IGR J17303-0601 is a new intermediate polar

ATel #463; B. T. Gaensicke (Warwick), T. R. Marsh (Warwick), A. Edge (Durham), P. Rodriguez-Gil (IAC), D. Steeghs (CfA), S. Araujo-Betancor (STScI), E. Harlaftis (NO Athens), O. Giannakis (NO Athens), S. Pyrzas (Thessaloniki), L. Morales-Rueda (Nijmegen), A. Aungwerojwit (Warwick)
on 15 Apr 2005; 08:24 UT
Credential Certification: Boris Gaensicke (Boris.Gaensicke@warwick.ac.uk)

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We have identified IGR J17303-0601 (1RXS J173021.5-055933) as an intermediate polar (IP). The optical counterpart is USNOA2.0 0825_10606993 (RA=17h30m21.9s Dec=-05d59m31s). Using optical photometry obtained in 2003 at the JKT and at the OGS we determine the white dwarf spin period to be 120s, which is the second-shortest spin period discovered so far (after AE Aqr, Pspin=33s). The spin folded light curve has a double-pulse structure, suggesting that both accreting poles / accretion curtains contribute to the optical light. Time-resolved spectroscopy obtained using the Calar Alto 2.m, the INT, the WHT, and the Magellan-Clay telescope show a radial velocity variation of 925.27min which we interpret as the orbital period of the system. It may be that IGR J17303-0601 is in a similar evolutionary state as AE Aqr, i.e. a post thermal-timescale mass transfer system (Schenker et al. 2002, MNRAS 337, 1105), and we encourage additional follow-up observations probing for radio / optical flares, as well as monitoring the spin period for a period change. The list of 123 IBIS/ISGRI sources from the galactic plane survey (Bird et al. 2004, ApJ Letters 607, 33) contains 6 confirmed cataclysmic variables, of which 4 IPs (including the IGR J17303-0601), one dwarf nova and one polar. It appears that at low galactic latitudes the combination of large X-ray luminosities and hard spectra makes IPs the predominant CV subtype picked up by INTEGRAL, and follow-up observations of unidentified INTEGRAL sources may well lead to the discovery of additional IPs.