Probing the tidal disruption event iPTF16axa with CLOUDY and disc-wind models

TL;DR

This paper combines disc-wind and CLOUDY models to analyze the optical/UV emission and spectral lines of the TDE iPTF16axa, revealing properties of the wind, the disrupted star, and line luminosity mechanisms.

Contribution

It introduces a combined approach using disc-wind and CLOUDY models to interpret TDE emission and spectral features, providing new insights into the wind structure and stellar progenitor.

Findings

Consistent wind parameters from both models match observations.

Super-solar He abundance explains He II line enhancement.

Disrupted star likely a red giant.

Abstract

We present both a disc-wind model on the optical/UV emission continuum and CLOUDY modelling on the spectral lines of the tidal disruption event (TDE) iPTF16axa to understand the disc-wind emission and the properties of the atmosphere that impacts the line luminosity of the TDE. Assuming the optical/UV emission from the wind due to the disc super-Eddington phase, we use the steady structured disc-wind model with a spherical wind with constant velocity to fit the observations on multiple days. The extracted parameters are stellar-mass $M_{\star} = 6.20 \pm 1.19 M_{\odot}$, disc radiative efficiency $\log_{\rm 10}(\eta) = -1.22 \pm 1.327$, wind inner radius $r_l = (2.013 \pm 0.551) \times 10^{14}~{\rm cm}$ and velocity $v_w = 18999.4 \pm 1785.1 ~{\rm km~s^{-1}}$. The photosphere temperature for wind emission is $ \sim 2 \times 10^4~{\rm K}$ and the disc single blackbody temperature is $\sim 0.995 \times 10^5~{\rm K}$. We also perform CLOUDY modelling to explain the observed He and H line luminosities that estimate a wind inner radius $r_l = 7.07 \times 10^{14}~{\rm cm}$ and velocity $v_w = 1.3 \times 10^4~{\rm km~s^{-1}}$. The independent analyses of iPTF16axa using CLOUDY and disc-wind models show comparable results that agree with observations. The CLOUDY modelling finds that both the super solar abundance of He and a smaller He II line optical depth is responsible for the enhancement of He II line luminosity over the H$\alpha$ line luminosity. The super-solar abundance of He II agrees with a relatively large stellar mass and suggests that the disrupted star might have been a red giant.