IGR J19552+0044: A new asynchronous short period polar: "Filling the gap between intermediate and ordinary polars"

TL;DR

This paper confirms IGR J19552+0044 as an asynchronous polar with the largest known asynchronism, achieved through detailed optical and X-ray observations revealing its complex variability and magnetic properties.

Contribution

It provides the first definitive classification of IGR J19552+0044 as an asynchronous polar with a significant asynchronism degree, filling the gap between intermediate and ordinary polars.

Findings

Confirmed IGR J19552+0044 as an asynchronous polar

Discovered the largest known asynchronism degree in polars

Identified cyclotron emission indicating a magnetic field below 20 MG

Abstract

Based on XMM--Newton X-ray observations IGR J19552+0044 appears to be either a pre-polar or an asynchronous polar. We conducted follow-up optical observations to identify the sources and periods of variability precisely and to classify this X-ray source correctly. 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. We found firm evidence of discording spectroscopic (81.29+/-0.01m) and photometric (83.599+/-0.002m) 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. 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%).