send offprint request to: Y.H. Zhang

Received: 19 April 1995
Accepted: 25 September 1995

Abstract

The paper presents the first evidence for long-term optical variability and colour behaviour of the X-ray-selected BL Lacertae object PKS 2155-304, which is the first example of its class. Our results show that the amplitude of the optical variations of PKS 2155-304 has been only about 1.4 magnitudes from its photometric history; no significant correlation between brightness and colours is found for PKS 2155-304. Our recent CCD photometry of PKS 2155-304 during September-October 1993 and July 1994 showed that it was the same brightness state as that in November 1991 (Smith et al. 1992).