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  • richardmitnick 8:40 am on March 30, 2017 Permalink | Reply
    Tags: AGN's, , , , , TXS 0828+193, TXS0211−122   

    From Keck and IAC via phys.org: “Expanding super bubble of gas detected around massive black holes in the early universe” 

    Keck Observatory

    Keck Observatory.
    Keck, with Subaru and IRTF (NASA Infrared Telescope Facility). Vadim Kurland

    Keck Observatory


    Instituto de Astrofísica e Ciências do Espaço


    Left – Composite image of a large gas blob of glowing hydrogen gas, shown by a Lyman-alpha optical image (colored yellow) from the Subaru telescope (NAOJ). A galaxy located in the blob is visible in a broadband optical image (white) from the Hubble Space Telescope and an infrared image from the Spitzer Space Telescope (red). Finally, the Chandra X-ray Observatory image in blue shows evidence for a growing supermassive black hole in the center of the galaxy. Radiation and outflows from this active black hole are powerful enough to light up and heat the gas in the blob.

    In a study led by Sandy Morais, a PhD student at Instituto de Astrofísica e Ciências do Espaço and Faculty of Sciences of the University of Porto (FCUP), researchers found massive super bubbles of gas and dust around two distant radio galaxies about 11.5 billion light years away.

    Andrew Humphrey (IA & University of Porto), the leader of the project, commented: “By studying violent galaxies like these, we have gained a new insight into the way supermassive black holes affect the evolution of the galaxies in which they reside.”

    The researchers used two of the largest observatories available today, the Keck II (Hawaii) and the Gran Telescópio de Canárias (GTC), to observe TXS0211−122 and TXS 0828+193, two powerful radio galaxies, harboring the most energetic type of Active Galactic Nuclei (AGN) known. This type of galaxy houses the most massive black holes and have the most powerful continuous energy ejections known.

    The team discovered expanding super bubbles of gas around each of TXS 0211-122 and TXS 0828+193, most likely caused by “feedback” activity whereby the AGN injects vast quantities of energy into its host galaxy, creating a powerful wind that sweeps up gas and dust into an expanding super bubble.

    Study of the symbiosis between the supermassive black hole and the galaxy is a key to understanding the evolution of the most massive galaxies. Ultraviolet emission from the black hole’s accretion disk can inhibit star formation temporarily, by ionizing the Interstellar medium, and the great outflows of gas towards the black hole can lead to permanent inhibition of star formation.

    Schematic of the expanding gas Bubble, over a radio image of the full field of TXS 0828+193. Credit: Morais et al. 2017

    More information: S. G. Morais et al. Ionization and feedback in Lyα haloes around two radio galaxies at∼ 2.5, Monthly Notices of the Royal Astronomical Society (2017). DOI: 10.1093/mnras/stw2926

    See the full article here .

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    To advance the frontiers of astronomy and share our discoveries with the world.

    The W. M. Keck Observatory operates the largest, most scientifically productive telescopes on Earth. The two, 10-meter optical/infrared telescopes on the summit of Mauna Kea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometer and world-leading laser guide star adaptive optics systems. Keck Observatory is a private 501(c) 3 non-profit organization and a scientific partnership of the California Institute of Technology, the University of California and NASA.

    Today Keck Observatory is supported by both public funding sources and private philanthropy. As a 501(c)3, the organization is managed by the California Association for Research in Astronomy (CARA), whose Board of Directors includes representatives from the California Institute of Technology and the University of California, with liaisons to the board from NASA and the Keck Foundation.
    Keck UCal

    Institute of Astrophysics and Space Sciences

    Institute of Astrophysics and Space Sciences (IA) is a new but long anticipated research infrastructure with a national dimension. It embodies a bold but feasible vision for the development of Astronomy, Astrophysics and Space Sciences in Portugal, taking full advantage and fully realizing the potential created by the national membership of the European Space Agency (ESA) and the European Southern Observatory (ESO). IA resulted from the merging the two most prominent research units in the field in Portugal: the Centre for Astrophysics of the University of Porto (CAUP) and the Center for Astronomy and Astrophysics of the University of Lisbon (CAAUL). It currently hosts more than two-thirds of all active researchers working in Space Sciences in Portugal, and is responsible for an even greater fraction of the national productivity in international ISI journals in the area of Space Sciences. This is the scientific area with the highest relative impact factor (1.65 times above the international average) and the field with the highest average number of citations per article for Portugal.

