Optical Studies of Ten Hard X-ray Selected Cataclysmic Binaries

Abstract

We conducted time-resolved optical spectroscopy and/or photometry of ten cataclysmic binaries that were discovered in hard X-ray surveys, with the goal of measuring their orbital periods and searching for evidence that they are magnetic. Four of the objects in this study are new optical identifications: IGR J18017$-$3542, PBC J1841.1+0138, IGR J18434$-$0508, and Swift J1909.3+0124. A 311.8 s, coherent optical pulsation is detected from PBC J1841.1+0138, as well as eclipses with a period of 0.221909 days. A 152.49 s coherent period is detected from IGR J18434$-$0508. A probable period of 389 s is seen in IGR J18151$-$1052, in agreement with a known X-ray spin period. We also detect a period of 803.5 s in an archival X-ray observation of Swift J0717.8$-$2156. The latter four objects are thus confirmed magnetic CVs of the intermediate polar class. An optical period of 1554 s in AX J1832.3$-$0840 also confirms the known X-ray spin period, but a stronger signal at 2303 s is present whose interpretation is not obvious. We also studied the candidate intermediate polar Swift J0820.6$-$2805, which has low and high states differing by $\approx4$ mag, and optical periods or QPOs not in agreement with proposed X-ray periods. Of note is an unusually long 2.06 day orbital period for Swift J1909.3+0124, manifest in the radial velocity variation of photospheric absorption lines of an early K-type companion star. The star must be somewhat evolved if it is to fill its Roche lobe.