2018/09/30 by Zhaosheng Li, Valery F. Suleimanov, Juri Poutanen +4 · 19 citations
Physics and Astronomy · #Absorption edge #Astrophysical Phenomena and Observations #Gamma-ray bursts and supernovae #Neutron star #Photoionization #Photosphere #Pulsars and Gravitational Waves Research #RADIUS #Redshift #Spectral line #astro-ph.HE
paper · pdf · doi:10.3847/1538-4357/aade8e
published in The Astrophysical Journal 866(1), 53 (IOP Publishing) · matches the published version
openalex created_date 2018/09/27 · openalex publication_date 2018/10/10 · arxiv created 2018/10/12 · arxiv updated 2018/10/15 · openalex updated_date 2026/08/05
Abstract Thermonuclear X-ray bursts on the surface of neutron stars (NSs) can enrich the photosphere with metals, which may imprint photoionization edges on the burst spectra. We report here the discovery of absorption edges in the spectra of the type I X-ray burst from the NS low-mass X-ray binary GRS 1747−312 in Terzan 6 during observations by the Rossi X-ray Timing Explorer . We find that the edge energy evolves from 9.45 ± 0.51 to ∼6 keV and then back to 9.44 ± 0.40 keV during the photospheric radius expansion phase and remains at 8.06 ± 0.66 keV in the cooling tail. The photoionization absorption edges of hydrogen-like Ni, Fe, or an Fe/Ni mixture and the bound–bound transitions of metals may be responsible for the observed spectral features. The ratio of the measured absorption edge energy in the cooling tail to the laboratory value of the hydrogen-like Ni(Fe) edge energy allows us to estimate the gravitational redshift factor 1 + z = 1.34 ± 0.11(1 + z = 1.15 ± 0.09). The evolution of the spectral parameters during the cooling tail are well described by metal-rich atmosphere models. The combined constraints on the NS mass and radius from the direct cooling method and the tidal deformability strongly suggest very high atmospheric abundance of the iron group elements and limit the distance to the source to 11 ± 1 kpc.