Double-Peaked Balmer Emission Indicating Prompt Accretion Disk Formation in an X-Ray Faint Tidal Disruption Event

Understand

We present the multi-wavelength analysis of the tidal disruption event (TDE) AT~2018hyz (ASASSN-18zj).

• From follow-up optical spectroscopy, we detect the first unambiguous case of resolved double-peaked Balmer emission in a TDE.
• The distinct line profile can be well-modelled by a low eccentricity ($e\approx0.1$) accretion disk extending out to $\sim$100 $R_{p}$ and a Gaussian component originating from non-disk clouds, though a bipolar outflow origin cannot be completely ruled out.
• Our analysis indicates that in AT~2018hyz, disk formation took place promptly after the most-bound debris returned to pericenter, which we estimate to be roughly tens of days before the first detection.