A long-lived neutron star merger remnant in GW170817: Constraints and clues from X-ray observations

L. Piro, E. Troja, B. Zhang, G. Ryan, H. Van Eerten, R. Ricci, M. H. Wieringa, A. Tiengo, N. R. Butler, S. B. Cenko, O. D. Fox, H. G. Khandrika, G. Novara, A. Rossi, T. Sakamoto

Research output: Contribution to journalArticle

37 Scopus citations

Abstract

Multimessenger observations of GW170817 have not conclusively established whether the merger remnant is a black hole (BH) or a neutron star (NS). We show that a long-lived magnetized NS with a poloidal field B ≈ 1012 G is fully consistent with the electromagnetic dataset, when spin-down losses are dominated by gravitational wave (GW) emission. The required ellipticity ϵ ≳ 10-5 can result from a toroidal magnetic field component much stronger than the poloidal component, a configuration expected from an NS newly formed from a merger. Abrupt magnetic dissipation of the toroidal component can lead to the appearance of X-ray flares, analogous to the one observed in gamma-ray burst (GRB) afterglows. In the X-ray afterglow of GW170817, we identify a low-significance (≳3σ) temporal feature at 155 d, consistent with a sudden reactivation of the central NS. Energy injection from the NS spin-down into the relativistic shock is negligible, and the underlying continuum is fully accounted for by a structured jet seen off-axis. Whereas radio and optical observations probe the interaction of this jet with the surrounding medium, observations at X-ray wavelengths, performed with adequate sampling, open a privileged window on to the merger remnant.

Original languageEnglish (US)
Pages (from-to)1912-1921
Number of pages10
JournalMonthly Notices of the Royal Astronomical Society
Volume483
Issue number2
DOIs
StatePublished - Jan 1 2019

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Keywords

  • Gamma
  • Gravitational waves
  • Ray burst: general
  • Stars: neutron

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Piro, L., Troja, E., Zhang, B., Ryan, G., Van Eerten, H., Ricci, R., Wieringa, M. H., Tiengo, A., Butler, N. R., Cenko, S. B., Fox, O. D., Khandrika, H. G., Novara, G., Rossi, A., & Sakamoto, T. (2019). A long-lived neutron star merger remnant in GW170817: Constraints and clues from X-ray observations. Monthly Notices of the Royal Astronomical Society, 483(2), 1912-1921. https://doi.org/10.1093/mnras/sty3047