    • RIcardo Reis 5:49 am on March 31, 2017 Permalink | Reply

      This research was NOT made by Instituto de Astrofisica de Canarias in Spain, but by Instituto de Astrofísica e Ciências do Espaço in Portugal.
      In fact, if you check the paper (https://academic.oup.com/mnras/article-lookup/doi/10.1093/mnras/stw2926), this research has no one from IAC.


    • richardmitnick 7:47 am on March 31, 2017 Permalink | Reply

      Thank you very much for the correction. I did not read far enough and got myself stuck in the acronym. I believe that I have sufficiently corrected the post. Please look at it again and let me know what you think.

      Thanks again for your help.


  • richardmitnick 2:02 pm on March 15, 2017 Permalink | Reply
    Tags: , AGN's, , , , Corona and Jet, ,   

    From AAS NOVA: “A Connection Between Corona and Jet” 


    American Astronomical Society

    15 March 2017
    Susanna Kohler

    Artist’s impression of an AGN according to the unified model. Credit: ESA/NASA, the AVO project and Paolo Padovani

    The structure immediately around a supermassive black hole at the heart of an active galaxy can tell us about how material flows in and out of these monsters — but this region is hard to observe! A new study provides us with clues of what might be going on in these active and energetic cores of galaxies.

    In- and Outflows

    In active galactic nuclei (AGN), matter flows both in and out. As material flows toward the black hole via its surrounding accretion disk, much of this gas and dust can then be expelled from the vicinity via highly collimated jets.

    Top: The fraction of X-rays that is reflected decreases as jet power increases. Bottom: the distance between the corona and the reflecting part of the disk increases as jet power increases. [Adapted from King et al. 2017]

    To better understand this symbiosis between accretion and outflows, we examine what’s known as the “corona” — the hot, X-ray-emitting gas that’s located in the closest regions around the black hole. But because the active centers of galaxies are generally obscured by surrounding gas and dust, it’s difficult for us to learn about the structure of these inner regions near the black hole.

    Where are the X-rays of the corona produced: in the inner accretion flow, or at the base of the jet? How far away is this corona from the disk? And how does the corona’s behavior relate to that of the jet?

    Reflected Observations

    To address some of these questions, a group of scientists led by Ashley King (Einstein Fellow at Stanford University) has analyzed X-ray observations from NuSTAR and XMM-Newton of over 40 AGN. The team examined the reflections of the X-rays off of the accretion disk and used two measurements to learn about the structure around the black hole:

    the fraction of the corona’s X-rays that are reflected by the disk, and
    the time lag between the original and reflected X-rays, which reveals the distance from the corona to the reflecting part of the disk.

    A visualization of the authors’ model for an AGN. The accretion disk is red, corona is green, and jet is blue. The corona shines on the disk, causing the inner regions (colored brighter) to fluoresce, “reflecting” the radiation. As the accretion rate increases from the top to the bottom panel, the jet power increases and the dominant reflective part of the disk moves outward due to the ionization of the inner region (which puffs up into a torus). [Adapted from King et al. 2017]

    King and collaborators find two interesting relationships between the corona and the jet: there is an inverse correlation between jet power and reflection fraction, and there is a correlation between jet power and the distance of the corona from the reflecting part of the disk the disk. These observations indicate that there is a relationship between changes in the corona and jet production in AGN.

    Modeling the Corona

    The authors use these observations to build a self-consistent model of an AGN’s corona. In their picture, the corona is located at the base of the jet and moves mildly relativistically away from the disk, propagating into the large-scale jets.

    As the velocity of the corona increases, more of its radiation is relativistically beamed away from the accretion disk, which decreases the fraction of X-rays that are reflected — explaining the inverse correlation between jet power and reflection fraction.

