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A 682-second X-ray Periodicity in CH Cygni: Evidence for a Magnetic White Dwarf

Manuel Pichardo Marcano, Thomas J. Maccarone, Liliana E. Rivera Sandoval

TL;DR

This study addresses whether magnetism is common in white dwarfs within symbiotic stars by targeting CH Cygni with X-ray timing. Using XMM-Newton observations, the authors detect a coherent pulsation at $P_{spin} = 682.5 \pm 7$ s, interpreted as the spin of a magnetic WD. This finding provides strong evidence for magnetic accretion in CH Cygni and supports a magnetic-propeller model for its jet activity and state changes, aligning with longstanding theoretical proposals. CH Cygni thus joins R Aqr as one of the few WD symbiotic systems with confirmed X-ray pulsations, with implications for the prevalence of magnetism in accreting WDs and the mechanisms driving jets in symbiotic binaries.

Abstract

Symbiotic stars are interacting binaries consisting of a red giant and typically a white dwarf, important as potential Type Ia supernova progenitors. Despite theoretical predictions that white dwarfs in symbiotic systems should often be magnetic, direct evidence has been elusive. We report the discovery of a $682.5 \pm 7$ s periodicity in the XMM-Newton X-ray light curve that we interpret as the spin period of the WD in CH Cygni. This detection provides strong evidence for a magnetic white dwarf in CH Cygni, making it only the second WD symbiotic star with confirmed X-ray pulsations after R Aquarii. Our discovery supports the magnetic propeller model previously proposed for CH Cygni's jet activity and state transitions.

A 682-second X-ray Periodicity in CH Cygni: Evidence for a Magnetic White Dwarf

TL;DR

This study addresses whether magnetism is common in white dwarfs within symbiotic stars by targeting CH Cygni with X-ray timing. Using XMM-Newton observations, the authors detect a coherent pulsation at s, interpreted as the spin of a magnetic WD. This finding provides strong evidence for magnetic accretion in CH Cygni and supports a magnetic-propeller model for its jet activity and state changes, aligning with longstanding theoretical proposals. CH Cygni thus joins R Aqr as one of the few WD symbiotic systems with confirmed X-ray pulsations, with implications for the prevalence of magnetism in accreting WDs and the mechanisms driving jets in symbiotic binaries.

Abstract

Symbiotic stars are interacting binaries consisting of a red giant and typically a white dwarf, important as potential Type Ia supernova progenitors. Despite theoretical predictions that white dwarfs in symbiotic systems should often be magnetic, direct evidence has been elusive. We report the discovery of a s periodicity in the XMM-Newton X-ray light curve that we interpret as the spin period of the WD in CH Cygni. This detection provides strong evidence for a magnetic white dwarf in CH Cygni, making it only the second WD symbiotic star with confirmed X-ray pulsations after R Aquarii. Our discovery supports the magnetic propeller model previously proposed for CH Cygni's jet activity and state transitions.
Paper Structure (11 sections, 5 equations, 3 figures, 1 table)

This paper contains 11 sections, 5 equations, 3 figures, 1 table.

Table of Contents

  1. Introduction
  2. Data Analysis and Results
  3. XMM-data
  4. Timing Analysis
  5. Discussion
  6. The magnetic field of CH Cygni
  7. Previous periodicity searches
  8. CH Cygni as a Magnetic Propeller
  9. Comparison with Other SS
  10. Conclusion
  11. XMM-Newton Power Spectrum and ASCA Light Curve

Figures (3)

  • Figure 1: Left: $\chi^2$ statistic as a function of trial period from the epoch folding search of the XMM-Newton EPIC-pn light curve. A highly significant isolated peak is detected at 682.5 s. Right: XMM-Newton EPIC-pn light curve of CH Cygni folded at the 682.5 s period using 32 phase bins. Two cycles are shown for clarity. A marginal secondary peak is visible near phase 0.7.
  • Figure 2: Power spectrum of the XMM-Newton EPIC light curve of CH Cygni. The spectrum is shown in Leahy normalization. The red line marks the detected periodicity at 682.5 s.
  • Figure 3: ASCA X-ray light curve of CH Cygni folded on the 682.5 s period detected with XMM-Newton using 32 phase bins. The profile shows marginal variability at the $1–2\%$ level, similar to that seen in the XMM-Newton data.