Evidence for Dynamically Driven Formation of the GW170817 Neutron Star Binary in NGC 4993

  title={Evidence for Dynamically Driven Formation of the GW170817 Neutron Star Binary in NGC 4993},
  author={Antonella Palmese and William G. Hartley and Federica Tarsitano and C. J. Conselice and Ofer Lahav and Sahar Allam and James T. Annis and H. Lin and Marcelle Soares-Santos and Douglas L. Tucker and Dillon J. Brout and Manda Banerji and Keith C. Bechtol and H. Thomas Diehl and Andrew S. Fruchter and Juan Garc{\'i}a-Bellido and Ken Herner and Andrew J. Levan and T. S. Li and Chris Lidman and Kuntal Misra and Masao Sako and Dan Scolnic and M. Smith and Timothy M. C. Abbott and Filipe B. Abdalla and A. Benoit-L{\'e}vy and E. Bertin and David Brooks and Elizabeth Buckley-Geer and Aurelio Carnero Rosell and Matias Carrasco Kind and Jorge Carretero and Francisco J. Castander and Carlos E. Cunha and Chris D'Andrea and L. N. da Costa and C. Davis and Darren Lee Depoy and Shantanu Desai and J. P. Dietrich and Peter Doel and Alex Drlica-Wagner and T. F. Eifler and August E. Evrard and Brenna L. Flaugher and Pablo Fosalba and Joshua A. Frieman and E. Gaztanaga and David W. Gerdes and T. Giannantonio and Daniel Gruen and Robert A. Gruendl and Julia Gschwend and Gaston R. Guti{\'e}rrez and Klaus Honscheid and B. Jain and David J. James and Tesla E. Jeltema and M. W. G. Johnson and M. D. Johnson and E. Krause and Richard Kron and Kyler W. Kuehn and S. E. Kuhlmann and N. Kuropatkin and M. Lima and Marcio A. G. Maia and M March and Jennifer L. Marshall and R. McMahon and Felipe Menanteau and C J Miller and Ramon Miquel and Eric H. Neilsen and R. L. C. Ogando and A. A. Plazas and Kevin Alexander Reil and A. K. Romer and E. Sanchez and R. H. Schindler and R. C. Smith and Flavia Sobreira and Eric Suchyta and Mollye E. C. Swanson and Gregory G. Tarl{\'e} and D. Thomas and R. C. Thomas and Alistair R. Walker and Jochen Weller and Y. Zhang and Joe Zuntz},
  journal={The Astrophysical Journal Letters},
We present a study of NGC 4993, the host galaxy of the GW170817 gravitational-wave event, the GRB 170817A short gamma-ray burst (sGRB), and the AT 2017gfo kilonova. We use Dark Energy Camera imaging, AAT spectra, and publicly available data, relating our findings to binary neutron star (BNS) formation scenarios and merger delay timescales. NGC 4993 is a nearby early-type galaxy, with an i-band Sérsic index n = 4.0 and low asymmetry (A = 0.04 ± 0.01). These properties are unusual for sGRB hosts… 

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