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Title: The Old Host-galaxy Environment of SSS17a, the First Electromagnetic Counterpart to a Gravitational-wave Source

We present an analysis of the host-galaxy environment of Swope Supernova Survey 2017a (SSS17a), the discovery of an electromagnetic counterpart to a gravitational-wave source, GW170817. SSS17a occurred 1.9 kpc (in projection; 10 farcs 2) from the nucleus of NGC 4993, an S0 galaxy at a distance of 40 Mpc. We present a Hubble Space Telescope (HST) pre-trigger image of NGC 4993, Magellan optical spectroscopy of the nucleus of NGC 4993 and the location of SSS17a, and broadband UV-through-IR photometry of NGC 4993. The spectrum and broadband spectral-energy distribution indicate that NGC 4993 has a stellar mass of $$\mathrm{log}(M/{M}_{\odot })={10.49}_{-0.20}^{+0.08}$$ and star formation rate of 0.003 $${M}_{\odot }$$ yr -1, and the progenitor system of SSS17a likely had an age of >2.8 Gyr. There is no counterpart at the position of SSS17a in the HST pre-trigger image, indicating that the progenitor system had an absolute magnitude $${M}_{V}\gt -5.8$$ mag. We detect dust lanes extending out to almost the position of SSS17a and >100 likely globular clusters associated with NGC 4993. The offset of SSS17a is similar to many short gamma-ray-burst offsets, and its progenitor system was likely bound to NGC 4993. The environment of SSS17a is consistent with an old progenitor system such as a binary neutron star system.
 [1] ;  [1] ;  [2] ;  [1] ;  [3] ; ORCiD logo [1] ;  [2] ;  [1] ;  [4] ;  [3] ;  [1] ;  [3] ; ORCiD logo [2] ; ORCiD logo [1] ; ORCiD logo [5] ;  [6] ;  [1] ; ORCiD logo [7] ;  [1]
  1. Univ. of California, Santa Cruz, CA (United States)
  2. The Observatories of the Carnegie Institution for Science, Pasadena, CA (United States)
  3. Carnegie Observatories, La Serena (Chile)
  4. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Univ. of California, Berkeley, CA (United States)
  5. Univ. of California, Santa Cruz, CA (United States); Univ. of Copenhagen, Copenhagen (Denmark)
  6. Space Telescope Science Institute, Baltimore, MD (United States); The Johns Hopkins Univ., Baltimore, MD (United States)
  7. The Observatories of the Carnegie Institution for Science, Pasadena, CA (United States); Univ. of Hawaii, Honolulu, HI (United States)
Publication Date:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
The Astrophysical Journal. Letters
Additional Journal Information:
Journal Volume: 848; Journal Issue: 2; Journal ID: ISSN 2041-8213
Institute of Physics (IOP)
Research Org:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
Country of Publication:
United States
79 ASTRONOMY AND ASTROPHYSICS; galaxies: individual (NGC 4993); stars: individual (SSS17a)
OSTI Identifier: