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  • richardmitnick 9:46 am on July 1, 2020 Permalink | Reply
    Tags: "Excess neutrinos and missing gamma rays?", , , , , Gamma Rays, , , ,   

    From Pennsylvania State University: “Excess neutrinos and missing gamma rays?” 

    Penn State Bloc

    From Pennsylvania State University

    June 30, 2020
    Sam Sholtis

    Coronae of supermassive black holes may be the hidden sources of mysterious cosmic neutrinos seen on Earth.

    1
    NASA Hubble Space Telescope image of Galaxy NGC 1068 with its active black hole shown as an illustration in the zoomed-in inset. A new model suggests that the corona around such supermassive black holes could be the source of high-energy cosmic neutrinos observed by the IceCube Neutrino Observatory. Image: NASA/JPL-Caltech

    The origin of high-energy cosmic neutrinos observed by the IceCube Neutrino Observatory, whose detector is buried deep in the Antarctic ice, is an enigma that has perplexed physicists and astronomers.

    U Wisconsin ICECUBE neutrino detector at the South Pole

    A new model could help explain the unexpectedly large flux of some of these neutrinos inferred by recent neutrino and gamma-ray data. A paper by Penn State researchers describing the model, which points to the supermassive black holes found at the cores of active galaxies as the sources of these mysterious neutrinos, appears June 30 in the journal Physical Review Letters.

    “Neutrinos are subatomic particles so tiny that their mass is nearly zero and they rarely interact with other matter,” said Kohta Murase, assistant professor of physics and of astronomy and astrophysics at Penn State and a member of Center for Multimessenger Astrophysics in the Institute for Gravitation and the Cosmos (IGC), who led the research. “High-energy cosmic neutrinos are created by energetic cosmic-ray accelerators in the universe, which may be extreme astrophysical objects such as black holes and neutron stars. They must be accompanied by gamma rays or electromagnetic waves at lower energies, and even sometimes gravitational waves. So, we expect the levels of these various ‘cosmic messengers’ that we observe to be related. Interestingly, the IceCube data have indicated an excess emission of neutrinos with energies below 100 teraelectron volt (TeV), compared to the level of corresponding high-energy gamma rays seen by the Fermi Gamma-ray Space Telescope.”

    NASA/Fermi Gamma Ray Space Telescope

    Scientists combine information from all of these cosmic messengers to learn about events in the universe and to reconstruct its evolution in the burgeoning field of “multimessenger astrophysics.” For extreme cosmic events, like massive stellar explosions and jets from supermassive black holes, that create neutrinos, this approach has helped astronomers pinpoint the distant sources and each additional messenger provides additional clues about the details of the phenomena.

    For cosmic neutrinos above 100 TeV, previous research by the Penn State group [Nature Physics] showed that it is possible to have concordance with high-energy gamma rays and ultra-high-energy cosmic rays which fits with a multimessenger picture. However, there is growing evidence for an excess of neutrinos below 100 TeV, which cannot simply be explained. Very recently, the IceCube Neutrino Observatory reported another excess of high-energy neutrinos in the direction of one of the brightest active galaxies, known as NGC 1068, in the northern sky.

    “We know that the sources of high-energy neutrinos must also create gamma rays, so the question is: Where are these missing gamma rays?” said Murase. “The sources are somehow hidden from our view in high-energy gamma rays, and the energy budget of neutrinos released into the universe is surprisingly large. The best candidates for this type of source have dense environments, where gamma rays would be blocked by their interactions with radiation and matter but neutrinos can readily escape. Our new model shows that supermassive black hole systems are promising sites and the model can explain the neutrinos below 100 TeV with modest energetics requirements.”

    The new model suggests that the corona — the aura of superhot plasma that surrounds stars and other celestial bodies — around supermassive black holes found at the core of galaxies, could be such a source. Analogous to the corona seen in a picture of the Sun during a solar eclipse, astrophysicists believe that black holes have a corona above the rotating disk of material, known as an accretion disk, that forms around the black hole through its gravitational influence. This corona is extremely hot (with a temperature of about one billion degrees kelvin), magnetized, and turbulent. In this environment, particles can be accelerated, which leads to particle collisions that would create neutrinos and gamma rays, but the environment is dense enough to prevent the escape of high-energy gamma rays.

    “The model also predicts electromagnetic counterparts of the neutrino sources in ‘soft’ gamma-rays instead of high-energy gamma rays,” said Murase. “High-energy gamma rays would be blocked but this is not the end of the story. They would eventually be cascaded down to lower energies and released as ‘soft’ gamma rays in the megaelectron volt range, but most of the existing gamma-ray detectors, like the Fermi Gamma-ray Space Telescope, are not tuned to detect them.”

    There are projects under development that are designed specifically to explore such soft gamma-ray emission from space. Furthermore, upcoming and next-generation neutrino detectors, KM3Net in the Mediterranean Sea and IceCube-Gen2 in Antarctica will be more sensitive to the sources.

    Artist’s expression of the KM3NeT neutrino telescope

    IceCube Gen-2 DeepCore anotated

    The promising targets include NGC 1068 in the northern sky, for which the excess neutrino emission was reported, and several of the brightest active galaxies in the southern sky.

    “These new gamma-ray and neutrino detectors will enable deeper searches for multimessenger emission from supermassive black hole coronae,” said Murase. “This will make it possible to critically examine if these sources are responsible for the large flux of mid-energy level neutrinos observed by IceCube as our model predicts.”

    In addition to Murase, the research team at Penn State includes the former IGC fellow Shigeo S. Kimura and Eberly Chair Professor Emeritus Peter Mészáros.

    The Alfred P. Sloan Foundation, the U.S. National Science Foundation, the Japanese Society for the Promotion of Science, NASA, the Penn State Institute for Gravitation and the Cosmos, and the Eberly Foundation funded this work.

    See the full article here .

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    Penn State Campus

    About Penn State

    WHAT WE DO BEST

    We teach students that the real measure of success is what you do to improve the lives of others, and they learn to be hard-working leaders with a global perspective. We conduct research to improve lives. We add millions to the economy through projects in our state and beyond. We help communities by sharing our faculty expertise and research.

    Penn State lives close by no matter where you are. Our campuses are located from one side of Pennsylvania to the other. Through Penn State World Campus, students can take courses and work toward degrees online from anywhere on the globe that has Internet service.

    We support students in many ways, including advising and counseling services for school and life; diversity and inclusion services; social media sites; safety services; and emergency assistance.

    Our network of more than a half-million alumni is accessible to students when they want advice and to learn about job networking and mentor opportunities as well as what to expect in the future. Through our alumni, Penn State lives all over the world.

    The best part of Penn State is our people. Our students, faculty, staff, alumni, and friends in communities near our campuses and across the globe are dedicated to education and fostering a diverse and inclusive environment.

     
  • richardmitnick 2:22 pm on January 31, 2020 Permalink | Reply
    Tags: , , , , Gamma Rays, , The blazar Markarian 501, University of La Laguna (Spain),   

    From University of La Laguna (Spain) via phys.org: “Astronomers investigate broadband variability of the blazar Markarian 501” 

    1

    From University of La Laguna (Spain)

    via


    From phys.org

    January 30, 2020
    Tomasz Nowakowski

    1
    Sloan Digital Sky Survey image of the blazar Markarian 501. Credit: Sloan Digital Sky Survey.

    SDSS Telescope at Apache Point Observatory, near Sunspot NM, USA, Altitude2,788 meters (9,147 ft)

    An international team of astronomers has studied variable broadband emission of the gamma-ray blazar Markarian 501 during a period of its high X-ray activity. The research, published January 21 on the arXiv preprint server [Astronomy & Astrophysics, forthcoming https://doi.org/10.1051/0004-6361/201834603 ], could lend better understanding of emission mechanisms in blazars.

