VLASS 发现一个演化时标为十年级的明亮银河系射电暂现源
VLASS Discovery of a Luminous Galactic Radio Transient Evolving on Decade Timescales
AI总结：
该研究通过多波段分析发现银河系射电暂现源VT J1906+0849，其演化时标为十年级，性质类似微类星体SS 433，或为研究致密天体吸积与喷流提供新样本。
AI中文摘要：
我们对射电暂现源 VT J1906+0849 开展了多波段分析，该源是在甚大阵天空巡天（Very Large Array Sky Survey, VLASS）第1期发现的70毫央斯基（mJy）源，此前美国国家射电天文台甚大阵天空巡天（NRAO VLA Sky Survey, NVSS）在21年前未探测到它。射电观测显示，该源首次于2005年被探测到，2014年峰值亮度大于等于200毫央斯基（mJy），随后逐渐变暗，直至2025年末再次增亮。该暂现源位于银纬约0.74°处，其光学-红外对应体的性质支持它起源于银河系。在距离大于等于15千秒差距（kpc）的情况下，其极端射电光度很可能来自致密天体的持续吸积。然而，Swift-X射线望远镜（Swift-XRT）未探测到它，表明它相对于银河系X射线双星族而言是X射线暗弱的，且射电辐射在时变和谱特性上与X射线双星不同。宽带射电光谱显示同步自吸收， equipartition（ equipartition 即能量均分）和甚长基线干涉测量（very long baseline interferometry）的尺寸约束表明，尽管在5年多的时间里谱发生了显著演化，但射电辐射区域几乎没有膨胀。近红外光谱显示一条单一的宽发射线，其中心稳定但宽度和光度可变。我们将该特征归因于蓝移的 Brγ（溴化氢伽马线），它追踪了持续的不对称、速度约为2000千米每秒（km s⁻¹）的外流。这些特性不同于任何已发现的银河系射电源。一种可能的解释是，VT J1906+0849是微类星体 SS 433的年轻类似物，其致密的盘风限制了持续供能的同步辐射外流。这种喷流-风相互作用解释了紧凑、缓慢膨胀的射电源，也可能是其缺乏明亮X射线发射的原因。
英文摘要：
We present a multiwavelength analysis of the radio transient VT J1906+0849, discovered as a 70 mJy source in Epoch 1 of the Very Large Array Sky Survey (VLASS), 21 yr after an NRAO VLA Sky Survey (NVSS) non-detection. Radio observations reveal the source was first detected in 2005, peaking at $\gtrsim200$ mJy in 2014, then declining until a late 2025 rebrightening. The transient sits at a Galactic latitude of $\approx0.74^\circ$ and the properties of its optical-infrared counterpart support a Galactic origin. At $d\gtrsim15$ kpc, the extreme radio luminosity is likely powered by sustained accretion onto a compact object. However, a Swift-XRT non-detection shows it is X-ray faint relative to the Galactic X-ray binary population, and the radio emission is distinct from X-ray binaries in its temporal and spectral behavior. Broadband radio spectra suggest synchrotron self-absorption, but size constraints from equipartition and very long baseline interferometry show little to no expansion in the radio-emitting region over 5+ yr, despite significant spectral evolution. Near-infrared spectroscopy reveals a single broad emission line with a stable centroid but variable width and luminosity. We attribute this feature to blueshifted Br$γ$ tracing a persistent asymmetric $\approx2000$ km s$^{-1}$ outflow. These properties are unlike any previously identified Galactic radio source. One possible interpretation is that VT J1906+0849 is a young analog of the microquasar SS 433, with a dense disk wind confining a continuously powered synchrotron outflow. This jet-wind interaction explains the compact, slowly expanding radio source and may contribute to the absence of bright X-ray emission.
