X-ray observations of the BL Lacertae object OJ 287 with ASCA

Reports have been made on the X-ray properties of the BL Lacertae object OJ 287, obtained with ASCA on 1994 November 18-19. Although the observation was made during a period of enhanced optical intensity, the obtained 0.5-10 keV flux falls below those from previous X-ray observations. Intensity variations on time scales of a few hours were detected, with a typical peak-to-peak amplitude of 20%. The X-ray spectra acquired with the SIS and the GIS are described consistently with a single power-law model with the galactic absorption, and the required photon index, similar to 1.7, is flatter than most of those previously observed from this object. The derived monochromatic X-ray flux at 1 keV, 0.76 mu Jy, exceeds the extrapolation from the lower frequency continua, which is based on near-simultaneous multi-band observations. A discussion is made concerning the origin of X-ray emission from OJ 287 in terms of the synchrotron and synchrotron-self-Compton mechanisms.