Abstract
We present spectroscopic X-ray data of two candidate ultracompact X-ray binaries (UCXBs): 4U 0614+091 and 4U 1543-624. We confirm the presence of a broad O viii Ly alpha reflection line (at a parts per thousand 18 angstrom) using XMM-Newton and Chandra observations obtained in 2012 and 2013. The donor star in these sources is a carbon-oxygen or oxygen-neon-magnesium white dwarf. Hence, the accretion disc is enriched with oxygen which makes the O viii Ly alpha line particularly strong. Modelling the X-ray reflection off a carbon- and oxygen-enriched, hydrogen- and helium-poor disc with models assuming solar composition likely biases several of the best-fitting parameters. In order to describe the X-ray reflection spectra self-consistently, we modify the currently available xillver reflection model. We present initial grids that can be used to model X-ray reflection spectra in UCXBs with carbon-oxygen-rich (and hydrogen- and helium-poor) accretion disc. We find that the new reflection model provides a better overall description of the reflection spectra of 4U 0614+091 and 4U 1543-624 than the reflection models that assume solar abundances.
Original language | English |
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Journal | Monthly Notices of the Royal Astronomical Society |
Volume | 442 |
Issue number | 2 |
Pages (from-to) | 1157-1165 |
Number of pages | 9 |
ISSN | 0035-8711 |
DOIs | |
Publication status | Published - 2014 |
Keywords
- ASTRONOMY
- SOLAR-SYSTEM ABUNDANCES
- 4U 0614+091
- BLACK-HOLE
- INTERSTELLAR-MEDIUM
- SPECTRA
- 4U-1543-624
- ELEMENTS
- STAR
- SPECTROSCOPY
- LINES
- accretion, accretion discs
- X-rays: binaries
- X-ray reflection