618 research outputs found
Foliar C, N, and P stoichiometry characterize successful plant ecological strategies in the Sonoran Desert
Ecological processes are centered to water availability in drylands; however, less known nutrient stoichiometry can help explain much of their structure and ecological interactions. Here we look to the foliar stoichiometry of carbon (C), nitrogen (N), and phosphorus (P) of 38 dominant plant species from the Sonoran Desert, grouped in four different functional types to describe ecological characteristics and processes. We found that foliar N, C:N, C:P, and N:P stoichiometric ratios, but not P, were higher than those known to most other ecosystems and indicate P but not N limitations in leaves. Biological N fixers (BNF) had even higher leaf N concentrations, but bio-elemental concentrations and stoichiometry ratios were not different to other non-N-fixing legume species which underscores the need to understand the physiological mechanisms for high N, and to how costly BNF can succeed in P-limiting drylands environments. Stoichiometry ratios, and to lesser extent elemental concentrations, were able to characterize BNF and colonizing strategies in the Sonoran Desert, as well as explain leaf attribute differences, ecological processes, and biogeochemical niches in this dryland ecosystem, even when no direct reference is made to other water-limitation strategies
Evaluación actual y propuestas para el desarrollo urbano en México
La revista Problemas del Desarrollo recoge en su colección de ediciones especiales las disertaciones y ponencias que se presentan en los seminarios, simposia y conferencias a que convoca y realiza anualmente el Instituto de Investigaciones Económicas de la Universidad Nacional Autónoma de México.
El propósito es contribuir a la mayor difusión de textos de contenido analítico, descriptivo y propositivo que se presentan en tales actos y que tienen gran valor para el mejor conocimiento y comprensión de la estructura y problemática económica y social de nuestro país. Pero también la revista quiere convertirse en foro abierto para la expresión de comentarios y ampliaciones que deseen hacer los lectores de estas ediciones especiales sobre temas particulares de los comprendidos en cada uno de sus libros. Estos aportes, por lo tanto, serán muy bien recibidos. Para ello, solo se requiere que los lectores los remitan, por escrito, al Instituto de Investigaciones Económicas, Torre II de Humanidades, Ciudad Universitaria
First Sagittarius A* Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole in the Center of the Milky Way
We present the first Event Horizon Telescope (EHT) observations of Sagittarius A* (Sgr A*), the Galactic center source associated with a supermassive black hole. These observations were conducted in 2017 using a global interferometric array of eight telescopes operating at a wavelength of λ = 1.3 mm. The EHT data resolve a compact emission region with intrahour variability. A variety of imaging and modeling analyses all support an image that is dominated by a bright, thick ring with a diameter of 51.8 \ub1 2.3 μas (68% credible interval). The ring has modest azimuthal brightness asymmetry and a comparatively dim interior. Using a large suite of numerical simulations, we demonstrate that the EHT images of Sgr A* are consistent with the expected appearance of a Kerr black hole with mass ∼4
7 106 M☉, which is inferred to exist at this location based on previous infrared observations of individual stellar orbits, as well as maser proper-motion studies. Our model comparisons disfavor scenarios where the black hole is viewed at high inclination (i > 50\ub0), as well as nonspinning black holes and those with retrograde accretion disks. Our results provide direct evidence for the presence of a supermassive black hole at the center of the Milky Way, and for the first time we connect the predictions from dynamical measurements of stellar orbits on scales of 103-105 gravitational radii to event-horizon-scale images and variability. Furthermore, a comparison with the EHT results for the supermassive black hole M87* shows consistency with the predictions of general relativity spanning over three orders of magnitude in central mass
