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

Abstract

ABSTRACT We present both a disc-wind model on the optical/ultraviolet (UV) emission continuum and cloudy modelling on the spectral lines of the tidal disruption event (TDE) intermediate Palomar Transient Factory (iPTF)16axa 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⋆ = 6.20 ± 1.19M⊙, disc radiative efficiency log10(η) = −1.22 ± 1.327, wind inner radius rl = (2.013 ± 0.551) × 1014 cm, and velocity vw = 18999.4 ± 1785.1 km s−1. The photosphere temperature for wind emission is ∼2 × 104 K and the disc single blackbody temperature is ∼0.995 × 105 K. We also perform cloudy modelling to explain the observed He and H line luminosities that estimate a wind inner radius rl = 7.07 × 1014 cm and velocity vw = 1.3 × 104 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 Hα 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.