2020/09/07 by Anna V. Payne, Benjamin J. Shappee, Jason T. Hinkle +24 · 1 citation
Physics and Astronomy · #astro-ph.HE
paper · pdf · doi:10.3847/1538-4357/abe38d
26 pages, 15 figures, 7 tables. Will be submitted to ApJ. The latest flare is currently ongoing, as we predicted
arxiv created 2020/09/07 · arxiv updated 2021/04/14
We present the discovery that ASASSN-14ko is a periodically flaring AGN at the center of the galaxy ESO 253-G003. At the time of its discovery by the All-Sky Automated Survey for Supernovae (ASAS-SN), it was classified as a supernova close to the nucleus. The subsequent six years of V- and g-band ASAS-SN observations reveal that ASASSN-14ko has nuclear flares occurring at regular intervals. The seventeen observed outbursts show evidence of a decreasing period over time, with a mean period of P0 = 114.2 ± 0.4 days and a period derivative of P = -0.0017±0.0003. The most recent outburst in May 2020, which took place as predicted, exhibited spectroscopic changes during the rise and a had a UV bright, blackbody spectral energy distribution similar to tidal disruption events (TDEs). The X-ray flux decreased by a factor of 4 at the beginning of the outburst and then returned to its quiescent flux after ~8 days. TESS observed an outburst during Sectors 4-6, revealing a rise time of 5.60 ± 0.05 days in the optical and a decline that is best fit with an exponential model. We discuss several possible scenarios to explain ASASSN-14ko's periodic outbursts, but currently favor a repeated partial TDE. The next outbursts should peak in the optical on UT 2020-09-7.4 ± 1.1 and UT 2020-12-26.5 ± 1.4.