A Universal Power-law Prescription for Variability from Synthetic Images of Black Hole Accretion Flows
We present a framework for characterizing the spatiotemporal power spectrum of the variability expected from the horizon-scale emission structure around supermassive black holes, and we apply this framework to a library of general relativistic magnetohydrodynamic (GRMHD) simulations and associated general relativistic ray-traced images relevant for Event Horizon Telescope (EHT) observations of Sgr A*. We find that the variability power spectrum is generically a red-noise process in both the temporal and spatial dimensions, with the peak in power occurring on the longest timescales and largest spatial scales. When both the time-averaged source structure and the spatially integrated light-curve variability are removed, the residual power spectrum exhibits a universal broken power-law behavior. On small spatial frequencies, the residual power spectrum rises as the square of the spatial frequency and is proportional to the variance in the centroid of emission. Beyond some peak in variability power, the residual power spectrum falls as that of the time-averaged source structure, which is similar across simulations; this behavior can be naturally explained if the variability arises from a multiplicative random field that has a steeper high-frequency power-law index than that of the time-averaged source structure. We briefly explore the ability of power spectral variability studies to constrain physical parameters relevant for the GRMHD simulations, which can be scaled to provide predictions for black holes in a range of systems in the optically thin regime. We present specific expectations for the behavior of the M87* and Sgr A* accretion flows as observed by the EHT
Familial hypercholesterolaemia in children and adolescents from 48 countries: a cross-sectional study
Background: Approximately 450 000 children are born with familial hypercholesterolaemia worldwide every year, yet only 2·1% of adults with familial hypercholesterolaemia were diagnosed before age 18 years via current diagnostic approaches, which are derived from observations in adults. We aimed to characterise children and adolescents with heterozygous familial hypercholesterolaemia (HeFH) and understand current approaches to the identification and management of familial hypercholesterolaemia to inform future public health strategies. Methods: For this cross-sectional study, we assessed children and adolescents younger than 18 years with a clinical or genetic diagnosis of HeFH at the time of entry into the Familial Hypercholesterolaemia Studies Collaboration (FHSC) registry between Oct 1, 2015, and Jan 31, 2021. Data in the registry were collected from 55 regional or national registries in 48 countries. Diagnoses relying on self-reported history of familial hypercholesterolaemia and suspected secondary hypercholesterolaemia were excluded from the registry; people with untreated LDL cholesterol (LDL-C) of at least 13·0 mmol/L were excluded from this study. Data were assessed overall and by WHO region, World Bank country income status, age, diagnostic criteria, and index-case status. The main outcome of this study was to assess current identification and management of children and adolescents with familial hypercholesterolaemia. Findings: Of 63 093 individuals in the FHSC registry, 11 848 (18·8%) were children or adolescents younger than 18 years with HeFH and were included in this study; 5756 (50·2%) of 11 476 included individuals were female and 5720 (49·8%) were male. Sex data were missing for 372 (3·1%) of 11 848 individuals. Median age at registry entry was 9·6 years (IQR 5·8-13·2). 