We present new VLBI images of supernova 1986J, taken at 5, 8.4 and 22 GHz between t=22 to 25 yr after the explosion. The shell expands as t^(0.69+-0.03). We estimate the progenitor's mass-loss rate at (4 ~ 10) * 10^-5 Msol/yr (for v_w = 10 km/s). Two bright spots are seen in the images. The first, in the northeast, is now fading. The second, very near the center of the projected shell and unique to SN1986J, is still brightening relative to the shell, and now dominates the VLBI images. It is marginally resolved at 22 GHz (diameter ~0.3 mas; ~5 * 10^16 cm at 10 Mpc). The integrated VLA spectrum of SN1986J shows an inversion point and a high-frequency turnover, both progressing downward in frequency and due to the central bright spot. The optically-thin spectral index of the central bright spot is indistinguishable from that of the shell. The small proper motion of 1500+-1500 km/s of the central bright spot is consistent with our previous interpretation of it as being associated with the expected black-hole or neutron-star remnant. Now, an alternate scenario seems also plausible, where the central bright spot, like the northeast one, results when the shock front impacts on a condensation within the circumstellar medium (CSM). The condensation would have to be so dense as to be opaque at cm wavelengths (~1000x denser than the average corresponding CSM) and fortuitously close to the center of the projected shell. We include a movie of the evolution of SN1986J at 5 GHz from t=0 to 25 yr.
We report on new Very Long Baseline Interferometry radio measurements of supernova 2014C in the spiral galaxy NGC 7331, made with the European VLBI Network ~5 yr after the explosion, as well as on flux density measurements made with the Jansky Very Large Array (VLA). SN 2014C was an unusual supernova, initially of Type Ib, but over the course of ~1 yr it developed strong H$α$ lines, implying the onset of strong interaction with some H-rich circumstellar medium (CSM). The expanding shock-front interacted with a dense shell of circumstellar material during the first year, but has now emerged fro…
We present broadband radio flux-density measurements supernova (SN) 1996cr, made with MeerKAT, ATCA and ALMA, and images made from very long baseline interferometry (VLBI) observations with the Australian Long Baseline Array. The spectral energy distribution of SN 1996cr in 2020, at age, $t \sim$8700 d, is a power-law, with flux density, $S \propto ν^{-0.588 \pm 0.011}$ between 1 and 34 GHz, but may steepen at $>35$ GHz. The spectrum has flattened since $t = 5370$ d (2010). Also since $t = 5370$ d, the flux density has declined rapidly, with $S_{\rm 9 \, GHz} \propto t^{-2.9}$. The VLBI image …
The study of blazar jet has been performed for several decades via the VLBI technique, while its generation and propagation stay unclear. In the present work, we compiled a sample of 407 VLBI detected \textit{Fermi} blazars (VFBs) and studied the correlations between apparent velocity (${\rm log}\,β_{\rm app}$) and jet/accretion disk properties. We found a positive correlation between $γ$-ray luminosity (${\rm log}\,L_{\rm γ}$) and ${\rm log}\,β_{\rm app}$, the correlation suggests that the apparent motion of jet knot is related to the jet power.
