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 rougly 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 .
We compare the photometric and spectroscopic signatures of iPTF16axa with 11 TDE candidates in the literature with well-sampled optical light curves .
Based on a single-temperature fit to the optical and near-UV photometry , most of these TDE candidates have peak luminosities confined between log ( L [ erg s ^ { -1 } ] ) = 43.4-44.4 , with constant temperatures of a few \times 10 ^ { 4 } K during their power-law declines , implying blackbody radii on the order of ten times the tidal disruption radius , that decrease monotonically with time .
For TDE candidates with hydrogen and helium emission , the high helium-to-hydrogen ratios suggest that the emission arises from high-density gas , where nebular arguments break down .
We find no correlation between the peak luminosity and the black hole mass , contrary to the expectations for TDEs to have \dot { M } \propto M _ { BH } ^ { -1 / 2 } .