10 099 (89·9%) of 11 235 included individuals had a final genetically confirmed diagnosis of familial hypercholesterolaemia and 1136 (10·1%) had a clinical diagnosis. Genetically confirmed diagnosis data or clinical diagnosis data were missing for 613 (5·2%) of 11 848 individuals. Genetic diagnosis was more common in children and adolescents from high-income countries (9427 [92·4%] of 10 202) than in children and adolescents from non-high-income countries (199 [48·0%] of 415). 3414 (31·6%) of 10 804 children or adolescents were index cases. Familial-hypercholesterolaemia-related physical signs, cardiovascular risk factors, and cardiovascular disease were uncommon, but were more common in non-high-income countries. 7557 (72·4%) of 10 428 included children or adolescents were not taking lipid-lowering medication (LLM) and had a median LDL-C of 5·00 mmol/L (IQR 4·05-6·08). Compared with genetic diagnosis, the use of unadapted clinical criteria intended for use in adults and reliant on more extreme phenotypes could result in 50-75% of children and adolescents with familial hypercholesterolaemia not being identified. Interpretation: Clinical characteristics observed in adults with familial hypercholesterolaemia are uncommon in children and adolescents with familial hypercholesterolaemia, hence detection in this age group relies on measurement of LDL-C and genetic confirmation. Where genetic testing is unavailable, increased availability and use of LDL-C measurements in the first few years of life could help reduce the current gap between prevalence and detection, enabling increased use of combination LLM to reach recommended LDL-C targets early in life
Resolving the inner parsec of the blazar J1924–2914 with the Event Horizon Telescope
Rest of authors: Ikeda, Shiro; Impellizzeri, C. M. Violette; Inoue, Makoto; James, David J.; Jannuzi, Buell T.; Jeter, Britton; Jiang, Wu; Jimenez-Rosales, Alejandra; Johnson, Michael D.; Joshi, Abhishek, V; Jung, Taehyun; Karami, Mansour; Karuppusamy, Ramesh; Kawashima, Tomohisa; Keating, Garrett K.; Kettenis, Mark; Kim, Dong-Jin; Kim, Jae-Young; Kim, Jongsoo; Kim, Junhan; Kino, Motoki; Koay, Jun Yi; Kocherlakota, Prashant; Kofuji, Yutaro; Koch, Patrick M.; Koyama, Shoko; Kramer, Carsten; Kramer, Michael; Kuo, Cheng-Yu; La Bella, Noemi; Lauer, Tod R.; Lee, Daeyoung; Lee, Sang-Sung; Leung, Po Kin; Levis, Aviad; Li, Zhiyuan; Lindahl, Greg; Lindqvist, Michael; Liu, Kuo; Liuzzo, Elisabetta; Lo, Wen-Ping; Lobanov, Andrei P.; Lonsdale, Colin; Mao, Jirong; Marchili, Nicola; Markoff, Sera; Marrone, Daniel P.; Marscher, Alan P.; Matsushita, Satoki; Matthews, Lynn D.; Medeiros, Lia; Menten, Karl M.; Michalik, Daniel; Mizuno, Izumi; Mizuno, Yosuke; Moran, James M.; Mueller, Cornelia; Mus, Alejandro; Musoke, Gibwa; Myserlis, Ioannis; Nadolski, Andrew; Nagai, Hiroshi; Nagar, Neil M.; Nakamura, Masanori; Narayan, Ramesh; Narayanan, Gopal; Natarajan, Iniyan; Nathanail, Antonios; Neilsen, Joey; Neri, Roberto; Ni, Chunchong; Noutsos, Aristeidis; Nowak, Michael A.; Oh, Junghwan; Okino, Hiroki; Olivares, Hector; Ortiz-Leon, Gisela N.; Oyama, Tomoaki; Ozel, Feryal; Palumbo, Daniel C. M.; Paraschos, Georgios Filippos; Park, Jongho; Parsons, Harriet; Patel, Nimesh; Pen, Ue-Li; Pietu, Vincent; Plambeck, Richard; PopStefanija, Aleksandar; Porth, Oliver; Potzl, Felix M.; Prather, Ben; Preciado-Lopez, Jorge A.; Psaltis, Dimitrios; Pu, Hung-Yi; Rao, Ramprasad; Rawlings, Mark G.; Raymond, Alexander W.; Rezzolla, Luciano; Ricarte, Angelo; Ripperda, Bart; Roelofs, Freek; Rogers, Alan; Ros, Eduardo; Romero-Canizales, Cristina; Roshanineshat, Arash; Rottmann, Helge; Roy, Alan L.; Ruiz, Ignacio; Ruszczyk, Chet; Rygl, Kazi L. J.; Sanchez, Salvador; Sanchez-Arguelles, David; Sanchez-Portal, Miguel; Sasada, Mahito; Satapathy, Kaushik; Savolainen, Tuomas; Schloerb, F. Peter; Schuster, Karl-Friedrich; Shao, Lijing; Shen, Zhiqiang; Small, Des; Sohn, Bong Won; SooHoo, Jason; Souccar, Kamal; Sun, He; Tazaki, Fumie; Tetarenko, Alexandra