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 ($R_{\rm out}$) as a free parameter, integrating it into standard X-ray fitting package to enable self-consistent and simultaneous fitting of X-ray spectra and UV/optical/NIR photometry. We apply the model to the late-time data ($\Delta t \approx 350-1300$ days) of the tidal disruption event (TDE) ASASSN-14li. We show that at these late-times the multi-wavelength emission of the source can be fully described by a bare compact accretion disk. We obtain a black hole mass ($M_{\rm BH}$) of $7^{+3}_{-2}\times10^{6} M_{\odot}$, consistent with host-galaxy scaling relations; and an $R_{\rm out}$ of $45 \pm 13 \, R_{\rm g}$, 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 on the scale/energetics of TDE emission. We also apply the model to the soft/high state of the intermediate-mass black hole (IMBH) 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 $M_{\rm BH} = 4^{+3}_{-1} \times 10^{4} M_{\odot}$ and $R_{\rm out} \approx {\rm few} \times 10^{3} \, R_{\rm g}$, in agreement with previous findings. The relativistic model can constrain the inclination ($i$) of HLX-1 to be $10^o \leq i \leq 70^o$.