    Blazars are very compact quasars associated with supermassive black holes at the centers of active, giant elliptical galaxies. They belong to a larger group of active galaxies that host active galactic nuclei (AGN), and their characteristic features are relativistic jets pointed almost exactly toward the Earth. Based on their optical emission properties, astronomers divide blazars into two classes: flat-spectrum radio quasars (FSRQs) that feature prominent and broad optical emission lines, and BL Lacertae objects (BL Lacs), which do not.

    Located some 456 million light years away, Markarian 501 (or Mrk 501 for short), is a well-known gamma-ray blazar. It belongs to BL Lacertae objects, and its optical spectra are dominated by the non-thermal continuum from the jet.

    Observations of Mrk 501 conducted in 1996 using the Whipple Observatory have shown that it emits very high-energy (VHE) gamma-rays (over 100 GeV).

    CfA Whipple Observatory, located near Amado, Arizona on the slopes of Mount Hopkins, Altitude 2,606 m (8,550 ft)

    CfA/VERITAS, a major ground-based gamma-ray observatory with an array of four 12m Čerenkov Telescopes for gamma-ray astronomy in the GeV – TeV energy range. Located at Fred Lawrence Whipple Observatory,Mount Hopkins, Arizona, US in AZ, USA, Altitude 2,606 m (8,550 ft)

    So far, it is one of only few VHE objects detectable with currently available telescopes in relatively short time, even during low-state emission periods. This makes Mrk 501 an excellent target for long-term multi-wavelength monitoring.

    So a group of astronomers led by Josefa Becerra Gonzalez of University of La Laguna, Spain, performed an extensive multi-instrument observational campaign to characterize and study the temporal evolution of the broadband emission of Mrk 501, focusing on July 2014, when the source exhibited very high X-ray activity. For this purpose, they employed various space telescopes and ground-based observatories, including the Major Atmospheric Gamma Imaging Čerenkov Telescopes (MAGIC), First G-APD Čerenkov Telescope (FACT), Fermi Gamma-ray Space Telescope and the Neil Gehrels Swift Gamma-ray Burst Observatory.

    MAGIC Čerenkov gamma ray telescope on the Canary island of La Palma, Spain, Altitude 2,200 m (7,200 ft)

    FACT-the first G-APD Čerenkov Telescope on the Canary Island of La Palma, Spain -IOP Science

    NASA/Fermi LAT


    NASA/Fermi Gamma Ray Space Telescope

    NASA Neil Gehrels Swift Observatory

    “We presented observational and theoretical results derived with multi-instrument data from Mrk 501 collected during a two-week period in July 2014, when the X-ray activity was at its highest among the 14 years of operation of the Neil Gehrels Swift Gamma-ray Burst Observatory,” the astronomers wrote in the paper.

    In general, the VHE emission from Mrk 501 was found to be elevated during the X-ray outburst of July 2014, with a gamma-ray flux above 0.15 TeV. During this two-week period, the flux variations in the radio, optical, and GeV bands were found to be mild, but quite substantial in the X-ray bands, and especially substantial in the VHE bands (the VHE variability was identified to be twice as large as the X-ray variability).

    A detailed study of the temporal evolution of the broadband spectral energy distribution (SED) during the outburst period has been performed. The results show that the daily evolution of X-ray and gamma-ray bands could be well described with a one-zone synchrotron self-Compton (SSC) model with variations in the break energy of the electron energy distribution (EED), and with some adjustments in the magnetic field strength and spectral shape of the EED.

    Taking these results into account, the astronomers concluded that the variations in the broadband emission of the studied blazar may be due to changes in the acceleration and cooling of the electrons in the shock in jet model.

    Moreover, a narrow feature was identified at about 3.0 TeV in the VHE gamma-ray spectrum from the MAGIC telescopes. The authors of the paper presented some scenarios that may explain the nature of this feature, however further studies are needed to confirm which one is the most plausible.

    “We investigated three theoretical scenarios that could reproduce it: a) pileup in the electron energy distribution due to stochastic acceleration; b) a structured jet with two-SSC emitting regions (related or not related), with one region dominated by an extremely narrow electron energy distribution; and c) an emission produced via an IC [inverse Compton] pair cascade induced by electrons accelerated in a magnetospheric vacuum gap, in addition to the SSC emission from a more conventional region along the jet of Mrk 501,” the researchers concluded.

    See the full article here .

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    About Science X in 100 words
    Science X™ is a leading web-based science, research and technology news service which covers a full range of topics. These include physics, earth science, medicine, nanotechnology, electronics, space, biology, chemistry, computer sciences, engineering, mathematics and other sciences and technologies. Launched in 2004 (Physorg.com), Science X’s readership has grown steadily to include 5 million scientists, researchers, and engineers every month. Science X publishes approximately 200 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide. Science X community members enjoy access to many personalized features such as social networking, a personal home page set-up, article comments and ranking, the ability to save favorite articles, a daily newsletter, and other options.
    Mission 12 reasons for reading daily news on Science X Organization Key editors and writersinclude 1.75 million scientists, researchers, and engineers every month. Phys.org publishes approximately 100 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide. Quancast 2009 includes Phys.org in its list of the Global Top 2,000 Websites. Phys.org community members enjoy access to many personalized features such as social networking, a personal home page set-up, RSS/XML feeds, article comments and ranking, the ability to save favorite articles, a daily newsletter, and other options.

    History

    The Universidad de La Laguna (ULL) is the oldest institution of higher education learning in the Canary Islands, and it is possible to trace its history back more than 200 years. Its founding decree, signed by King Charles IV of Spain, is dated the 11th March 1792. Since that date, it has undergone changes and been known by different names until finally being given its current name in 1913.

    Two hundred years after it was founded, the Universidad de La Laguna continues to be a beacon for society in the Canary Islands that, using the Atlantic as a bridge, has stretched out its hand to the rest of the world. Currently, this public institution is home to more than 25,000 individuals who are either students, academic or research staff, or administrative staff and service personnel.

    The university’s course catalogue includes: 45 undergraduate degrees; 21 official graduate courses in the process of being phased out and 30 official master’s degrees; 52 doctoral programs; and 25 master’s degrees unique to this university. In addition, 17,813 students are currently enrolled in degrees, and 2918 in courses in the process of being phased out.

    The ULL is now undergoing internal restructuring to revamp its offerings. It has placed particular emphasis on the use of new information and communication technologies and telematics programs throughout the institution. All the activities being run under this initiative have been centralized under the control of the Virtual Teaching Unit (Unidad de Docencia Virtual).

    The geographical position of Canary Islands in the Atlantic region places them between three continents, which means that, from a strategic point of view, the universities located on the islands are well placed to become important hubs of reference and flagships of knowledge and learning in the Atlantic.

     
  • richardmitnick 10:07 am on January 15, 2020 Permalink | Reply
    Tags: "Galactic gamma-ray sources reveal birthplaces of high-energy particles", , Gamma Rays, Joint US-Mexico-European HAWC Observatory, , , ,   

    From Los Alamos National Laboratory: “Galactic gamma-ray sources reveal birthplaces of high-energy particles” 

    LANL bloc

    From Los Alamos National Laboratory

    Jan. 14, 2020
    ames Riordon
    Communications Office
    (505) 667-3272
    riordon@lanl.gov

    Researchers with the joint US-Mexico-European HAWC Observatory have identified a host of galactic sources of super-high-energy gamma rays.

    HAWC High Altitude Čerenkov Experiment, a
    US Mexico Europe collaboration located on the flanks of the Sierra Negra volcano in the Mexican state of Puebla at an altitude of 4100 meters(13,500ft), at WikiMiniAtlas 18°59′41″N 97°18′30.6″W. searches for cosmic rays

    1
    A map of the galactic plane indicates the highest energy gamma ray sources yet discovered. The sources comprise a new catalog compiled by the members of the High Altitude Water Čerenkov Observatory collaboration.