    At the same time, the increased mass accretion further ionizes the inner disk region, pushing the dominant reflection region to further out in the disk — which explains the correlation between jet power and the distance from corona to reflection region.

    King and collaborators show that this model is fully consistent with the X-ray observations of the 40 AGN they examined. Future X-ray observations of the strongest radio jet sources will help us to further pin down what’s happening at the heart of active galaxies.


    Ashley L. King et al 2017 ApJ 835 226. doi:10.3847/1538-4357/835/2/226

    See the full article here .

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  • richardmitnick 3:14 pm on September 5, 2016 Permalink | Reply
    Tags: AGN's, , ,   

    From astrobites: “Making of an Active Galactic Nucleus” 

    Astrobites bloc


    Sep 5, 2016
    Benny Tsang

    Title: Multi-phase Nature of a Radiation-driven Fountain with Nuclear Starburst in a Low-mass Active Galactic Nucleus
    Authors: Keiichi Wada, Marc Schartmann, Rowin Meijerink
    First Author’s Institution: Kagoshima University, Kagoshima 890-0065, Japan
    Status: Accepted for publication in ApJL

    An AGN is the center of a galaxy with a black hole actively feeding on gas while giving out luminous radiation across the electromagnetic spectrum. The color reflects the temperature of the gas/dust around it, red/orange parts are hot and the dark parts are cool. The video starts with a face-on view of a gas disk, followed by an inclined view showing the cold, dusty molecular gas (the clumpy dark lanes) obscuring the central source.

    The traditional unified model of AGN consists of a bright central radiation source surrounded by a donut-shaped dusty torus, as shown schematically in Figure 1. Different types of AGNs could then be understood as models with various jet structures and radiation power levels viewed from different angles. However, recent mid-infrared observations found that in some AGNs dust emission comes from the polar regions, but not from the dusty tori. Since we don’t expect any dust in the polar regions, the traditional picture is therefore shown to be incomplete!

    Figure 1. Schematic representation of the unified AGN model. Various types of AGN can be understood as the result of different viewing angles, whether the central black hole is producing a jet, and the power level of the central source. (Credit: Beckmann & Shrader 2012)

    The dusty-torus picture proves to be very useful in explaining the nature of AGNs. However, no one really understands how these tori come to be and how exactly they determine the AGN properties. The lead author of today’s paper has come up with a model explaining the production of the torus structure, known as the “radiation-driven fountain” model. In this picture, the intense radiation from the central source drives a vertical circulation of gas, naturally creating a thick disk resembling a dusty torus. We will see at the end of this astrobite that this model could produce the polar dust emission unexplained by the traditional model.

    Today’s paper applies the “radiation-driven fountain” model with improved radiation physics to produce synthetic observations of the nearest AGN – the Circinus Galaxy, and compares them with actual observations. In particular, the major improvement is the chemistry of the X-ray dominated regions near the central source, which is crucial in producing reliable synthetic observations. Model parameters are chosen to match those of the Circinus. The simulation starts with a central black hole of 2 million solar masses surrounded by an initially thin gas disk. The radiation from the central regions stirs up and drives a circulation of gas under the gravity of the black hole. Energy input from supernova explosions is also included.

    Figure 2. Density distributions of atomic (upper) and molecular (lower) gas in the radiation-driven fountain model. Left and right panels correspond to face-on and edge-on views, respectively.

    Figure 2 shows the distributions of atomic and molecular gas. On the top right panel we see the edge-on view of the disk. The thickness of the disk is comparable to its diameter, it shows that the fountain flows can indeed produce a geometrically thick disk with hollow cones above and below. This is a big deal because we now have a natural way of getting a structure resembling the traditional dusty torus! Supernova feedback is also shown to be required to maintain the thick disk structure for low-mass AGN like the Circinus. The authors also perform radiation transfer calculations to predict the spectral energy distributions (SEDs) of the Circinus Galaxy. The model-predicted SEDs at different inclination angles (black) are plotted together with the actual observations (blue) in Figure 3. Models with inclination angles greater than 70° match the actual observations quite well. From mid-infrared image of Circinus the inclination angle is inferred to be ~75°, confirming the SED analysis.

