The super-soft source XMMU J052016.0-692505 in the LMC. A likely white dwarf Be/X-ray binary
Abstract
Aims.We report the discovery of the super-soft X-ray source XMMU J052016.0-692505 in the LMC with XMM-Newton.
Methods: .We analyse the EPIC spectra of XMMU J052016.0-692505 and study the likely optical counterpart LMCV2135.
Results: .Using an absorbed blackbody spectrum we derive a bolometric luminosity of ⪆ 1034 erg s-1 for the X-ray source at LMC distance. Assuming that the bolometric luminosity does not exceed the Eddington luminosity of a ~ 1.0 M⊙ star we derive a blackbody temperature of (25-70) eV and an LMC absorbing column density of < 6× 1021 cm-2. The likely optical counterpart of XMMU J052016.0-692505 is the LMC variable star LMCV2135 which is a MACHO and OGLE variable. The infrared and optical colors and magnitudes of this star are consistent with a hot star of likely spectral type B. The long-term MACHO light curve shows variability with a timescale of ∼ 500 and ∼ 1000 days. The optical spectra obtained at the 1.9-meter telescope of the South African Astronomical Observatory show strong Hα and Hβ emission lines (with EWH_α∼ 34 Å) which indicate a B0-3e star. The radial velocities of the Hα and Hβ emission lines show a variation from ∼ 400-450 km s-1 to ∼ 5-20 km s-1 which is consistent with the systemic velocity of the LMC and an intrinsic variation most likely due to the rotation of the Be disk. We discuss LMCV2135/XMMU J052016.0-692505 as a Be/white dwarf binary system in the LMC. The super-soft X-ray spectrum of the source could be due to a stable nuclear burning white dwarf with a mass of ∼ 0.9-1.0 M⊙.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- October 2006
- DOI:
- 10.1051/0004-6361:20065490
- Bibcode:
- 2006A&A...458..285K
- Keywords:
-
- Magellanic Clouds;
- X-rays: stars;
- X-rays: binaries;
- stars: emission-line;
- Be;
- stars: general