    Nine sources of extremely high-energy gamma rays comprise a new catalog compiled by researchers with the High-Altitude Water Čerenkov (HAWC) Gamma-Ray Observatory. All produce gamma rays with energies over 56 trillion electron volts (TeV) and three emit gamma rays extending to 100 TeV and beyond, making these the highest-energy sources ever observed in our galaxy. The catalog helps to explain where the particles originate and how they are accelerated to such extremes.

    “The Earth is constantly being bombarded with charged particles called cosmic rays, but because they are charged, they bend in magnetic fields and don’t point back to their sources. We rely on gamma rays, which are produced close to the sources of the cosmic rays, to narrow down their origins,” said Kelly Malone, an astrophysicist in the Neutron Science and Technology group at Los Alamos National Laboratory and a member of the HAWC scientific collaboration. “There are still many unanswered questions about cosmic-ray origins and acceleration. High energy gamma rays are produced near cosmic-ray sites and can be used to probe cosmic-ray acceleration. However, there is some ambiguity in using gamma rays to study this, as high-energy gamma rays can also be produced via other mechanisms, such as lower-energy photons scattering off of electrons, which commonly occurs near pulsars.”


    Newly Discovered Gamma Ray Sources Have the Highest Energy Ever Recorded.

    The newly cataloged astrophysical gamma-ray sources have energies about 10 times higher than can be produced using experimental particle colliders on Earth. While higher-energy astrophysical particles have been previously detected, this is the first time specific galactic sources have been pinpointed. All of the sources have extremely energetic pulsars (highly magnetized rotating neutron stars) nearby. The number of sources detected may indicate that ultra-high-energy emission is a generic feature of powerful particle winds coming from pulsars embedded in interstellar gas clouds known as nebulae, and that more detections will be forthcoming.

    The HAWC Gamma-Ray Observatory consists of an array of water-filled tanks sitting high on the slopes of the Sierra Negra volcano in Puebla, Mexico, where the atmosphere is thin and offers better conditions for observing gamma rays. When these gamma rays strike molecules in the atmosphere they produce showers of energetic particles. Although nothing can travel faster than the speed of light in a vacuum, light moves more slowly through water. As a result, some particles in cosmic ray showers travel faster than light in the water inside the HAWC detector tanks. The faster-than-light particles, in turn, produce characteristic flashes of light called Čerenkov radiation. By recording the Čerenkov flashes in the HAWC water tanks, researchers can reconstruct the sources of the particle showers to learn about the particles that caused them in the first place.

    The HAWC collaborators plan to continue searching for the sources of high-energy cosmic rays. By combining their data with measurements from other types of observatories such as neutrino, x-ray, radio and optical telescopes, they hope to disentangle the astrophysical mechanisms that produce the cosmic rays that continuously rain down on our planet.

    Science paper:
    Multiple Galactic Sources with Emission Above 56 TeV Detected by HAWC
    Physical Review Letters

    See the full article here .

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    Los Alamos National Laboratory’s mission is to solve national security challenges through scientific excellence.

    LANL campus

    Los Alamos National Laboratory, a multidisciplinary research institution engaged in strategic science on behalf of national security, is operated by Los Alamos National Security, LLC, a team composed of Bechtel National, the University of California, The Babcock & Wilcox Company, and URS for the Department of Energy’s National Nuclear Security Administration.

    Los Alamos enhances national security by ensuring the safety and reliability of the U.S. nuclear stockpile, developing technologies to reduce threats from weapons of mass destruction, and solving problems related to energy, environment, infrastructure, health, and global security concerns.

    Operated by Los Alamos National Security, LLC for the U.S. Dept. of Energy’s NNSA

     
  • richardmitnick 2:52 pm on March 20, 2019 Permalink | Reply
    Tags: Arizona, , , Gamma Rays, Muon Hunters 2: Return of the Ring- launches new Zooniverse citizen science project on March 14th 2019., VERITAS (Very Energetic Radiation Imaging Telescope Array System) gamma-ray observatory—a part of the Center for Astrophysics | Harvard & Smithsonian at the Fred Lawrence Whipple Observatory in , Zooniverse- the largest online platform for collaborative volunteer research   

    From Harvard-Smithsonian Center for Astrophysics: “Astrophysicists Once Again Seek Public’s Help to Unmask Muons Disguised as Gamma Rays” 

    Harvard Smithsonian Center for Astrophysics


    From Harvard-Smithsonian Center for Astrophysics

    March 14, 2019

    Amy Oliver
    Public Affairs
    Fred Lawrence Whipple Observatory
    Center for Astrophysics | Harvard & Smithsonian
    amy.oliver@cfa.harvard.edu

    Tyler Jump
    Public Affairs
    Center for Astrophysics | Harvard & Smithsonian
    +1 617-495-7462

    Minneapolis, MN & Amado, AZ –
    Muon Hunters 2: Return of the Ring, launches new Zooniverse citizen science project on March 14th, 2019.

    1
    After achieving highly successful results with their citizen science project, Muon Hunters, in 2017, scientists from the VERITAS (Very Energetic Radiation Imaging Telescope Array System) gamma-ray observatory—a part of the Center for Astrophysics | Harvard & Smithsonian at the Fred Lawrence Whipple Observatory in Amado, Arizona, USA—collaboration are once again asking the public for help in identifying hundreds of thousands of ring patterns produced in the cameras at VERITAS.

    Scientists use VERITAS to study gamma rays—the most energetic radiation in the universe—in order to explore the most exotic and extreme processes and physical conditions in space, like black holes, supernovae, and pulsars.

    Like the original project, Muon Hunters 2: Return of the Ring, will engage citizen scientists to identify patterns from muons—elementary particles like electrons, but heavier—and distinguish them from those produced by gamma rays, which the telescopes are designed to detect.

    “At VERITAS, we’re searching for gamma rays, which have the shortest wavelengths and the highest energy of any portion of the electromagnetic spectrum,” said Dr. Michael Daniel, Operations Manager, VERITAS. Muons are background that we have to get rid of so that we can more easily identify gamma rays, but they’re also useful to help us calibrate our telescopes. That’s where Muon Hunters, and the citizen scientists behind it, come in.”

    New to Muon Hunters 2 is the manner in which data will be presented to citizen scientists. Muon Hunters 2 will present images in a grid pattern, rather than individually, to bring additional efficiency to the project.

    “This time around, we’re trying to make both the project and the telescopes more efficient,” said Dr. Lucy Fortson, University of Minnesota Physics and Astronomy Professor and VERITAS researcher. “We use a machine to help the people work more efficiently and the classifications we get from citizen scientists help the machine to work more efficiently, so it’s a virtuous loop. Scientists will use the images that citizen scientists have identified to better train their computer programs to automatically tell the difference between muons and gamma rays.”

    Muon Hunters 2: The Return of the Ring, is run by Zooniverse, the largest online platform for collaborative volunteer research, in conjunction with VERITAS. Citizen science projects at Zooniverse allow researchers to efficiently and effectively comb through large amounts of complex data utilizing the enthusiastic efforts of millions of volunteers from around the world. Other current Zooniverse projects include Snapshot Safari, in which volunteers identify wildlife to help scientists understand the diversity and dynamics of wildlife populations across the African continent.

    The original Muon Hunters project welcomed 6,107 citizen scientists who made 2,161,338 classifications of 135,000 objects. “We are hoping to have as many, if not more, classifications than we had in the original project,” said Fortson. “The more data we get, the more efficient we can be, and that’s great for both the scientists and the machines.”

    Citizen scientists can become Muon Hunters here.

    About VERITAS

    VERITAS (Very Energetic Radiation Imaging Telescope Array System) is a ground-based array of four, 12-m optical reflectors for gamma-ray astronomy located at the Center for Astrophysics | Harvard & Smithsonian, Fred Lawrence Whipple Observatory in Amado, Arizona. VERITAS detects gamma rays via the extremely brief flashes of blue “Cherenkov” light they create when they are absorbed in the Earth’s atmosphere.

