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  • richardmitnick 12:45 pm on January 23, 2015 Permalink | Reply
    Tags: , , , Gamma Rays,   

    From phys.org: “Three extremely luminous gamma-ray sources discovered in Milky Way’s satellite galaxy” 


    Jan 23, 2015
    Thomas Zoufal

    Optical image of the Milky Way and a multi-wavelength (optical, Hα) zoom into the Large Magellanic Cloud with superimposed H.E.S.S. sky maps. Credit: Milky Way image: © H.E.S.S. Collaboration, optical: SkyView, A. Mellinger

    Once again, the High Energy Stereoscopic System, H.E.S.S., has demonstrated its excellent capabilities. In the Large Magellanic Cloud, it discovered most luminous very high-energy gamma-ray sources: three objects of different type, namely the most powerful pulsar wind nebula, the most powerful supernova remnant, and a shell of 270 light years in diameter blown by multiple stars, and supernovae – a so-called superbubble.

    High Energy Stereoscopic System

    The Large Magellanic Cloud

    This is the first time that stellar-type gamma-ray sources are detected in an external galaxy, at these gamma-ray energies. The superbubble represents a new source class in very high-energy gamma rays.

    Very high-energy gamma rays are the best tracers of cosmic accelerators such as supernova remnants and pulsar wind nebulae – end-products of massive stars. There, charged particles are accelerated to extreme velocities. When these particles encounter light or gas in and around the cosmic accelerators, they emit gamma rays. Very high-energy gamma rays can be measured on Earth by observing the Cherenkov light emitted from the particle showers produced by incident gamma rays high up in the atmosphere using large telescopes with fast cameras.

    The Large Magellanic Cloud (LMC) is a dwarf satellite galaxy of our Milky Way, located about 170.000 light years away and showing us its face. New, massive stars are formed at a high rate in the LMC, and it harbors numerous massive stellar clusters. The LMC’s supernova rate relative to its stellar mass is five times that of our Galaxy. The youngest supernova remnant in the local group of galaxies, SN 1987A, is also a member of the LMC. Therefore, the H.E.S.S. scientists dedicated significant observation to searching for very high-energy gamma rays from this cosmic object.

    Local Group

    SN1987a before and after by David Malin Anglo-Australian Telescope

    For a total of 210 hours, the High Energy Stereoscopic System (H.E.S.S.) has observed the largest star-forming region within the LMC called Tarantula Nebula. For the first time in a galaxy outside the Milky Way, individual sources of very high-energy gamma rays could be resolved: three extremely energetic objects of different type.

    This first light image of the TRAPPIST national telescope at La Silla shows the Tarantula Nebula, located in the Large Magellanic Cloud (LMC) — one of the galaxies closest to us. Also known as 30 Doradus or NGC 2070, the nebula owes its name to the arrangement of bright patches that somewhat resembles the legs of a tarantula. Taking the name of one of the biggest spiders on Earth is very fitting in view of the gigantic proportions of this celestial nebula — it measures nearly 1000 light-years across! Its proximity, the favourable inclination of the LMC, and the absence of intervening dust make this nebula one of the best laboratories to help understand the formation of massive stars better. The image was made from data obtained through three filters (B, V and R) and the field of view is about 20 arcminutes across.

    The so-called superbubble 30 Dor C is the largest known X-ray-emitting shell and appears to have been created by several supernovae and strong stellar winds. Superbubbles are broadly discussed as (complementary or alternative to individual supernova remnants) factories where the galactic cosmic rays are produced. The H.E.S.S. results demonstrate that the bubble is a source of, and filled by, highly energetic particles. The superbubble represents a new class of sources in the very high-energy regime.

    Pulsars are highly magnetized, fast rotating neutron stars that emit a wind of ultra-relativistic particles forming a nebula. The most famous one is the Crab Nebula, one of the brightest sources in the high-energy gamma-ray sky.

    This is a mosaic image, one of the largest ever taken by NASA’s Hubble Space Telescope of the Crab Nebula, a six-light-year-wide expanding remnant of a star’s supernova explosion. Japanese and Chinese astronomers recorded this violent event nearly 1,000 years ago in 1054, as did, almost certainly, Native Americans.

