Periodic X-ray modulation in Swift J0732.5-1331

ATel #765; P. J. Wheatley, T. R. Marsh (Warwick), W. Clarkson (STScI)
on 14 Mar 2006; 18:31 UT
Credential Certification: Peter Wheatley (p.j.wheatley@warwick.ac.uk)

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We report the results of a Swift timing analysis of the probable new intermediate polar Swift J0732.5-1331 (ATEL #697, #735, #757, #760, and #763). This object was detected as a hard X-ray source with Swift (ATEL #697) and found to have the optical spectrum of a magnetic cataclysmic variable (ATEL #735, #763). A fast optical pulsation was also detected (512.42 s; ATEL #757) leading to its classification as a probable new intermediate polar.

Further analysis of the Swift data reported in ATEL #697 shows that the optical pulsation is detected also in X-rays. The X-ray power spectrum suffers from severe aliasing, but the second highest peak lies precisely at the frequency of the optical pulsation. This strongly supports the classification of Swift J0732.5-1331 as an intermediate polar.

The X-ray modulation is single peaked, in contrast to the optical (ATEL #757). It is strong below 2keV, but absent at higher energies. This is characteristic of photoelectric absorption and is often seen in intermediate polars. Re-analysis of the Swift X-ray spectrum shows that a partial-covering absorption model allows the fitted temperature to drop below that quoted in ATEL #697 to values typical of intermediate polars (kT~20keV).

The Swift ultra-violet power spectra also suffer from severe aliasing, but a strong peak is seen in the UVM2 (2200 Ang) power spectrum precisely at the optical pulsation frequency. No power is seen at the first harmonic, indicating that the ultra-violet modulation is single peaked.

Swift X-ray and UV power spectra and folded light curves