Revisiting optical tidal disruption events with iPTF16axa

Understand

We report the discovery by the intermediate Palomar Transient Factory (iPTF) of a candidate tidal disruption event (TDE) iPTF16axa at $z=0.108$, and present its broadband photometric and spectroscopic evolution from 3 months of follow-up observations with ground-based telescopes and Swift.

• The light curve is well fitted with a $t^{-5/3}$ decay, and we constrain the rise-time to peak to be $<$49 rest-frame days after disruption, which is roughly consistent with the fallback timescale expected for the $\sim 5\times$10$^{6}$ $M_\odot$ black hole inferred from the stellar velocity dispersion of the host galaxy.
• The UV and optical spectral energy distribution (SED) is well described by a constant blackbody temperature of T$\sim$ 3$\times$10$^4$ K over the monitoring period, with an observed peak luminosity of 1.1$\times$10$^{44}$ erg s$^{-1}$.
• The optical spectra are characterized by a strong blue continuum and broad HeII and H$\alpha$ lines characteristic of TDEs.