The Long Term Evolution of ASASSN-14li

Abstract

We present late-time optical spectroscopy taken with the Large Binocular Telescope's Multi-Object Double Spectrograph, late-time SWIFT UVOT and XRT observations, as well as improved ASAS-SN pre-discovery limits on the nearby (d=90.3 Mpc, z=0.0206) tidal disruption event (TDE) ASASSN-14li. The late-time optical spectra show H$\alpha$ emission well in excess of that seen in the SDSS host galaxy spectrum, indicating that the processes powering the luminous flares associated with TDEs can operate for several hundreds of days. The SWIFT observations reveal the presence of lingering apparently thermal UV (T${}_{\mathrm{UV}}\sim 3.5\times 10^4$ K) and X-ray (T${}_{\mathrm{X}}\sim 7\times 10^5$ K) emission. The characteristic temperatures evolve by, at most, a factor of $\sim 2$ over the 600 day follow-up campaign. The X-ray, UV, and H$\alpha$ luminosities evolve roughly in tandem and at a rate that is consistent with a power-law decay at late times. This behavior is in stark contrast with the majority of optically discovered TDEs, which are X-ray faint and evolve on shorter timescales. Finally we address how the unique properties of ASASSN-14li can be used to probe the relationship between the TDE rate and host galaxy properties.

15 pages, 8 figures. For a brief video summarizing the paper, see https://www.youtube.com/watch?v=DsNaCUeqr_g

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Cited by in corpus (16)

• On the mass and luminosity functions of tidal disruption flares: rate suppression due to black hole event horizons
• Ultrafast Outflow in Tidal Disruption Event ASASSN-14li
• The spectral evolution of disc dominated tidal disruption events
• X-ray properties of TDEs
• The ASAS-SN Bright Supernova Catalog $-$ II. 2015
• Distinguishing Tidal Disruption Events from Impostors
• MUSE Reveals a Recent Merger in the Post-starburst Host Galaxy of the TDE ASASSN-14li
• Long-term radio and X-ray evolution of the tidal disruption event ASASSN-14li
• Optical/UV-to-X-Ray Echoes from the Tidal Disruption Flare ASASSN-14li
• A Swift Fix for Nuclear Outbursts
• Extreme variability in an active galactic nucleus: Gaia16aax
• The TDE ASASSN-14li and its host resolved at parsec scales with the EVN
• Scary Barbie: An Extremely Energetic, Long-Duration Tidal Disruption Event Candidate Without a Detected Host Galaxy at z = 0.995
• Optical/UV Emission in the Tidal Disruption Event ASASSN-14li: Implications of Disc Modeling
• Spectroscopic monitoring of the candidate tidal disruption event in F01004-2237
• A tidal disruption event in the nearby ultra-luminous infrared galaxy F01004-2237