2001PASP..113.1386M

We present results of analyses of observations of the X-ray source 2A 1704+241 with the ROSAT Position Sensitive Proportional Counter (PSPC) and the High Resolution Imager (HRI). The source 2A 1704+241 was first associated with the M giant star HD 154791 based on observations with the HEAO 1 scanning modulation collimator and the Einstein IPC and analysis of a spectrum of HD 154791 obtained with the International Ultraviolet Explorer. This identification was unusual because there are few bright X-ray binaries associated with an M giant star. We observed 2A 1704+241 with the PSPC and the HRI in order to determine more accurately the position of the X-ray source and in order to study the previously seen 900 s variability in the Einstein data. Based on the previous identification and determination of the position of MS 1703.7+2417, an active galactic nucleus in the field, and the position of three previously unreported X-ray sources that we have associated with stars in the USNO-A2.0 catalog, we have greatly reduced the X-ray positional error of 2A 1704+241. HD 154791 remains the prime candidate as the optical counterpart of the X-ray source. While the 50% modulation in the X-ray flux seen by the Einstein IPC is apparent in the ROSAT data, it appears to be at a slightly different frequency.