Photon rings near the edge of a black hole shadow is supposed to be a unique tool to validate general relativity and provide reliable measurements of principal black hole parameters: spin and mass. Such measurements are possible though only for nearby supermassive black holes (SMBH) with Space-Earth Very Long Baseline Interferometry (S-VLBI) in the submillimeter wavelength range. For subrings to be distinguished S-EVLBI observations with long baselines at the Lagrangian Sun-Earth L2 libration point are needed. However, the average fluxes of nearby SMBH: Sagittarius A$^\ast$ (Sgr A$^\ast$) and M87$^\ast$ -- $F_ν\sim 1$ Jy, are still insufficient to detect the signal from the photon rings with even such long baselines. We argue that only manifestations of flares in the submillimeter waveband in their accretion disks can reveal observable signals from the photon rings with the S-EVLBI at L2. Such observations will become possible within the planned join program of the {\it Event Horizon Telescope} (EHT) and {\it Millimetron Space Observatory} (MSO), and within the planned {\it next generation EHT} (ngEHT) project. Two different observational tests for photons rings are discussed. The first one involves observations of a time series of responds from subsequent subrings as can be seen in a 1D visibility function within the join EHT-MSO configuration, the second one -- measurements of an increase of the angle between subsequent subrings in the 2D VLBI image which can be obtained within the ngEHT project.
The soft gamma repeater SGR 1806-20 is most famous for its giant flare from 2004, which yielded the highest gamma-ray flux ever observed on Earth. The flare emphasized the importance of determining the distance to the SGR, thus revealing the flare's energy output, with implications on SGRs energy budget and giant flare rates. We analyze x-ray scattering echoes observed by Swift/XRT following the 2006 August 6 intermediate burst of SGR 1806-20. Assuming positions and opacities of the molecular clouds along the line-of-sight from previous works, we derive direct constrains on the distance to SGR…
We carried out the first multi-wavelength (optical/UV and X-ray) photometric reverberation mapping of a tidal disruption flare (TDF) ASASSN-14li. We find that its X-ray variations are correlated with and lag the optical/UV fluctuations by 32$\pm$4 days. Based on the direction and the magnitude of the X-ray time lag, we rule out X-ray reprocessing and direct emission from a standard circular thin disk as the dominant source of its optical/UV emission. The lag magnitude also rules out an AGN disk-driven instability as the origin of ASASSN-14li and thus strongly supports the tidal disruption pict…
Reflection of X-ray emission on molecular clouds in the inner $\sim$ 100 pc of our Galaxy reveals that, despite being extremely quiet at the moment, our supermassive black hole Sgr A* should have experienced bright flares of X-ray emission in the recent past. Thanks to the improving characterisation of the reflection signal, we are able to infer parameters of the most recent flare(s) (age, duration and luminosity) and relative line-of-sight disposition of the brightest individual molecular complexes. We show that combining these data with measurements of polarisation in the reflected X-ray con…
Bright, short duration X-ray flares from accreting compact objects produce thin, dust scattering rings that enable dust echo tomography: high precision distance measurements and mapping of the line-of-sight distribution of dust. This work looks to the past activity of X-ray transient outbursts in order to predict the number of sight lines available for dust echo tomography. We search for and measure the properties of 3$σ$ significant flares in the 2-4 keV light curves of all objects available in the public MAXI archive. We derive a fluence sensitivity limit of $10^{-3}$ erg cm$^{-2}$ for the t…
Testing the Association of Supermassive Black Hole Infrared Flares and High-energy Neutrinos
MIT Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology（麻省理工学院）；Department of Astronomy and Columbia Astrophysics Laboratory, Columbia University（哥伦比亚大学）；Center for Computational Astrophysics, Flatiron Institute（西蒙斯基金会平顿研究所计算天体物理中心）；Department of Physics, Norwegian University of Science and Technology（挪威科技大学）
The innermost regions of accretion disks around black holes are strongly irradiated by X-rays that are emitted from a highly variable, compact corona, in the immediate vicinity of the black hole. The X-rays that are seen reflected from the disk and the time delays, as variations in the X-ray emission echo or reverberate off the disk provide a view of the environment just outside the event horizon. I Zwicky 1 (I Zw 1), is a nearby narrow line Seyfert 1 galaxy. Previous studies of the reverberation of X-rays from its accretion disk revealed that the corona is composed of two components; an exten…
Prominent K-shell emission lines of neutral iron (hereafter, FeI-K) and hard-continuum X-rays were found from molecular clouds (MCs) in the Sagittarius B (Sgr B) region with the two separate Suzaku observations in 2005 and 2009. The X-ray flux of FeI-K decreased in correlation to the hard-continuum flux by factor of 0.4-0.5 in 4 years, which is nearly equal to the light-travelling across the MCs. The rapid and correlated time-variability, the equivalent width of FeI-K, and the K-edge absorption depth of FeI are consistently explained by "X-ray echoes" due to the fluorescent and Thomson-scatter…