    Figure 3. Modeled spectral energy distributions (SEDs) of the Circinus Galaxy at various inclined angles (top to bottom 0°, 30°, 60°, 70°, 80°, 90°).

    Although the model does not provide a full explanation for everything about AGNs, this work is undoubtedly a beautiful attempt at combining advanced theoretical modeling and edge-cutting observations to learn about the nature. For this we are grateful for the authors’ hard work.

    See the full article here .

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    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

  • richardmitnick 10:32 am on July 3, 2016 Permalink | Reply
    Tags: AGN's, , ,   

    From Edinburgh: “Chance microlensing events enable astronomers to probe distant quasars” 


    University of Edinburgh

    Some galaxies pump out vast amounts of energy from a very small volume of space, typically not much bigger than our own solar system. The cores of these galaxies, so-called active galactic nuclei or AGNs, are often hundreds of millions or even billions of light-years away, so are difficult to study in any detail. Natural gravitational ‘microlenses’ can provide a way to probe these objects, and now a team of astronomers have seen hints of the extreme AGN brightness changes that hint at their presence.

    Leading the microlensing work, PhD student Alastair Bruce of the University of Edinburgh presents their work today (1 July) at the National Astronomy Meeting in Nottingham.

    Artist’s rendering of ULAS J1120+0641, a very distant quasar powered by a black hole with a mass two billion times that of the Sun. Natural gravitational ‘microlenses’ can provide a way to probe these objects, and now a team of astronomers have seen hints of quasar brightness changes that hint at their presence. Image credit: ESO/M. Kornmesser.

    The energy output of an AGN (quasars being the most energetic and distant forms of active galactic nuclei) is often equivalent to that of a whole galaxy of stars. This is an output so intense that most astronomers believe only gas falling in towards a supermassive black hole — an object with many millions of times the mass of the Sun — can generate it. As the gas spirals towards the black hole it speeds up and forms a disc, which heats up and releases energy before the gas meets its demise.

    Scientists are particularly interested in seeing what happens to the gas as it approaches the black hole. But studying such small objects at such large distances is tricky, as they simply look like points of light in even the best telescopes. Observations with spectroscopy (where light from an object is dispersed into its component colours) show that fast moving clouds of emitting material surround the disc but the true size of the disc and exact location of the clouds are very difficult to pin down.

    Bruce will describe how astronomers can make use of cosmic coincidences, and benefit from a phenomenon described by Einstein’s general theory of relativity more than a century ago. In his seminal theory, Einstein described how light travels in curved paths under the influence of a gravitational field. So massive objects like black holes, but also planets and stars, can act to bend light from a more distant object, effectively becoming a lens.

    A schematic diagram showing how microlensing affects our view of quasars, the most luminous active galactic nuclei (AGNs). Image credit: Alastair Bruce / University of Edinburgh.

    This means that if a planet or star in an intervening galaxy passes directly between the Earth and a more distant AGN, over a few years or so they act as a lens, focusing and intensifying the signal coming from near the black hole. This type of lensing, due to a single star, is termed microlensing. As the lensing object travels across the AGN, emitting regions are amplified to an extent that depends on their size, providing astronomers with valuable clues.

    Bruce and his team believe they have already seen evidence for two microlensing events associated with AGN. These are well described by a simple model, displaying a single peak and a tenfold increase in brightness over several years. Microlensing in AGNs has been seen before, but only where the presence of the galaxy was already known. Now Bruce and his team are seeing the extreme changes in brightness that signifies the discovery of both previously unknown microlenses and AGNs.

    Bruce says: “Every so often, nature lends astronomers a helping hand and we see a very rare event. It’s remarkable that an unpredictable alignment of objects billions of light-years away could help us probe the surroundings of black holes. In theory, microlensing could even let us see detail in accretion discs and the clouds in their vicinity. We really need to take advantage of these opportunities whenever they arise.”

    There are expected to be fewer than 100 active AGN microlensing events on the sky at any one time, but only some will be at or near their peak brightness. The big hope for the future is the Large Synoptic Survey Telescope (LSST), a project the UK recently joined.

