IGR J19552+0044: A new asynchronous short period polar

Abstract

Context. Based on XMM-Newton X-ray observations IGR J19552+0044 appears to be either a pre-polar or an asynchronous polar. Aims. We conducted follow-up optical observations to identify the sources and periods of variability precisely and to classify this X-ray source correctly. Methods. Extensive multicolor photometric and medium-to high-resolution spectroscopy observations were performed and period search codes were applied to sort out the complex variability of the object. Results. We found firm evidence of discording spectroscopic (81.29 ± 0.01 m) and photometric (83.599 ± 0.002 m) periods that we ascribe to the white dwarf (WD) spin period and binary orbital period, respectively. This confirms that IGR J19552+0044 is an asynchronous polar. Wavelength dependent variability and its continuously changing shape point at a cyclotron emission from a magnetic WD with a relatively low magnetic field below 20 MG. Conclusions. The difference between the WD spin period and the binary orbital period proves that IGR J19552+0044 is a polar with the largest known degree of asynchronism (0.97 or 3%).

Hard X-ray cataclysmic variables

“…Interesting case is IGR J19552+0044 found to display two close long periods of 1.69 h and 1.35 h interpreted as the orbital and spin periods, respectively (Bernardini et al, 2013). These have been recently improved with a long optical campaign resulting in P Ω =1.393 h and P ω =1.355 h (Tovmassian et al, 2017). The spin-to-orbit period ratio is remarkably high, P ω /P Ω = 0.97 making IGR J19552+0044 the IP with the lowest degree of asynchronism, and joining "Paloma" which has a spin-to-orbit period ratio ∼0.83 (Joshi et al, 2016).…”

Fast-cadence TESS Photometry and Doppler Tomography of the Asynchronous Polar CD Ind: A Revised Accretion Geometry from Newly Proposed Spin and Orbital Periods

“…The Doppler tomograms of CD Ind are remarkable in comparison to other asynchronous polars. Doppler tomography of BY Cam (Schwarz et al 2005), IGR J19552+0044 (Tovmassian et al 2017), and V1432 Aql (Schwope 2001, Fig . 10) provides compelling evidence that the accretion flows in those systems are far more extended than in synchronous polars.…”

“…While the beat periods in IPs are very short and are often very close to the WD spin period, APs have very long beat periods-ranging from 2.0 d for IGR J19552+0044 (Tovmassian et al 2017) to 64 d for V1432 Aql (Littlefield et al 2015)-due to the small fractional difference between ω and Ω. Although it is difficult to obtain continuous observations of a full beat cycle, these observations provide snapshots of the variable accretion geometry as different field lines interact with the accretion stream.…”

Optical Studies of 15 Hard X-Ray Selected Cataclysmic Binaries

“…Polars are also circularly polarized in the optical, and have optical/IR humps in their spectra; both these features are from cyclotron radiation in the strong magnetic field. There are also a few asynchronous polars, in which the spin and orbit periods can differ by as much as a few percent (e.g., Halpern et al 2017;Tovmassian et al 2017).…”