Confirmation of 1RXS J165443.5–191620 as an intermediate polar and its orbital and spin periods

¹ Department of AstrophysicsRadboud University Nijmegen, PO Box 9010, 6500 GL Nijmegen, The Netherlands
e-mail: s.scaringi@astro.ru.nl
² Department of Physics and Astronomy, University of Southampton, Highfield, Southampton, SO17 1BJ, UK
³ Department of Astronomy, Columbia University, 550 West 120th Street, New York, NY 10027, USA
⁴ Department of Physics and Astronomy, Dartmouth College, 6127 Wilder Laboratory, Hanover, NH 03755-3528, USA
⁵ CBA Pretoria, PO Box 11426, Tiegerpoort 0056, South Africa
⁶ CBA Nelson, 8 Regent Lane, Richmond, Nelson, New Zealand
⁷ CBA New Mexico, PO Box 1351, Cloudcroft, NM, 88317, USA
⁸ CBA Pukekohe, 19 Cape Vista Crescent, Pukekohe 2120, New Zealand
⁹ CBA San Mateo, 5 Inverness Way, Hillsborough, CA, 94010, USA
¹⁰ CBA Perth, 295 Camberwarra Drive, Craigie, Western Australia 6025, Australia

Received: 26 January 2011
Accepted: 23 March 2011

Abstract

Aims. We investigate the physical nature of the X-ray emitting source 1RXS J165443.5−191620 through optical photometry and time-resolved spectroscopy.

Methods. Optical photometry is obtained from a variety of telescopes all over the world spanning  ≈27 days. Additionally, time-resolved spectroscopy is obtained from the MDM observatory.

Results. The optical photometry clearly displays modulations consistent with those observed in magnetic cataclysmic variables: a low-frequency signal interpreted as the orbital period, a high-frequency signal interpreted as the white dwarf spin period, and an orbital sideband modulation. Our findings and interpretations are further confirmed through optical, time-resolved spectroscopy that displays Hα radial velocity shifts modulated on the binary orbital period.

Conclusions. We confirm that 1RXS J165443.5−191620 is an intermediate polar with a spin period of 546 s and an orbital period of 3.7 h. In particular, 1RXS J165443.5−191620 is part of a growing subset of intermediate polars that display hard X-ray emission above 15 keV, white dwarf spin periods below 30 min, and spin-to-orbital ratios below 0.1.