黑洞吸积体XTE J1550-564宽带谱中致密喷流占主导地位的证据
Evidence for a compact jet dominating the broadband spectrum of the black hole accretor XTE J1550-564
摘要：
黑洞X射线双星XTE J1550-564在2000年的爆发过程中被广泛地监测到X射线，光学和红外波长。我们表明，它是可能的，以分离的光学/近红外（OIR）喷流发射的OIR光盘发射。聚焦于喷流成分，我们发现，随着源在X射线硬态中的衰减，OIR喷流发射具有与光学薄同步辐射一致的光谱指数（α ~ -0.6 to-0.7，其中F_nu \propto nu^alpha）。这种喷流发射与X射线通量密切线性相关; L_OIR，喷流\propto L_X^（0.98 ± 0.08）表明它们有共同的起源。OIR、X射线和OIR到X射线光谱指数与单一幂律（α = -0.73）一致，这支持了这一点。表面上，紧凑的同步加速器喷流因此可以在硬态下的低光度下占X射线通量的~ 100%。与此同时，（i）在喷流开始占主导地位的点处，X射线通量的幂律衰减出现过剩，（ii）X射线光谱略有软化，这似乎是由于高能量截止或断裂转移到较低能量，以及（iii）X射线均方根变化增加。这可能是迄今为止最有力的证据，证明致密、稳定的喷流的同步加速器发射主导了X射线双星的X射线通量。对于XTEJ 1550 -564，这可能发生在亮度范围~（2 e-4 - 2 e-3）LEdd内。然而，在硬态上升的爆发和最初的硬态下降，同步加速器射流只能提供一小部分（百分之几）的X射线通量。因此，热康普顿化和同步加速器喷流都能在吸积黑洞中产生硬X射线幂律。
英文摘要：
[abridged] The black hole X-ray binary XTE J1550-564 was monitored extensively at X-ray, optical and infrared wavelengths throughout its outburst in 2000. We show that it is possible to separate the optical/near-infrared (OIR) jet emission from the OIR disc emission. Focussing on the jet component, we find that as the source fades in the X-ray hard state, the OIR jet emission has a spectral index consistent with optically thin synchrotron emission (alpha ~ -0.6 to -0.7, where F_nu \propto nu^alpha). This jet emission is tightly and linearly correlated with the X-ray flux; L_OIR,jet \propto L_X^(0.98 +- 0.08) suggesting a common origin. This is supported by the OIR, X-ray and OIR to X-ray spectral indices being consistent with a single power law (alpha = -0.73). Ostensibly the compact, synchrotron jet could therefore account for ~ 100 % of the X-ray flux at low luminosities in the hard state. At the same time, (i) an excess is seen over the power law decay of the X-ray flux at the point in which the jet would start to dominate, (ii) the X-ray spectrum slightly softens, which seems to be due to a high energy cut-off or break shifting to a lower energy, and (iii) the X-ray rms variability increases. This may be the strongest evidence to date of synchrotron emission from the compact, steady jet dominating the X-ray flux of an X-ray binary. For XTE J1550-564, this is likely to occur within the luminosity range ~ (2 e-4 - 2 e-3) L_Edd on the hard state decline of this outburst. However, on the hard state rise of the outburst and initially on the hard state decline, the synchrotron jet can only provide a small fraction (~ a few per cent) of the X-ray flux. Both thermal Comptonization and the synchrotron jet can therefore produce the hard X-ray power law in accreting black holes.
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