    NASA Hubble Telescope
    NASA/ESA Hubble

    The orange filaments are the tattered remains of the star and consist mostly of hydrogen. The rapidly spinning neutron star embedded in the center of the nebula is the dynamo powering the nebula’s eerie interior bluish glow. The blue light comes from electrons whirling at nearly the speed of light around magnetic field lines from the neutron star. The neutron star, like a lighthouse, ejects twin beams of radiation that appear to pulse 30 times a second due to the neutron star’s rotation. A neutron star is the crushed ultra-dense core of the exploded star.

    The Crab Nebula derived its name from its appearance in a drawing made by Irish astronomer Lord William Parsons, 3rd Earl of Rosse in 1844, using a 36-inch telescope. When viewed by Hubble, as well as by large ground-based telescopes such as the European Southern Observatory’s Very Large Telescope, the Crab Nebula takes on a more detailed appearance that yields clues into the spectacular demise of a star, 6,500 light-years away.

    ESO VLT Interferometer
    ESO/ VLT

    The newly composed image was assembled from 24 individual Wide Field and Planetary Camera 23 exposures taken in October 1999, January 2000, and December 2000. The colors in the image indicate the different elements that were expelled during the explosion. Blue in the filaments in the outer part of the nebula represents neutral oxygen, green is singly-ionized sulfur, and red indicates doubly-ionized oxygen.

    NASA Hubble WFPC2
    WFPC2 (no longer in service)

    The pulsar PSR J0537−6910 driving the wind nebula N 157B discovered by the H.E.S.S. telescopes in the LMC is in many respects a twin of the very powerful Crab pulsar in our own Galaxy. However, its pulsar wind nebula N 157B outshines the Crab Nebula by an order of magnitude, in very high-energy gamma rays. Reasons are the lower magnetic field in N 157B and the intense starlight from neighboring star-forming regions, which both promote the generation of high-energy gamma rays.

    The supernova remnant N 132D, known as a bright object in the radio and infrared bands, appears to be one of the oldest – and strongest – supernova remnants still glowing in very high-energy gamma rays. Between 2500 and 6000 years old – an age where models predict that the supernova explosion front has slowed down and it ought no longer be efficiently accelerating particles – it still outshines the strongest supernova remnants in our Galaxy. The observations confirm suspicions raised by other H.E.S.S. observations, that supernova remnants can be much more luminous than thought before.

    Observed at the limits of detectability, and partially overlapping with each other, these new sources challenged the H.E.S.S. scientists. The discoveries were only possible due to the development of advanced methods of interpreting the Cherenkov images captured by the telescopes, improving in particular the precision with which gamma-ray directions can be determined.

    “Both the pulsar wind nebula and the supernova remnant, detected in the Large Magellanic Cloud by H.E.S.S., are more energetic than their most powerful relatives in the Milky Way. Obviously, the high star formation rate of the LMC causes it to breed very extreme objects”, summarizes Chia Chun Lu, a student who analyzed the LMC data as her thesis project. “Surprisingly, however, the young supernova remnant SN 1987A did not show up, in contrast to theoretical predictions. But we’ll continue the search for it,” adds her advisor Werner Hofmann, director at the MPI for Nuclear Physics in Heidelberg and for many years H.E.S.S. spokesperson.

    Indeed, the new H.E.S.S. II 28 m telescope will boost performance of the H.E.S.S. telescope system, and in the more distant future the planned Cherenkov Telescope Array (CTA) will provide even deeper and higher-resolution gamma-ray images of the LMC – in the plans for science with CTA, the satellite galaxy is already identified as a “Key Science Project” deserving special attention.

    Cherenkov Telescope Array

    The H.E.S.S. Telescopes

    The collaboration: The High Energy Stereoscopic System (H.E.S.S.) team consists of scientists from Germany, France, the United Kingdom, Namibia, South Africa, Ireland, Armenia, Poland, Australia, Austria, the Netherlands and Sweden, supported by their respective funding agencies and institutions.

    The instrument: The results were obtained using the High Energy Stereoscopic System (H.E.S.S.) telescopes in Namibia, in South-West Africa. This system of four 13 m diameter telescopes – recently complemented with the huge 28 m H.E.S.S. II telescope – is one of the most sensitive detectors of very high-energy gamma rays. These are absorbed in the atmosphere, where they create a short-lived shower of particles. The H.E.S.S. telescopes detect the faint, short flashes of bluish light which these particles emit (named Cherenkov light, lasting a few billionths of a second), collecting the light with big mirrors which reflect onto extremely sensitive cameras. Each image gives the position on the sky of a single gamma-ray photon, and the amount of light collected gives the energy of the initial gamma ray. Building up the images photon by photon allows H.E.S.S. to create maps of astronomical objects as they appear in gamma rays.

