A long-lived neutron star merger remnant in GW170817: constraints and clues from X-ray observations
Date Issued
2019
Author(s)
•
Troja, E.
•
Zhang, B.
•
Ryan, G.
•
van Eerten, H.
•
•
Wieringa, M. H.
•
Tiengo, A.
•
Butler, N. R.
•
Cenko, S. B.
•
Fox, O. D.
•
Khandrika, H. G.
•
Novara, G.
•
•
Sakamoto, T.
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 ∊ ≳ 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.
Volume
483
Issue
2
Start page
1912
Issn Identifier
0035-8711
Ads BibCode
2019MNRAS.483.1912P
Rights
open.access
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