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

Abstract

ASASSN-14ae is a candidate tidal disruption event (TDE) found at the centre of SDSS J110840.11+340552.2 (d ≃ 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≃8×1043 erg s-1 and a total integrated energy of E ≃ 1.7 × 1050 erg radiated over the ~5 months of observations presented. The blackbody temperature of the transient remains roughly constant at T ~ 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 ∝ e-t/t0 with t0 ≃ 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.