    The H.E.S.S. telescopes have been operating since late 2002; in September 2012 H.E.S.S. celebrated the first decade of operation, by which time the telescopes had recorded 9415 hours of observations, and detected 6361 million air shower events. H.E.S.S. has discovered the majority of the about 150 known cosmic objects emitting very high-energy gamma rays. In 2006, the H.E.S.S. team was awarded the Descartes Prize of the European Commission, in 2010 the Rossi Prize of the American Astronomical Society. A study performed in 2009 listed H.E.S.S. among the top 10 observatories worldwide.

    See the full article here.

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  • richardmitnick 1:46 pm on January 20, 2015 Permalink | Reply
    Tags: , Gamma Rays, 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.

  • richardmitnick 9:45 am on January 1, 2015 Permalink | Reply
    Tags: , Gamma Rays,   

    From NASA Science News: “Terrestrial Gamma-ray Flashes, More Common Than Previously Thought?” 

    NASA Science Science News

    Dec 31, 2014
    Dr. Tony Phillips

    Each day, thunderstorms around the world produce about a thousand quick bursts of gamma rays, some of the highest-energy light naturally found on Earth. By merging records of events seen by NASA’s Fermi Gamma-ray Space Telescope with data from ground-based radar and lightning detectors, scientists have completed the most detailed analysis to date of the types of thunderstorms involved.

    NASA Fermi Telescope

    “Remarkably, we have found that any thunderstorm can produce gamma rays, even those that appear to be so weak a meteorologist wouldn’t look twice at them,” said Themis Chronis, who led the research at the University of Alabama in Huntsville (UAH).

    New research merging Fermi data with information from ground-based radar and lightning networks shows that terrestrial gamma-ray flashes arise from an unexpected diversity of storms and may be more common than currently thought. Play video

    The outbursts, called terrestrial gamma-ray flashes (TGFs), were discovered in 1992 by NASA’s Compton Gamma-Ray Observatory, which operated until 2000. TGFs occur unpredictably and fleetingly, with durations less than a thousandth of a second, and remain poorly understood.

    NASA Compton Gamma Ray Observatory

    In late 2012, Fermi scientists employed new techniques that effectively upgraded the satellite’s Gamma-ray Burst Monitor (GBM), making it 10 times more sensitive to TGFs and allowing it to record weak events that were overlooked before.

    “As a result of our enhanced discovery rate, we were able to show that most TGFs also generate strong bursts of radio waves like those produced by lightning,” said Michael Briggs, assistant director of the Center for Space Plasma and Aeronomic Research at UAH and a member of the GBM team.

    Previously, TGF positions could be roughly estimated based on Fermi’s location at the time of the event. The GBM can detect flashes within about 500 miles (800 kilometers), but this is too imprecise to definitively associate a TGF with a specific storm.

    Ground-based lightning networks use radio data to pin down strike locations. The discovery of similar signals from TGFs meant that scientists could use the networks to determine which storms produce gamma-ray flashes, opening the door to a deeper understanding of the meteorology powering these extreme events.

    Chronis, Briggs and their colleagues sifted through 2,279 TGFs detected by Fermi’s GBM to derive a sample of nearly 900 events accurately located by the Total Lightning Network operated by Earth Networks in Germantown, Maryland, and the World Wide Lightning Location Network, a research collaboration run by the University of Washington in Seattle. These systems can pinpoint the location of lightning discharges — and the corresponding signals from TGFs — to within 6 miles (10 km) anywhere on the globe.

    From this group, the team identified 24 TGFs that occurred within areas covered by Next Generation Weather Radar (NEXRAD) sites in Florida, Louisiana, Texas, Puerto Rico and Guam. For eight of these storms, the researchers obtained additional information about atmospheric conditions through sensor data collected by the Department of Atmospheric Science at the University of Wyoming in Laramie.

    “All told, this study is our best look yet at TGF-producing storms, and it shows convincingly that storm intensity is not the key,” said Chronis, who will present the findings Wed., Dec. 17, in an invited talk at the American Geophysical Union meeting in San Francisco. A paper describing the research has been submitted to the Bulletin of the American Meteorological Society.