J.; Tilanus, Remo P. J.; Titus, Michael; Torne, Pablo; Trent, Tyler; Trippe, Sascha; van Bemmel, Ilse; van Langevelde, Huib Jan; van Rossum, Daniel R.; Vos, Jesse; Wagner, Jan; Ward-Thompson, Derek; Wardle, John; Weintroub, Jonathan; Wex, Norbert; Wharton, Robert; Wiik, Kaj; Witzel, Gunther; Wondrak, Michael; Wong, George N.; Wu, Qingwen; Yamaguchi, Paul; Yoon, Doosoo; Young, Andre; Young, Ken; Younsi, Ziri; Yuan, Feng; Yuan, Ye-Fei; Zensus, J. Anton; Zhang, Shuo; Zhao, Shan-Shan.The blazar J1924–2914 is a primary Event Horizon Telescope (EHT) calibrator for the Galactic center’s black hole
Sagittarius A*. Here we present the first total and linearly polarized intensity images of this source obtained with
the unprecedented 20 μas resolution of the EHT. J1924–2914 is a very compact flat-spectrum radio source with
strong optical variability and polarization. In April 2017 the source was observed quasi-simultaneously with the
EHT (April 5–11), the Global Millimeter VLBI Array (April 3), and the Very Long Baseline Array (April 28),
giving a novel view of the source at four observing frequencies, 230, 86, 8.7, and 2.3 GHz. These observations
probe jet properties from the subparsec to 100 pc scales. We combine the multifrequency images of J1924–2914 to
study the source morphology. We find that the jet exhibits a characteristic bending, with a gradual clockwise
rotation of the jet projected position angle of about 90° between 2.3 and 230 GHz. Linearly polarized intensity
images of J1924–2914 with the extremely fine resolution of the EHT provide evidence for ordered toroidal
magnetic fields in the blazar compact core.We thank the anonymous reviewer for their thoughtful and
helpful comments. The Event Horizon Telescope Collaboration
thanks the following organizations and programs: the Academy
of Finland (projects 274477, 284495, 312496, 315721); the
Agencia Nacional de Investigación y Desarrollo (ANID), Chile
via NCN19_058 (TITANs) and Fondecyt 3190878, the
Alexander von Humboldt Stiftung; an Alfred P. Sloan Research
Fellowship; Allegro, the European ALMA Regional Centre
node in the Netherlands, the NL astronomy research network
NOVA and the astronomy institutes of the University of
Amsterdam, Leiden University and Radboud University; the
black hole Initiative at Harvard University, through a grant
(60477) from the John Templeton Foundation; the China Scholarship Council; Consejo Nacional de Ciencia y Tecnología
(CONACYT, Mexico, projects U0004-246083, U0004-
259839, F0003-272050, M0037-279006, F0003-281692,
104497, 275201, 263356); the Delaney Family via the Delaney
Family John A. Wheeler Chair at Perimeter Institute; Dirección
General de Asuntos del Personal Académico-Universidad
Nacional Autónoma de México (DGAPA-UNAM, projects
IN112417 and IN112820); the European Research Council
Synergy Grant “BlackHoleCam: Imaging the Event Horizon of
Black Holes” (grant 610058); the Generalitat Valenciana
postdoctoral grant APOSTD/2018/177 and GenT Program
(project CIDEGENT/2018/021); MICINN Research Project
PID2019-108995GB-C22; the Gordon and Betty Moore
Foundation (grant GBMF-3561); the Istituto Nazionale di
Fisica Nucleare (INFN) sezione di Napoli, iniziative specifiche
TEONGRAV; the International Max Planck Research School
for Astronomy and Astrophysics at the Universities of Bonn
and Cologne; Joint Princeton/Flatiron and Joint Columbia/
Flatiron Postdoctoral Fellowships, research at the Flatiron
Institute is supported by the Simons Foundation; the Japanese
Government (Monbukagakusho: MEXT) Scholarship; the
Japan Society for the Promotion of Science (JSPS) Grant-in-
Aid for JSPS Research Fellowship (JP17J08829); the Key
Research Program of Frontier Sciences, Chinese Academy of
Sciences (CAS, grants QYZDJ-SSW-SLH057, QYZDJSSWSYS008,
ZDBS-LY-SLH011); the Leverhulme Trust Early
Career Research Fellowship; the Max-Planck-Gesellschaft (MPG); the Max Planck Partner Group of the MPG and the
CAS; the MEXT/JSPS KAKENHI (grants 18KK0090,
