M87核区X射线辐射起源的研究  

On the Origin of X-ray Emission in M 87

作　　者：于照茏[1] 

机构地区：[1]中国科学院上海天文台,上海200030

出　　处：《天文学进展》2011年第1期81-85,共5页Progress In Astronomy

基　　金：国家自然科学基金项目(10773024;10833002;10821302;和10825314);科技部973项目(2009CB824800)

摘　　要：利用耦合的吸积-喷流模型,对巨椭圆星系M 87(NGC 4486)核区的高分辨率观测到的多波段能谱分布进行了研究,重点是核区的X射线辐射起源问题。研究结果表明,M87核区的X射线辐射是由喷流主导的,而不是此前认为的由径移主导的吸积流(ADAFs)主导的。We investigate the origin of the X-ray emission in the nucleus region of the giant elliptical galaxy M 87 （NGC 4486）, via fitting the observed high-resolution spectral energy distributions （SEDs）. We use the coupled ADAF-jet model to fit this multi-wavelength spectrum, especially focusing on the X-ray band. In this model, the whole accretion disk is described by ADAF, and does not include the truncated standard disk. A fraction of accretion matter is assumed to be transferred into the vertical direction to form a jet in the innermost region of accretion disk. Both simulations and analytical works indicate that only a fraction of the gas available at large radius actually accretes onto the black hole, and the outflow is very important. We therefore parameterize the accretion rate with a parameter s, defined such that M= Mout （R/Rout）s. In our calculation we adopt typical values of a = 0.3, = 0.9, 5 = 0.5 and s = 0.3. The jet model is based on the internal shock scenario. We assume a constant electron temperature Te in the jet, and the jet has a conical geometry with half-opening angle Ф= 0.1. We also assume that a small fraction of the electrons in the jet are accelerated into a power-law energy distribution with index p via the internal shocks. The values of the free parameters adopted in jet model are Mjet = 1.× 10^-8MEdd, Гj = 70, p = 2.5, εe = 0.2, and εB = 0.02. We can successfully fit the spectrum of M 87 using the coupled ADAF-jet model. The adopted accretion rate at the radius of 10^3Rs is Mtr = 7.× 10^-5MEdd ≈ 0.252MBondi. This value is consistent with the observed Bondi accretion rate. Moreover, Mjet/M（5Rs） ≈ 10^-3. This means that only a little of gas into jet can produce enough flux. Our results indicate that the X-ray emission of M 87 is dominated by jet rather than ADAF. This result is consistent with the prediction of Yuan and Cui, and also consistent with the high-resolution observations in the nucleus region of M 87.

关 键 词：吸积 喷流 X射线辐射 活动星系核 

分 类 号：P157.6[天文地球—天文学]