    Scientists suspect that TGFs arise from strong electric fields near the tops of thunderstorms. Updrafts and downdrafts within the storms force rain, snow and ice to collide and acquire electrical charge. Usually, positive charge accumulates in the upper part of the storm and negative charge accumulates below. When the storm’s electrical field becomes so strong it breaks down the insulating properties of air, a lightning discharge occurs.

    Under the right conditions, the upper part of an intracloud lightning bolt disrupts the storm’s electric field in such a way that an avalanche of electrons surges upward at high speed. When these fast-moving electrons are deflected by air molecules, they emit gamma rays and create a TGF.

    About 75 percent of lightning stays within the storm, and about 2,000 of these intracloud discharges occur for each TGF Fermi detects.

    The new study confirms previous findings indicating that TGFs tend to occur near the highest parts of a thunderstorm, between about 7 and 9 miles (11 to 14 kilometers) high. “We suspect this isn’t the full story,” explained Briggs. “Lightning often occurs at lower altitudes and TGFs probably do too, but traveling the greater depth of air weakens the gamma rays so much the GBM can’t detect them.”

    Based on current Fermi statistics, scientists estimate that some 1,100 TGFs occur each day, but the number may be much higher if low-altitude flashes are being missed.

    While it is too early to draw conclusions, Chronis notes, there are a few hints that gamma-ray flashes may prefer storm areas where updrafts have weakened and the aging storm has become less organized. “Part of our ongoing research is to track these storms with NEXRAD radar to determine if we can relate TGFs to the thunderstorm life cycle,” he said.

    See the full article here.

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  • richardmitnick 9:45 pm on July 31, 2014 Permalink | Reply
    Tags: , , , Gamma Rays, ,   

    From SLAC Lab: “Despite Extensive Analysis, Fermi Bubbles Defy Explanation” 

    SLAC Lab

    July 31, 2014

    Scientists from Stanford and the Department of Energy’s SLAC National Accelerator Laboratory have analyzed more than four years of data from NASA’s Fermi Gamma-ray Space Telescope, along with data from other experiments, to create the most detailed portrait yet of two towering bubbles that stretch tens of thousands of light-years above and below our galaxy.

    This artist’s representation shows the Fermi bubbles towering above and below the galaxy. (NASA’s Goddard Space Flight Center)

    NASA Fermi Telescope

    The bubbles, which shine most brightly in energetic gamma rays, were discovered almost four years ago by a team of Harvard astrophysicists led by Douglas Finkbeiner who combed through data from Fermi’s main instrument, the Large Area Telescope.

    NASA Fermi LAT Large Area Telescope
    NASA/Fermi LAT

    The new portrait, described in a paper that has been accepted for publication in The Astrophysical Journal, reveals several puzzling features, said Dmitry Malyshev, a postdoctoral researcher at the Kavli Institute for Particle Astrophysics and Cosmology who co-led on the analysis.

    For example, the outlines of the bubbles are quite sharp, and the bubbles themselves glow in nearly uniform gamma rays over their colossal surfaces, like two 30,000-light-year-tall incandescent bulbs screwed into the center of the galaxy.

    Their size is another puzzle. The farthest reaches of the Fermi bubbles boast some of the highest energy gamma rays, but there’s no discernable cause for them that far from the galaxy.

    Finally, although the parts of the bubbles closest to the galactic plane shine in microwaves as well as gamma rays, about two-thirds of the way out the microwaves fade and only gamma rays are detectable. Not only is this different from other galactic bubbles, but it makes the researchers’ work that much more challenging, said Malyshev’s co-lead, KIPAC postdoctoral researcher Anna Franckowiak.

    KIPAC researchers Dmitry Malyshev (left) and Anna Franckowiak with the magazine issues that contain the articles about the Fermi bubbles they co-authored for the general public. Malyshev’s is in the July 2014 issue of Scientific American, while Franckowiak’s article is in the July 2014 issue of Physics Today. (SLAC National Accelerator Laboratory)

    “Since the Fermi bubbles have no known counterparts in other wavelengths in areas high above the galactic plane, all we have to go on for clues are the gamma rays themselves,” she said.

    What Blew The Bubbles?

    Soon after the initial discovery theorists jumped in, offering several explanations for the bubbles’ origins. For example, they could have been created by huge jets of accelerated matter blasting out from the supermassive black hole at the center of our galaxy. Or they could have been formed by a population of giant stars, born from the plentiful gas surrounding the black hole, all exploding as supernovae at roughly the same time.

    “There are several models that explain them, but none of the models is perfect,” Malyshev said. “The bubbles are rather mysterious.”

