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  • richardmitnick 9:08 pm on November 16, 2017 Permalink | Reply
    Tags: HAWC detector, , High-Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory, , , 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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    Scientific American, the oldest continuously published magazine in the U.S., has been bringing its readers unique insights about developments in science and technology for more than 160 years.

  • richardmitnick 11:40 am on May 9, 2016 Permalink | Reply
    Tags: , , , High-Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory   

    From New Scientist: “Water telescope’s first sky map shows flickering black holes” 


    New Scientist

    18 April 2016 [just appeared on social media]

    Lisa Grossman

    HAWC High Altitude Cherenkov Experiment, HAWC Collaboration
    HAWC High Altitude Cherenkov Gamma-Ray Collaboration, HAWC Observatory, Sierra Negra volcano near Puebla, Mexico

    Twinkle, twinkle, little black hole. The High Altitude Water Cherenkov observatory has released its first map of the sky, including the first measurements of how often black holes flicker on and off. It has also caught pulsars, supernova remnants, and other bizarre cosmic beasts.

    “This is our deepest look at two-thirds of the sky, as well as the highest energy photons we’ve ever seen from any source,” says Brenda Dingus of Los Alamos National Laboratory, who presented the map at the American Physical Society meeting in Salt Lake City, Utah on 18 April. “We’re at the high energy frontier.”

    HAWC has been operating from the top of a mountain in central Mexico for about a year, and has caught some of the highest-energy photons ever observed. It is sensitive to gamma rays between 0.1 and 100 teraelectronvolts (TeV) in energy – more than 7 times higher energy than the particles produced in the Large Hadron Collider. The most energetic photon they’ve picked up so far is 60 TeV.

    HAWC’s map of the gamma ray sky. HAWC Collaboration

    But this is no normal telescope. “HAWC doesn’t look or work like any other observatory,” Dingus says. The detector is made up of 300 water tanks filled with 200,000 litres of purified water each (see main image, above). When high-energy particles go through the water, they emit a blue light called Cherenkov radiation. Physicists can use that light to reconstruct where the particles came from.

    HAWC doesn’t observe the extremely high-energy photons directly. They are blocked by our atmosphere – luckily for us, as they can damage living tissue. Instead the detector catches the spray of secondary particles that gamma rays produce when they strike the atmosphere, called air showers.

    “20,000 air shower particles per second hit our detector,” Dingus says. “In fact they’re hitting us right now.”

    In the first year of data, HAWC picked up 40 distinct sources of gamma rays, 10 of which had not been seen in gamma rays before. The team is now working to figure out if they were associated with any other known objects that have been seen in other wavelengths like visible or infrared light.

    One, for instance, was associated with a known supernova remnant from an energetic pulsar, says Michelle Hui of NASA’s Marshall Spaceflight Center in Huntsville, Alabama. When massive stars die as supernovas, they slough off material in a cloud called a supernova remnant. The shock wave from the explosion then sweeps through the cloud and accelerates particles in it to extremely high energies, where they radiate gamma rays.

    Another source is a known pulsar 26,000 light years away. A nearby third is still being identified, and might be related to the supernova remnant.

    Three new sources of gamma rays spotted by HAWC. HAWC Collaboration

    Flickering black holes

    HAWC can also pick up gamma rays from galaxies outside the Milky Way, the sources of which are much more mysterious. We think they are caused by the black holes at galactic centres, but the details of how the photons gain so much energy are murky.

    Because it is watching 24 hours a day, the detector can pick up changes in gamma ray brightness more reliably than ever before. Just 10 days ago, HAWC spotted a flare in a galaxy called Markarian 501.

    “On April 5 we didn’t see it, on April 6 it got very bright, and by April 8 it had nearly disappeared again,” said Robert Lauer of the University of New Mexico. The team put out an announcement on the Astronomer’s Telegram network to alert other observatories to follow up in different wavelengths, although it has not had any responses yet.

    Previous telescopes that could catch such energetic photons could only look at one part of the sky at once, so they couldn’t measure the frequency of these flares. Over the next five years, HAWC will be able to make the first measurements of how often they happen. This level of flaring seems to happen about 5 to 10 times per year, Lauer says, but it seems to vary from galaxy to galaxy.

    HAWC will also be able to see such a flare from the black hole at the centre of our own galaxy.

    “We know these things happen, so we expect them to happen here,” Hui says. “We just don’t know how often.”

    See the full article here .

