[Paper Review] Dissecting accretion and outflows in accreting white dwarf binaries

D. de Martino, G. Sala+23 more|arXiv (Cornell University)|Jan 12, 2015

Astrophysical Phenomena and Observations1 references3 citations

TL;DR

This white paper proposes that the LOFT mission will revolutionize the study of accretion and outflows in white dwarf binaries by enabling high-sensitivity, high-time-resolution X-ray spectroscopy and timing in the hard X-ray band. It focuses on magnetic and non-magnetic cataclysmic variables, novae, and dwarf novae, aiming to detect fast aperiodic variability, characterize hard X-ray emission during outbursts, and probe disc-jet connections through coordinated multi-wavelength observations.

ABSTRACT

This is a White Paper in support of the mission concept of the Large Observatory for X-ray Timing (LOFT), proposed as a medium-sized ESA mission. We discuss the potential of LOFT for the study of accreting white dwarfs. For a summary, we refer to the paper.

Motivation & Objective

• To understand the physics of matter accretion onto white dwarfs by studying both magnetic and non-magnetic systems with high time-resolution X-ray observations.
• To investigate the mechanisms of mass ejection in nova outbursts by monitoring hard X-ray emission onset and spectral variability.
• To resolve the diversity of dwarf nova outbursts and probe conditions for disc-jet launching via time-resolved X-ray spectroscopy.
• To enable multi-wavelength coordination with optical, infrared, and radio facilities to test the universality of disc-jet connections across accretion systems.
• To characterize the poorly understood hard X-ray tails in white dwarf binaries, which are key to diagnosing accretion flow and ejection processes.

Proposed method

• Utilize LOFT’s Large Area Detector (LAD) with 8.5 m² effective area in the 2–30 keV range for high-throughput X-ray timing and spectroscopy.
• Conduct phase-resolved spectroscopy on selected samples of 10 magnetic and 10 non-magnetic white dwarf binaries to detect low-amplitude, fast aperiodic and periodic variabilities.
• Monitor approximately three novae per year to detect the onset of hard X-ray emission and track spectral evolution during outbursts.
• Perform time-resolved spectroscopy and fast timing on ~3 dwarf novae per year to study non-periodic variability and spectral evolution in the hard X-ray domain.
• Leverage LOFT’s on-board alert system to trigger rapid follow-up observations with ground-based optical, IR, and radio facilities.
• Coordinate with future surveys (e.g., eROSITA, Gaia, LSST, SKA) and large ground-based facilities (e.g., E-ELT, 4MOST, LAMOST, WEAVE) for multi-wavelength context and target selection.

Experimental results

Research questions

• RQ1 How does matter accrete onto white dwarfs, and what are the signatures of accretion flow in hard X-ray variability and spectroscopy?
• RQ2 What triggers and powers hard X-ray emission during nova outbursts, and how does it evolve spectrally and temporally?
• RQ3 What causes the diversity in dwarf nova outburst behavior, and what physical conditions enable disc-jet launching in these systems?
• RQ4 Is there a universal connection between disc accretion and jet formation in low-mass X-ray binaries and cataclysmic variables, as suggested by recent radio detections?
• RQ5 How do the X-ray and radio luminosities correlate during transient outbursts, and what does this imply for jet formation mechanisms?

Key findings

• LOFT will detect low-amplitude, fast aperiodic and periodic variabilities in hard X-rays for the first time in both magnetic and non-magnetic white dwarf binaries.
• LOFT will characterize the spectral evolution of hard X-ray emission during nova outbursts with unprecedented timing and spectral resolution.
• LOFT will provide the first detailed time-resolved spectroscopy of hard X-ray emission in dwarf novae, revealing non-periodic variability and accretion dynamics.
• The mission will enable the detection of hard X-ray tails in accreting white dwarf systems, which are key diagnostics of accretion and ejection processes.
• LOFT’s synergy with future surveys (e.g., eROSITA, Gaia, LSST) will allow the identification and characterization of ~10,000 new white dwarf binary candidates.
• Multi-wavelength coordination with radio facilities like SKA will test the universality of disc-jet connections across accretion systems, particularly in high-accretion-rate non-magnetic CVs.