    Creating the portrait wasn’t easy.

    “It’s very tricky to model,” said Franckowiak. “We had to remove all the foreground gamma-ray emissions from the data before we could clearly see the bubbles.”

    From the vantage point of most Earth-bound telescopes, all but the highest-energy gamma rays are completely screened out by our atmosphere. It wasn’t until the era of orbiting gamma-ray observatories like Fermi that scientists discovered how common extra-terrestrial gamma rays really are. Pulsars, supermassive black holes in other galaxies and supernovae are all gamma rays point sources, like distant stars are point sources of visible light, and all those gamma rays had to be scrubbed from the Fermi data. Hardest to remove were the galactic diffuse emissions, a gamma ray fog that fills the galaxy from cosmic rays interacting with interstellar particles.

    “Subtracting all those contributions didn’t subtract the bubbles,” Franckowiak said. “The bubbles do exist and their properties are robust.” In other words, the bubbles don’t disappear when other gamma-ray sources are pulled out of the Fermi data – in fact, they stand out quite clearly.

    Franckowiak says more data is necessary before they can narrow down the origin of the bubbles any further.

    “What would be very interesting would be to get a better view of them closer to the galactic center,” she said, “but the galactic gamma ray emissions are so bright we’d need to get a lot better at being able to subtract them.”

    Fermi is continuing to gather the data Franckowiak wants, but for now, both researchers said, there are a lot of open questions.

    See the full article here.

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    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.

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  • richardmitnick 4:10 pm on July 31, 2014 Permalink | Reply
    Tags: , , , , Gamma Rays,   

    From NASA/Fermi: “NASA’s Fermi Space Telescope Reveals New Source of Gamma Rays” 

    NASA Fermi

    July 31, 2014
    No Writer Credit

    Observations by NASA’s Fermi Gamma-ray Space Telescope of several stellar eruptions, called novae, firmly establish these relatively common outbursts almost always produce gamma rays, the most energetic form of light.

    These images show Fermi data centered on each of the four gamma-ray novae observed by the LAT. Colors indicate the number of detected gamma rays with energies greater than 100 million electron volts (blue indicates lowest, yellow highest). Image Credit: NASA/DOE/Fermi LAT Collaboration

    “There’s a saying that one is a fluke, two is a coincidence, and three is a class, and we’re now at four novae and counting with Fermi,” said Teddy Cheung, an astrophysicist at the Naval Research Laboratory in Washington, and the lead author of a paper reporting the findings in the Aug. 1 edition of the journal Science.

    A nova is a sudden, short-lived brightening of an otherwise inconspicuous star caused by a thermonuclear explosion on the surface of a white dwarf, a compact star not much larger than Earth. Each nova explosion releases up to 100,000 times the annual energy output of our sun. Prior to Fermi, no one suspected these outbursts were capable of producing high-energy gamma rays, emission with energy levels millions of times greater than visible light and usually associated with far more powerful cosmic blasts.

    Fermi’s Large Area Telescope (LAT) scored its first nova detection, dubbed V407 Cygni, in March 2010. The outburst came from a rare type of star system in which a white dwarf interacts with a red giant, a star more than a hundred times the size of our sun. Other members of the same unusual class of stellar system have been observed “going nova” every few decades.

    NASA Fermi LAT Large Area Telescope
    NASA/Fermi LAT

    The white dwarf star in V407 Cygni, shown here in an artist’s concept, went nova in 2010. Scientists think the outburst primarily emitted gamma rays (magenta) as the blast wave plowed through the gas-rich environment near the system’s red giant star. Image Credit: NASA’s Goddard Space Flight Center/S. Wiessinger

    In 2012 and 2013, the LAT detected three so-called classical novae which occur in more common binaries where a white dwarf and a sun-like star orbit each other every few hours.

    “We initially thought of V407 Cygni as a special case because the red giant’s atmosphere is essentially leaking into space, producing a gaseous environment that interacts with the explosion’s blast wave,” said co-author Steven Shore, a professor of astrophysics at the University of Pisa in Italy. “But this can’t explain more recent Fermi detections because none of those systems possess red giants.”

    Fermi detected the classical novae V339 Delphini in August 2013 and V1324 Scorpii in June 2012, following their discovery in visible light. In addition, on June 22, 2012, the LAT discovered a transient gamma-ray source about 20 degrees from the sun. More than a month later, when the sun had moved farther away, astronomers looking in visible light discovered a fading nova from V959 Monocerotis at the same position.

