DISCOVERY OF X-RAY EMISSION FROM THE FIRST Be/BLACK HOLE SYSTEM

作者：Munar Adrover P^*; Paredes J M; Ribo M; Iwasawa K; Zabalza V; Casares J

来源：Astrophysical Journal Letters, 2014, 786(2): L11.

DOI：10.1088/2041-8205/786/2/L11

• binaries : general
• stars : black holes
• stars : emission-line, Be
• stars : individual (MWC 656)
• X-rays : binaries
• X-rays : individual (MWC 656)

MWC 656 (=HD 215227) was recently discovered to be the first binary system composed of a Be star and a black hole (BH). We observed it with XMM-Newton, and detected a faint X-ray source compatible with the position of the optical star, thus proving it to be the first Be/BH X-ray binary. The spectrum analysis requires a model fit with two components, a blackbody plus a power law, with k(B)T = 0.07(-0.03)(+0.04) keV and a photon index Gamma = 1.0 +/- 0.8, respectively. The non-thermal component dominates above similar or equal to 0.8 keV. The obtained total flux is F(0.3-5.5keV) = (4.6(-1.1)(+1.3)) x 10(14) erg cm (2) s (1). At a distance of 2.6 +/- 0.6 kpc the total flux translates into a luminosity L-X = (3.7 +/- 1.7) x 10(31) erg s(-1). Considering the estimated range of BH masses to be 3.8-6.9M(circle dot), this luminosity represents (6.7 +/- 4.4) x 10(-8)L(Edd), which is typical of stellar-mass BHs in quiescence. We discuss the origin of the two spectral components: the thermal component is associated with the hot wind of the Be star, whereas the power-law component is associated with emission from the vicinity of the BH. We also find that the position of MWC 656 in the radio versus X-ray luminosity diagram may be consistent with the radio/X-ray correlation observed in BH low-mass X-ray binaries. This suggests that this correlation might also be valid for BH high-mass X-ray binaries (HMXBs) with X-ray luminosities down to similar to 10(-8)L(Edd). MWC 656 will allow the accretion processes and the accretion/ejection coupling at very low luminosities for BH HMXBs to be studied.

• 出版日期2014-5-10