    LSST/Camera, built at SLAC
    LSST Interior
    LSST telescope, currently under construction at Cerro Pachón Chile
    LSST/Camera, built at SLAC;LSST telescope, currently under construction at Cerro Pachón Chile

    From 2019 on, it will survey half the sky every few days, so has the potential to watch the characteristic changes in the appearance of the AGNs as the lensing events take place.

    See the full article here.

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  • richardmitnick 2:17 pm on November 20, 2015 Permalink | Reply
    Tags: AGN's, , , ,   

    From Nautilus: “This Is Why It’s Hard to Recognize a Black Hole” 



    Nov 18, 2015
    Summer Ash

    Black Beauty: The supermassive black hole at the center of this galaxy, around 11 million light years away toward the constellation Centaurus, is currently classified as a quasar. It is roughly 55 million times more massive than our Sun. Its collimated jets, in blue, surpass the diameter of the entire galaxy, extending up to 13,000 light years. The Milky Way, by comparison, is roughly ten times this length. NASA/CXC/CfA/R.Kraft et al.; MPIfR/ESO/APEX/A.Weiss et al.; ESO/WFI.

    Astronomers can sometimes be literal to a fault. We like to call things as we see them. For example, if it’s red and it’s huge: Red Giant. White and small: White Dwarf. Massive explosion: Big Bang. Dark and sucks everything in: Black Hole. Most of the time, classifying objects this way works fine—either it’s new, or it’s something we already know of. But sometimes, as with Pluto, we make new observations that force us to question the name, reassess the object, and identify it differently. You might think this never happens with something as clearly defined as a black hole, but you’d be wrong.

    Though we can’t observe them directly, we can see how the two types of black holes—stellar mass and supermassive—affect their surroundings. Stellar mass black holes, the product of a dying star going supernova and collapsing on itself, are the more familiar, predicted nearly a century ago by [Albert] Einstein’s theory of general relativity; They usually only affect the behavior of the nearest star or two. Supermassive black holes, on the other hand, are over a million times more massive. We still don’t know how these form, but we believe they exist at the center of almost every galaxy, sometimes having the power to alter the appearance of their entire galaxy.

    This capacity for mass distortion makes characterizing supermassive black holes particularly tricky.

    As the stars, gas, and dust in the center of a galaxy get closer and closer to a supermassive black hole, they get packed tighter and tighter into a smaller and smaller space, heating up until, at a critical distance, everything is ripped apart, reduced to atomic particles. When we spot supermassive black holes, it’s this heat radiating away from the orbiting debris—known as an accretion disk—that we actually see, not the black hole itself. Some supermassive black holes “eat” more than others and, in the process, give off significantly more light than their less active brethren. These active galactic nuclei, or AGN for short, are some of the most powerful, most energetic forces in the Universe. Not only do they give off heat, they also often eject material in the form of collimated (beamed) jets, perpendicular to the plane of the disk, which blast their way out of the galaxy’s core—dwarfing in size not just the accretion disk, but also the galaxy itself. What’s more, some AGN have a dusty torus, the geometric equivalent of a donut, in the same plane as their accretion disk, but much, much bigger and thicker. So thick, in fact, that if you looked at them from the side, you wouldn’t see the disk at all, much less the black hole in the center (as seen in the image above).

    Despite having this standard model of an AGN—a supermassive black hole surrounded by an accretion disk with jets streaming out in opposite directions, all encompassed by a dusty torus—making sense of our observations is still a challenge: The light we see doesn’t always paint the same picture. Sometimes we see jets, sometimes we don’t. Sometimes we see the torus, sometimes we don’t. Sometimes we see light so concentrated and bright that we can’t even tell if there’s a galaxy there at all. We label these sightings accordingly: AGN at great distances with cores so bright, they outshine all their stars in optical light, are called quasars (for “quasi-stellar”), like the one pictured above; AGN that glow strongly in the infrared are called Seyferts, after the astronomer Carl Seyfert, who first identified them in 1943; And AGN, with cores and jets whose emitted light dominates in the radio spectrum, are called radio galaxies.