JP18K13594, JP18K03656, JP18H03721, 18K03709,
18H01245, 25120007); the Malaysian Fundamental Research
Grant Scheme (FRGS) FRGS/1/2019/STG02/UM/02/6; the
MIT International Science and Technology Initiatives (MISTI)
Funds; the Ministry of Science and Technology (MOST) of
Taiwan (105-2112-M-001-025-MY3, 106-2112-M-001-011,
106-2119- M-001-027, 107-2119-M-001-017, 107-2119-M-
001-020, 107-2119-M-110-005, 108-2112-M-001-048, and
109-2124-M-001-005); the National Aeronautics and Space
Administration (NASA, Fermi Guest Investigator grant
80NSSC20K1567, NASA Astrophysics Theory Program grant
80NSSC20K0527, NASA NuSTAR award 80NSSC20K0645);
the National Institute of Natural Sciences (NINS) of Japan; the
National Key Research and Development Program of China
(grant 2016YFA0400704, 2016YFA0400702); the National
Science Foundation (NSF, grants AST-0096454, AST-
0352953, AST-0521233, AST-0705062, AST-0905844, AST-
0922984, AST-1126433, AST-1140030, DGE-1144085, AST-
1207704, AST-1207730, AST-1207752, MRI-1228509, OPP-
1248097, AST-1310896, AST-1555365,AST-1615796, AST-
1715061, AST-1716327, AST-1903847,AST-2034306); the
Natural Science Foundation of China (grants 11573051,
11633006, 11650110427, 10625314, 11721303, 11725312,
11933007, 11991052, 11991053); a fellowship of China
Postdoctoral Science Foundation (2020M671266); the Natural Sciences and Engineering Research Council of Canada
(NSERC, including a Discovery Grant and the NSERC
Alexander Graham Bell Canada Graduate Scholarships-Doctoral
Program); the National Youth Thousand Talents Program
of China; the National Research Foundation of Korea (the
Global PhD Fellowship Grant: grants NRF-
2015H1A2A1033752, 2015- R1D1A1A01056807, the Korea
Research Fellowship Program: NRF-2015H1D3A1066561, Basic Research Support Grant 2019R1F1A1059721); the
Netherlands Organization for Scientific Research (NWO) VICI
award (grant 639.043.513) and Spinoza Prize SPI 78-409; the
New Scientific Frontiers with Precision Radio Interferometry
Fellowship awarded by the South African Radio Astronomy
Observatory (SARAO), which is a facility of the National
Research Foundation (NRF), an agency of the Department of
Science and Technology (DST) of South Africa; the Onsala
Space Observatory (OSO) national infrastructure, for the
provisioning of its facilities/observational support (OSO
receives funding through the Swedish Research Council under
grant 2017-00648) the Perimeter Institute for Theoretical
Physics (research at Perimeter Institute is supported by the
Government of Canada through the Department of Innovation,
Science and Economic Development and by the Province of
Ontario through the Ministry of Research, Innovation and
Science); the Spanish Ministerio de Economía y Competitividad
(grants PGC2018-098915-B-C21, AYA2016-80889-P,
PID2019-108995GB-C21); the State Agency for Research of
the Spanish MCIU through the “Center of Excellence Severo
Ochoa” award for the Instituto de Astrofísica de Andalucía
(SEV-2017-0709); the Toray Science Foundation; the Consejería
de Economía, Conocimiento, Empresas y Universidad of the
Junta de Andalucía (grant P18-FR-1769), the Consejo Superior
de Investigaciones Científicas (grant 2019AEP112); the US
Department of Energy (USDOE) through the Los Alamos
National Laboratory (operated by Triad National Security, LLC,
for the National Nuclear Security Administration of the USDOE
(Contract 89233218CNA000001); the European Unionʼs Horizon
2020 research and innovation program under grant
agreement No 730562 RadioNet; ALMA North America
Development Fund; the Academia Sinica; Chandra DD7-
18089X and TM6-17006X; the GenT Program (Generalitat
Valenciana) Project CIDEGENT/2018/021. This work used the
Extreme Science and Engineering Discovery Environment
(XSEDE), supported by NSF grant ACI-1548562, and CyVerse,
supported by NSF grants DBI-0735191, DBI-1265383, and
DBI-1743442. XSEDE Stampede2 resource at TACC was
allocated through TG-AST170024 and TG-AST080026N.
