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  • richardmitnick 3:46 pm on May 24, 2021 Permalink | Reply
    Tags: "Confirming a Cosmic-Ray Bump", , Cosmic Rays,   

    From Physics (US) : “Confirming a Cosmic-Ray Bump” 

    About Physics

    From Physics (US)

    May 18, 2021
    Katherine Wright

    The DArk Matter Particle Explorer has made the most precise measurements of galactic cosmic rays to date.

    1
    For over 5 years, the DArk Matter Particle Explorer (DAMPE)[Chinese Academy of Sciences] has orbited Earth measuring cosmic rays.

    The team behind the telescope has now analyzed 4.5 years of cosmic-ray data, finding spectral features that don’t match predictions Physical Review Letters. While similar features were hinted at in other experiments, the measurements by DAMPE have a higher precision and cover a wider range of energies than any other single experiment. The findings could help researchers uncover the origin of galactic cosmic rays.

    Cosmic rays consist mostly of protons and helium ions and are thought to emanate from supernovae. On their journey to Earth the rays are deflected by interstellar magnetic fields, making it hard to determine their sources. But researchers hope that by measuring the energy spectra of cosmic rays, they can extract some information about the supernovae that sent them flying and about the structure of our Galaxy.

    In their analysis, the DAMPE team analyzed the energy spectrum of detected helium ions. These particles had energies from 70 GeV to 80 TeV, an order of magnitude higher than those detected with the Alpha Magnetic Spectrometer aboard the International Space Station (see Focus: New Data Reveal the Heavy Side of Cosmic Rays) and 100 times higher than those seen with the PAMELA satellite (see Synopsis: Solar Cycle Affects Cosmic Ray Positrons).

    At around 1.3 TeV the team observed the intensity of the spectrum start to rise, peaking at about 34 TeV. The statistical significance of the finding is 4.3 sigma. Signs of such a bump have been seen before, but the uncertainties in previous data were too large to confirm the bump’s presence. The team says that they think the bump-like feature might be caused by a nearby supernova, but that remains unconfirmed.

    See the full article here .

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    Physicists are drowning in a flood of research papers in their own fields and coping with an even larger deluge in other areas of physics. How can an active researcher stay informed about the most important developments in physics? Physics (US) highlights a selection of papers from the Physical Review journals. In consultation with expert scientists, the editors choose these papers for their importance and/or intrinsic interest. To highlight these papers, Physics features three kinds of articles: Viewpoints are commentaries written by active researchers, who are asked to explain the results to physicists in other subfields. Focus stories are written by professional science writers in a journalistic style and are intended to be accessible to students and non-experts. Synopses are brief editor-written summaries. Physics provides a much-needed guide to the best in physics, and we welcome your comments.

     
  • richardmitnick 6:44 pm on January 31, 2021 Permalink | Reply
    Tags: "We may have found the most powerful particle accelerator in the galaxy", A source of gamma rays exceeding 200 TeV called HAWC J1825-134., , , , Charged particles traveling through interstellar space respond to our galaxy's magnetic field., Cosmic Rays, , Gamma rays shoot straight-line through the galaxy allowing us to directly pinpoint their origins., , , When cosmic rays accidentally strike a cloud of interstellar gas they can emit gamma rays.   

    From SPACE.com: “We may have found the most powerful particle accelerator in the galaxy” 

    From SPACE.com

    1.29.21
    Paul Sutter

    And it’s quite a surprising source.

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    This image, created using data from the European Space Agency’s Herschel and Planck space telescopes, shows a piece of the Taurus Molecular Cloud.© ESA/Herschel/Planck; J. D. Soler, MPIA.

    ESA/Herschel spacecraft active from 2009 to 2013.

    ESA/Planck 2009 to 2013

    Astronomers have long wondered where high-energy cosmic rays come from within our galaxy.

    And now, new observations with the High Altitude Water Cherenkov Experiment (HAWC) observatory reveal an unlikely candidate: an otherwise mundane giant molecular cloud.

    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.

    Taking the knee

    Cosmic rays are not rays at all but rather tiny particles cruising through the universe at nearly the speed of light. They can be made of electrons, protons or even ions of heavier elements. They are created in all sorts of high-energy processes throughout the cosmos, from supernova explosions to the mergers of stars to the final insane moments when gas gets sucked up by a black hole.

    Cosmic rays come in all sorts of energies, and generally speaking the higher-energy cosmic rays are rarer than their low-energy relatives. This relationship changes in a very slight way at a particular energy — 10^15 electron-volts — which is called the “knee.” The electron-volt, or eV, is just the way that particle physicists enjoy measuring energy levels. For comparison, the most powerful particle collider on Earth, the Large Hadron Collider, can achieve 13 X 10^12 eV, which is often denoted as 13 tera electron-volts, or 13 TeV.

    CERN (CH) LHC Map

    Above an energy of 10^15 eV, cosmic rays are much rarer than you would expect. This has led astronomers to believe that any cosmic rays at this energy level and higher come from outside the galaxy, while processes within the Milky Way are capable of producing cosmic rays up to and including 10^15 eV.

    For those of you keeping score at home, whatever is creating these cosmic rays would be in the “peta” range of Greek prefixes, and therefore over 1,000 times more powerful than our best particle accelerators — natural “PeVatrons” roaming the galaxy.

    A hawkeyed sleuth

    The mission is simple: find the source of PeV-scale cosmic rays in the Milky Way. But despite their energies, it’s hard to pinpoint their origins. That’s because cosmic rays are made of charged particles, and charged particles traveling through interstellar space respond to our galaxy’s magnetic field. Thus when you see a high-energy cosmic ray coming from a particular direction in the sky, you actually have no idea where it truly came from — its path has bent and curved over the course of its journey to Earth.

    But instead of hunting for cosmic rays directly, we can search for some of their relatives. When cosmic rays accidentally strike a cloud of interstellar gas, they can emit gamma rays, a high-energy form of radiation. These gamma rays shoot straight-line through the galaxy, allowing us to directly pinpoint their origins.

    Cosmic rays produced by high-energy astrophysics sources (ASPERA collaboration – AStroParticle ERAnet).

    So if we see a source of strong gamma-ray emission, we can look for nearby sources of PeV cosmic rays.

    This was the method employed by a team of researchers using HAWC, which is located on the Sierra Negra Volcano of south-central Mexico. HAWC “stares” up at the sky with a series of tanks filled with ultra-pure water. When high-energy particles or radiation enter the tanks, they emit a flash of blue light, allowing astronomers to trace back the source onto the sky.

    Detailed in a paper recently appearing in The Astrophysical Journal Letters, the astronomers found a source of gamma rays exceeding 200 TeV, which could only be created by even more powerful cosmic rays — the kinds of cosmic rays that reach up into the PeV scale. The source, called HAWC J1825-134, lies roughly in the direction of the galactic center. HAWC J1825-134 appears to us as a bright blotch of gamma rays, illuminated by some unknown fount of cosmic rays — perhaps the most powerful known source of cosmic rays in the Milky Way.

    An unlikely heavyweight

    A few of the usual suspect sources of high-energy cosmic rays sit within a few thousand light-years of HAWC J1825-134, but none of them can easily explain the signal.

    For example, the galactic center itself is a known generator of intense cosmic ray action, but it’s way too far away from HAWC J1825-134, so it has no bearing on this measurement.

    There are some supernova remnants, and supernovae sure are powerful. But all the supernovae in the region of HAWC J1825-134 went off ages ago — far too long in the past to be creating these high-energy cosmic rays now.

    Pulsars — the rapidly spinning dense remnant cores of massive stars — also produce copious amounts of cosmic rays. But those too sit too far away from the source of gamma rays — the energies of the electrons and protons coming off the pulsar just aren’t punchy enough to travel the thousands of light-years to the location of the gamma ray emission.

    Surprisingly, the source of these record-breaking cosmic rays appears to be none other than a giant molecular cloud. These clouds are giant, lumbering brutes, filled with dust and gas, that roam the galaxy. They occasionally contract in on themselves and turn into stars, but otherwise they can remain cool and loose for billions of years. Not causing anyone any serious threat — and barely even noticeable unless you have good infrared telescopes — they are the last place you would expect to find such insanely high energies.

    Located within the cloud complex is a cluster of newborn stars, but even the crankiest and loudest of baby stars aren’t thought to be powerful enough to launch cosmic rays like this. The researchers themselves admit that they don’t know how this cloud is doing it, but somehow, when nobody was paying attention, it generated some of the most powerful particles in the entire galaxy.

    See the full article here .

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  • richardmitnick 11:10 am on July 1, 2020 Permalink | Reply
    Tags: "Binary star as a cosmic particle accelerator", , , , Cosmic Rays, , , , , Very high-energy gamma radiation   

    From DESY: “Binary star as a cosmic particle accelerator” 

    From DESY

    2020/07/01

    Specialized telescope provides evidence of very high-energy gamma radiation from Eta Carinae.

    With a specialised telescope in Namibia a DESY-led team of researchers has proven a certain type of binary star as a new kind of source for very high-energy cosmic gamma-radiation. Eta Carinae is located 7500 light years away in the constellation Carina (the ship’s keel) in the Southern Sky and, based on the data collected, emits gamma rays with energies all the way up to 400 gigaelectronvolts (GeV), some 100 billion times more than the energy of visible light.

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    Eta Carinae. NASA

    The team headed by DESY’s Stefan Ohm, Eva Leser and Matthias Füßling is presenting its findings, made at the gamma-ray observatory High Energy Stereoscopic System (H.E.S.S.), in the journal Astronomy & Astrophysics. [see also in Astronomy and Astrophysics] specially created multimedia animation explains the phenomenon. “With such visualizations we want to make the fascination of research tangible,” emphasises DESY’s Director of Astroparticle Physics, Christian Stegmann.


    Animation: DESY, Science Communication Lab; Sound by Alva Noto.

    Eta Carinae is a binary system of superlatives, consisting of two blue giants, one about 100 times, the other about 30 times the mass of our sun. The two stars orbit each other every 5.5 years in very eccentric elliptical orbits, their separation varying approximately between the distance from our Sun to Mars and from the Sun to Uranus. Both these gigantic stars fling dense, supersonic stellar winds of charged particles out into space. In the process, the larger of the two loses a mass equivalent to our entire Sun in just 5000 years or so. The smaller one produces a fast stellar wind travelling at speeds around eleven million kilometres per hour (about one percent of the speed of light).

    A huge shock front is formed in the region where these two stellar winds collide, heating up the material in the wind to extremely high temperatures. At around 50 million degrees Celsius, this matter radiates brightly in the X-ray range. The particles in the stellar wind are not hot enough to emit gamma radiation, though. “However, shock regions like this are typically sites where subatomic particles are accelerated by strong prevailing electromagnetic fields,” explains Ohm, who is the head of the H.E.S.S. group at DESY.

    H.E.S.S. Čerenkov Telescope Array, located on the Cranz family farm, Göllschau, in Namibia, near the Gamsberg searches for cosmic rays, altitude, 1,800 m (5,900 ft)

    When particles are accelerated this rapidly, they can also emit gamma radiation. In fact, the satellites “Fermi”, operated by the US space agency NASA, and AGILE, belonging to the Italian space agency ASI, already detected high-energy gamma rays of up to about 10 GeV coming from Eta Carinae in 2009.

    NASA/Fermi LAT


    NASA/Fermi Gamma Ray Space Telescope

    Italian Space Agency AGILE Spacecraft

    Subatomic hailstorm

    Different models have been proposed to explain how this gamma radiation is produced,” Füßling reports. “It could be generated by accelerated electrons or by high-energy atomic nuclei.” Determining which of these two scenarios is correct is crucial: very energetic atomic nuclei account for the bulk of the so-called Cosmic Rays, a subatomic cosmic hailstorm striking Earth constantly from all directions. Despite intense research for more than 100 years, the sources of the Cosmic Rays are still not exhaustively known. Since the electrically charged atomic nuclei are deflected by cosmic magnetic fields as they travel through the universe, the direction from which they arrive at Earth no longer points back to their origin. Cosmic gamma rays, on the other hand, are not deflected. So, if the gamma rays emitted by a specific source can be shown to originate from high-energy atomic nuclei, one of the long-sought accelerators of cosmic particle radiation will have been identified.

    “In the case of Eta Carinae, electrons have a particularly hard time getting accelerated to high energies, because they are constantly being deflected by magnetic fields during their acceleration, which makes them lose energy again,” says Leser. “Very high-energy gamma radiation begins above the 100 GeV range, which is rather difficult to explain in Eta Carinae to stem from electron acceleration.” The satellite data already indicated that Eta Carinae also emits gamma radiation beyond 100 GeV, and H.E.S.S. has now succeeded in detecting such radiation up to energies of 400 GeV around the time of the close encounter of the two blue giants in 2014 and 2015. This makes the binary star the first known example of a source in which very high-energy gamma radiation is generated by colliding stellar winds.

    “The analysis of the gamma radiation measurements taken by H.E.S.S. and the satellites shows that the radiation can best be interpreted as the product of rapidly accelerated atomic nuclei,” says DESY’s PhD student Ruslan Konno, who has published a companion study, together with scientists from the Max Planck Institute for Nuclear Physics in Heidelberg. “This would make the shock regions of colliding stellar winds a new type of natural particle accelerator for cosmic rays.” With H.E.S.S., which is named after the discoverer of Cosmic Rays, Victor Franz Hess, and the upcoming Čerenkov Telescope Array (CTA), the next-generation gamma-ray observatory currently being built in the Chilean highlands, the scientists hope to investigate this phenomenon in greater detail and discover more sources of this kind.