    VERITAS is supported by grants from the U.S. Department of Energy Office of Science, the U.S. National Science Foundation, and the Smithsonian Institution, and by NSERC in Canada.

    The VERITAS Collaboration consists of about 80 scientists from 20 institutions in the United States, Canada, Germany and Ireland.

    For more information about VERITAS visit http://veritas.sao.arizona.edu

    About Muon Hunters

    Muon Hunters is a citizen science-based data collection and identification project led by the University of Minnesota and Zooniverse. The project receives data from VERITAS telescopes and direct support from specific VERITAS collaborating institutions including the University of California-Los Angeles; University of California-Santa Cruz; McGill University, Canada; Deutsches Electron-Synchrotron Laboratory, Berlin, Germany; Barnard College/Columbia University; Cal State University – East Bay; University College Dublin, Ireland; and the Center for Astrophysics | Harvard & Smithsonian. In addition, Muon Hunters is supported by the ASTERICS program of the European Union.

    For more information about Muon Hunters, visit http://www.muonhunters.org

    For more information, contact:
    Dr. Lucy Fortson
    Zooniverse
    lffortson@gmail.com

    See the full article here .


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    The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

     
  • richardmitnick 1:23 pm on September 14, 2018 Permalink | Reply
    Tags: , , Gamma Rays, , ,   

    From Lawrence Berkeley National Lab: “Gamma Rays, Watch Out: There’s a New Detector in Town” 

    Berkeley Logo

    From Lawrence Berkeley National Lab

    September 14, 2018
    Theresa Duque
    tnduque@lbl.gov
    (510) 495-2418

    1
    Heather Crawford and her team of researchers are developing a prototype for an ultrahigh-rate high-purity germanium detector that can count 2 to 5 million gamma rays per second while maintaining high resolution. (Credit: Marilyn Chung/Berkeley Lab)

    Heather Crawford has always had a natural bent for science. When she was a high school student in her native Canada, she took all the science electives within reach without a second thought. She went into college thinking she would study biochemistry, but that all changed when she took her first class in nuclear science – the study of the subatomic world. Her professors noticed her talent for nuclear chemistry, and soon she found herself working as an undergraduate researcher in nuclear science at TRIUMF, the accelerator facility in Vancouver, Canada.

    Today, Crawford is a staff scientist in the Nuclear Science Division at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab). With funding from an Early Career Laboratory Directed Research and Development (LDRD) award announced last year, she and her team of researchers have been developing a prototype for an ultrahigh-rate high-purity germanium (HPGe) detector that can count 2 to 5 million gamma rays per second while maintaining high resolution, allowing them to accurately measure the energy spectrum under extreme conditions. A conventional HPGe detector loses resolution when it goes above 50,000 counts per second.

    Gamma rays hail from nuclear decays and reactions within neutron stars, supernova explosions, and regions around black holes. But they also have origins here on Earth: Gamma rays are generated by radioactive decay, or reactions in nuclear power plants, for example. Their ubiquity thus serves as an all-purpose clue for solving wide-ranging mysteries, from tracking down isotope “fingerprints” of elements in stars, to assessing the impact of a nuclear power plant disaster.

    Crawford said that the ultrafast, high-resolution detector will allow scientists to do more research in less time, collecting gamma-ray statistics at 10 to 100 times the rate previously possible. This opens up new possibilities for gamma-ray spectroscopy in the rarest nuclear systems, such as superheavy elements. “Whenever you’re doing gamma-ray spectroscopy, it’s about resolution and efficiency – ideally, you want an experiment to run for a couple of weeks, not years,” she added.

    With the design for the small yet mighty detector finalized last month – the device measures just 3 inches wide and 3 inches tall – Crawford and her team look forward to testing the prototype, which was fabricated at Berkeley Lab’s Semiconductor Detector Laboratory, as an individual detector, and then moving toward an array.

    “This LDRD gave us a unique opportunity to gain a deeper understanding of how germanium detectors work. Berkeley Lab has always been at the forefront of physics and nuclear science. If our prototype works, we will continue to move forward and push the science of both HPGe detectors and heavy elements,” she said.

    See the full article here .


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    A U.S. Department of Energy National Laboratory Operated by the University of California

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  • richardmitnick 11:53 am on July 12, 2018 Permalink | Reply
    Tags: A cosmic particle spewed from a distant galaxy strikes Earth, , , , , , Gamma Rays, , , , ,   

    From Astronomy Magazine: “A cosmic particle spewed from a distant galaxy strikes Earth” 

    Astronomy magazine

    From Astronomy Magazine

    July 12, 2018
    Michelle Hampson

    The rare detection of a high-energy neutrino hints at how these strange particles are created.

    U Wisconsin ICECUBE neutrino detector at the South Pole



    IceCube Gen-2 DeepCore PINGU annotated

    Four billion years ago, an immense galaxy with a black hole at its heart spewed forth a jet of particles at nearly the speed of light. One of those particles, a neutrino that is just a fraction of the size of a regular atom, traversed across the universe on a collision course for Earth, finally striking the ice sheet of Antarctica last September. Coincidentally, a neutrino detector planted by scientists within the ice recorded the neutrino’s charged interaction with the ice, which resulted in a blue flash of light lasting just a moment. The results are published today in the journal Science.

    This detection marks the second time in history that scientists have pinpointed the origins of a neutrino from outside of our solar system. And it’s the first time they’ve confirmed that neutrinos are created in the supermassive black holes at the centers of galaxies — a somewhat unexpected source.

    Neutrinos are highly energetic particles that rarely ever interact with matter, passing through it as though it weren’t even there. Determining the type of cosmological events that create these particles is critical for understanding the nature of the universe. But the only confirmed source of neutrinos, other than our Sun, is a supernova that was recorded in 1987.

    2
    The most recent Hubble image of SN 1987A, taken in January 2017, captures the glow of hydrogen gas around the supernova remnant.
    NASA, ESA, and R. Kirshner (Harvard-Smithsonian Center for Astrophysics and Gordon and Betty Moore Foundation) and P. Challis (Harvard-Smithsonian Center for Astrophysics)

    Physicists have a number of theories about what sort of astronomical events may create neutrinos, with some suggesting that blazars could be a source. Blazars are massive galaxies with black holes at their center, trying to suck in too much matter at once, causing jets of particles to be ejected outward at incredible speeds. Acting like the giant counterparts to terrestrial particle accelerators, blazar jets are believed to produce cosmic rays that can in turn create neutrinos.

    “This [detection] in particular is a chance of nature,” says Darren Grant, a lead scientist of the team that first discovered the high-energy neutrino, as part of the neutrino detection project IceCube. “There’s a blazar there that just happened to turn on at the right time and we happened to capture it. It’s one of those eureka moments. You hope to experience those a few times in your career and this was one of them, where everything aligned.”

    A cosmic messenger

    On September 22, 2017, the neutrino reached the Antarctica ice sheet, passing by an ice crystal at just the right angle to cause a subatomic particle (called a muon) to be created from the interaction. The resulting blue flash was recorded by one of IceCube’s 5,160 detectors, embedded within the ice. Grant was in the office when the detection occurred. This neutrino was about 300 million times more energetic than those that are emitted by the Sun.

    Grant and his colleague briefly admired the excellent image depicting the trajectory of the muon, which provides basic information necessary to begin tracing back the neutrino’s origin. However, they weren’t overly excited quite yet. His team observes about 10 to 20 high-energy neutrinos each year, but the right combination of events — in space, time and energy, for example — is required to precisely pinpoint the source of the neutrino. Such an alignment had eluded scientists so far. As Grant’s team began their analysis, though, they began to narrow in on a region: an exceptionally bright blazar called TXS 0506+056.