XSEDE JetStream resource at PTI and TACC was allocated
through AST170028. The simulations were performed in part on
the SuperMUC cluster at the LRZ in Garching, on the LOEWE
cluster in CSC in Frankfurt, and on the HazelHen cluster at the
HLRS in Stuttgart. This research was enabled in part by support
provided by Compute Ontario (http://computeontario.ca),
Calcul Quebec (http://www.calculquebec.ca) and Compute
Canada (http://www.computecanada.ca). We thank the staff at
the participating observatories, correlation centers, and institutions
for their enthusiastic support. This paper makes use of the
following ALMA data: ADS/JAO.ALMA#2016.1.01154.V
and ADS/JAO.ALMA2016.1.00413.V. ALMA is a partnership
of the European Southern Observatory (ESO; Europe, representing
its member states), NSF, and National Institutes of Natural
Sciences of Japan, together with National Research Council
(Canada), Ministry of Science and Technology (MOST;
Taiwan), Academia Sinica Institute of Astronomy and Astrophysics
(ASIAA; Taiwan), and Korea Astronomy and Space
Science Institute (KASI; Republic of Korea), in cooperationwith
the Republic of Chile. The Joint ALMA Observatory is operated
by ESO, Associated Universities, Inc. (AUI)/NRAO, and the
National Astronomical Observatory of Japan (NAOJ). The
NRAO is a facility of the NSF operated under cooperative
agreement by AUI. APEX is a collaboration between the Max-
Planck-Institut für Radioastronomie (Germany), ESO, and the
Onsala Space Observatory (Sweden). The SMA is a joint project
between the SAO and ASIAA and is funded by the Smithsonian
Institution and the Academia Sinica. The JCMT is operated by
the East Asian Observatory on behalf of the NAOJ, ASIAA, and
KASI, as well as the Ministry of Finance of China, Chinese
Academy of Sciences, and the National Key R&D Program (No.
2017YFA0402700) of China. Additional funding support for the
JCMT is provided by the Science and Technologies Facility
Council (UK) and participating universities in the UK and
Canada. The LMT is a project operated by the Instituto Nacional
de Astrófisica, Óptica, y Electrónica (Mexico) and the University
of Massachusetts at Amherst (USA). The IRAM 30 m telescope
on Pico Veleta, Spain is operated by IRAM and supported by
CNRS (Centre National de la Recherche Scientifique, France),
MPG (Max-Planck- Gesellschaft, Germany) and IGN (Instituto
Geográfico Nacional, Spain). The SMT is operated by the
Arizona Radio Observatory, a part of the Steward Observatory
of the University of Arizona, with financial support of operations
from the State of Arizona and financial support for instrumentation
development from the NSF. Support for SPT participation in
the EHT is provided by the National Science Foundation
through award OPP-1852617 to the University of Chicago.
Partial support is also provided by the Kavli Institute of
Cosmological Physics at the University of Chicago. The SPT
hydrogen maser was provided on loan from the GLT, courtesy
of ASIAA. The EHTC has received generous donations of
FPGA chips from Xilinx Inc., under the Xilinx University
Program. The EHTC has benefited from technology shared under open-source license by the Collaboration for Astronomy
Signal Processing and Electronics Research (CASPER). The
EHT project is grateful to T4Science and Microsemi for their
assistance with Hydrogen Masers. This research has made use of
NASAʼs Astrophysics Data System. We gratefully acknowledge
the support provided by the extended staff of the ALMA, both
from the inception of the ALMA Phasing Project through the
observational campaigns of 2017 and 2018. We would like to
thank A. Deller and W. Brisken for EHT-specific support with
the use of DiFX. We acknowledge the significance that
Maunakea, where the SMA and JCMT EHT stations are located,
has for the indigenous Hawaiian people.
We also thank Alexandra Elbakyan for her contributions to
the open science initiative. This research has made use of data
obtained with the Global Millimeter VLBI Array (GMVA),
coordinated by the VLBI group at the Max-Planck-Institut für
Radioastronomie (MPIfR). The GMVA consists of telescopes
operated by MPIfR, IRAM, Onsala, Metsahovi, Yebes, the
Korean VLBI Network, the Green Bank Observatory, and the
Very Long Baseline Array (VLBA). The VLBA and the GBT
are facilities of the National Science Foundation under
cooperative agreement by Associated Universities, Inc. The
data were correlated at the DiFX correlator of the MPIfR in
Bonn, Germany. We thank the National Science Foundation
(awards OISE-1743747, AST-1816420, AST-1716536, AST-
1440254, AST-1935980) and the Gordon and Betty Moore
Foundation (GBMF-5278) for financial support of this work.
