CXO J004318.8+412016, a steady supersoft X-ray source in M 31
Date Issued
2017
Author(s)
•
Luna, G. J. M.
•
Kotulla, R.
•
Gallager, J. S.
•
•
Mikolajewska, J.
•
Harbeck, D.
•
Bianchini, A.
•
Chiosi, E.
•
•
•
Kaur, A.
•
Mapelli, M.
•
•
Odendaal, A.
•
•
Wade, J.
•
Zemko, P.
Abstract
We obtained an optical spectrum of a star we identify as the optical counterpart of the M31 Chandra source CXO J004318.8+412016, because of prominent emission lines of the Balmer series, of neutral helium, and a He II line at 4686 Å. The continuum energy distribution and the spectral characteristics demonstrate the presence of a red giant of K or earlier spectral type, so we concluded that the binary is likely to be a symbiotic system. CXO J004318.8+412016 has been observed in X-rays as a luminous supersoft source (SSS) since 1979, with effective temperature exceeding 40 eV and variable X-ray luminosity, oscillating between a few times 1035 erg s-1 and a few times 1037 erg s-1 in the space of a few weeks. The optical, infrared and ultraviolet colours of the optical object are consistent with an an accretion disc around a compact object companion, which may be either a white dwarf or a black hole, depending on the system parameters. If the origin of the luminous supersoft X-rays is the atmosphere of a white dwarf that is burning hydrogen in shell, it is as hot and luminous as post-thermonuclear flash novae, yet no major optical outburst has ever been observed, suggesting that the white dwarf is very massive (m ≥ 1.2 M☉) and it is accreting and burning at the high rate \dot{m} > 10^{-8} M☉ yr-1 expected for Type Ia supernovae progenitors. In this case, the X-ray variability may be due to a very short recurrence time of only mildly degenerate thermonuclear flashes.
Volume
470
Issue
2
Start page
2212
Issn Identifier
0035-8711
Ads BibCode
2017MNRAS.470.2212O
Rights
open.access
File(s)![Thumbnail Image]()
Loading...
Name
Orio_2017.pdf
Description
Pdf editoriale
Size
1.48 MB
Format
Adobe PDF
Checksum (MD5)
add3b667e3ef044bda18df24ea23beb3