    Čerenkov Telescope Array, http://www.isdc.unige.ch/cta/ at Cerro Paranal, located in the Atacama Desert of northern Chile searches for cosmic rays on Cerro Paranal at 2,635 m (8,645 ft) altitude, 120 km (70 mi) south of Antofagasta; and at at the Instituto de Astrofisica de Canarias (IAC), Roque de los Muchachos Observatory in La Palma, Spain

    Cosmic road trip

    Thanks to detailed observations of Eta Carinae at all wavelengths, the properties of the stars, their orbits and stellar winds have been determined relatively accurately. This has given astrophysicists a better picture of the binary star system and its history. To illustrate the new observations of Eta Carinae, the DESY astrophysicists have produced a video animation together with the animation specialists of the award-winning Science Communication Lab [above]. The computer-generated images are close to reality because the measured orbital, stellar and wind parameters were used for this purpose. The internationally acclaimed multimedia artist Carsten Nicolai, who uses the pseudonym Alva Noto for his musical works, created the sound for the animation.

    “I find science and scientific research extremely important,” says Nicolai, who sees close parallels in the creative work of artists and scientists. For him, the appeal of this work also lay in the artistic mediation of scientific research results: “particularly the fact that it is not a film soundtrack, but has a genuine reference to reality,” emphasizes the musician and artist. Together with the exclusively composed sound, this unique collaboration of scientists, animation artists and musician has resulted in a multimedia work that takes viewers on an extraordinary journey to a superlative double star some 7500 light years away.

    See the full article here .


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    desi

    DESY is one of the world’s leading accelerator centres. Researchers use the large-scale facilities at DESY to explore the microcosm in all its variety – from the interactions of tiny elementary particles and the behaviour of new types of nanomaterials to biomolecular processes that are essential to life. The accelerators and detectors that DESY develops and builds are unique research tools. The facilities generate the world’s most intense X-ray light, accelerate particles to record energies and open completely new windows onto the universe. 
That makes DESY not only a magnet for more than 3000 guest researchers from over 40 countries every year, but also a coveted partner for national and international cooperations. Committed young researchers find an exciting interdisciplinary setting at DESY. The research centre offers specialized training for a large number of professions. DESY cooperates with industry and business to promote new technologies that will benefit society and encourage innovations. This also benefits the metropolitan regions of the two DESY locations, Hamburg and Zeuthen near Berlin.

    DESY Petra III interior

    DESY Petra III

    DESY/FLASH

    H1 detector at DESY HERA ring

    DESY DORIS III

     
  • richardmitnick 2:38 pm on June 18, 2020 Permalink | Reply
    Tags: "Spotted: A Galactic PeVatron?", , Cosmic Rays, , More modest cosmic rays reach “only” peta-electron-volt (PeV) energies — that’s 10^15 eV., We’ve now identified a new potential galactic PeVatron: the remnant produced by a past supernova explosion just 2600 light-years from Earth.   

    From AAS NOVA: “Spotted: A Galactic PeVatron?” 

    AASNOVA

    From AAS NOVA

    17 June 2020
    Susanna Kohler

    HAWC High Altitude Čerenkov Experiment, />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

    Speeding charged particles — far more energetic than any we can create in laboratory particle accelerators — constantly bombard the Earth’s atmosphere. But what extreme environments produce these high-energy particles? A new study may have identified one cosmic accelerator in our galaxy.

    Charged Arrivals

    At any given moment, protons and atomic nuclei are whizzing through our galaxy, sometimes at nearly the speed of light. These charged particles — cosmic rays —span a wide range of energies, with the most energetic packing the same punch as a 90 kilometer-per-hour (56 mph) baseball!

    Cosmic rays produced by high-energy astrophysics sources (ASPERA collaboration – AStroParticle ERAnet)

    More modest cosmic rays reach “only” peta-electron-volt (PeV) energies — that’s 10^15 eV, still more than 100 times more energetic than the particles accelerated by the record-holding Large Hadron Collider. We think that these PeV particles were produced somewhere within our own galaxy.

    If we could unravel their secrets, these cosmic rays could provide clues about how stars evolve and how energy is transported throughout the galaxy. First, however, we need to figure out where they came from. Are their sources supernova remnants? Microquasars? Superbubbles? What galactic PeVatrons accelerated these particles to their tremendous speeds?

    Road Map to a Birthplace

    Unfortunately, we can’t just trace cosmic rays backwards to figure out their origins. Because these particles are charged, their trajectories are deflected by interstellar magnetic fields — which means that the direction a cosmic ray arrived from probably isn’t the direction of its source.

    To address this challenge, high-energy astronomers search for more direct messengers that are produced as cosmic rays are accelerated — like extremely energetic gamma-ray radiation.

    When PeV particles accelerated by a galactic PeVatron collide with gas and dust in the vicinity of their origin, they should produce very high-energy tera-electron-volt (TeV, or 10^12 eV) gamma-ray photons. These photon by-products won’t be deflected by magnetic fields, so their arrival at gamma-ray observatories on Earth provides a clearer path back to the source of the PeV cosmic rays.

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    Top: significance map from HAWC showing the location of gamma-ray emission from near SNR G106.3+2.7. Bottom: Molecular hydrogen column density around the HAWC-detected source (shown in gray contours). The detectors VERITAS and Milagro have also observed very high-energy gamma-ray emission from this region; their detection centers are also marked. [Adapted from Albert et al. 2020]

    Hunting for Galactic Accelerators

    So how’s the search for these characteristic TeV gamma-rays going? With one possible success on the books so far — scientists think there’s a galactic PeVatron at the center of our galaxy, but we haven’t yet determined the source — we’ve now identified a new potential galactic PeVatron: the remnant produced by a past supernova explosion just 2,600 light-years from Earth.

    In a new publication, a team of scientists from the High-Altitude Water Čerenkov Gamma-Ray Observatory (HAWC) announces the detection of TeV gamma-ray emission from the same region as supernova remnant SNR G106.3+2.7.

    Though the team can’t rule out other causes of the emission, this signal has a spectrum that’s consistent with what we’d expect to be produced by PeV protons colliding with gas and dust. The origin near SNR G106.3+2.7 supports a picture in which charged particles can be accelerated across the shocks of supernova remnants and flung into space with PeV energies.

    So might the mystery of galactic PeVatrons be solved with supernova remnants? We don’t know for sure yet, but future high-energy gamma-ray observations are sure to help us further identify the sources of the speeding charged particles in our galaxy.

    Citation

    “HAWC J2227+610 and Its Association with G106.3+2.7, a New Potential Galactic PeVatron,” A. Albert et al 2020 ApJL 896 L29.
    https://iopscience.iop.org/article/10.3847/2041-8213/ab96cc

    See the full article here .


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    1

    AAS Mission and Vision Statement

    The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

    The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
    The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
    The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
    The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
    The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

    Adopted June 7, 2009

     
  • richardmitnick 9:34 am on March 18, 2020 Permalink | Reply
    Tags: "An Iced Cosmic-Ray Macchiato", , , , , Cosmic Rays,   

    From astrobites: “An Iced Cosmic-Ray Macchiato” 

    Astrobites bloc

    From astrobites

    1
    Artist’s impression of the shower of particles caused when a cosmic ray, a charged particle often produced by a distant astrophysical source, hits Earth’s upper atmosphere. [J. Yang/NSF]

    Title: Bottom-up Acceleration of Ultra-High-Energy Cosmic Rays in the Jets of Active Galactic Nuclei
    Authors: Rostom Mbarek and Damiano Caprioli
    First Author’s Institution: University of Chicago

    Status: Published in ApJ

    Our universe is littered with particles of unbelievably high energy, called cosmic rays. The most extreme of these particles carry the same amount of energy as a professional tennis serve, like the Oh-My-God Particle detected nearly 30 years ago. The catch: we don’t know exactly what processes can pack so much energy into a single particle. The authors of today’s article discuss how these particles might gain their energy in a way analogous to your morning trip to Dunkin’™.

    Cosmic Rays at a Glance

    Cosmic rays are atomic nuclei that have been accelerated to high energies in astrophysical environments, such as supernova remnants or active galactic nuclei. Although they might seem like a great tool in the multi-messenger astronomy toolbox, astronomy with cosmic rays is no simple task, as these particles get deflected by extragalactic magnetic fields.

    2
    Cosmic rays (red) consist of individual protons and nuclei of heavier elements. They are deflected by magnetic fields along their cosmological odysseys and can’t be used to point back to the place of their origin. [IceCube Neutrino Observatory]

    Despite efforts to pinpoint the origins of cosmic rays, especially those of the highest energies, we’ve come up empty-handed (check out these bites for previous studies: Galactic cosmic rays, cosmic-ray anisotropy).

    Even though we can’t measure where they come from, we do know their energies, and a variety of cosmic-ray experiments detect millions of these particles every year. Many of them are thousands to millions of times more energetic than the particles in the largest terrestrial particle accelerator, the Large Hadron Collider, but we don’t know how the highest energy cosmic rays get their energy.

    Cosmic-Ray Acceleration: Old News

    Many theories of cosmic-ray acceleration tend to revolve around the idea of Fermi acceleration. In this scenario, objects such as supernova remnants can create shocks, consisting of material moving together with supersonic speeds, and these shocks can accelerate particles to high energies. As a shock wave propagates, particles bounce back and forth across the shock boundary. Over time, successive bounces across the shock front lead to a net transfer of energy to the particles.

    While Fermi acceleration does a good job of explaining cosmic rays with moderate energies and has been a staple of models for decades, it has a few pitfalls, and many argue that it can’t provide the whole story for cosmic-ray acceleration at the highest energies.

    A Cosmic Cup o’ Joe

    The authors of today’s paper propose a new way of looking at cosmic-ray acceleration: the espresso mechanism. Why espresso? Because instead of gradually gaining energy over time, particles gain their energy from a single shot.

    3
    In the “espresso mechanism”, particles gain tremendous amounts of energy from entering a jet for a short period of time. Here, a particle with initial momentum and energy pi, Ei enters a jet with characteristic Lorentz factor Γ and leaves the jet with an energy equal to roughly Γ2Ei. [Caprioli et al. 2018]

    Consider an object with a jet, such as an active galaxy. If a low-energy cosmic ray enters the jet (or steam), then it can be shot down the barrel of the jet and get kicked out at much higher energy. In many cases, particle energies can increase by a factor Γ2, where Γ is the Lorentz factor (this reflects how fast the jet is moving). For some jets, this means particles can exit nearly 1,000 times as energetic as they were when they entered the jet.

    4
    In realistically modeled jets, material tends to clump in some regions, and these regions of overdensity (color scale in figure) cause the jet to locally move faster or slower. [Mbarek & Caprioli 2019]

    While this espresso scheme sounds great in principle, many previous calculations have relied on spherical cow treatments of jets, when in reality they are remarkably dynamic and complex structures.

    That’s where the authors of today’s paper come into play. These authors take a simple treatment of the espresso mechanism and complexify it by performing a full magnetohydrodynamic (MHD) simulation of ultrarelativistic jets. This takes factors like small-scale fluctuations of jet speed and jet density into account, to give a more accurate picture of the dynamics of jets.

    By simulating the full structure of jets, the authors find that complex environments don’t weaken the promises of espresso acceleration. In fact, the very imperfections that manifest in realistic jets can help with particle acceleration. What’s more, jet perturbations allow particles to receive double or even triple shots of energy.

    Throughout the paper, the authors describe the emergent spectra of espresso-accelerated cosmic rays. In doing this, they find that espresso acceleration is consistent with current measurements of ultra-high-energy cosmic rays in terms of energy, chemical composition, and spatial distributions, an accomplishment which no other model of cosmic-ray acceleration can boast.

    6

    Sample particle trajectories (black curves) are overlaid on top of slices of the jet, with jet velocity represented by the color in the top panels. Bottom panels show the amount of energy gained along the particle paths, showing that particles can leave jets with much more energy than they entered with. [Mbarek & Caprioli 2019]

    In light of all of this, it’s probably safe to say that the future of cosmic-ray science will be very caffeinated.

    See the full article here .


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    What do we do?

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

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

     
  • richardmitnick 10:17 am on February 28, 2020 Permalink | Reply
    Tags: "Stunning Images Capture Cosmic Ray Tracks", , Cosmic Rays, Cosmic rays are made mostly from the result of supernovae explosions and reaching us at nearly the speed of light., Losing more energy as it travels round and round the particle creates the curious circles in the images called “loopers.”, Particles with no electric charge always move in straight lines; however they cannot even be seen by the detector., , , STAR is only able to track charged particles which get pulled by the the detector’s magnetic field creating a curve., The “heart” of the STAR detector is its Time Projection Chamber- a four-meter-wide 4.2-meter-long cylinder filled with a gas mixture of argon and methane.   

    From Brookhaven National Lab: “Stunning Images Capture Cosmic Ray Tracks” 

    From Brookhaven National Lab

    February 26, 2020
    Erika Peters
    epeters@bnl.gov

    The beauty in science shines through at RHIC’s STAR detector [below] and makes a cosmic connection.

    1
    To help calibrate the STAR detector, physicists track and capture images of showers of cosmic rays streaming from space. Can you pick out which image shows tracks from a particle collision at RHIC (hint: the collision occurred at the center of the detector)?

    These images capture the movement and collisions of “cosmic rays”—mysterious particles originating somewhere in deep space—as they stream through the STAR detector at the Relativistic Heavy Ion Collider (RHIC) [below]. The results are profoundly beautiful.

