2026/05/31 by Julian Gerber, Jeremy Hare, John A. Tomsick +4
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Stellar, planetary, and galactic studies #astro-ph.HE
paper · pdf · doi:10.1093/mnras/stag1307
openalex publication_date 2026/07/14 · openalex created_date 2026/07/15 · openalex updated_date 2026/08/01
ABSTRACT IGR J20084+3221 is a previously unclassified Galactic source first detected by the International Gamma-Ray Astrophysics Laboratory (INTEGRAL). Chandra observations led to possible classifications of either a magnetic cataclysmic variable (mCV) or a high-mass X-ray binary (HMXB) based on the hardness of its spectrum. Here, we report follow-up observations taken by XMM–Newton, NuSTAR, and the Hale Telescope at Palomar Observatory. Based on these observations, we conclude that IGR J20084+3221 is most likely an intermediate polar (IP) type mCV. Timing analysis of the X-ray data found a significant peak period of P=635.0± 0.4 s, which we interpret to be the spin period of the white dwarf (WD). The X-ray spectrum is well fit to an absorbed bremsstrahlung model with components accounting for partial covering, reflection, and a fluorescent Fe-line, all typical for an IP. The optical spectrum shows clear emission lines, consistent with emission dominated by an accretion disc. We find counterparts to the source across the optical and infrared (IR) bands, and, despite uncertainties in the distance and extinction, we estimate that the source is too faint in the IR to be an HMXB. Given the evidence pointing towards an IP classification, we fit the X-ray spectrum to a post-shock region model where we find a WD mass of M=1.09+0.12-0.11 \rm M\odot , larger than the average mass for a WD in an mCV.