Hydrodynamic Evolution and Detectability of Nova Remnants in the Galactic Center

TL;DR

This work investigates the hydrodynamic evolution and multiwavelength detectability of nova remnants in the Galactic Center by performing 1D PLUTO simulations of 79 nova models in GC-like hot ISM. By coupling the ejecta–ISM interaction to NEI X-ray emissivity, free-free radio, and Pa$\alpha$ line synthesis, the authors quantify detectability with Chandra, JVLA, and HST, finding 6, 44, and 51 detectable models respectively, with detectable windows spanning weeks to >100 years. A Monte Carlo population study for NSC CVs yields detection probabilities of ~20% (X-ray), ~8% (radio), and ~18% (Pa$\alpha$) under fiducial assumptions, implying nova remnants are rare but potentially observable with next-generation facilities (JWST, AXIS, SKA). The results suggest X-ray observations are the most favorable path to discovery, enabling constraints on the CV population and GC ISM via remnant abundances and energetics. Overall, the study highlights a feasible, multiwavelength strategy to uncover nova remnants in the GC and to leverage future observatories for population and environment insights.

Abstract

Thousands of X-ray sources have been detected in the Galactic center (GC), most believed to be cataclysmic variables (CVs). As a potential probe of the old stellar population, in particular CVs, the existence and detectability of novae in the GC remain elusive, due to the prohibitive extinction toward the GC and their relatively low occurrence rate. Nova remnants evolving in the characteristic hot ($T\sim{10^{6}~\rm K}$) and dense ($n_e\sim{10~\rm cm^{-3}}$) interstellar medium in the GC may shed light on recent novae and provide useful insight on the GC ecosystem. In this work, we perform hydrodynamical simulations of putative nova remnants in the GC environment and calculate their time-dependent multiwavelength emission to estimate the detectability. Among 79 models sampling the nova parameter space (primarily ejecta mass and velocity), 6, 44, and 51 modelled nova remnants are detectable at their X-ray, radio, and Paschen-$α$ maximum, respectively, for existing Chandra, VLA, and HST observations of the GC. The predicted peak luminosities are $\sim10^{32}~\rm erg~s^{-1}$, $\sim10^{31}~\rm erg~s^{-1}$, and $\sim10^{36}~\rm erg~s^{-1}$ in these three bands and the detectable window ranges from weeks to notably hundred years. By specifying a CV population of the nuclear star cluster, we estimate the probability of detecting at least one remnant to be 20%, 8%, and 18% in X-rays, radio, and Pa$α$. The nova remnant would be best resolved in the X-ray band. Our study highlights the potential for detecting nova remnants through further observations, leveraging JWST and the potentially forthcoming AXIS and SKA.

Figures (12)

• Figure 1: Ejecta masses and average velocities of simulated nova outbursts from 2005ApJ...623..398Y model grid. $M_{\rm WD}$ is WD mass in units of $\rm M_\odot$, differentiated by symbol shapes; $\log\dot{M}$ is mass transfer rate in units of $\rm M_\odot~yr^{-1}$ and logarithm, differentiated by symbol colors. The grey dashed lines indicate the kinetic energy of each nova outburst in units of erg.
• Figure 2: Snapshots of one model N06 for example. Top: number density distribution. Shaded region represents the density of ejecta component. Middle: temperature distribution. Bottom: radial velocity distribution, with positive value as outward motion. In all panels, the number indicates the time of snapshot in units of year.
• Figure 3: Synthetic X-ray light curve of simulated remnants with peaked 2--8 keV luminosities above $10^{30}~\rm erg~s^{-1}$. The time is relative to the ejection at the inner boundary. Dashed, solid, and dash-dotted lines indicate WD mass of 0.65, 1.00, and 1.25 solar masses, respectively. Colors of the curves represent kinetic energy of the ejecta. The horizontal, dashed line is the point-source detection limit of Chandra observations of the GC, $L_{\rm det}\approx10^{31}~\rm erg~s^{-1}$2018ApJS..235...26Z.
• Figure 4: Synthetic X-ray light curves of the shocked ISM (solid curves) and ejecta (dashed curves) for three X-ray detectable models N06 (blue), N47 (green), and N48 (red).
• Figure 5: Synthetic radio light curve at 5 GHz ( C band) of detectable simulated novae. The radio luminosity is defined as $\nu L_\nu$ at $\nu=5~\rm GHz$. The line styles indicate WD mass and colors of the curves represent ejecta mass. The horizontal, dashed line is the detection limit of JVLA observations of the GC, which is a $10\sigma$ detection limit of 70 $\mu\rm Jy$2020ApJ...905..173Z. The grey shaded region represents undetectable stages.