    Resembling a swirling witch’s cauldron of glowing vapors, the black hole-powered core of a nearby active galaxy appears in this colorful NASA Hubble Space Telescope image. The galaxy lies 13 million light-years away in the southern constellation Circinus.
    This galaxy is designated a type 2 Seyfert, a class of mostly spiral galaxies that have compact centers and are believed to contain massive black holes. Seyfert galaxies are themselves part of a larger class of objects called Active Galactic Nuclei or AGN. AGN have the ability to remove gas from the centers of their galaxies by blowing it out into space at phenomenal speeds. Astronomers studying the Circinus galaxy are seeing evidence of a powerful AGN at the center of this galaxy as well.
    Much of the gas in the disk of the Circinus spiral is concentrated in two specific rings — a larger one of diameter 1,300 light-years, which has already been observed by ground-based telescopes, and a previously unseen ring of diameter 260 light-years.
    In the Hubble image, the smaller inner ring is located on the inside of the green disk. The larger outer ring extends off the image and is in the plane of the galaxy’s disk. Both rings are home to large amounts of gas and dust as well as areas of major “starburst” activity, where new stars are rapidly forming on timescales of 40 – 150 million years, much shorter than the age of the entire galaxy.
    At the center of the starburst rings is the Seyfert nucleus, the believed signature of a supermassive black hole that is accreting surrounding gas and dust. The black hole and its accretion disk are expelling gas out of the galaxy’s disk and into its halo (the region above and below the disk). The detailed structure of this gas is seen as magenta-colored streamers extending towards the top of the image.
    In the center of the galaxy and within the inner starburst ring is a V-shaped structure of gas. The structure appears whitish-pink in this composite image, made up of four filters. Two filters capture the narrow lines from atomic transitions in oxygen and hydrogen; two wider filters detect green and near-infrared light. In the narrow-band filters, the V-shaped structure is very pronounced. This region, which is the projection of a three-dimensional cone extending from the nucleus to the galaxy’s halo, contains gas that has been heated by radiation emitted by the accreting black hole. A “counter-cone,” believed to be present, is obscured from view by dust in the galaxy’s disk. Ultraviolet radiation emerging from the central source excites nearby gas causing it to glow. The excited gas is beamed into the oppositely directed cones like two giant searchlights.
    Located near the plane of our own Milky Way Galaxy, the Circinus galaxy is partially hidden by intervening dust along our line of sight. As a result, the galaxy went unnoticed until about 25 years ago. This Hubble image was taken on April 10, 1999 with the Wide Field Planetary Camera 2.
    The research team, led by Andrew S. Wilson of the University of Maryland, is using these visible light images along with near-infrared data to further understand the dynamics of this powerful galaxy.
    Date 10 April 1999

    If they are all fueled by supermassive black holes, why don’t all AGN look the same? One reason could be our point of view. The theory of AGN unification posits that all AGN have the same basic building blocks (accretion disk, jets, torus); The striking differences we observe, according to this theory, are all due to their orientation in space.

    Here on Earth, we only have one vantage point from which to observe the cosmos. We see galaxies randomly distributed around us, some of them edge-on, some of them face-on, and the rest at all the angles in-between. We cannot fly around to look at these galaxies from any other angle than the one they present to us. But with the advent of supercomputers, we can now simulate these galaxies better than ever before and virtually fly around them as much as we like, enjoying the sights from any angle. We can take an AGN and turn it so we’re looking straight down one of the jets, towards the galactic core, making it resemble a blazar, sort of a blazing quasar. Start tilting the AGN until the jet is rotated ninety degrees away from us, and it appears to morph from a blazar to a quasar to, finally, a Seyfert.

    Yet AGN unification is far from a settled problem in astrophysics. There could be other factors at play than just our point of view, like physical processes in and around black holes we don’t fully understand or measurements we haven’t thought to take. As we build better telescopes and amass new data, we can only hope that we’ll see these active galactic nuclei for what they really are. Otherwise, we might need a lot more names.

    See the full article here .

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