Swift-XRT identification of IGR J19267+1325 as an Intermediate Polar

ATel #1669; P. A. Evans, A. P. Beardmore, J. P. Osborne (U. Leicester)
on 20 Aug 2008; 18:17 UT
Credential Certification: Julian P Osborne (julo@star.le.ac.uk)

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We report Swift-XRT observations of IGR J19267+1325 (ATEL #1649,#1323), taken between 2008 August 19.43 and 2008 August 19.91. In ATEL #1653, Steeghs et al. presented optical spectroscopy and suggested that this object is a nearby, probably magnetic, cataclysmic variable.

We have obtained ~12 ks of Swift data on this target, in 6 pointings of ~2 ks each. The source is clearly detected, with a mean XRT count rate of 0.089 (+/-0.005) counts per second, consistent with the flux from the previous Swift observations (ATEL #1323).

We find strong evidence for a periodic modulation with a period of 938.6 (+5.6, -5.9) s and an amplitude of 0.022 (+/- 0.007) counts per second, i.e. 25% (+/- 8%) . This is typical of the white-dwarf spin periods of the Intermediate Polar (IP) subclass of magnetic cataclysmic variables. As this period is shorter than the CV orbital period minimum of ~75 min, and consistent with its relatively hard X-ray spectrum, we thus identify this system as an IP (eg http://asd.gsf c.nasa.gov/Koji.Mukai/iphome/iphome.html).

One of the main features of IPs is that they show modulation on multiple periods. We see some evidence for a longer period in this system also. Fits to the light curve suggests two possible periods for this modulation: 9254 (+2000, -429) s and 16500 (+1900, -1500) s. The former is consistent with being a harmonic of the latter, thus we prefer the longer one. This period, 4.58 hours, is typical of the orbital periods of cataclysmic variables above the period gap, and we tentatively suggest it is the orbital period of the system. The best fitting amplitude is 0.015 (+/- 0.007) counts per second, i.e. 18% (+/- 8%). Our phase and cycle coverage of these periods is limited, and we regard the detection of this period as subject to confirmation by other data.

The Swift-UVOT was used to obtain data in the UVW1 (2600+/-600 Angstrom) filter. The source is detected at ~0.1 counts per second. The periodogram derived from this data is very noisy, however using the CLEAN algorithm a moderately strong peak is seen at the 938 s period seen in the X-ray data. Folding on this period shows a modulation with amplitude ~0.01 counts per second.