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  • richardmitnick 1:22 pm on June 2, 2018 Permalink | Reply
    Tags: , , HESS Cherenkov Telescope Array, 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.

    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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  • richardmitnick 2:58 pm on January 22, 2018 Permalink | Reply
    Tags: "Cosmic messenger" particles, , , , , HESS Cherenkov Telescope Array, , KM3NeT neutrino telescope, , , , , ,   

    From Penn State: “Three types of extreme-energy space particles may have unified origin” 

    Penn State Bloc

    Pennsylvania State University

    22 January 2018
    Kohta Murase
    (+1) 814-863-9594

    Barbara Kennedy (PIO):
    (+1) 814-863-4682

    [ Barbara K. Kennedy ]

    This image illustrates the “multi-messenger” emission from a gigantic reservoir of cosmic rays that are accelerated by powerful jets from a supermassive black hole. Credit: Kanoko Horio.

    One of the biggest mysteries in astroparticle physics has been the origins of ultrahigh-energy cosmic rays, very high-energy neutrinos, and high-energy gamma rays. Now, a new theoretical model reveals that they all could be shot out into space after cosmic rays are accelerated by powerful jets from supermassive black holes and they travel inside clusters and groups of galaxies. It also shows that these space particles could travel inside clusters and groups of galaxies.

    The model explains the natural origins of all three types of “cosmic messenger” particles simultaneously, and is the first astrophysical model of its kind based on detailed numerical computations. A scientific paper that describes this model, produced by Penn State and University of Maryland scientists, will be published as an Advance Online Publication on the website of the journal Nature Physics on January 22, 2018.

    “Our model shows a way to understand why these three types of cosmic messenger particles have a surprisingly similar amount of power input into the universe, despite the fact that they are observed by space-based and ground-based detectors over ten orders of magnitude in individual particle energy,” said Kohta Murase, assistant professor of physics and astronomy and astrophysics at Penn State. “The fact that the measured intensities of very high-energy neutrinos, ultrahigh-energy cosmic rays, and high-energy gamma rays are roughly comparable tempted us to wonder if these extremely energetic particles have some physical connections. The new model suggests that very high-energy neutrinos and high-energy gamma rays are naturally produced via particle collisions as daughter particles of cosmic rays, and thus can inherit the comparable energy budget of their parent particles. It demonstrates that the similar energetics of the three cosmic messengers may not be a mere coincidence.”

    Ultrahigh-energy cosmic rays are the most energetic particles in the universe — each of them carries an energy that is too high to be produced even by the Large Hadron Collider, the most powerful particle accelerator in the world. Neutrinos are mysterious and ghostly particles that hardly ever interact with matter. Very high-energy neutrinos, with energy more than one million mega-electronvolts, have been detected in the IceCube neutrino observatory in Antarctica.

    U Wisconsin IceCube neutrino observatory

    U Wisconsin IceCube experiment at the South Pole

    U Wisconsin ICECUBE neutrino detector at the South Pole

    IceCube Gen-2 DeepCore PINGU

    IceCube reveals interesting high-energy neutrino events

    Gamma rays have the highest-known electromagnetic energy — those with energies more than a billion times higher than a photon of visible light have been observed by the Fermi Gamma-ray Space Telescope and other ground-based observatories.

    NASA/Fermi LAT

    NASA/Fermi Gamma Ray Space Telescope

    “Combining all information on these three types of cosmic messengers is complementary and relevant, and such a multi-messenger approach has become extremely powerful in the recent years,” Murase said.

    Murase and the first author of this new paper, Ke Fang, a postdoctoral associate at the University of Maryland, attempt to explain the latest multi-messenger data from very high-energy neutrinos, ultrahigh-energy cosmic rays, and high-energy gamma rays, based on a single but realistic astrophysical setup. They found that the multi-messenger data can be explained well by using numerical simulations to analyze the fate of these charged particles.

    “In our model, cosmic rays accelerated by powerful jets of active galactic nuclei escape through the radio lobes that are often found at the end of the jets,” Fang said. “Then we compute the cosmic-ray propagation and interaction inside galaxy clusters and groups in the presence of their environmental magnetic field. We further simulate the cosmic-ray propagation and interaction in the intergalactic magnetic fields between the source and the Earth. Finally we integrate the contributions from all sources in the universe.”

    The leading suspects in the half-century old mystery of the origin of the highest-energy cosmic particles in the universe were in galaxies called “active galactic nuclei,” which have a super-radiating core region around the central supermassive black hole. Some active galactic nuclei are accompanied by powerful relativistic jets. High-energy cosmic particles that are generated by the jets or their environments are shot out into space almost as fast as the speed of light.

    “Our work demonstrates that the ultrahigh-energy cosmic rays escaping from active galactic nuclei and their environments such as galaxy clusters and groups can explain the ultrahigh-energy cosmic-ray spectrum and composition. It also can account for some of the unexplained phenomena discovered by ground-based experiments,” Fang said. “Simultaneously, the very high-energy neutrino spectrum above one hundred million mega-electronvolts can be explained by particle collisions between cosmic rays and the gas in galaxy clusters and groups. Also, the associated gamma-ray emission coming from the galaxy clusters and intergalactic space matches the unexplained part of the diffuse high-energy gamma-ray background that is not associated with one particular type of active galactic nucleus.”

    “This model paves a way to further attempts to establish a grand-unified model of how all three of these cosmic messengers are physically connected to each other by the same class of astrophysical sources and the common mechanisms of high-energy neutrino and gamma-ray production,” Murase said. “However, there also are other possibilities, and several new mysteries need to be explained, including the neutrino data in the ten-million mega-electronvolt range recorded by the IceCube neutrino observatory in Antarctica. Therefore, further investigations based on multi-messenger approaches — combining theory with all three messenger data — are crucial to test our model.”