    The rays, made mostly from the result of supernovae explosions and reaching us at nearly the speed of light, are not just things of beauty. Physicists conducting research at RHIC—a U.S. Department of Energy Office of Science user facility for nuclear physics research at Brookhaven National Laboratory—use their signals as a tool for calibrating the massive detectors collecting data for the collider’s physics experiments.

    The “heart” of the STAR detector is its Time Projection Chamber, a four-meter-wide, 4.2-meter-long cylinder filled with a gas mixture of argon and methane, explained Irakli Chakaberia, a research scientist on the STAR experiment. Each of the detector’s endcaps has 12 “sectors,” each with 72 padrows that sense electric charge, acting as a camera that can capture over 2,000 images a second. Tracing the trails of a shower of cosmic rays passing through the gas helps scientists know if their detector components are all working correctly.

    The higher the energy of the original cosmic track, the bigger the proliferation of the shower, creating what appear to be more “lively” images with many tracks in the chamber. How linear the path appears helps show the particle’s speed—the faster the particle moves, the straighter its path. Particles with no electric charge always move in straight lines; however, they cannot even be seen by the detector. STAR is only able to track charged particles, which get pulled by the the detector’s magnetic field, creating a curve. Those with lower momentum, called “soft” particles, are pulled more by the detector’s magnets and curve more than faster ones.

    “Based on the direction of the curve, we can tell whether the particle is positively or negatively charged,” Chakaberia said.

    When a cosmic ray particle collides with an atom of the gas in the detector, it might produce a “softer” particle moving with lower energy. Losing more energy as it travels round and round, the particle creates the curious circles in the images called “loopers.” Sometimes in the initial cascade, there are particles “soft” enough to loop around on their own.

    Even though physicists use powerful computers to analyze data from STAR, “nothing replaces an actual human eye,” Chakaberia said.

    “For example, when looking at some cosmic data, there was a case where tens of tracks were reconstructed in a single detector sector,” Chakaberia said. “This could, in principle, happen, but after checking the event display by eye it was obvious that it was a result of noise in that sector. The software couldn’t distinguish between the noise and real events to some degree. So these track displays help a lot to figure out what’s going on.”

    After cosmic rays have done their job testing and calibrating, STAR is ready to capture the thousands of tracks produced by ion collisions at RHIC. To increase the chance of two ions colliding, billions are aimed at each other with each pass through the detector, and the tracks reveal more of the beauty and the art that can be found in science. In this case, all the particle tracks emerge from the center of the detector, where the collision takes place. (Can you find the one ion-collision event in the images shown here?)

    Nuclear physicists analyze the ion-collision tracks to learn about a remarkable state of matter created in RHIC’s heavy-ion collisions. This “quark-gluon plasma” is a soup of particles that mimics what the universe was like just after the Big Bang. It’s a kind of cosmic connection: Scientists use a detector calibrated by particles from the cosmos to learn more about the marvelous and mystifying universe that created them.

    Research at RHIC/STAR is funded by the DOE Office of Science and by funders of the STAR collaboration listed here.

    See the full article here .


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    BNL Campus

    Brookhaven campus

    BNL Center for Functional Nanomaterials

    BNL NSLS-II


    BNL NSLS II

    BNL RHIC Campus

    BNL/RHIC Star Detector

    BNL Phenix Detector

    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world. Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.

     
  • richardmitnick 8:49 am on February 28, 2020 Permalink | Reply
    Tags: "IceCube identifies four galaxies as likely sources of cosmic rays", , , Cosmic Rays, , From U Wisconsin IceCube Collaboration, ,   

    From U Wisconsin IceCube Collaboration via physicsworld.com: “IceCube identifies four galaxies as likely sources of cosmic rays” 

    U Wisconsin ICECUBE neutrino detector at the South Pole

    From U Wisconsin IceCube Collaboration

    via

    physicsworld.com

    26 Feb 2020
    Sam Jarman

    A huge observatory at the South Pole has identified four galaxies as likely sources of cosmic rays. Rather than detecting cosmic rays, the team analysed a decade’s worth of data gathered by the IceCube Neutrino Observatory to pinpoint the sources, which are expected to also emit huge numbers of neutrinos. The team says that this is the best-ever identification of cosmic ray sources.

    Cosmic rays are high-energy charged particles that originate outside the solar system.

    Cosmic rays produced by high-energy astrophysics sources (ASPERA collaboration – AStroParticle ERAnet)

    They are thought to be created by violent astrophysical processes capable of accelerating particles to near the speed of light. However, working-out exactly where cosmic rays come from has proven very difficult because their trajectories are deflected by the magnetic fields permeating interstellar space. Cosmic neutrinos offer a solution because they should be produced in the same places as cosmic rays but are not deflected by magnetic fields.

    IceCube comprises of strings of photomultiplier tubes that are suspended within a cubic kilometre of ice at the South Pole [see images below]. Occasionally a muon neutrino will collide with an atom in the ice, creating a muon that will then emit Cherenkov light as it travels through the ice. This light is detected by the photomultipliers and the signal can be used to work-out where the neutrino came from.

    Atmospheric background

    Locating neutrino sources in the cosmos is not easy because the IceCube detector is swamped by signals from muons and muon neutrinos created by cosmic ray collisions with the atmosphere. These create a large and diffuse background signal and the challenge is to pick-out point sources of cosmic neutrinos within this background.

    The IceCube team used a new data-analysis technique that could process all full-sky observations made between April 2008 and July 2018 – something that was not possible before for software-related reasons. The quasar-like galaxy NGC 1068 emerged as a particularly likely source of cosmic ray neutrinos, standing out of the background with a 2.9σ statistical significance. When combined with three other galaxies that were identified, the four sources collectively stand above the background at a statistical significance of 3.3σ.

    Although this remains well short of the 5σ that is normally considered a discovery, the IceCube analysis is strongest evidence that these four galaxies are cosmic-ray emitters. The researchers now hope that their results will motivate further studies of these sources by looking for more neutrinos as well as gamma rays and X-rays – which are also associated with cosmic-ray sources.

    The study is described in Physical Review Letters.

    See the full article here .

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    PhysicsWorld is a publication of the Institute of Physics. The Institute of Physics is a leading scientific society. We are a charitable organisation with a worldwide membership of more than 50,000, working together to advance physics education, research and application.

    We engage with policymakers and the general public to develop awareness and understanding of the value of physics and, through IOP Publishing, we are world leaders in professional scientific communications.
    IOP Institute of Physics

    IceCube is a particle detector at the South Pole that records the interactions of a nearly massless sub-atomic particle called the neutrino. IceCube searches for neutrinos from the most violent astrophysical sources: events like exploding stars, gamma ray bursts, and cataclysmic phenomena involving black holes and neutron stars. The IceCube telescope is a powerful tool to search for dark matter, and could reveal the new physical processes associated with the enigmatic origin of the highest energy particles in nature. In addition, exploring the background of neutrinos produced in the atmosphere, IceCube studies the neutrinos themselves; their energies far exceed those produced by accelerator beams. IceCube is the world’s largest neutrino detector, encompassing a cubic kilometer of ice.

