VLBI observations of the shortest orbital period black hole binary, MAXI J1659-152
Z. Paragi, A. J. van der Horst, T. Belloni, J. C. A. Miller-Jones, J. Linford, G. Taylor, J. Yang, M. A. Garrett, J. Granot, C. Kouveliotou, E. Kuulkers, R. A. M. J. Wijers
备注：
12 pages, 6 figures, 1 table. Accepted for publication in MNRAS
The X-ray transient MAXI J1659-152 was discovered by Swift/BAT and it was initially identified as a GRB. Soon its Galactic origin and binary nature were established. There exists a wealth of multi-wavelength monitoring data for this source, providing a great coverage of the full X-ray transition in this candidate black hole binary system. We obtained two epochs of European VLBI Network (EVN) electronic-VLBI (e-VLBI) and four epochs of Very Long Baseline Array (VLBA) data of MAXI J1659-152 which show evidence for outflow in the early phases. The overall source properties (polarization, milliarcsecond-scale radio structure, flat radio spectrum) are described well with the presence of a compact jet in the system through the transition from the hard-intermediate to the soft X-ray spectral state. The apparent dependence of source size and the radio core position on the observed flux density (luminosity dependent core shift) support this interpretation as well. We see no evidence for major discrete ejecta during the outburst. For the source proper motion we derive 2 sigma upper limits of 115 microas/day in right ascension, and 37 microas/day in declination, over a time baseline of 12 days. These correspond to velocities of 1400 km/s and 440 km/s, respectively, assuming a source distance of 7 kpc.
Shocks in the Symbiotic Recurrent Nova V3890 Sgr: VLBI Radio Imaging and Fermi GeV Gamma-Rays
Michigan State University（密歇根州立大学）；Institute for Advanced Study, Princeton（普林斯顿高等研究院）；Columbia University（哥伦比亚大学）；National Radio Astronomy Observatory（美国国家射电天文台）；Flatiron Institute（平顿研究所）；Chalmers University of Technology（查尔姆斯理工大学）
MeqSilhouette : A mm-VLBI observation and signal corruption simulator
事件视界望远镜（EHT）的目标是在空间上分辨银河系中心（Sgr A $^\star$）和M87中超大质量黑洞的轮廓（或阴影）。主要科学目标是在强场状态下检验广义相对论，并在事件视界尺度上探测吸积和喷气发射物理学。这可以通过（亚）毫米波长的甚长基线干涉测量技术来实现，该技术可以实现$\sim10~μ$ -角秒级的角分辨率。然而，这种方法受到独特的观测挑战，包括对流层和星际介质中的散射;极化和总强度的快速时变源结构;以及不可忽略的天线指向误差。在这篇文章中，在一个系列的第一篇文章中，我们提出了MeqSilhouette软件包，这是专门设计用于精确模拟EHT观测。它包括一些信号损坏的现实描述，可以限制测量关键科学参数的能力。这可用于量化校准要求、测试参数估计和成像策略，并调查可能存在的系统不确定性。在这样做的过程中，可以在观测能力和理论预测之间建立更强的联系，目标是从即将到来的EHT灵敏度的数量级增加中最大限度地提高科学产出。
