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

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Burgess,  J. M.
High Energy Astrophysics, MPI for Extraterrestrial Physics, Max Planck Society;

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Troja, E., van Eerten, H., Ryan, G., Ricci, R., Burgess, J. M., Wieringa, M. H., et al. (2019). A year in the life of GW 170817: the rise and fall of a structured jet from a binary neutron star merger. Monthly Notices of the Royal Astronomical Society, 489(2), 1919-1926. doi:10.1093/mnras/stz2248.


Cite as: http://hdl.handle.net/21.11116/0000-0005-4E39-5
Abstract
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 Chandra X-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 × 1039 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 × 1050 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.