    IceCube employs more than 5000 detectors lowered on 86 strings into almost 100 holes in the Antarctic ice NSF B. Gudbjartsson, IceCube Collaboration

    Lunar Icecube

    IceCube DeepCore annotated

    IceCube PINGU annotated


    DM-Ice II at IceCube annotated

     
  • richardmitnick 3:16 am on December 19, 2019 Permalink | Reply
    Tags: "WashU physicists launch cosmic ray telescope from Antarctica", , , , , Cosmic Rays, , , Washington Unversity in St. Louis   

    From Washington University in St.Louis: “WashU physicists launch cosmic ray telescope from Antarctica” 

    Wash U Bloc

    From Washington University in St.Louis

    December 15, 2019
    Talia Ogliore
    talia.ogliore@wustl.edu

    1
    The Super Trans-Iron Galactic Element Recorder (SuperTIGER) instrument is used to study the origin of cosmic rays. (Photo courtesy SuperTIGER team)

    A team of Washington University in St. Louis scientists at McMurdo Station, Antarctica, successfully launched its SuperTIGER (Super Trans-Iron Galactic Element Recorder) instrument, which is used to study the origin of cosmic rays.

    Cosmic rays produced by high-energy astrophysics sources (ASPERA collaboration – AStroParticle ERAnet)

    Cosmic rays are high-energy particles from beyond the solar system that bombard Earth’s atmosphere. SuperTIGER is designed to measure the rare, heavy elements in cosmic rays that hold clues about where these particles are made. The new research might also help explain how these energetic particles are accelerated to attain a speed that is close to the speed of light.

    SuperTIGER is a collaboration among Washington University, Goddard Space Flight Center, California Institute of Technology Jet Propulsion Laboratory and the University of Minnesota.

    “After three Antarctic seasons — with 19 launch attempts, two launches and one recovery of the payload from a crevasse field — it is wonderful to have SuperTIGER-2 finally reach float altitude and begin collecting scientific data. The third season is the charm!” said Brian Rauch, research assistant professor of physics in Arts & Sciences at Washington University and principal investigator for SuperTIGER.

    The launch occurred at about 2:55 a.m. local time Dec. 16 in New Zealand (7:55 a.m. U.S. Central time). Under cloudy skies and temperatures of about 28 degrees Fahrenheit, researchers watched as the SuperTIGER instrument was carried aloft by a giant 39.5 million-cubic-foot scientific balloon. The balloon will ultimately reach a height of about 129,000 feet — nearly four times the typical cruising altitude of commercial airliners.

    At this height, the detectors on SuperTIGER will fly above 99.5% of the atmosphere on Earth.

    Researchers said that SuperTIGER will keep recording data as long as the conditions allow them to keep the balloon afloat. SuperTIGER’s 2012-13 flight lasted 55 days.

    Data collected during the ongoing flight will be used to test emerging models of cosmic-ray origins in clumps of hot, massive and relatively short-lived stars known as OB associations, as well as testing models for determining which particles will be accelerated from such associations.

    The balloon that carries SuperTIGER is also transporting four, smaller experimental devices that are piggybacked onto its core scientific payload. The list includes two experiments by Washington University researchers: one developed by James H. Buckley, professor of physics, called APT-Lite; and another by Alex Meshik, research professor of physics, to help solve a longstanding “xenon paradox.”

    Individuals who are interested in following SuperTIGER as the flight progresses can follow along on the Washington University team’s Twitter account, @SuperTigerLDB, or by following the Twitter handle @NASAUniverse.


    Super Tiger Launch December 16, 2019

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    Wash U campus

    Washington University’s mission is to discover and disseminate knowledge, and protect the freedom of inquiry through research, teaching, and learning.

    Washington University creates an environment to encourage and support an ethos of wide-ranging exploration. Washington University’s faculty and staff strive to enhance the lives and livelihoods of students, the people of the greater St. Louis community, the country, and the world.

     
  • richardmitnick 2:13 pm on November 21, 2019 Permalink | Reply
    Tags: , , , Cosmic Rays, , , H.E.S.S. Čerenkov Telescope Array located on the Cranz family farm Göllschau in Namibia near the Gamsberg,   

    From DESY: “Gamma-Ray Bursts with record energy” 

    DESY
    From DESY

    2019/11/20

    First detection of the cosmic monster explosions with ground-based gamma-ray telescopes.

    The strongest explosions in the universe produce even more energetic radiation than previously known: Using specialised telescopes, two international teams have registered the highest energy gamma rays ever measured from so-called gamma-ray bursts, reaching about 100 billion times as much energy as visible light. The scientists of the H.E.S.S. and MAGIC telescopes present their observations in independent publications in the journal Nature.

    A very-high-energy component deep in the γ-ray burst afterglow; The H.E.S.S. collaboration Nature

    Teraelectronvolt emission from the γ-ray burst GRB 190114C; The MAGIC collaboration Nature

    These are the first detections of gamma-ray bursts with ground-based gamma-ray telescopes. DESY plays a major role in both observatories, which are operated under the leadership of the Max Planck Society.

    H.E.S.S. Čerenkov Telescope Array, located on the Cranz family farm, Göllschau, in Namibia, near the Gamsberg searches for cosmic rays, altitude, 1,800 m (5,900 ft)

    MAGIC Čerenkov telescopes at the Observatorio del Roque de los Muchachos (Garfia, La Palma, Spain)), Altitude 2,396 m (7,861 ft)

    Gamma-ray bursts (GRB) are sudden, short bursts of gamma radiation happening about once a day somewhere in the visible universe. According to current knowledge, they originate from colliding neutron stars or from supernova explosions of giant suns collapsing into a black hole. “Gamma-ray bursts are the most powerful explosions known in the universe and typically release more energy in just a few seconds than our Sun during its entire lifetime – they can shine through almost the entire visible universe,” explains David Berge, head of gamma-ray astronomy at DESY. The cosmic phenomenon was discovered by chance at the end of the 1960s by satellites used to monitor compliance with the nuclear test ban on Earth.

    Since then, astronomers have been studying gamma-ray bursts with satellites, as Earth’s atmosphere very effectively absorbs gamma rays. Astronomers have developed specialised telescopes that can observe a faint blue glow called Čerenkov light that cosmic gamma rays induce in the atmosphere, but these instruments are only sensitive to gamma rays with very high energies. Unfortunately, the brightness of gamma-ray bursts falls steeply with increasing energy. Čerenkov telescopes have identified many sources of cosmic gamma rays at very high energies, but no gamma-ray bursts. Satellites, on the other hand, have much too small detectors to be sensitive to the low brightness of gamma-ray bursts at very high energies. So, it was effectively unknown, if the monster explosions emit gamma rays also in the very-high-energy regime.