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  • richardmitnick 7:27 pm on April 18, 2016 Permalink | Reply
    Tags: , , , High-Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory   

    From phys.org: “HAWC Gamma-ray Observatory reveals new look at the very-high-energy sky” 


    April 18, 2016

    View of two-thirds of the entire sky with very-high-energy gamma rays observed by HAWC. Many sources are clearly visible in our own Milky Way galaxy, as well as two other galaxies: Markarian 421 and Markarian 501. Some well-known constellations are shown as a reference. The center of the Milky Way is located toward Sagittarius. Credit: HAWC Collaboration

    The United States and Mexico constructed the High Altitude Water Cherenkov (HAWC) Gamma-ray Observatory to observe some of the most energetic phenomena in the known universe—the aftermath when massive stars die, glowing clouds of electrons around rapidly spinning neutron stars, and supermassive black holes devouring matter and spitting out powerful jets of particles. These violent explosions produce high-energy gamma rays and cosmic rays, which can travel large distances—making it possible to see objects and events far outside our own galaxy.

    HAWC High Altitude Cherenkov Experiment
    HAWC High Altitude Cherenkov Experiment

    Today, scientists operating HAWC released a new survey of the sky made from the highest energy gamma rays ever observed. The new sky map, which uses data collected since the observatory began running at full capacity last March, offers a deeper understanding of high-energy processes taking place in our galaxy and beyond.

    “HAWC gives us a new way to see the high-energy sky,” said Jordan Goodman, professor of physics at the University of Maryland, and U.S. lead investigator and spokesperson for the HAWC collaboration. “This new data from HAWC shows the galaxy in unprecedented detail, revealing new high-energy sources and previously unseen details about existing sources.”

    HAWC researchers presented the new observation data and sky map April 18, 2016, at the American Physical Society meeting. They also participated in a press conference at the meeting.

    The new sky map shows many new gamma ray sources within our own Milky Way galaxy. Because HAWC observes 24 hours per day and year-round with a wide field-of-view and large area, the observatory boasts a higher energy reach especially for extended objects. In addition, HAWC can uniquely monitor for gamma ray flares by sources in our galaxy and other active galaxies, such as Markarian 421 and Markarian 501.

    HAWC observations show that a previously known gamma ray source in the Milky Way galaxy, TeV J1930+188, which is probably due to a pulsar wind nebula, is far more complicated than originally thought. Where researchers previously identified a single gamma ray source, HAWC identified several hot spots. Credit: HAWC Collaboration

    One of HAWC’s new observations provides a better understanding of the high-energy nature of the Cygnus region—a northern constellation lying on the plane of the Milky Way. A multitude of neutron stars and supernova remnants call this star nursery home. HAWC scientists observed previously unknown objects in the Cygnus region and identified objects discovered earlier with sharper resolution.

    In a region of the Milky Way where researchers previously identified a single gamma ray source named TeV J1930+188, HAWC identified several hot spots, indicating that the region is more complicated than previously thought.

    “Studying these objects at the highest energies can reveal the mechanism by which they produce gamma rays and possibly help us unravel the hundred-year-old mystery of the origin of high-energy cosmic rays that bombard Earth from space,” said Goodman.

    HAWC—located 13,500 feet above sea level on the slopes of Mexico’s Volcán Sierra Negra—contains 300 detector tanks, each holding 50,000 gallons of ultrapure water with four light sensors anchored to the floor. When gamma rays or cosmic rays reach Earth’s atmosphere they set off a cascade of charged particles, and when these particles reach the water in HAWC’s detectors, they produce a cone-shaped flash of light known as Cherenkov radiation. The effect is much like a sonic boom produced by a supersonic jet, because the particles are traveling slightly faster than the speed of light in water when they enter the detectors.

    The light sensors record each flash of Cherenkov radiation inside the detector tanks. By comparing nanosecond differences in arrival times at each light sensor, scientists can reconstruct the angle of travel for each particle cascade. The intensity of the light indicates the primary particle’s energy, and the pattern of detector hits can distinguish between gamma rays and cosmic rays. With 300 detectors spread over an area equivalent to more than three football fields, HAWC “sees” these events in relatively high resolution.

    “Unlike traditional telescopes, with HAWC we have now an instrument that surveys two-thirds of the sky at the highest energies, day and night,” said Andrés Sandoval, Mexico spokesperson for HAWC.

    HAWC exhibits 15-times greater sensitivity than its predecessor—an observatory known as Milagro that operated near Los Alamos, New Mexico, and ceased taking data in 2008. In eight years of operation, Milagro found new sources of high-energy gamma rays, detected diffuse gamma rays from the Milky Way galaxy and discovered that the cosmic rays hitting earth had an unexpected non-uniformity.