    The new model is expected to motivate studies of galaxy clusters and groups, as well as the development of other unified models of high-energy cosmic particles. It is expected to be tested rigorously when observations begin to be made with next-generation neutrino detectors such as IceCube-Gen2 and KM3Net, and the next-generation gamma-ray telescope, Cherenkov Telescope Array.

    Artist’s expression of the KM3NeT neutrino telescope

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

    “The golden era of multi-messenger particle astrophysics started very recently,” Murase said. “Now, all information we can learn from all different types of cosmic messengers is important for revealing new knowledge about the physics of extreme-energy cosmic particles and a deeper understanding about our universe.”

    The research was partially supported by the National Science Foundation (grant No. PHY-1620777) and the Alfred P. Sloan Foundation.

    See the full article here .

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  • richardmitnick 9:08 pm on November 16, 2017 Permalink | Reply
    Tags: HAWC detector, HESS Cherenkov Telescope Array, , , , Through a Gas - Darkly: Scientists Trace the Origins of Earth’s Antimatter   

    From SA: “Through a Gas, Darkly: Scientists Trace the Origins of Earth’s Antimatter” 

    Scientific American

    Scientific American

    November 16, 2017
    Charles Q. Choi

    An image of the HAWC detector consisting of 300 large water tanks, each with four photodetectors for measuring the particle showers produced by cosmic rays. HAWC is located more than four kilometers above sea level inside the Parque Nacional Pico de Orizaba, in Mexico. Credit: Jordan A. Goodman

    For the past decade or so scientists have noticed Earth is being bombarded with far more antimatter than expected. Now they are closing in on this strange bombardment’s source, tentatively linking it with the enigmatic dark matter thought to make up roughly five sixths of all matter in the universe.

    Every particle of normal matter has an antimatter counterpart, equal in mass but opposite in charge. For instance, the antiparticle of the negatively charged electron is the positively charged positron, a particle that makes up the bulk of antimatter striking the top of Earth’s atmosphere from outer space. When a particle meets its antiparticle, they annihilate each other, typically releasing energetic photons called gamma rays as a result.

    In 2008 researchers using the space-based PAMELA (Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics) detector found the number of high-energy protons hitting Earth to be roughly three times greater than predicted by standard models.

    PAMELA. The Wizard collaboration

    These results were later confirmed by the Fermi Gamma-ray Space Telescope as well as the Alpha Magnetic Spectrometer (AMS-02), which is mounted on the International Space Station. Ever since, astrophysicists have been debating where all these excess positrons might come from.

    NASA/Fermi Telescope

    NASA/AMS02 device

    One promising explanation: the excess could come from nearby pulsars, rapidly whirling remnants of expired massive stars that violently expel positrons and a menagerie of other high-energy particles as they spin. A more exotic possibility is that this antimatter is given off by decaying particles of dark matter, the theoretical invisible substance astronomers have so far “detected” only via its apparent gravitational effects on normal matter.

    To see if pulsars might solve this antimatter puzzle, an international team of researchers analyzed data from the High-Altitude Water Cherenkov (HAWC) gamma-ray observatory, located on the flanks of a volcano about four hours east of Mexico City. When gamma rays from annihilated positrons smash into Earth’s atmosphere, they rip apart atoms, generating showers of particles that hurtle downward at nearly the speed of light. These showers produce minuscule flashes of light when they hit the water held in 300 corrugated steel tanks at HAWC. Observers can detect and record the flashes, using them to deduce the energies and cosmic origins of the gamma rays that triggered the particle cascades.

    The scientists focused on gamma rays originating from the vicinity of two nearby pulsars that could blast Earth with positrons—Geminga and PSR B0656+14, located some 815 and 950 light-years from Earth, respectively. “HAWC scans about one third of the sky overhead, giving us the first wide-angle view of high-energy light from the sky,” says study co-author Jordan Goodman, a particle astrophysicist at the University of Maryland, College Park. “Before HAWC there were observatories that were highly sensitive to high-energy gamma rays, but they had relatively limited fields of view. With HAWC, we can see how gamma rays are diffusing from these pulsars across wide regions of sky.” The researchers detailed their findings in the November 17 Science.

    Goodman and his colleagues used HAWC to map how these pulsars’ positron-generated gamma-ray emissions radiated across patches of sky, each about 65 light-years across. They found each pulsar is surrounded by a kind of murky “fog,” from which relatively few positrons can escape to strike Earth. Positrons help create this gamma-ray fog when they slam into the cosmic microwave background radiation, the photons of light left over from the big bang that formed the universe. By mapping the extent of the fog around each pulsar, the HAWC team could estimate how fast and how far most of the positrons can travel. Their results suggest these pulsars “cannot be the source of the excess positrons measured by AMS-02 and preceding experiments,” says John Wefel, a particle astrophysicist emeritus at Louisiana State University who did not take part in the study.

    Even so, the positron excess remains “one of the most exciting mysteries in astrophysics,” says Justin Vandenbroucke, a particle astrophysicist at the University of Wisconsin–Madison, also unaffiliated with the work. It could be that the positrons come from other conventional astrophysical sources such as high-energy particles produced by black holes siphoning gas from nearby companion stars. Or they do come from pulsars, but somehow take more complicated paths through space to reach Earth than those assumed by the HAWC team. More certainty may come as HAWC and the upcoming Cherenkov Telescope Array gather data from a larger numbers of nearby pulsars.

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

    For now, though, when it comes to all the potential suspects in the antimatter mystery, “the only one left standing seems to be dark matter,” Goodman says. “We’re not saying what AMS and PAMELA have detected is dark matter—we’re just saying that we’ve given an alibi to the other major suspects, the pulsars.”

    See the full article here .

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