We demonstrate that polarimetric interferometry can be used to extract precise spatial information about compact polarized flares of Sgr A*. We show that, for a faint dynamical component, a single interferometric baseline suffices to determine both its polarization and projected displacement from the quiescent intensity centroid. A second baseline enables two-dimensional reconstruction of the displacement, and additional baselines can self-calibrate using the flare, enhancing synthesis imaging of the quiescent emission. We apply this technique to simulated 1.3-mm wavelength observations of a "…
We use a combination of high-resolution very long baseline interferometry (VLBI) radio and multi-wavelength flux density and polarization observations to constrain the physics of the dissipation mechanism powering the broadband flares in 3C 279 during an episode of extreme flaring activity in 2013-2014. Six bright flares superimposed on a long-term outburst are detected at $γ$-ray energies. Four of the flares have optical and radio counterparts. The two modes of flaring activity (faster flares sitting on top of a long term outburst) present at radio, optical, $γ$-ray frequencies are missing in…
Light curves for more than century optical photometric observations of the blazar OJ 287 reveals strong flares with a quasi-period of about 12 years. For a long time, this period has been interpreted by processes in a binary black hole system. We propose an alternative explanation for this period, which is based on Doppler factor periodic variations of the emitting region caused by jet helicity. Using multi-epoch very large baseline interferometry (VLBI) observations carried out in a framework of the MOJAVE (Monitoring Of Jets in Active galactic nuclei with VLBA Experiments) program and other …
We continue our earlier studies of quasi-periodic oscillations (QPOs) in the power spectra of accreting, rapidly-rotating black holes that originate from the geometric "light echoes" of X-ray flares occurring within the black hole ergosphere. Our present work extends our previous treatment to three-dimensional photon emission and orbits to allow for arbitrary latitudes in the positions of the distant observers and the X-ray sources in place of the mainly equatorial positions and photon orbits of the earlier consideration. Following the trajectories of a large number of photons we calculate the…
We present the jet kinematics of the flat spectrum radio quasar (FSRQ) 4C +21.35 using time-resolved KaVA very long baseline interferometry array radio maps obtained from September 2014 to July 2016. During two out of three observing campaigns, observations were performed bi-weekly at 22 and 43 GHz quasi-simultaneously. At 22 GHz, we identified three jet components near the core with apparent speeds up to (14.4+/-2.1)c. The timing of the ejection of a new component detected in 2016 is consistent with a gamma-ray flare in November 2014. At 43 GHz, we found four inner jet (<3 mas) components wit…
University of Turku（图尔库大学）；Aalto University Metsähovi Radio Observatory（阿尔托大学梅塔霍维射电天文台）；Max-Planck-Institut für Radioastronomie（马克斯·普朗克射电天文研究所）；Foundation for Research and Technology - Hellas（希腊研究与技术基金会）；Boston University（波士顿大学）；Saint Petersburg State University（圣彼得堡国立大学）；NASA Marshall Space Flight Center（美国国家航空航天局马歇尔太空飞行中心）；Université de Strasbourg（斯特拉斯堡大学）；Ruprecht-Karls-Universität Heidelberg（海德堡大学）；IAA-CSIC（安达卢西亚天体物理研究所（西班牙高等科学研究委员会））；University of New Hampshire（新罕布什尔大学）；ASI - Agenzia Spaziale Italiana（意大利航天局）；INAF, Istituto di Astrofisica e Planetologia Spaziali（意大利国家天体物理研究所空间天体物理学与行星科学研究所）；Physical Research Laboratory（物理研究实验室）；Universities Space Research Association（大学空间研究协会）；Universitá degli Studi di Roma "Tor Vergata"（罗马二大（托维尔加塔大学））
Images of supermassive black holes produced using very long baseline interferometry provide a pathway to directly observing effects of a highly curved spacetime, such as a bright ``photon ring'' that arises from strongly lensed emission. In addition, the emission near supermassive black holes is highly variable, with bright high-energy flares regularly observed. We demonstrate that intrinsic variability can introduce prominent associated changes in the relative brightness of the photon ring. We analyze both semianalytic toy models and GRMHD simulations with magnetic flux eruption events, showi…
Recent implications of results from quantum information theory applied to black holes has led to the confusing conclusions that requires either abandoning the equivalence principle (e.g. the firewall picture), or the no-hair theorem (e.g. the fuzzball picture), or even more unpalatable options. The recent discovery of a pulsar orbiting a black hole opens up new possibilities for tests of theories of gravity. We examine possible observational effects of semiclassical quantum gravity in the vicinity of black holes, as probed by pulsars and event horizon telescope imaging of flares. Pulsar radiat…
Spectral index evolution of the limb-brightened jet in 3C 84
Max-Planck-Institut für Radioastronomie（马克斯·普朗克射电天文研究所）；Finnish Centre for Astronomy with ESO, University of Turku（图尔库大学欧洲南方天文台芬兰天文学中心）；Aalto University Metsähovi Radio Observatory（阿尔托大学梅特霍维射电天文台）；Center for Astrophysics | Harvard & Smithsonian（哈佛与史密森尼天体物理中心）；Dept. of Physics & Astronomy, Sejong University（世宗大学物理与天文学系）；Department of Astrophysics, Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Radboud University（拉德堡德大学数学、天体物理学和粒子物理研究所天体物理学系）；Ulsan National Institute of Science and Technology（蔚山科学技术院）
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)…
