微类星体GRS 1915+105的视差距离及其黑洞质量的修正估计
A Parallax Distance to the Microquasar GRS 1915+105 and a Revised Estimate of its Black Hole Mass
摘要：
利用甚长基线阵列，我们测量了微类星体GRS 1915+105的三角视差，它包含一个黑洞和一个K巨星伴星。由此得到的直接距离估计值为8.6（+2.0，-1.6）kpc，修正后的黑洞质量估计值为12.4（+2.0，-1.8）Msun。GRS 1915+105与一些HII区域和水脉泽的距离大致相同，这些区域与银河系人马座旋臂中的高质量恒星形成有关。GRS 1915+105向东和向北的绝对自行分别为-3.19 +/- 0.03 mas/y和-6.24 +/- 0.05 mas/y，这对应于视差距离处22 +/-24 km/s的适度特有速度，表明该双星在黑洞形成时没有受到大的速度反冲。在一个观测时期，GRS 1915+105显示出沿其接近喷流方向的超光速运动。考虑到以前对喷流运动的观测，GRS 1915+105中的喷流可以用60 +/- 5度的喷流倾斜度和0.65 c和0.81 c之间的可变流速来建模，这可能表明喷流在距离黑洞>2000 AU的地方减速。最后，利用我们对距离的测量和对黑洞质量和倾角的估计，我们暂时证实了我们早先的结果，即黑洞旋转得非常快。
英文摘要：
Using the Very Long Baseline Array, we have measured a trigonometric parallax for the micro quasar GRS 1915+105, which contains a black hole and a K-giant companion. This yields a direct distance estimate of 8.6 (+2.0,-1.6) kpc and a revised estimate for the mass of the black hole of 12.4 (+2.0,-1.8) Msun. GRS 1915+105 is at about the same distance as some HII regions and water masers associated with high-mass star formation in the Sagittarius spiral arm of the Galaxy. The absolute proper motion of GRS 1915+105 is -3.19 +/- 0.03 mas/y and -6.24 +/- 0.05 mas/y toward the east and north, respectively, which corresponds to a modest peculiar speed of 22 +/-24 km/s at the parallax distance, suggesting that the binary did not receive a large velocity kick when the black hole formed. On one observational epoch, GRS 1915+105 displayed superluminal motion along the direction of its approaching jet. Considering previous observations of jet motions, the jet in GRS 1915+105 can be modeled with a jet inclination to the line of sight of 60 +/- 5 deg and a variable flow speed between 0.65c and 0.81c, which possibly indicates deceleration of the jet at distances from the black hole >2000 AU. Finally, using our measurements of distance and estimates of black hole mass and inclination, we provisionally confirm our earlier result that the black hole is spinning very rapidly.
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