iPTF16fnl: A Faint and Fast Tidal Disruption Event in an E+A Galaxy

DOI: 
10.3847/1538-4357/aa7579
Publication date: 
01/07/2017
Main author: 
Blagorodnova, N.
IAA authors: 
Castro-Tirado, A. J.
Authors: 
Blagorodnova, N.;Gezari, S.;Hung, T.;Kulkarni, S. R.;Cenko, S. B.;Pasham, D. R.;Yan, L.;Arcavi, I.;Ben-Ami, S.;Bue, B. D.;Cantwell, T.;Cao, Y.;Castro-Tirado, A. J.;Fender, R.;Fremling, C.;Gal-Yam, A.;Ho, A. Y. Q.;Horesh, A.;Hosseinzadeh, G.;Kasliwal, M. M.;Kong, A. K. H.;Laher, R. R.;Leloudas, G.;Lunnan, R.;Masci, F. J.;Mooley, K.;Neill, J. D.;Nugent, P.;Powell, M.;Valeev, A. F.;Vreeswijk, P. M.;Walters, R.;Wozniak, P.
Journal: 
The Astrophysical Journal
Refereed: 
Yes
Publication type: 
Article
Volume: 
844
Pages: 
46
Abstract: 

We present ground-based and Swift observations of iPTF16fnl, a likely tidal disruption event (TDE) discovered by the intermediate Palomar Transient Factory (iPTF) survey at 66.6 Mpc. The light curve of the object peaked at an absolute mag {M}<SUB>g</SUB>=-17.2. The maximum bolometric luminosity (from optical and UV) was {L}<SUB>p</SUB>≃ (1.0+/- 0.15)× {10}<SUP>43</SUP> erg s<SUP>−1</SUP>, an order of magnitude fainter than any other optical TDE discovered so far. The luminosity in the first 60 days is consistent with an exponential decay, with L\propto {e}<SUP>-(t-{t</SUP><SUB>0</SUB>)/τ }, where t <SUB>0</SUB> = 57631.0 (MJD) and τ ≃ 15 days. The X-ray shows a marginal detection at {L}<SUB>X</SUB>={2.4}<SUB>-1.1</SUB><SUP>1.9</SUP>× {10}<SUP>39</SUP> erg s<SUP>−1</SUP> (Swift X-ray Telescope). No radio counterpart was detected down to 3σ, providing upper limits for monochromatic radio luminosities of {ν L}<SUB>ν </SUB>〈 2.3× {10}<SUP>36</SUP> erg s<SUP>−1</SUP> and {ν L}<SUB>ν </SUB>〈 1.7× {10}<SUP>37</SUP> erg s<SUP>−1</SUP> (Very Large Array, 6.1 and 22 GHz). The blackbody temperature, obtained from combined Swift UV and optical photometry, shows a constant value of 19,000 K. The transient spectrum at peak is characterized by broad He ii and Hα emission lines, with FWHMs of about 14,000 km s<SUP>−1</SUP> and 10,000 km s<SUP>−1</SUP>, respectively. He i lines are also detected at λλ 5875 and 6678. The spectrum of the host is dominated by strong Balmer absorption lines, which are consistent with a post-starburst (E+A) galaxy with an age of ∼650 Myr and solar metallicity. The characteristics of iPTF16fnl make it an outlier on both luminosity and decay timescales, as compared to other optically selected TDEs. The discovery of such a faint optical event suggests a higher rate of tidal disruptions, as low-luminosity events may have gone unnoticed in previous searches.

Database: 
ADS
SCOPUS
URL: 
https://www.scopus.com/inward/record.uri?eid=2-s2.0-85026406715&doi=10.3847%2f1538-4357%2faa7579&partnerID=40&md5=4d29b4a05a3ea26ed6a7d70af754492f
ADS Bibcode: 
2017ApJ...844...46B
Keywords: 
accretion;accretion disks;black hole physics;galaxies: nuclei;stars: individual: iPTF16fnl;Astrophysics - High Energy Astrophysical Phenomena