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    IceCube employs more than 5,000 detectors lowered on 86 strings into almost 100 holes in the Antarctic ice.
    NSF / B. Gudbjartsson, IceCube Collaboration

    Upon the detection, an automatic alert was sent to other astronomy teams around the world, which monitor various incoming cosmic signals, such as radio and gamma rays. A few days later a team of scientists using the MAGIC telescope in the Canary Islands responded with some exciting news: the arrival of the neutrino had coincided with a burst of gamma rays – which are extremely energetic photons – also coming from the direction of TXS 0506+056.

    MAGIC Cherenkov gamma ray telescope on the Canary island of La Palma, Spain, Altitude 2,200 m (7,200 ft)

    Other teams analyzing the region following the initial detection observed changes in X-ray emissions and radio signals too. Collectively, the data is a huge step forward for physicists in understanding blazars, and high-energy cosmological events in general.

    John Learned of University of Hawaii, Manoa, who was not involved in the study, says that the data linking the blazar as the source is “overwhelmingly convincing” and he emphasizes the importance of this finding. “This is the realization of many long-standing scientific dreams. Neutrinos at high energies can tell us about the guts of these extremely luminous objects … The implications of the finding are that we are now finally … [able] to see inside the most dense and luminous objects, and to further our grasp of the ‘deus ex machina’ which drives them and powers these awesome phenomena.”

    For example, this detection also provides the first evidence that a blazar can produce the high-energy protons needed to generate neutrinos such as the one IceCube saw.

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    Blazars are active supermassive black holes sucking in immense amounts of material, which form swirling accretion disks and generate high-powered particle jets that churn out particles that astronomers have believed eventually result in neutrinos. DESY, Science Communication Lab

    Sources of high-energy protons also remain largely a mystery, so the identification of one such source is another big step forward for astronomers. “It’s really quite convincing that we’ve unlocked one piece of that puzzle,” says Grant.

    Gems from the past

    And it gets even better. “We looked back at [archival] data [that had been collected since 2010], in the direction of this particular blazar source, and what we discovered was really quite remarkable,” Grant says. A barrage of high-energy neutrinos and gamma rays from TXS 0506+056 reached Earth in late 2014 and early 2015. At the time, IceCube’s real-time alert system was not fully functioning, so other scientific teams were not aware of the detection. But now these previous neutrinos are on scientists’ radar, providing a more long-term glimpse into the life of a blazar.

    “That was really icing on the cake, because what [the archived data indicated] was that the source had been active in neutrinos in the past, and then again, with this very high-energy neutrino in September — those are the pieces that really start to come together, to make a picture of what’s happening there,” explains Grant.

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    The alert IceCube sent once the neutrino’s interaction with the ice was detected resulted in follow-up observations from about 20 Earth- and space-based observatories. This immense effort resulted in the clear identification of a distant blazar as the source of the neutrino — as well as gamma rays, X-rays, radio emission, and optical light.
    Nicolle R. Fuller/NSF/IceCube

    The data also reveal that radio emissions from TXS 0506+056 gradually increased in the 18 months leading up to the September neutrino detection. Greg Sivakoff, an associate professor at the University of Alberta who helped analyze the data, says one possibility is that the black hole began to consume surrounding matter much faster during this time, causing the jet of particles being emitted to speed up. He says, “If the jet gets too fast too quickly, it might run into some of its own material, creating what astronomers call a shock. Shocks have long been used in astronomy to explain how particles are accelerated to high energies. We are not sure that this is the answer yet, but this may be part of the story.”

    Scientists are continuing to monitor TXS 0506+056, hoping to learn more about this colossal event. One team conducted a detailed analysis to determine how far away the blazar is from us, astounded to discover that it is a whopping four billion light years away. While TXS 0506+056 was always considered a bright object in the sky, this luminosity at such a distance makes it one of the brightest objects in the universe. No doubt future studies of this powerful blazar will yield valuable insights into the most energetic events to occur in our universe.

    Learned says, “We are just opening a new door and I would love to be able to say what we shall find beyond. But I guarantee that initiating this new means of observing the universe will bring surprises and new insights. In an extreme analogy it is like asking Galileo what his new astronomical telescope will reveal.”

    See the full article here .
    See also From CfA: VERITAS Supplies Critical Piece to Neutrino Discovery Puzzle


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  • richardmitnick 1:22 pm on June 2, 2018 Permalink | Reply
    Tags: , Gamma Rays, , HESS proves the power of TeV astronomy, MAGIC observatory in the Canary Islands, ,   

    From CERN Courier: “HESS proves the power of TeV astronomy” 


    From CERN Courier

    Jun 1, 2018
    Merlin Kole
    Department of Particle Physics
    University of Geneva.

    1
    Supernova-remnant candidates

    For hundreds of years, discoveries in astronomy were all made in the visible part of the electromagnetic spectrum. This changed in the past century when new objects started being discovered at both longer wavelengths, such as radio, and shorter wavelengths, up to gamma-ray wavelengths corresponding to GeV energies. The 21st century then saw another extension of the range of astronomical observations with the birth of TeV astronomy.

    The High Energy Stereoscopic System (HESS) – an array of five telescopes located in Namibia in operation since 2002 – was the first large ground-based telescope capable of measuring TeV photons (followed shortly afterwards by the MAGIC observatory in the Canary Islands and, later, VERITAS in Arizona).

    HESS Cherenkov Telescope Array, located on the Cranz family farm, Göllschau, in Namibia, altitude, 1,800 m (5,900 ft) near the Gamsberg searches for cosmic rays

    MAGIC Cherenkov gamma ray telescope on the Canary island of La Palma, Spain Altitude 2,200 m (7,200 ft) Edit this at Wikidata

    CfA/VERITAS, a major ground-based gamma-ray observatory with an array of four 12m optical reflectors for gamma-ray astronomy in the GeV – TeV energy range. Located at Fred Lawrence Whipple Observatory in AZ, USA, Altitude 2,606 m (8,550 ft)

    To celebrate its 15th anniversary, the HESS collaboration has published its largest set of scientific results to date in a special edition of Astronomy and Astrophysics. Among them is the detection of three new candidates for supernova remnants that, despite being almost the size of the full Moon on the sky, had thus far escaped detection.

    Supernova remnants are what’s left after massive stars die. They are the prime suspect for producing the bulk of cosmic rays in the Milky Way and are the means by which chemical elements produced by supernovae are spread in the interstellar medium. They are therefore of great interest for different fields in astrophysics.

    HESS observes the Milky Way in the energy range 0.03–100 TeV, but its telescopes do not directly detect TeV photons. Rather, they measure the Cherenkov radiation produced by showers of particles generated when these photons enter Earth’s atmosphere. The energy and direction of the primary TeV photons can then be determined from the shape and direction of the Cherenkov radiation.

    Using the characteristics of known TeV-emitting supernova remnants, such as their shell-like shape, the HESS search revealed three new objects at gamma-ray wavelengths, prompting the team to search for counterparts of these objects in other wavelengths. Only one, called HESS J1534-571 (figure, left), could be connected to a radio source and thus be classified as a supernova remnant. For the two other sources, HESS J1614-518 and HESS J1912+101, no clear counterparts were found. These objects thus remain candidates for supernova remnants.

    The lack of an X-ray counterpart to these sources could have implications for cosmic-ray acceleration mechanisms. The cosmic rays thought to originate from supernova remnants should be directly connected to the production of high-energy photons. If the emission of TeV photons is a result of low-energy photons being scattered by high-energy cosmic-ray electrons originating from a supernova remnant (as described by leptonic emission models), soft X-rays would also be produced while such electrons travelled through magnetic fields around the remnant. The lack of detection of such X-rays could therefore indicate that the TeV photons are not linked to such scattering but are instead associated with the decay of high-energy cosmic-ray pions produced around the remnant, as described by hadronic emission models. Searches in the X-ray band with more sensitive instruments than those available today are required to confirm this possibility and bring deeper insight into the link between supernova remnants and cosmic rays.

