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Evidence for X-Ray emission in excess to the Jet-afterglow Decay 3.5 yr after the binary neutron star merger GW 170817 : a new emission component
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(2022) Evidence for X-Ray emission in excess to the Jet-afterglow Decay 3.5 yr after the binary neutron star merger GW 170817 : a new emission component. The Astrophysical Journal Letters, 927 (1). L17. doi:10.3847/2041-8213/ac504a ISSN 2041-8213.
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Official URL: https://doi.org/10.3847/2041-8213/ac504a
Abstract
For the first ∼3 yrs after the binary neutron star merger event GW 170817, the radio and X-ray radiation has been dominated by emission from a structured relativistic off-axis jet propagating into a low-density medium with n < 0.01 cm−3. We report on observational evidence for an excess of X-ray emission at δt > 900 days after the merger. With L x ≈ 5 × 1038 erg s−1 at 1234 days, the recently detected X-ray emission represents a ≥3.2σ (Gaussian equivalent) deviation from the universal post-jet-break model that best fits the multiwavelength afterglow at earlier times. In the context of JetFit afterglow models, current data represent a departure with statistical significance ≥3.1σ, depending on the fireball collimation, with the most realistic models showing excesses at the level of ≥3.7σ. A lack of detectable 3 GHz radio emission suggests a harder broadband spectrum than the jet afterglow. These properties are consistent with the emergence of a new emission component such as synchrotron radiation from a mildly relativistic shock generated by the expanding merger ejecta, i.e., a kilonova afterglow. In this context, we present a set of ab initio numerical relativity binary neutron star (BNS) merger simulations that show that an X-ray excess supports the presence of a high-velocity tail in the merger ejecta, and argues against the prompt collapse of the merger remnant into a black hole. Radiation from accretion processes on the compact-object remnant represents a viable alternative. Neither a kilonova afterglow nor accretion-powered emission have been observed before, as detections of BNS mergers at this phase of evolution are unprecedented.
Item Type: | Journal Article | ||||||
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Subjects: | Q Science > QB Astronomy Q Science > QC Physics |
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Divisions: | Faculty of Science, Engineering and Medicine > Science > Physics | ||||||
SWORD Depositor: | Library Publications Router | ||||||
Library of Congress Subject Headings (LCSH): | Neutron stars, X-ray bursts, X-ray astronomy, Electromagnetic waves, X-rays, Chandra X-ray Observatory (U.S.) | ||||||
Journal or Publication Title: | The Astrophysical Journal Letters | ||||||
Publisher: | The American Astronomical Society | ||||||
ISSN: | 2041-8213 | ||||||
Official Date: | 8 March 2022 | ||||||
Dates: |
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Volume: | 927 | ||||||
Number: | 1 | ||||||
Article Number: | L17 | ||||||
DOI: | 10.3847/2041-8213/ac504a | ||||||
Status: | Peer Reviewed | ||||||
Publication Status: | Published | ||||||
Re-use Statement: | ** From IOP Publishing via Jisc Publications Router ** History: received 30-04-2021; oa-requested 30-04-2021; rev-recd 28-12-2021; accepted 25-01-2022; ppub 01-03-2022; epub 08-03-2022; open-access 08-03-2022. ** Licence for this article: http://creativecommons.org/licenses/by/4.0/ | ||||||
Access rights to Published version: | Open Access (Creative Commons) | ||||||
Date of first compliant deposit: | 18 December 2023 | ||||||
Date of first compliant Open Access: | 18 December 2023 | ||||||
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