ASASSN-14ae: a tidal disruption event at 200 Mpc

ASASSN-14ae is a candidate tidal disruption event (TDE) found at the centre of SDSS J110840.11+340552.2 (d similar or equal to 200 Mpc) by the All-Sky Automated Survey for Supernovae (ASAS-SN). We present ground-based and Swift follow-up photometric and spectroscopic observations of the source, finding that the transient had a peak luminosity of L similar or equal to 8 x 10(43) erg s(-1) and a total integrated energy of E similar or equal to 1.7 x 10(50) erg radiated over the similar to 5 months of observations presented. The blackbody temperature of the transient remains roughly constant at T similar to 20 000 K while the luminosity declines by nearly 1.5 orders of magnitude during this time, a drop that is most consistent with an exponential, L proportional to e(-t/t0) with t(0) similar or equal to 39 d. The source has broad Balmer lines in emission at all epochs as well as a broad He II feature emerging in later epochs. We compare the colour and spectral evolution to both supernovae and normal AGN to show that ASASSN-14ae does not resemble either type of object and conclude that a TDE is the most likely explanation for our observations. At z = 0.0436, ASASSN-14ae is the lowest-redshift TDE candidate discovered at optical/UV wavelengths to date, and we estimate that ASAS-SN may discover 0.1-3 of these events every year in the future.