    The new supernova-remnant detections by HESS demonstrate the power of TeV astronomy to identify new objects. The latest findings increase the anticipation for a range of discoveries from the future Cherenkov Telescope Array (CTA). With more than 100 telescopes, CTA will be more sensitive to TeV photons than HESS, and it is expected to substantially increase the number of detected supernova remnants in the Milky Way.

    See the full article here. .


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    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS
    CERN ATLAS New

    ALICE
    CERN ALICE New

    CMS
    CERN CMS New

    LHCb
    CERN LHCb New II

    LHC

    CERN LHC Map
    CERN LHC Grand Tunnel

    CERN LHC particles

     
  • richardmitnick 8:26 am on January 11, 2018 Permalink | Reply
    Tags: , , , Comet 41P/Tuttle-Giacobini-Kresák — 41P for short, , Gamma Rays, , Unprecedented slowdown in the rotation of a comet   

    From Orbiter.ch: “NASA’s Newly Renamed Swift Mission Spies a Comet Slowdown” 

    1

    Orbiter.ch

    1.10.18

    NASA Neil Gehrels Swift Observatory

    1
    NASA – Swift Mission patch.

    Observations by NASA’s Swift spacecraft, now renamed the Neil Gehrels Swift Observatory after the mission’s late principal investigator, have captured an unprecedented change in the rotation of a comet. Images taken in May 2017 reveal that comet 41P/Tuttle-Giacobini-Kresák — 41P for short — was spinning three times slower than it was in March, when it was observed by the Discovery Channel Telescope at Lowell Observatory in Arizona.

    The abrupt slowdown is the most dramatic change in a comet’s rotation ever seen.


    Swift Mission Catches a Comet Slowdown. NASA’s Swift satellite detected an unprecedented slowdown in the rotation of comet 41P/Tuttle-Giacobini-Kresák when it passed nearest to Earth in early 2017. Watch to learn more. Video Credits: NASA’s Goddard Space Flight Center.

    “The previous record for a comet spindown went to 103P/Hartley 2, which slowed its rotation from 17 to 19 hours over 90 days,” said Dennis Bodewits, an associate research scientist at the University of Maryland (UMD) in College Park who presented the findings Wednesday, Jan. 10, at the American Astronomical Society (AAS) meeting in Washington. “By contrast, 41P spun down by more than 10 times as much in just 60 days, so both the extent and the rate of this change is something we’ve never seen before.”

    The comet orbits the Sun every 5.4 years, traveling only about as far out as the planet Jupiter, whose gravitational influence is thought to have captured it into its present path. Estimated to be less than 0.9 mile (1.4 kilometers) across, 41P is among the smallest of the family of comets whose orbits are controlled by Jupiter. This small size helps explain how jets on the surface of 41P were able to produce such a dramatic spindown.

    As a comet nears the Sun, increased heating causes its surface ice to change directly to a gas, producing jets that launch dust particles and icy grains into space. This material forms an extended atmosphere, called a coma. Water in the coma quickly breaks up into hydrogen atoms and hydroxyl molecules when exposed to ultraviolet sunlight. Because Swift’s Ultraviolet/Optical Telescope (UVOT) is sensitive to UV light emitted by hydroxyl, it is ideally suited for measuring how comet activity levels evolve throughout the orbit.

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    Image above: On March 14, 2017, two weeks before its closest approach to Earth, comet 41P/Tuttle-Giacobini-Kresák glides beneath the galaxy NGC 3198. The green glow comes from light emitted by diatomic carbon molecules. Image Credits: Copyright 2017 by Chis Schur, used with permission.

    Ground-based observations established the comet’s initial rotational period at about 20 hours in early March 2017 and detected its slowdown later the same month. The comet passed 13.2 million miles (21.2 million km) from Earth on April 1, and eight days later made its closest approach to the Sun. Swift’s UVOT imaged the comet from May 7 to 9, revealing light variations associated with material recently ejected into the coma. These slow changes indicated 41P’s rotation period had more than doubled, to between 46 and 60 hours.

    UVOT-based estimates of 41P’s water production, coupled with the body’s small size, suggest that more than half of its surface area contains sunlight-activated jets. That’s a far greater fraction of active real estate than on most comets, which typically support jets over only about 3 percent of their surfaces.

    “We suspect that the jets from the active areas are oriented in a favorable way to produce the torques that slowed 41P’s spin,” said Tony Farnham, a principal research scientist at UMD. “If the torques continued acting after the May observations, 41P’s rotation period could have slowed to 100 hours or more by now.”

    Such a slow spin could make the comet’s rotation unstable, allowing it to begin tumbling with no fixed rotational axis. This would produce a dramatic change in the comet’s seasonal heating. Bodewits and his colleagues note that extrapolating backward suggests the comet was spinning much faster in the past, possibly fast enough to induce landslides or partial fragmentation and exposing fresh ice. Strong outbursts of activity in 1973 and 2001 may be related to 41P’s rotational changes.

    A less extreme relationship between a comet’s shape, activity and spin was previously seen by the European Space Agency’s Rosetta mission, which entered orbit around comet 67P/Churyumov-Gerasimenko in 2014. The comet’s spin sped up by two minutes as it approached the Sun, and then slowed by 20 minutes as it moved farther away. As with 41P, scientists think these changes were produced by the interplay between the comet’s shape and the location and activity of its jets.

    A paper detailing these findings will be published in the journal Nature on Jan. 11.

    NASA’s Swift spacecraft has conducted a broad array of science investigations for 13 years — monitoring comets, studying stars hosting exoplanets, and catching outbursts from supernovas, neutron stars and black holes — and it continues to be fully operational. NASA announced at the AAS meeting that the mission has now been renamed in honor of Neil Gehrels, who helped develop Swift and served as its principal investigator until his death on Feb. 6, 2017.

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    Neil Gehrels

    Neil Gehrels Maniac Lecture, September 29, 2015 [1 hour]

    Video above: Neil Gehrels talks about his adventures in astrophysics in this talk given at NASA’s Goddard Space Flight Center in 2015. Video Credits: NASA’s Goddard Space Flight Center Library.

    Swift’s rapid scheduling capability, plus a trio of telescopes covering optical to gamma-ray wavelengths, continues to deliver important contributions in the study of gamma-ray bursts — the most powerful explosions in the universe — while maintaining a critical role in monitoring how astronomical objects as diverse as comets, stars and galaxies change over time.

    “The Neil Gehrels Swift Observatory is a name that reflects Swift’s current status as the go-to facility for rapid-response, multiwavelength follow-up of time-variable sources,” said Paul Hertz, director of NASA’s Astrophysics Division in Headquarters, Washington. “With Swift, Neil helped usher in the era of time-domain astronomy. He would have been very excited about today’s discovery.”

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    Image above: NASA’s Swift spacecraft, now renamed the Neil Gehrels Swift Observatory after the mission’s late principal investigator, has become the go-to facility for rapid-response, multiwavelength follow-up of time-variable sources. This illustration highlights the diversity of Swift’s work, which ranges from comets in our solar system to observations of variable sources in our galaxy and beyond. Image Credits: NASA’s Goddard Space Flight Center.

    “Swift is still going strong, and we continue to receive four urgent ‘target-of-opportunity’ observing requests from the broader astronomical community each day,” said S. Bradley Cenko, who was recently appointed as the mission’s principal investigator. “Neil’s leadership and vision continue to guide the project, and we can think of no better way to honor this legacy than with the new name.”

    Prof. Neil Gehrels (Future Time Dimension)

    Video above: The Dan David Prize compiled this video tribute to Goddard’s Neil Gehrels, who was posthumously named a 2017 laureate. Video Credits: Dan David Prize.

