2002/06/30 by Adrienne M. Juett, Adrienne Juett, Deepto Chakrabarty · 3 citations
Physics and Astronomy · #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Cosmic Phenomena #Atomic physics #Neon #Neutron star #Observatory #Physics #Pulsars and Gravitational Waves Research #Spectral line #Spectral resolution #Spectrometer #Spectroscopy #astro-ph
paper · pdf · doi:10.1086/379188
published as Astrophys.J. 599 (2003) 498-508 · 11 pages, 5 figures, major revisions including addition of XMM spectral analysis, accepted for publication in the Astrophysical Journal, vol. 599
arxiv created 2003/08/21 · openalex publication_date 2003/12/01 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We present high-resolution spectroscopy of the neutron star/low-mass X-ray binaries 2S 0918-549 and 4U 1543-624 with the High Energy Transmission Grating Spectrometer on board the Chandra X-Ray Observatory and the Reflection Grating Spectrometer on board XMM-Newton . Previous low-resolution spectra of both sources showed a broad, linelike feature at 0.7 keV that was originally attributed to unresolved line emission. We recently showed that this feature could also be due to excess neutral Ne absorption, and this is confirmed by the new high-resolution Chandra and XMM spectra. The Chandra spectra are each well fitted by an absorbed-power-law+blackbody model with a modified Ne/O number ratio of 0.52 ± 0.12 for 2S 0918-549 and 1.5 ± 0.3 for 4U 1543-624, compared to the interstellar medium value of 0.18. The XMM spectrum of 2S 0918-549 is best fitted by an absorbed-power-law model with a Ne/O number ratio of 0.46 ± 0.03, consistent with the Chandra result. On the other hand, the XMM spectrum of 4U 1543-624 is softer and less luminous than the Chandra spectrum and has a best-fit Ne/O number ratio of 0.54 ± 0.03. The difference between the measured abundances and the expected interstellar ratio, as well as the variation of the column densities of O and Ne in 4U 1543-624, supports the suggestion that there is absorption local to these binaries. We propose that the variations in the O and Ne column densities of 4U 1543-624 are caused by changes in the ionization structure of the local absorbing material. It is important to understand the effect of ionization on the measured absorption columns before the abundance of the local material can be determined. This work supports our earlier suggestion that 2S 0918-549 and 4U 1543-624 are ultracompact binaries with Ne-rich companions.