Gravitational waves from a merged hyper-massive neutron star

[beecee]

https://phys.org/news/2018-11-gravitational-merged-hyper-massive-neutron-star.html

For the first time astronomers have detected gravitational waves from a merged, hyper-massive neutron star. The scientists, Maurice van Putten of Sejong University in South Korea, and Massimo della Valle of the Osservatorio Astronomico de Capodimonte in Italy, publish their results in Monthly Notices of the Royal Astronomical Society: Letters.

Read more at: https://phys.org/news/2018-11-gravitational-merged-hyper-massive-neutron-star.html#jCp

the paper: 

https://academic.oup.com/mnrasl/article/482/1/L46/5090425

Observational evidence for extended emission to GW170817

ABSTRACT

The recent LIGO event GW170817 is the merger of a double neutron star system with an associated short GRB170817A with 2.9 ± 0.3 s soft emission over 8–70 keV. This association has a Gaussian equivalent level of confidence of 5.1σ. The merger produced a hypermassive neutron star or stellar mass black hole with prompt or continuous energy output powering GRB170817A. Here, we report on a possible detection of extended emission (EE) in gravitational radiation during GRB170817A: a descending chirp with characteristic time-scale τs=3.01±0.2τs=3.01±0.2 s in a (H1,L1)-spectrogram up to 700 Hz with Gaussian equivalent level of confidence greater than 3.3σ based on causality alone following edge detection applied to (H1,L1)-spectrograms merged by frequency coincidences. Additional confidence derives from the strength of this EE. The observed frequencies below 1 kHz indicate a hypermassive magnetar rather than a black hole, spinning down by magnetic winds and interactions with dynamical mass ejecta.

3 CONCLUSIONS

We present observational evidence for a descending chirp for the first five seconds post-merger to GW170817 (Fig. 2). By frequency, it potentially indicates a magnetar as the central engine of GRB170817A, well below the minimum of 2 kHz emission from high density matter about the ISCO of a 3M⊙3M⊙ black hole. The ultimate fate of the magnetar is uncertain, whether it survives as a pulsar with a spin frequency of 49 Hz or collapses to a black hole at a later stage. The physical mechanism by which the magnetar is protected against prompt collapse is not well understood, but lifetimes of 10 s such as observed here have been anticipated for proto-magnetars (Ravi & Lasky 2014). Our observation of an extended lifetime appears particularly reasonable in light of the recent LIGO determination of a relatively low total mass of 2.73+0.04−0.01M⊙2.73−0.01+0.04M⊙ of the progenitor binary (Abbott et al. 2018) that is just 20 per cent above the neutron star mass of 2.27+0.17−0.15M⊙2.27−0.15+0.17M⊙ in PSR J2215+5135 (Linares, Shahbaz & Casares 2018) and on par with the supermassive PSR J1748-2021B (Freire et al. 2008; Özel & Freire 2016). Future observations promise to significantly improve on these initial observations, and to determine to what extend GRB170817A is representative for canonical SGRBs.

Edited November 14, 2018 by beecee