    Goddard manages the Swift mission in collaboration with Penn State in University Park, the Los Alamos National Laboratory in New Mexico and Orbital Sciences Corp. in Dulles, Virginia. Other partners include the University of Leicester and Mullard Space Science Laboratory in the United Kingdom, Brera Observatory and the Italian Space Agency in Italy.

    Swift Mission Overview

    See the full article here .

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  • richardmitnick 8:55 pm on October 5, 2017 Permalink | Reply
    Tags: , , , , , Crab Pulsar- a fast-rotating neutron star, CTA-Cherenkov Telescope Array, , Gamma Rays,   

    From H.E.S.S.: “The Crab Nebula is Extended” 

    HESS Cherenkov Telescope Array, located on the Cranz family farm, Göllschau, in Namibia, near the Gamsberg

    H.E.S.S.

    October 2017

    The Crab Nebula is one of the best-studied astrophysical objects of all time and shines across the whole accessible electromagnetic spectrum, from radio wavelengths up to very high energy (VHE, E > 100 GeV*) gamma-rays ([1], [2]).

    Supernova remnant Crab nebula. NASA/ESA Hubble

    X-ray picture of Crab pulsar, taken by Chandra

    It is powered by the Crab Pulsar, a fast-rotating neutron star (period P = 33 ms) possessing an ultra-strong magnetic field. It was created during a supernova explosion seen in the constellation Taurus in 1054 A.D. A part of the rotational energy of the Crab Pulsar is converted into electron-positron pairs, forming a pulsar wind. The electrons and positrons are shocked and accelerated to ultra-relativistic energies at the wind termination shock. These high-energy particles propagate outwards and lose energy via the emission of synchrotron and Inverse Compton (IC) radiation resulting from interactions with magnetic and photon fields, respectively. The synchrotron radiation ranges from the radio regime up to around 1 GeV, and its emissivity depends on the density of high-energy particles and the strength of the magnetic field. Thus, the spatial extent of the synchrotron emission is determined by a convolution of the local electron distributions with the magnetic field, where the latter is expected to vary significantly through the nebula. The second important emission mechanism is IC scattering: Energetic electrons and positrons can transfer a fraction of their energy onto photons thereby transforming these to high-energy and VHE gamma-rays. In the case of the Crab Nebula, the dominant target photon field is the synchrotron emission of the nebula itself, generated by the same particle population. This photon field is expected to be more homogeneous than the magnetic field. Thus the IC emission can be taken as a much more reliable tracer of the distribution of relativistic electrons, revealing more about the underlying physics of one of the Milky Way’s most prominent and interesting particle accelerators.

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    Fig 1: Top: Distribution of gamma-ray candidates from the Crab Nebula (Data ON) together with background events (Data OFF) as a function of the squared distance to the source position. The simulated PSF and the PSF convolved with the best-fit Gaussian are shown for comparison as well. Bottom: Significance of the bin-wise deviation (MC – Data) of the measured events when compared to the PSF (black) and the convolved one (orange).

    Until now, the morphology of the Crab Nebula has only been resolved with radio, optical, and X-ray telescopes, up to photon energies of around 80 keV [1,3]; at higher energies, no extension could be measured mainly due to the worse angular resolution of the corresponding instruments. For telescopes like H.E.S.S., the expected size of the Crab Nebula is several times smaller than the point spread function (PSF**). In such a case, the intrinsic extension of the source only leads to a slight broadening of the signal as compared to the PSF, which itself however strongly depends on the actual observation and instrument conditions. For the first time, we employ simulations that take into account all these conditions and thus lead to a considerably improved PSF description [4]. This allows to probe source extensions well below one arcminute***, which corresponds to a new level of resolving source sizes in VHE gamma-ray astronomy.

    Here we used 25.7 hours of high-quality observations of the Crab Nebula, taken with all four of the small telescopes of H.E.S.S. The analysis settings were chosen to achieve a good PSF; for this source and observation conditions, 68% of the gamma-rays from a point source are reconstructed within 0.05° (3 arcminutes) of the source direction.

    The distribution of events from the Crab Nebula as a function of the (squared) distance to the source is shown in Figure 1 (blue crosses). For comparison, the PSF is shown as well (black) and is obviously highly inconsistent with the data, where the probability for consistency of the two distributions amounts to merely around 10-14. The broadening of the data distribution with respect to the PSF can only be explained when assuming an intrinsic source extension. The PSF was iteratively convolved with a Gaussian source model of different width. The extension is obtained by comparing the compatibility of the data and the convolved PSF each time, and the best-fit extension is found to be σCrab = 52.2” ± 2.9” ± 7.8”sys. This Gaussian width σCrab corresponds to 39% source containment. The size of the Crab Nebula in gamma-rays has been measured for the first time and can now be put in context to its morphology seen at other wavelengths.

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    Fig 2: Extension of the Crab Nebula as seen with H.E.S.S. (solid white circles, corresponding to Gaussian width), overplotted on the UV (top) and X-ray (bottom) image. The bright dot in the middle corresponds to emission from the Crab Pulsar, whereas the inner ring around the pulsar that is visible in the X-ray image is supposed to be related to the wind termination shock ([5], [6]). For illustration purposes, the VHE extension circle is centered on the pulsar position.

    Our resulting Gaussian width is overplotted on images of the Crab Nebula at UV wavelengths (λ = 291 nm) and X-ray energies (0.1 – 10 keV) on the top and bottom of Figure 2, respectively. While the gamma-ray extension is obviously small compared to the optical/UV size, it is the other way around when comparing the gamma-ray to X-ray extension. This can be understood when considering the energetics of the electron population responsible for the respective emission.

    The X-ray emission of the Crab Nebula is confined to a smaller region than the UV emission, because the latter is mainly from electrons with E ~ 1 TeV, whereas the former, the X-ray emission, is mainly from electrons with larger energies (~ 10 TeV). Since electrons lose energy more efficiently at higher energies, a shrinking of the pulsar wind nebula with increasing energy is indeed expected. Until now, the window between UV and X-ray energies and the corresponding morphology has never been constrained observationally. Now with our new H.E.S.S. measurement, we are closing that gap by measuring the extension of the IC emission of the Crab Nebula in the range where electrons with energies of several TeV dominate. This naturally explains why the size we obtain lies in between the UV and X-ray extension.

    Resolving the extension of the Crab Nebula with the H.E.S.S. array is a milestone in the study of the gamma-ray sky with Cherenkov telescopes, and demonstrates the power of simulations to characterize the instrument performance, with potential applications for the upcoming CTA era.

    (*) 1 GeV = 109 eV and one eV (abbreviation of electron-volt) is a unit of energy which, by definition, represents the amount of energy gained by an electron when accelerated by an electric potential difference of 1 volt.

    (**) The PSF corresponds to the distribution of reconstructed event directions from a point source. In other words, it describes how a gamma-ray point source appears widened up the instrument.

    (***) One arcminute corresponds to 1/60th of 1°. An arcminute (or 1′) can be further subdivided into 60 arcseconds (60”). 1° thus equals 3600”, making it the angular equivalent of an hour.

    References [sorry, no links]:

    [1] Hester, J. J. The Crab Nebula: An Astrophysical Chimera. ARA&A 46, 127-155 (Sept. 2008)
    [2] Bühler, R. & Blandford, R.: The surprising Crab pulsar and its nebula: a review. Reports on Progress in Physics 77, 066901 (June 2014)
    [3] Madsen et al.: Broadband X-ray Imaging and Spectroscopy of the Crab Nebula and Pulsar with NuStar. ApJ 801, 66 (March 2015)
    [4] Holler et al.: Run-Wise Simulations for Imaging Atmospheric Cherenkov Telescope Arrays. Proceedings of the 35th ICRC, contribution 755 (July 2017)
    [5] Weisskopf et al.: Discovery of Spatial and Spectral Structure in the X-ray Emission from the Crab Nebula. ApJ Letter 536, 81-84 (June 2000)
    [6] Gaensler, B. M. & Slane, P. O.: The Evolution and Structure of Pulsar Wind Nebulae. ARA&A 44, 17-47 (Sept. 2006)

    See the full article here .

