Chandra, NuSTAR, and Optical Observations of the Cataclysmic Variables IGR J17528-2022 and IGR J20063+3641

TL;DR

This study combines X-ray and optical observations to identify and classify two INTEGRAL sources, revealing one as a magnetic cataclysmic variable and the other as an intermediate polar, with detailed spectral and periodic analysis.

Contribution

It provides the first optical counterpart identification for IGR J17528-2022 and confirms the classification of IGR J20063+3641 as an intermediate polar through combined multi-wavelength observations.

Findings

IGR J17528-2022 is a strong magnetic CV candidate.

IGR J20063+3641 is an intermediate polar with a 172.46 s spin period.

Both sources' X-ray spectra are well fit by absorbed partially covered thermal bremsstrahlung models.

Abstract

We report on Chandra, NuSTAR, and MDM observations of two INTEGRAL sources, namely IGR J17528-2022 and IGR J20063+3641. IGR J17528-2022 is an unidentified INTEGRAL source, while IGR J20063+3641 was recently identified as a magnetic cataclysmic variable (mCV) by Halpern et al. (2018). The Chandra observation of IGR J17528-2022 has allowed us to locate the optical counterpart to the source and to obtain its optical spectrum, which shows a strong H$\alpha$ emission line. The optical spectrum and flickering observed in the optical time-series photometry in combination with the X-ray spectrum, which is well fit by an absorbed partially covered thermal bremsstrahlung model, suggests that this source is a strong mCV candidate. The X-ray observations of IGR J20063+3641 reveal a clear modulation with a period of 172.46$\pm0.01$ s, which we attribute to the white dwarf spin period. Additional MDM spectroscopy of the source has also allowed for a clear determination of the orbital period at 0.731$\pm0.015$ d. The X-ray spectrum of this source is also well fit by an absorbed partially covered thermal bremsstrahlung model. The X-ray spectrum, spin periodicity, and orbital periodicity allow this source to be further classified as an intermediate polar.