We present ground-based and Swift observations of iPTF16fnl , a likely tidal disruption event ( TDE ) discovered by the intermediate Palomar Transient Factory ( iPTF ) survey at 66.6 Mpc .
The lightcurve of the object peaked at absolute M _ { g } = -17.2 mag .
The maximum bolometric luminosity ( from optical and UV ) was L _ { p } ~ { } \simeq~ { } ( 1.0 \pm 0.15 ) \times 10 ^ { 43 } erg s ^ { -1 } , an order of magnitude fainter than any other optical TDE discovered so far .
The luminosity in the first 60 days is consistent with an exponential decay , with L \propto e ^ { - ( t - t _ { 0 } ) / \tau } , where t _ { 0 } = 57631.0 ( MJD ) and \tau \simeq 15 days .
The X-ray shows a marginal detection at L _ { X } = 2.4 ^ { 1.9 } _ { -1.1 } \times 10 ^ { 39 } erg s ^ { -1 } ( Swift X-ray Telescope ) .
No radio counterpart was detected down to 3 \sigma , providing upper limits for monochromatic radio luminosity of \nu L _ { \nu } < 2.3 \times 10 ^ { 36 } erg s ^ { -1 } and \nu L _ { \nu } < 1.7 \times 10 ^ { 37 } erg s ^ { -1 } ( VLA , 6.1 and 22 GHz ) .
The blackbody temperature , obtained from combined Swift UV and optical photometry , shows a constant value of 19,000 K. The transient spectrum at peak is characterized by broad He II and H \alpha emission lines , with an FWHM of about 14,000 km s ^ { -1 } and 10,000 km s ^ { -1 } respectively .
He I lines are also detected at \lambda \lambda 5875 and 6678 .
The spectrum of the host is dominated by strong Balmer absorption lines , which are consistent with a post-starburst ( E+A ) galaxy with an age of \sim 650 Myr and solar metallicity .
The characteristics of iPTF16fnl make it an outlier on both luminosity and decay timescales , as compared to other optically selected TDEs .
The discovery of such a faint optical event suggests a higher rate of tidal disruptions , as low luminosity events may have gone unnoticed in previous searches .