Black holes hold a tremendous discovery potential. In this paper the extent to which the Event Horizon Telescope and its next generation upgrade can resolve their structure is quantified. Black holes are characterized by a perfectly absorptive boundary, with a specific area determined by intrinsic parameters of the black hole. We use a general parametrization of spherically symmetric spacetimes describing deviations from this behavior, with parameters controlling the size of the central object and its interaction with light, in particular through a specular reflection coefficient $Γ$ and an in…
Fossil shell in 3C 84 as TeV $γ$-ray emitter and cosmic-ray accelerator
我们探索了受冲击的外部介质的物理特性（即，3C 84中与1960年左右出生的周期性射电瓣有关的一个壳）。在Ito等人先前的工作中，我们研究了在中央发动机停止喷气发射后这种壳层的动力学和辐射演化，我们发现化石壳层的辐射与快速衰落的射电瓣的辐射相似。我们将这个模型应用于3C 84，发现：（1）由数密度为0.3 cm $^{-3}$的冲击扩散环境物质构成的化石壳层，以来自中心致密区的射电辐射种子光子为辐射源，辐射出明亮的逆康普顿（IC）辐射，IC辐射超过切伦科夫望远镜阵列（CTA）的灵敏度阈值。(ii)当化石壳产生于数密度为$10^{3}$ cm $^{-3}$的几何厚电离等离子体中时，壳中的场强在磁场放大的存在下可达到约17 mG，射电发射变得与深成像VLBI观测的灵敏度相当。超高能宇宙射线（UHECRs）的可能产生的致密冲击等离子体也被认为是。
Nearby radio galaxies that contain jets are extensively studied with VLBI, addressing jet launching and the physical mechanisms at play around massive black holes. 3C 84 is unique in this regard, because the combination of its proximity and large SMBH mass provides a high spatial resolution to resolve the complex structure at the jet base. For 3C 84 an angular scale of 50 $μ$as corresponds to 200 - 250 Schwarzschild radii ($R_s$). Recent RadioAstron VLBI imaging at 22 GHz revealed an east-west elongated feature at the northern end of the VLBI jet, which challenges interpretations. Here we prop…
VLBI Observations of SN 2012au Reveal a Compact Radio Source a Decade Post Explosion
Dunlap Institute for Astronomy & Astrophysics, University of Toronto（多伦多大学邓普天体物理与天文研究所）；David A. Dunlap Department of Astronomy & Astrophysics, University of Toronto（多伦多大学大卫·A·邓普天文学与天体物理学系）；MIT Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology（麻省理工学院卡弗里天体物理学与空间研究所）；Center for Interdisciplinary Exploration and Research in Astronomy (CIERA), Northwestern University（西北大学跨学科天文探索与研究中心）；Anton Pannekoek Institute for Astronomy, University of Amsterdam（阿姆斯特丹大学安东·潘内科克天文研究所）；Joint Institute for VLBI ERIC（甚长基线干涉测量欧洲研究基础设施联合研究所）；ASTRON, Netherlands Institute for Radio Astronomy（荷兰射电天文研究所）；Trottier Space Institute, McGill University（麦吉尔大学特罗蒂尔太空研究所）
SN 2012au的VLBI观测显示，爆炸十年后仍存在紧凑的无线电源，排除了喷流假说，支持脉冲星风云解释，为研究脉冲星形成提供新机会。
The bright blazar OJ 287 is the best-known candidate for hosting a supermassive black hole binary system. It inspirals due to the emission of nanohertz gravitational waves (GWs). Observations of historical and predicted quasi-periodic high-brightness flares in its century-long optical lightcurve, allow us to determine the orbital parameters associated with the binary black hole (BBH) central engine. In contrast, the radio jet of OJ 287 has been covered with Very Long Baseline Interferometry (VLBI) observations for only about $30$ years and these observations reveal that the position angle (PA)…
VLBI-Enabled Localization of Continuous GW Sources
Kumamoto University（熊本大学）；National Astronomical Observatory of Japan（日本国立天文台）；Yamaguchi University（山口大学）；Kagoshima University（鹿儿岛大学）；Tohoku Institute of Technology（东北工业大学）；National Astronomical Research Institute of Thailand（泰国国立天文研究所）；Tohoku University（东北大学）；Japan Aerospace Exploration Agency（日本宇宙航空研究开发机构）
Jets which are powered by an AGN are a crucial element in the study of their central black holes (BH) and their immediate surroundings. The formation of such jets is the subject of intense research, mainly based on the dichotomy presented by the two main jet launching scenarios $-$ the one from Blandford & Payne (1982), and the one from Blandford & Znajek (1977). In this work we study the prominent and nearby radio galaxy 3C 84 (NGC 1275) with 15, 43, and 86 GHz quasi-simultaneous VLBI observations. From these we determine the jet apex to be located $83\pm7\,μ$as ($0.028-0.11$pc) upstream of t…