    “HAWC will collect more data in the next few years, allowing us to reach even higher energies,” said Goodman. “Combining HAWC observations with data from other instruments will allow us to extend the reach of our understanding of the most violent processes in the universe.”

    See the full article here .

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  • richardmitnick 1:46 pm on January 20, 2015 Permalink | Reply
    Tags: , , High-Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory   

    From Symmetry: “Scientists complete array on Mexican volcano” 


    January 16, 2015
    Eagle Gamma

    An international team of astrophysicists has completed an advanced detector to map the most energetic phenomena in the universe.

    On Thursday, atop Volcán Sierra Negra, on a flat ledge near the highest point in Mexico, technicians filled the last of a collection of 300 cylindrical vats containing millions of gallons of ultrapure water.

    Together, the vats serve as the High-Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory, a vast particle detector covering an area larger than 5 acres. Scientists are using it to catch signs of some of the highest-energy astroparticles to reach the Earth.



    Tree diagram showing the relationship between types and classification of most common particle detectors

    The vats sit at an altitude of 4100 meters (13,500 feet) on a rocky site within view of the nearby Large Millimeter Telescope Alfonso Serrano. The area remained undeveloped until construction of the LMT, which began in 1997, brought with it the first access road, along with electricity and data lines.

    Large Millimeter Telescope Alfonso Serrano
    Large Millimeter Telescope Alfonso Serrano

    Temperatures at the top of the mountain are usually just cool enough for snow year-round, even though the atmosphere at the bottom of the mountain is warm enough to host palm trees and agave.

    “The local atmosphere is part of the detector,” says Alberto Carramiñana, general director of INAOE, the National Institute of Astrophysics, Optics and Electronics.

    Scientists at HAWC are working to understand high-energy particles that come from space. High-energy gamma rays come from extreme environments such as supernova explosions, active galactic nuclei. and gamma-ray bursts. They’re also associated with high-energy cosmic rays, the origins of which are still unknown.

    When incoming gamma rays and cosmic rays from space interact with Earth’s atmosphere, they produce a cascade of particles that shower the Earth. When these high-energy secondary particles reach the vats, they shoot through the water inside faster than particles of light can, producing an optical shock wave called “Cherenkov radiation.” The boom looks like a glowing blue, violet or ultraviolet cone.

    NRC photo of Cherenkov effect in the Reed Research Reactor.

    The Pierre Auger Cosmic Ray Observatory in western Argentina, in operation since 2004, uses similar surface detector tanks to catch cosmic rays, but its focus is particles at higher energies—up to millions of giga-electronvolts. HAWC observes widely and deeply between the energy range of 100 giga-electronvolts and 100,000 giga-electronvolts.

    “HAWC is a unique water Cherenkov observatory, with no actual peer in the world,” Carramiñana says.

    Results from HAWC will complement the Fermi Gamma-ray Space Telescope, which observes at lower energy levels, as well as dozens of other tools across the electromagnetic spectrum.

    NASA Fermi Telescope

    The vats at HAWC are made of corrugated steel, and each one holds a sealed, opaque bladder containing 50,000 gallons of liquid, according to Manuel Odilón de Rosas Sandoval, HAWC tank assembly coordinator. Each tank is 4 meters (13 feet) high and 7.3 meters (24 feet) in diameter and includes four light-reading photomultiplier tubes to detect the Cherenkov radiation.

    From its perch, HAWC sees the high-energy spectrum, in which particles have more energy in their motion than in their mass. The device is open to particles from about 15 percent of the sky at a time and, as the Earth rotates, is exposed to about 2/3 of the sky per day.

    Combining data from the 1200 sensors, astrophysicists can piece together the precise origins of the particle shower. With tens of thousands of events hitting the vats every second, around a terabyte of data will arrive per day. The device will record half a trillion events per year.

    The observatory, which was proposed in 2006 and began construction in 2012, is scheduled to operate for 10 years. “I look forward to the operational lifetime of HAWC,” Carramiñana says. “We are not sure what we will find.”

    More than 100 researchers from 30 partner organizations in Mexico and the United States collaborate on HAWC, with two additional associated scientists in Poland and Costa Rica. Prominent American partners include the University of Maryland, NASA’s Goddard Space Flight Center and Los Alamos National Laboratory. Funding comes from the Department of Energy, the National Science Foundation and Mexico’s National Council of Science and Technology.

    See the full article here.

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    Symmetry is a joint Fermilab/SLAC publication.

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