    Astronomers estimate that between 20 and 50 novae occur each year in our galaxy. Most go undetected, their visible light obscured by intervening dust and their gamma rays dimmed by distance. All of the gamma-ray novae found so far lie between 9,000 and 15,000 light-years away, relatively nearby given the size of our galaxy.

    Novae occur because a stream of gas flowing from the companion star piles up into a layer on the white dwarf’s surface. Over time — tens of thousands of years, in the case of classical novae, and several decades for a system like V407 Cygni — this deepening layer reaches a flash point. Its hydrogen begins to undergo nuclear fusion, triggering a runaway reaction that detonates the accumulated gas. The white dwarf itself remains intact.

    Novae typically originate in binary systems containing sun-like stars, as shown in this artist’s rendering. A nova in a system like this likely produces gamma rays (magenta) through collisions among multiple shock waves in the rapidly expanding shell of debris. Image Credit: NASA’s Goddard Space Flight Center/S. Wiessinger

    One explanation for the gamma-ray emission is that the blast creates multiple shock waves that expand into space at slightly different speeds. Faster shocks could interact with slower ones, accelerating particles to near the speed of light. These particles ultimately could produce gamma rays.

    “This colliding-shock process must also have been at work in V407 Cygni, but there is no clear evidence for it,” said co-author Pierre Jean, a professor of astrophysics at the University of Toulouse in France. This is likely because gamma rays emitted through this process were overwhelmed by those produced as the shock wave interacted with the red giant and its surroundings, the scientists conclude.

    See the full article here.

    The Fermi Gamma-ray Space Telescope , formerly referred to as the Gamma-ray Large Area Space Telescope (GLAST), is a space observatory being used to perform gamma-ray astronomy observations from low Earth orbit. Its main instrument is the Large Area Telescope (LAT), with which astronomers mostly intend to perform an all-sky survey studying astrophysical and cosmological phenomena such as active galactic nuclei, pulsars, other high-energy sources and dark matter. Another instrument aboard Fermi, the Gamma-ray Burst Monitor (GBM; formerly GLAST Burst Monitor), is being used to study gamma-ray bursts. The mission is a joint venture of NASA, the United States Department of Energy, and government agencies in France, Germany, Italy, Japan, and Sweden.

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  • richardmitnick 1:03 pm on March 21, 2014 Permalink | Reply
    Tags: , , , , , Gamma Rays,   

    From Fermilab: “If it looks like dark matter and acts like dark matter …” 

    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    Friday, March 21, 2014
    Dan Hooper

    Are we seeing dark matter in the gamma-ray sky? It sure looks that way.

    Since early in the mission of the Fermi Gamma-ray Space Telescope, a number of scientists have noticed an interesting and fairly bright signal coming from the direction of the Galactic Center. Lisa Goodenough, then of New York University, and I wrote the first couple of papers on this observation in 2009 and 2010. What especially captured our attention was that the spectrum and spatial shape of this signal seemed to match what had been predicted to come from annihilating dark matter particles — an intriguing hint indeed.

    NASA Fermi Telescope
    NASA Fermi Gamma Ray Telescope

    The motivation for using gamma-ray telescopes to look for dark matter is simple. In many (if not most) theories of dark matter, when pairs of dark matter particles interact, they can annihilate each other, producing other kinds of energetic particles in their place. Given the large densities of dark matter that are present around the Galactic Center, dark matter particles are expected to annihilate there at a high rate, producing large fluxes of energetic gamma rays.

    In our new analysis, we reduced background contamination by making use of only the best-reconstructed events. We also performed a large number of tests and cross checks, many of which had not been carried out before. We examined multiple variations in our background model and looked for anything that might masquerade as a signal. What we found was remarkable: The signal from the Galactic Center was not only robust and statistically significant, but in every respect we could measure, it looked like annihilating dark matter.

    The resemblance was astonishing. First, the shape of the observed gamma ray spectrum is in excellent agreement with what we would expect from dark matter particles with a mass of about 35 GeV. Second, the spatial distribution of the photons looks very much like what we calculate based on numerical simulations, approximately spherically symmetric and falling off rapidly with distance from the Galactic Center. And third, the overall brightness of the gamma-ray signal implies a dark matter annihilation cross section (times relative velocity) of about 2×10-26 cm3/s, which is almost exactly the value predicted for a generic dark matter species that was produced in the big bang.