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    The High Energy Stereoscopic System

    H.E.S.S. is a system of Imaging Atmospheric Cherenkov Telescopes that investigates cosmic gamma rays in the energy range from 10s of GeV to 10s of TeV. The name H.E.S.S. stands for High Energy Stereoscopic System, and is also intended to pay homage to Victor Hess , who received the Nobel Prize in Physics in 1936 for his discovery of cosmic radiation. The instrument allows scientists to explore gamma-ray sources with intensities at a level of a few thousandths of the flux of the Crab nebula (the brightest steady source of gamma rays in the sky). H.E.S.S. is located in Namibia, near the Gamsberg mountain, an area well known for its excellent optical quality. The first of the four telescopes of Phase I of the H.E.S.S. project went into operation in Summer 2002; all four were operational in December 2003, and were officially inaugurated on September 28, 2004. A much larger fifth telescope – H.E.S.S. II – is operational since July 2012, extending the energy coverage towards lower energies and further improving sensitivity.

    crab
    Crab nebula

     
  • richardmitnick 5:40 am on October 4, 2017 Permalink | Reply
    Tags: , , , , , , , ESA e-ASTROGAM, , Gamma Rays,   

    From astrobites: “Future Gamma-ray Telescopes and the Search for Dark Matter” 

    Astrobites bloc

    Astrobites

    Oct 3, 2017
    Nora Shipp

    Title: Resolving Dark Matter Subhalos With Future Sub-GeV Gamma-Ray Telescopes
    Authors: Ti-Lin Chou, Dimitrios Tanoglidis, and Dan Hooper
    First Author’s Institution: Dept. of Physics, University of Chicago, USA

    Status: Submitted to the Journal of Cosmology and Astroparticle Physics (open access)

    We are surrounded by undetected dark matter.

    Caterpillar Project A Milky-Way-size dark-matter halo and its subhalos circled, an enormous suite of simulations . Griffen et al. 2016

    In fact, our entire Galaxy is enveloped in a large halo of it, but because dark matter does not emit or reflect light, the halo is completely invisible.

    Dark matter halo Image credit: Virgo consortium / A. Amblard / ESA

    Milky Way NASA/JPL-Caltech /ESO R. Hurt

    Inside this halo, orbiting our galaxy, are hundreds of smaller, equally invisible dark matter halos (Figure 1).

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    Figure 1. Galaxies like the Milky Way are surrounded by small dark matter halos (blue blobs). Some of these halos contain no stars, but could still produce gamma-rays from dark matter annihilation! Source: ESO

    The larger ones contain their own dwarf galaxies, but the smallest halos are so tiny that they contain no stars at all. However, if the leading theory of WIMP (Weakly Interacting Massive Particle) dark matter is correct, there is one way that we could actually see these dark matter halos without the help of any stars. If dark matter particles are their own antiparticle, they would annihilate when they come into contact with each other, producing various particles, including highly energetic photons known as gamma-rays.

    Gamma-rays have millions of times more energy than the optical photons that human eyes can see, yet these energetic particles are quite difficult to detect. The current leader in gamma-ray detection is the Fermi Gamma-ray Space Telescope, a satellite that has been orbiting the Earth, searching the sky for gamma-rays, for almost 10 years.

    NASA/Fermi Telescope

    NASA/Fermi LAT

    Since Fermi was first launched, scientists have searched the gamma-ray sky for evidence of dark matter annihilation. What makes this search really tricky is that dark matter is not the only thing that produces gamma-rays. The sky is actually full of gamma-rays coming from all directions, produced by clouds of gas, pulsars, and active galactic nuclei, among many other sources (Figure 2 [not shown in article, replaced here).

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    Fermi’s Latest Gamma-ray Census Highlights Cosmic Mysteries

    However, those tiny dark matter halos that don’t contain stars or gas or any kind of non-dark matter should only be producing gamma-rays from dark matter annihilation. The catch is that we have no idea where these dark matter halos are. Scientists, therefore, have searched all across the sky for gamma-rays that might be coming from dark halos, and they just might have found a couple.

    Two sources of gamma-rays fit all the requirements – they are in the right part of the sky, do not emit any other kind of light (as you’d expect from a halo containing only dark matter), and appear to extend wider across the sky than the single point of a far away star. However, it’s impossible to tell whether these sources are really extended like a dark matter halo or whether they are just two star-like points so close to each other that they blur together, appearing to Fermi as a single blob. Today’s paper considers whether a proposed successor to Fermi called e-ASTROGAM (Figure 3) will be able to resolve the mystery of these gamma-ray blobs.

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    Figure 3. A model of e-Astrogam, one potential successor to the Fermi Gamma-ray Space Telescope. Source: ESA

    Are they in fact dark matter halos (in which case this would be the first confirmed detection of dark matter annihilation!) or are they simply two points blurred into one?

    e-ASTROGAM would be quite similar to Fermi, but with several important changes. The biggest difference is that it would be able to detect gamma-rays at a slightly lower energy than Fermi, giving us a brand new view of the gamma-ray sky. In the context of today’s paper, however, the most significant difference is the angular resolution. Angular resolution determines how close together two objects can get before they blur together into a single blob. The angular resolution of e-ASTROGAM will be about 4-6 times better than Fermi’s in the energy range of these mysterious gamma-ray sources. According to the authors of today’s paper, this should definitely be enough to tell whether they are single extended objects or two independent points that are just too close together for Fermi to see (Figure 4).

    5
    Figure 4. Simulated images of two point sources as seen by Fermi and e-ASTROGAM. On the left, Fermi is unable to distinguish between the two objects, seeing only a single blob of gamma-rays. On the right, e-ASTROGAM, with its superior angular resolution, can tell that the single blob is actually two individual objects. Source: Figure 3 of the paper.

    In order to see just how well e-ASTROGAM will be able to see these objects, the authors modeled fake observations of dark matter annihilation from an extended halo and from two point sources. They determined for different halo sizes and dark matter particles how well e-ASTROGAM will be able to tell whether an object is one extended source or two points. Figure 5 illustrates the difference e-ASTROGAM will make in confirming the nature of these gamma-ray sources. The green and red lines represent how easily Fermi and e-ASTROGAM can distinguish pairs of sources (x-axis) as a function of source brightness (y-axis). e-ASTROGAM reaches much farther along the x-axis, indicating that it can much more easily resolve two point sources. The precise numbers change for different dark matter halos and particles, but in all cases e-ASTROGAM shows a significant improvement over Fermi.

    6
    Figure 5. This plot illustrates how e-ASTROGAM will be able to help distinguish between extended dark matter halos and two nearby points. The y-axis shows how bright the object in question is, and the x-axis is related to how easily the telescope can distinguish between two nearby points and a single extended object. Even with really bright objects Fermi (green) has a hard time distinguishing between the two scenarios, while e-ASTROGAM (red) can more easily tell the difference. Source: Figure 5 of the paper.

    A future gamma-ray telescope like e-ASTROGAM will be an essential tool in determining whether Fermi has in fact detected dark matter annihilation from dark halos. In addition to determining whether the two potential halos detected by Fermi are actually just pairs of close-together point sources, e-ASTROGAM may be able to detect gamma-rays from even more dark matter halos that are too faint for Fermi to observe on its own. e-ASTROGAM with its superior angular resolution and lower energy range would provide a brand new view of the gamma-ray universe, giving us unexpected insight into known and unknown sources of gamma-rays, and perhaps finally revealing the nature of dark matter.

    See the full article here .

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