Localized thermonuclear bursts from accreting magnetic white dwarfs

Area of Science:

• Astronomy and Astrophysics
• Stellar Evolution
• White Dwarf Phenomena

Background:

• Classical novae result from global thermonuclear runaways on accreting white dwarfs.
• Localized thermonuclear bursts on white dwarfs, analogous to X-ray bursts from neutron stars, have been theoretically predicted.
• Unexplained rapid optical/ultraviolet bursts with fast outflows have been observed in the accreting white dwarf system TV Columbae.

Purpose of the Study:

• To investigate the origin of unexplained rapid bursts in accreting white dwarf systems.
• To characterize the energy and properties of these bursts and compare them to known astrophysical phenomena.
• To propose a viable mechanism for the observed bursts.

Main Methods:

• Optical observations of bursts in TV Columbae, EI Ursae Majoris, and ASASSN-19bh.
• Analysis of burst energy, luminosity, and duration.
• Comparison of observed burst properties with theoretical models and other astrophysical events.

Main Results:

• Observed optical bursts in three accreting white dwarf systems: TV Columbae, EI Ursae Majoris, and ASASSN-19bh.
• These bursts, termed micronovae, have energies approximately 10^-6 times that of classical novae.
• The bursts exhibit rapid luminosity increases and fast outflows, resembling type-I X-ray bursts.

Conclusions:

• Accretion or magnetic reconnection events are excluded as the origin of these bursts.
• Thermonuclear runaway events within magnetically confined accretion columns are proposed as the cause of micronovae.
• Micronovae represent a new class of stellar explosion distinct from classical novae.