    Scientists have tried for many years, to catch a gamma-ray burst with Čerenkov telescopes. Then suddenly, between summer 2018 and January 2019, two international teams of astronomers, both involving DESY scientists, detected gamma rays from two GRB events for the first time from the ground. On 20 July 2018, faint afterglow emission of GRB 180720B in the gamma-ray regime was observed with the 28-metre telescope of the High-Energy Stereoscopic System H.E.S.S. in Namibia. On 14 January 2019, bright early emission from GRB 190114C was detected by the Major Atmospheric Gamma Imaging Čerenkov (MAGIC) telescopes on La Palma, and immediately announced to the astronomical community.

    Both observations were triggered by gamma-ray satellites of the US space agency NASA that monitor the sky for gamma-ray bursts and send automatic alerts to other gamma-ray observatories upon detection. “We were able to point to the region of origin so quickly that we could start observing only 57 seconds after the initial detection of the explosion,” reports Cosimo Nigro from the MAGIC group at DESY, who was in charge of the observation shift at that time. “In the first 20 minutes of observation, we detected about thousand photons from GRB 190114C.”

    MAGIC registered gamma-rays with energies between 200 and 1000 billion electron volts (0.2 to 1 teraelectronvolts). “These are by far the highest energy photons ever discovered from a gamma-ray burst,” says Elisa Bernardini, leader of the MAGIC group at DESY. For comparison: visible light is in the range of about 1 to 3 electron volts.

    The rapid discovery allowed to quickly alert the entire observational community. As a result, more than twenty different telescopes had a deeper look at the target. This allowed to pinpoint the details of the physical mechanism responsible for the highest-energy emission, as described in the second paper led by the MAGIC collaboration. Follow-up observations placed GRB 190114C at a distance of more than four billion light years. This means, its light travelled more than four billion years to us, or about a third of the current age of the universe.

    GRB 180720B, at a distance of six billion light years even further away, could still be detected in gamma rays at energies between 100 and 440 billion electron volts long after the initial blast. “Surprisingly, the H.E.S.S. telescope observed a surplus of 119 gamma quanta from the direction of the burst more than ten hours after the explosion event was first seen by satellites,” says Stefan Ohm, head of the H.E.S.S. group at DESY.

    “The detection came quite unexpected, as gamma-ray bursts are fading fast, leaving behind an afterglow which can be seen for hours to days across many wavelengths from radio to X-rays, but had never been detected in very-high-energy gamma rays before,” adds DESY theorist Andrew Taylor, who contributed to the H.E.S.S. analysis. “This success is also due to an improved follow-up strategy in which we also concentrate on observations at later times after the actual star collapse.”

    The detection of gamma-ray bursts at very high energies provides important new insights into the gigantic explosions. “Having established that GRBs produce photons of energies hundreds of billion times higher than visible light, we now know that GRBs are able to efficiently accelerate particles within the explosion ejecta,” says DESY researcher Konstancja Satalecka, one of the scientists coordinating GRB searches in the MAGIC collaboration. “What’s more, it turns out we were missing approximately half of their energy budget until now. Our measurements show that the energy released in very-high-energy gamma-rays is comparable to the amount radiated at all lower energies taken together. That is remarkable!”

    To explain how the observed very-high-energy gamma rays are generated is challenging. Both groups assume a two-stage process: First, fast electrically charged particles from the explosion cloud are deflected in the strong magnetic fields and emit so-called synchrotron radiation, which is of the same nature as the radiation that can be produced in synchrotrons or other particle accelerators on Earth, for example at DESY. However, only under fairly extreme conditions would the synchrotron photons from the explosion be able to reach the very high energies observed. Instead, the scientists consider a second step, where the synchrotron photons collide with the fast particles that generated them, which boosts them to the very high gamma-ray energies recorded. The scientists call the latter step inverse Compton scattering.

    Observation of inverse Compton emission from a long γ-ray burst; The MAGIC CollaborationNature

    “For the first time, the two instruments have measured gamma radiation from gamma-ray bursts from the ground,” concludes Berge. “These two groundbreaking observations have established gamma-ray bursts as sources for terrestrial gamma-ray telescopes. This has the potential to significantly advance our understanding of these violent phenomena.” The scientists estimate that up to ten such events per year can be observed with the planned Čerenkov Telescope Array (CTA), the next generation gamma-ray observatory. The CTA will consist of more than 100 individual telescopes of three types that will be built at two locations in the northern and southern hemispheres. DESY is responsible for the construction of the medium-sized telescopes and will host CTA’s Science Data Management Centre on its campus in Zeuthen. CTA observations are expected to start in 2023 at the earliest.

    ________________________________________
    Background information

    The detection of the very high-energy gamma rays on Earth was achieved with specialised telescopes that do not observe the cosmic gamma rays directly, but rather their effect on Earth’s atmosphere: When an energetic cosmic gamma ray hits Earth’s atmosphere, it shatters molecules and atoms.

    This process creates an avalanche of particles called an air shower.

    Cosmic rays produced by high-energy astrophysics sources (ASPERA collaboration – AStroParticle ERAnet)

    The shower particles are so energetic that they move faster through the air than light – although not faster than light in a vacuum, which according to Albert Einstein’s theory of relativity is the absolute upper speed limit. The result is a bluish glow, a kind of optical counterpart to the supersonic bang. This Čerenkov light, named after its discoverer, can be observed by Čerenkov telescopes such as those of the H.E.S.S. and MAGIC observatories or the planned CTA.

    The H.E.S.S. observations were first announced at the CTA science symposium in May 2019. The MAGIC observations were distributed in an Astronomers’ Telegram (ATel) on 14 January 2019.

    The H.E.S.S. consortium consists of more than 250 researchers from 41 institutes in 12 countries. The MAGIC consortium brings together 280 members from 37 institutes in 12 countries. The MAGIC group at DESY is partially funded by a grant from the Helmholtz Association for excellent women researchers.

    ________________________________________

    See the full article here .


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    desi

    DESY is one of the world’s leading accelerator centres. Researchers use the large-scale facilities at DESY to explore the microcosm in all its variety – from the interactions of tiny elementary particles and the behaviour of new types of nanomaterials to biomolecular processes that are essential to life. The accelerators and detectors that DESY develops and builds are unique research tools. The facilities generate the world’s most intense X-ray light, accelerate particles to record energies and open completely new windows onto the universe. 
That makes DESY not only a magnet for more than 3000 guest researchers from over 40 countries every year, but also a coveted partner for national and international cooperations. Committed young researchers find an exciting interdisciplinary setting at DESY. The research centre offers specialized training for a large number of professions. DESY cooperates with industry and business to promote new technologies that will benefit society and encourage innovations. This also benefits the metropolitan regions of the two DESY locations, Hamburg and Zeuthen near Berlin.