Support for this work was also provided by the NASA Hubble
Fellowship grant HST-HF2-51431.001-A awarded by the
Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc.,
for NASA, under contract NAS5-26555.http://iopscience.iop.org/0004-637Xam2023Physic
Broadband multi-wavelength properties of M87 during the 2017 Event Horizon Telescope campaign
In 2017, the Event Horizon Telescope (EHT) Collaboration succeeded in capturing the first direct image of the
center of the M87 galaxy. The asymmetric ring morphology and size are consistent with theoretical expectations
for a weakly accreting supermassive black hole of mass ∼6.5 × 109Me. The EHTC also partnered with several
international facilities in space and on the ground, to arrange an extensive, quasi-simultaneous multi-wavelength
campaign. This Letter presents the results and analysis of this campaign, as well as the multi-wavelength data as a
legacy data repository. We captured M87 in a historically low state, and the core flux dominates over HST-1 at
high energies, making it possible to combine core flux constraints with the more spatially precise very long
baseline interferometry data. We present the most complete simultaneous multi-wavelength spectrum of the active
nucleus to date, and discuss the complexity and caveats of combining data from different spatial scales into one
broadband spectrum. We apply two heuristic, isotropic leptonic single-zone models to provide insight into the
basic source properties, but conclude that a structured jet is necessary to explain M87’s spectrum. We can exclude
that the simultaneous γ-ray emission is produced via inverse Compton emission in the same region producing the
EHT mm-band emission, and further conclude that the γ-rays can only be produced in the inner jets (inward of
HST-1) if there are strongly particle-dominated regions. Direct synchrotron emission from accelerated protons and
secondaries cannot yet be excluded.http://iopscience.iop.org/2041-8205am2022Physic
Selective dynamical imaging of interferometric data
Recent developments in very long baseline interferometry (VLBI) have made it possible for the Event Horizon
Telescope (EHT) to resolve the innermost accretion flows of the largest supermassive black holes on the sky. The
sparse nature of the EHT’s (u, v)-coverage presents a challenge when attempting to resolve highly time-variable
sources. We demonstrate that the changing (u, v)-coverage of the EHT can contain regions of time over the course
of a single observation that facilitate dynamical imaging. These optimal time regions typically have projected
baseline distributions that are approximately angularly isotropic and radially homogeneous. We derive a metric of
coverage quality based on baseline isotropy and density that is capable of ranking array configurations by their
ability to produce accurate dynamical reconstructions. We compare this metric to existing metrics in the literature
and investigate their utility by performing dynamical reconstructions on synthetic data from simulated EHT
observations of sources with simple orbital variability. We then use these results to make recommendations for
imaging the 2017 EHT Sgr A* data sethttp://iopscience.iop.org/2041-8205Physic
The Polarized Image of a Synchrotron-emitting Ring of Gas Orbiting a Black Hole
Abstract: Synchrotron radiation from hot gas near a black hole results in a polarized image. The image polarization is determined by effects including the orientation of the magnetic field in the emitting region, relativistic motion of the gas, strong gravitational lensing by the black hole, and parallel transport in the curved spacetime. We explore these effects using a simple model of an axisymmetric, equatorial accretion disk around a Schwarzschild black hole. By using an approximate expression for the null geodesics derived by Beloborodov and conservation of the Walker–Penrose constant, we provide analytic estimates for the image polarization. We test this model using currently favored general relativistic magnetohydrodynamic simulations of M87*, using ring parameters given by the simulations. For a subset of these with modest Faraday effects, we show that the ring model broadly reproduces the polarimetric image morphology. Our model also predicts the polarization evolution for compact flaring regions, such as those observed from Sgr A* with GRAVITY. With suitably chosen parameters, our simple model can reproduce the EVPA pattern and relative polarized intensity in Event Horizon Telescope images of M87*. Under the physically motivated assumption that the magnetic field trails the fluid velocity, this comparison is consistent with the clockwise rotation inferred from total intensity images
- …