2006AJ....131..562H

We report follow-up XMM-Newton and ground-based optical observations of the unusual X-ray binary SDSS J102347.67+003841.2 (=FIRST J102347.6+003841) and a new candidate intermediate polar (IP) found in the Sloan Digital Sky Survey: SDSS J093249.57+472523.0. SDSS J1023 was observed in its low state, with similar magnitude/color (V=17.4 and B=17.9) and smooth orbital modulation as seen in most previous observations. We further refine the ephemeris (for photometric minimum) to HJD(TT)_min=2,453,081.8546(3)+E0.198094(1) days. It is easily detected in X-rays at an unabsorbed flux (0.01-10.0 keV) of 5x10^–13 ergs/cm2/s. Fitting a variety of models we find that (1) either a hot (kT≳15 keV) optically thin plasma emission model (bremsstrahlung or MEKAL) or a simple power law can provide adequate fits to the data; (2) these models prefer a low column density ∼10¹⁹/cm2; (3) a neutron star atmosphere plus power-law model (as found for quiescent low-mass X-ray binaries) can also produce a good fit (for plausible distances), although only for a much higher column ~4x10²⁰/cm2 and a very cool atmosphere (kT≲50 eV). These results support the case that SDSS J1023 is a transient LMXB and indeed place it in the subclass of such systems whose quiescent X-ray emission is dominated by a hard power-law component. Our optical photometry of SDSS J0932 reveals that it is a high-inclination eclipsing system. From our two epochs of data and seven eclipse times, we are able to derive a best-fit ephemeris for minimum light: HJD(TT)_min=2,453,122.2324(1)+E0.0661618(4) days, although aliases, with one cycle count different between epochs, are acceptable. The X-ray spectrum is well fit by either a hard bremsstrahlung or power law, with a partial covering absorption model, with a high covering fraction ∼0.9 and column ~10²³/cm2. Combined with its optical characteristics–high excitation emission lines and its brightness, yielding a large F_X/F_optratio–this highly absorbed X-ray spectrum argues that SDSS J0932 is a strong IP candidate. However, only more extensive optical photometry and a detection of its spin or spin-orbit beat frequency can confirm this classification.