# On the Observability of Recurrent Nova Super-Remnants

## TL;DR

This study models the growth and observability of nova super-remnants around recurrent novae, revealing how environmental factors and white dwarf properties influence their size, structure, and potential detectability in different astrophysical contexts.

## Contribution

It introduces a dynamic simulation of NSRs considering white dwarf evolution, expanding understanding of their formation, structure, and observational signatures around recurrent novae.

## Key findings

- NSRs form as large, low-density cavities with hot ejecta and surrounding cool shells.
- Higher environmental density and accretion rates limit NSR size.
- Only NSRs around high accretion rate novae are currently observable.

## Abstract

The nova super-remnant (NSR) surrounding M31N 2008-12a (12a), the annually erupting recurrent nova (RN), is the only known example of this phenomenon. As this structure has grown as a result of frequent eruptions from 12a, we might expect to see NSRs around other RNe; this would confirm the RN--NSR association and strengthen the connection between novae and type Ia supernovae (SN Ia) as NSRs centered on SN Ia provide a lasting, unequivocal signpost to the single degenerate progenitor type of that explosion. The only previous NSR simulation used identical eruptions from a static white dwarf (WD). In this Paper, we simulate the growth of NSRs alongside the natural growth/erosion of the central WD, within a range of environments, accretion rates, WD temperatures, and initial WD masses. The subsequent evolving eruptions create dynamic NSRs tens of parsecs in radius comprising a low-density cavity, bordered by a hot ejecta pile-up region, and surrounded by a cool high-density, thin, shell. Higher density environments restrict NSR size, as do higher accretion rates, whereas the WD temperature and initial mass have less impact. NSRs form around growing or eroding WDs, indicating that NSRs also exist around old novae with low-mass WDs. Observables such as X-ray and H$\alpha$ emission from the modelled NSRs are derived to aid searches for more examples; only NSRs around high accretion rate novae will currently be observable. The observed properties of the 12a NSR can be reproduced when considering both the dynamically grown NSR and photoionisation by the nova system.