The Size of Accretion Disks from Self-consistent X-Ray Spectra and UV/Optical/NIR Photometry Fitting: Applications to ASASSN–14li and HLX–1

Abstract

We implement a standard thin disk model with the outer disk radius (R_out) as a free parameter, integrating it into a standard X-ray fitting package to enable self-consistent and simultaneous fitting of X-ray spectra and Ultraviolet (UV), Optical, and Near-infrared (NIR) photometry. We apply the model to the late-time data (Δt ≈ 350–1300 days) of the tidal disruption event (TDE) ASASSN–14li. We show that at these late times, the multiwavelength emission of the source can be fully described by a bare compact accretion disk. We obtain a black hole mass (M_BH) of , consistent with host-galaxy scaling relations, and an R_out of 45 ± 13 R_g, consistent with the circularization radius, with possible expansion at the latest epoch. We discuss how simplistic models, such as a single-temperature blackbody fitted to either X-ray spectra or UV/optical photometry, lead to erroneous interpretations of the scale/energetics of TDE emission. We also apply the model to the soft/high state of the intermediate-mass black hole candidate HLX–1. The model fits the full spectral energy distribution (from X-rays to NIR) without needing an additional stellar population component. We investigate how relativistic effects improve our results by implementing a version of the model with full ray tracing calculations in the Kerr metric. For HLX–1, we find and R_out ≈ few × 10³ R_g, in agreement with previous findings. The relativistic model can constrain the inclination (i) of HLX–1 to be 10° ≤ i ≤70°.