A year in the life of GW 170817: the rise and fall of a structured jet from a binary neutron star merger

Eleanora Troja, Hendrik Van Eerten, Geoffrey Scott Ryan, R Ricci, J. Michael Burgess, M. H. Wieringa, L. Piro, S. B. Cenko, T. Sakamoto

Research output: Contribution to journalArticlepeer-review

128 Citations (SciVal)


We present the results of our year-long afterglow monitoring of GW 170817, the first binary neutron star merger detected by Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) and Advanced Virgo. New observations with the Australian Telescope Compact Array and the ChandraX-ray Telescope were used to constrain its late-time behaviour. The broad-band emission, from radio to X-rays, is well-described by a simple power-law spectrum with index β ∼ 0.585 at all epochs. After an initial shallow rise ∝t0.9, the afterglow displayed a smooth turnover, reaching a peak X-ray luminosity of LX ≈ 5 × 10 39 erg s -1 at 160 d, and has now entered a phase of rapid decline, approximately ∝t -2. The latest temporal trend challenges most models of choked jet/cocoon systems, and is instead consistent with the emergence of a relativistic structured jet seen at an angle of ≈22° from its axis. Within such model, the properties of the explosion (such as its blast wave energy EK ≈ 2 × 10 50 erg, jet width θc ≈ 4°, and ambient density n ≈ 3 × 10 -3 cm -3) fit well within the range of properties of cosmological short gamma-ray bursts.

Original languageEnglish
Pages (from-to)1919-1926
Number of pages8
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
Early online date13 Aug 2019
Publication statusPublished - 1 Oct 2019


  • Acceleration of particles
  • Gamma-ray burst: General
  • Gravitational waves

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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