Multi-wavelength studies of Gamma-ray detected Novae

Project Description:

A nova eruption results from a thermonuclear runaway at the base of a hydrogen-rich shell on the surface of an accreting white dwarf (WD) in a binary system (Gallagher & Starrfield, 1978; Starrfield et al., 2016). The released nuclear energy leads to a dramatic expansion of the WD atmosphere that is eventually ejected at velocities of ∼500–5000 km s−1 (Barlow et al., 1981; Yaron et al., 2005; Aydi et al., 2020), expelling ∼ 10−7–10−3 M⊙ of material (Gehrz et al., 1998; Nelson et al., 2014). The expanding envelope causes the optical brightness of the system to increase by 8–18 mag, reaching peak absolute magnitudes in the range MV = −4 to −10 mag. As the ejected envelope dissipates, the system brightness declines on timescales of days to months. Approximately 30 novae erupt in the Galaxy each year, with only ∼10 typically observed while others remain hidden by dust (Rector et al., 2022; Kawash et al., 2022; Zuckerman et al., 2023). Novae emit across the electromagnetic spectrum from TeV and GeV γ-rays to meter-wave radio wavelengths (Della Valle & Izzo, 2020; Chomiuk et al., 2021a). Galactic novae are now routinely detected in GeV γ-rays, with 23 systems detected by the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope since 2010. Most of these are classical novae: systems with main-sequence donors and very low density circumstellar material (CSM). The luminous γ-rays trace the presence of shocks that for dwarf-donor novae must be internal to the ejecta. The shocks accelerate particles to relativistic velocities, and it is thought that the relativistic hadrons produce γ-rays, while the relativistic leptons produce radio synchrotron (Marti-Devesa et al., 2025). Novae therefore serve as real-time laboratories for particle acceleration in shocks, and enable a comparison of hadronic and leptonic acceleration efficiency. Radio observations may directly trace these shock fronts and regions of particle acceleration. Meanwhile, free-free thermal emission traces the bulk of the ejected mass, which enables estimates of the density of the shock and the overall energetics of the eruption. Gamma-ray luminosities of novae are observed to vary by at least three orders of magnitude. Only 10 classical novae have been both observed in the radio and detected by Fermi), and there behaviour is diverse at both wavelengths (Chomiuk et al., 2021b).

Research Area:

Astronomy

Project Level:

Honours

This Project Is Offered At The Following Node(s):

(UCT)