    DESY Petra III interior


    DESY Petra III

    DESY/FLASH

    H1 detector at DESY HERA ring

    DESY DORIS III

     
  • richardmitnick 8:41 am on October 22, 2019 Permalink | Reply
    Tags: "New all-sky search reveals potential neutrino sources", , , , Cosmic Rays, , ,   

    From U Wisconsin IceCube Collaboration: “New all-sky search reveals potential neutrino sources” 

    U Wisconsin ICECUBE neutrino detector at the South Pole

    From From U Wisconsin IceCube Collaboration

    21 Oct 2019
    Madeleine O’Keefe

    For over a century, scientists have been observing very high energy charged particles called cosmic rays arriving from outside Earth’s atmosphere. The origins of these particles are very difficult to pinpoint because the particles themselves do not travel on a straight path to Earth. Even gamma rays, a type of high-energy photon that offers a little more insight, are absorbed when traversing long distances.

    The IceCube Neutrino Observatory, an array of optical modules buried in a cubic kilometer of ice at the South Pole, hunts for cosmic-ray sources inside and outside our galaxy—extending to galaxies more than billions of light years away—using hints from elusive particles called neutrinos. These neutrinos are expected to be produced by cosmic-ray collisions with gas or radiation near the sources.

    Unlike cosmic rays, neutrinos are not absorbed or diverted on their way to Earth, making them a practical tool for locating and understanding cosmic accelerators. If scientists can find a source of high-energy astrophysical neutrinos, this would be a smoking gun for a cosmic-ray source.

    After 10 years of searching for origins of astrophysical neutrinos, a new all-sky search provides the most sensitive probe of time-integrated neutrino emission of point-like sources. The IceCube Collaboration presents the results of this scan in a paper submitted recently to Physical Review Letters.

    1
    The pre-trial probability of the observed signal being due to background in a 5×5 degree window around the most significant point in the Northern Hemisphere (the hottest spot); the black cross marks the Fermi-3FGL coordinates of the galaxy NGC 1068. Credit: IceCube Collaboration

    Tessa Carver led this analysis under the supervision of Teresa Montaruli in the Département de Physique Nucléaire et Corpusculaire at the University of Geneva in Switzerland. “IceCube has already observed an astrophysical flux of neutrinos, so we know they exist and are detectable—we just don’t know exactly where they come from,” says Carver, now a postdoc at Cardiff University. “It is only a matter of time and precision until we can identify the sources behind this neutrino flux.”

    The principle challenge in searching for astrophysical neutrino sources with IceCube is the overwhelming background of events induced by cosmic-ray interactions in our atmosphere. The signal of faint neutrino sources needs to be extracted via sophisticated statistical analysis techniques.

    Using these methods, Carver and her collaborators “scanned” across the entire sky to look for point-like neutrino sources at arbitrary locations. This scanning method is able to identify very bright neutrino sources that could be invisible in gamma rays, which are also produced in cosmic-ray collisions.

    In order to be sensitive to dimmer sources, they also analyzed 110 galactic and extragalactic source candidates, which have been observed via gamma rays. They then combined the results obtained for individual sources in this list in a “population analysis,” which looks for a higher-than-expected rate of significant results from the individual source list search. This allows researchers to find significant neutrino emission, even if sources in the list are too weak to be observed individually.

    Researchers also employed a “stacking search” for three catalogs of gamma-ray sources within our galaxy. This search layers together all the emission from groups of known objects of the same type under the assumption that they have well-known emission properties. While it can significantly reduce the per-source emission required to observe a large excess of signal over the background, this search is limited in that it requires more knowledge of the sources in the catalog.

    2
    Skymap of -log10(plocal), where plocal is the local pre-trial p-value, for the area between ±82 degrees declination in equatorial coordinates. The Northern and Southern Hemisphere hotspots, defined as the most significant plocal in the given hemisphere, are indicated with black circles. Credit: IceCube Collaboration

    While the different analyses did not discover steady neutrino sources, the results are nevertheless exciting: some of the objects in the catalog of known sources showed a higher neutrino flux than expected, with excesses at the 3σ-level. In particular, the all-sky scan revealed that the “hottest” location in the sky is just 0.35 degrees away from the starburst galaxy NGC 1068, which has a 2.9σ excess over background. NGC 1068 is one of the closest black holes to us; it is embedded in a star-forming region with lots of matter for neutrinos to interact with while the high-energy gamma rays are attenuated, as shown by Fermi and MAGIC measurements.

    NASA/Fermi LAT


    NASA/Fermi Gamma Ray Space Telescope

    MAGIC Čerenkov telescopes at the Observatorio del Roque de los Muchachos (Garfia, La Palma, Spain)), Altitude 2,396 m (7,861 ft)

    This is the most significant excess seen besides TXS 0506-056, the 2017 source that IceCube found to be coincident with a gamma ray flare. Still, these potential neutrino sources require more data with a more-sensitive detector, like IceCube-Gen2, to be confirmed.

    The researchers also found that the Northern Hemisphere source catalog as a whole differed from background expectations with a significance of 3.3σ. Carver says these results demonstrate a strong motivation to continue to analyze the objects in the catalog. Time-dependent analyses, which search for flares of peaked emission, and the possibility of correlating neutrino emission with electromagnetic or gravitational wave observations for these and other sources may provide additional evidence of neutrino emission and insights into the neutrinos’ origin. With continued data-taking, more refined direction reconstruction, and the upcoming IceCube Upgrade, further improvements in sensitivity are on the horizon.

    “We are lucky to have the unique opportunity to be the first people to map the universe with neutrinos, which provides a brand-new perspective,” says Carver. “Also, this progress in neutrino astronomy is accompanied by great strides in gravitational wave physics and cosmic-ray physics.”

    Montaruli adds, “While we are at the dawn of a new era in astronomy that observes the universe not just with light, this is the first time we have begun to see potentially significant excesses of candidate neutrino events around interesting extragalactic objects in time-independent searches.”

    See the full article here .

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    Please help promote STEM in your local schools.

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    IceCube is a particle detector at the South Pole that records the interactions of a nearly massless sub-atomic particle called the neutrino. IceCube searches for neutrinos from the most violent astrophysical sources: events like exploding stars, gamma ray bursts, and cataclysmic phenomena involving black holes and neutron stars. The IceCube telescope is a powerful tool to search for dark matter, and could reveal the new physical processes associated with the enigmatic origin of the highest energy particles in nature. In addition, exploring the background of neutrinos produced in the atmosphere, IceCube studies the neutrinos themselves; their energies far exceed those produced by accelerator beams. IceCube is the world’s largest neutrino detector, encompassing a cubic kilometer of ice.

    IceCube employs more than 5000 detectors lowered on 86 strings into almost 100 holes in the Antarctic ice NSF B. Gudbjartsson, IceCube Collaboration

    Lunar Icecube

    IceCube DeepCore annotated

    IceCube PINGU annotated


    DM-Ice II at IceCube annotated

     
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