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

Here, 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 $${M}_{g}=-17.2$$. The maximum bolometric luminosity (from optical and UV) was $${L}_{p}\simeq (1.0\pm 0.15)\times {10}^{43}$$ erg s -1, 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 $$L\propto {e}^{-(t-{t}_{0})/\tau }$$, where t 0 = 57631.0 (MJD) and $$\tau \simeq 15$$ days. The X-ray shows a marginal detection at $${L}_{X}={2.4}_{-1.1}^{1.9}\times {10}^{39}$$ erg s -1 (Swift X-ray Telescope). No radio counterpart was detected down to 3σ, providing upper limits for monochromatic radio luminosities of $${\nu L}_{\nu }\lt 2.3\times {10}^{36}$$ erg s -1 and $${\nu L}_{\nu }\lt 1.7\times {10}^{37}$$ erg s -1 (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 -1 and 10,000 km s -1, 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. In conclusion, 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.
Authors:
 [1] ; ORCiD logo [2] ; ORCiD logo [3] ; ORCiD logo [1] ; ORCiD logo [4] ;  [5] ;  [6] ; ORCiD logo [7] ; ORCiD logo [8] ;  [9] ;  [10] ;  [11] ;  [12] ;  [13] ; ORCiD logo [14] ;  [15] ;  [1] ;  [16] ; ORCiD logo [7] ; ORCiD logo [1] more »;  [17] ;  [18] ; ORCiD logo [19] ;  [20] ; ORCiD logo [18] ; ORCiD logo [21] ;  [1] ; ORCiD logo [22] ;  [23] ;  [24] ;  [15] ;  [1] ;  [25] « less
  1. California Inst. of Technology (CalTech), Pasadena, CA (United States). Cahill Center for Astrophysics
  2. Univ. of Maryland, College Park, MD (United States). Dept. of Astronomy; Univ. of Maryland, College Park, MD (United States). Joint Space-Science Inst.
  3. Univ. of Maryland, College Park, MD (United States). Dept. of Astronomy
  4. Univ. of Maryland, College Park, MD (United States). Joint Space-Science Inst.; NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States)
  5. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Center for Space Research
  6. California Inst. of Technology (CalTech), Pasadena, CA (United States). Cahill Center for Astrophysics; California Inst. of Technology (CalTech), Pasadena, CA (United States). Infrared Processing and Analysis Center
  7. Univ. of California, Santa Barbara, CA (United States). Dept. of Physics; Las Cumbres Observatory, Goleta, CA (United States)
  8. Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (United States). Smithsonian Astrophysical Observatory; Weizmann Inst. of Science, Rehovot (Israel). Dept. of Particle Physics and Astrophysics
  9. California Inst. of Technology (CalTech), Pasadena, CA (United States). Jet Propulsion Lab.
  10. Jodrell Bank Centre for Astrophysics, Manchester (United Kingdom)
  11. Univ. of Washington, Seattle, WA (United States). Dept. of Astronomy
  12. Instituto de Astrofisica de Andalucia (IAA-CSIC), Granada (Spain); Univ. de Malaga (Spain). Unidad Asociada Departamento de Ingeniera de Sistemas y Automtica
  13. Univ. of Oxford, Oxford (United Kingdom). Dept. of Physics, Astrophysics
  14. Stockholm Univ. (Sweden). Oskar Klein Center, Dept. of Astronomy
  15. Weizmann Inst. of Science, Rehovot (Israel). Dept. of Particle Physics and Astrophysics
  16. Hebrew Univ. of Jerusalem (Israel). Racah Inst. of Physics
  17. Univ. of Oxford, Oxford (United Kingdom). Dept. of Physics, Astrophysics; National Tsing Hua Univ., Hsinchu (Taiwan). Inst. of Astronomy and Dept. of Physics
  18. California Inst. of Technology (CalTech), Pasadena, CA (United States). Infrared Processing and Analysis Center
  19. Weizmann Inst. of Science, Rehovot (Israel). Dept. of Particle Physics and Astrophysics; Univ. of Copenhagen (Denmark). The Niels Bohr Inst., Dark Cosmology Centre
  20. California Inst. of Technology (CalTech), Pasadena, CA (United States). Cahill Center for Astrophysics; Stockholm Univ. (Sweden). Oskar Klein Center, Dept. of Astronomy
  21. Univ. of Oxford, Oxford (United Kingdom). Dept. of Physics, Astrophysics
  22. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Univ. of California, Berkeley, CA (United States). Dept. of Astronomy
  23. Yale Univ., New Haven, CT (United States). Dept. of Physics and Yale Center for Astronomy & Astrophysics
  24. Special Astrophysical Observatory, Nizhnij Arkhyz, Karachai-Cherkessian Republic (Russia)
  25. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Publication Date:
Report Number(s):
LA-UR-17-27712
Journal ID: ISSN 1538-4357; TRN: US1800382
Grant/Contract Number:
AC52-06NA25396; AC02-05CH11231
Type:
Accepted Manuscript
Journal Name:
The Astrophysical Journal (Online)
Additional Journal Information:
Journal Name: The Astrophysical Journal (Online); Journal Volume: 844; Journal Issue: 1; Journal ID: ISSN 1538-4357
Publisher:
Institute of Physics (IOP)
Research Org:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE Laboratory Directed Research and Development (LDRD) Program; USDOE Office of Science (SC)
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; Astronomy and Astrophysics; accretion, accretion disks; black hole physics; galaxies nuclei; stars individual (iPTF16fnl)
OSTI Identifier:
1412867
Alternate Identifier(s):
OSTI ID: 1418302