# The true nature of Swift J0746.3-1608: a possible Intermediate Polar showing accretion state changes

## TL;DR

This paper presents evidence that SWIFT J0746.3-1608 is a magnetic cataclysmic variable of the Intermediate Polar type, characterized by accretion state changes and a 38-minute white dwarf rotation period, based on multi-wavelength observations.

## Contribution

It provides the first detection of the white dwarf's rotation period and characterizes its accretion and variability features, suggesting a rare long-term high/low state behavior in an IP.

## Key findings

- Detection of a 38-minute white dwarf rotation signal
- Observation of high and low accretion states over years
- Spectral evidence of optically thin thermal emission with iron excess

## Abstract

Optical and X-ray observations suggested that the 9.38 h binary, SWIFT J0746.3- 1608 could be a Cataclysmic Variable of the magnetic or nova-like type, or a low mass X-ray binary. Its optical, UV, and X-ray light curves are strongly variable over years. We report on a recent XMM-Newton observation (28 April 2018), when the source had recovered from a deep low state that likely begun mid-late 2011. We detect for the first time a signal at about 38 min that we interpret as the rotation of the accreting white dwarf primary. Its amplitude decreases with increasing energy, indicating localised photoelectric absorption from cold material. The X-ray spectrum shows optically thin thermal emission with excess at the iron complex, absorbed by a dense medium partially covering the X-ray source. Based on these features, we propose that SWIFT J0746.3-1608 is a magnetic CV of the Intermediate Polar (IP) type. The long-term light curves at different wavelengths show high and low states, a rare phenomenon in the IP subclass and observed so far in only three other systems. The long orbital period, the peculiar long term variability, and its proposed magnetic nature, makes SWIFT J0746.3-1608 an interesting evolutionary test case.