Six Months of Multi-Wavelength Follow-up of the Tidal Disruption
  Candidate ASASSN-14li and Implied TDE Rates from ASAS-SN
  We present ground-based and Swift photometric and spectroscopic observations
of the candidate tidal disruption event (TDE) ASASSN-14li, found at the center
of PGC 043234 ($d\simeq90$ Mpc) by the All-Sky Automated Survey for SuperNovae
(ASAS-SN). The source had a peak bolometric luminosity of $L\simeq10^{44}$ ergs
s$^{-1}$ and a total integrated energy of $E\simeq7\times10^{50}$ ergs radiated
over the $\sim6$ months of observations presented. The UV/optical emission of
the source is well-fit by a blackbody with roughly constant temperature of
$T\sim35,000$ K, while the luminosity declines by roughly a factor of 16 over
this time. The optical/UV luminosity decline is broadly consistent with an
exponential decline, $L\propto e^{-t/t_0}$, with $t_0\simeq60$ days.
ASASSN-14li also exhibits soft X-ray emission comparable in luminosity to the
optical and UV emission but declining at a slower rate, and the X-ray emission
now dominates. Spectra of the source show broad Balmer and helium lines in
emission as well as strong blue continuum emission at all epochs. We use the
discoveries of ASASSN-14li and ASASSN-14ae to estimate the TDE rate implied by
ASAS-SN, finding an average rate of $r \simeq 4.1 \times 10^{-5}~{\rm yr}^{-1}$
per galaxy with a 90% confidence interval of $(2.2 - 17.0) \times 10^{-5}~{\rm
yr}^{-1}$ per galaxy. ASAS-SN found roughly 1 TDE for every 70 Type Ia
supernovae in 2014, a rate that is much higher than that of other surveys.