    Although one can never be completely certain in science, and future observations and analysis related to this signal will be very important, this gamma-ray signal does look remarkably like annihilating dark matter. If so, it would represent the first detection of dark matter particles. It is an exciting time to be hunting for dark matter.

    Learn more about the finding in our new paper, which describes in more detail our updated analysis of the Fermi telescope’s gamma-ray data.

    See the full article here.

    Fermilab Campus

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics.

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  • richardmitnick 7:49 pm on November 21, 2013 Permalink | Reply
    Tags: , , , , Gamma Rays,   

    From Symmetry: “Cosmic explosion calls theory into question” 

    Observations of a rare cosmic explosion challenge scientists’ theoretical understanding of how gamma-ray bursts work.

    November 21, 2013
    No Writer Credit

    On April 27, a blast of light from a dying star in a distant galaxy washed over Earth. A trio of satellites, working in concert with ground-based robotic telescopes, captured the event, which was one of the brightest such “gamma-ray bursts” ever seen. Those observations are now challenging current theoretical understanding of how gamma-ray bursts work.

    Courtesy of NASA’s Goddard Space Flight Center

    “We expect to see an event like this only once or twice a century, so we’re fortunate it happened when we had a large array of sensitive space telescopes with complementary capabilities available to see it,” says Paul Hertz, director of NASA’s astrophysics division, which oversees several of the telescopes that saw the explosion.

    Gamma-ray bursts are the most luminous explosions in the cosmos. Astronomers think most occur when the core of a massive star runs out of nuclear fuel, collapses under its own weight, and forms a black hole. The baby black hole then accelerates jets of particles that drill all the way through the collapsing star and erupt into space at nearly the speed of light.

    This causes a burst of light in many wavelengths. Optical light is emitted from the eruption, while hot matter surrounding the black hole and internal shock waves produced by collisions within the jet are thought to emit gamma rays with energies in the million-electronvolt range, or roughly 500,000 times the energy of visible light. The highest-energy emission, with billion-electronvolt gamma rays, is thought to arise when the jet slams into its surroundings, forming an external shock wave.

    Yet, says Rob Preece of the University of Alabama, Huntsville, “the spectacular results… show that our widely accepted picture of [high-energy] gamma rays from internal shock waves is woefully inadequate.”

    Just as the optical flash peaked, the Fermi Gamma-ray Space Telescope detected a spike in billion-electronvolt gamma rays, providing the first detailed look at the relationship between a burst’s optical light and its high-energy gamma rays. The result defied expectations.

    “We thought the visible light for these flashes came from internal shocks, but this burst shows that it must come from the external shock, which produces the most energetic gamma rays,” says Sylvia Zhu, a Fermi Gamma-ray Space Telescope team member at the University of Maryland in College Park.

    More puzzling is a 32-billion-electronvolt gamma ray, which was detected nine hours after the burst’s onset. A late arrival with this kind of energy raises questions about how well scientists really understand the physics of the external shock wave.

    The burst’s extraordinary brightness enabled NASA’s newest X-ray observatory, the Nuclear Spectroscopic Telescope Array (NuSTAR), to make a first-time detection of a burst afterglow in high-energy, or “hard,” X-rays after more than a day.

    Taken together with data from the Fermi Gamma-ray Space Telescope, these observations challenge both a 30-year-old prediction limiting the highest-energy light and a 12-year-old prediction of how different emission mechanisms should shift in prominence as the burst fades.

    This gamma-ray burst is the subject of five papers published online Nov. 21. Four of these, published by Science Express, highlight contributions by Fermi, Swift and RAPTOR. The NuSTAR study is published by The Astrophysical Journal Letters.

    See the full article here.

    Symmetry is a joint Fermilab/SLAC publication.

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  • richardmitnick 8:28 am on April 7, 2013 Permalink | Reply
    Tags: , , , , Gamma Rays,   

    From H.E.S.S.: “Disentangling TeV emission in complex regions: the Scutum arm tangent 

    HESS Cherenko Array

    April 2013
    No Writer Credit

    “With increasing statistics of data and improved analysis methods, many of the extended H.E.S.S. gamma ray sources can be resolved into finer structures or even multiple sources. A nice example is a study of the region of Scutum arm tangent. The Scutum arm is one of the spiral arms of our Galaxy, and from the solar system one looks along the tangent of arm, at Galactic Longitude around 30 deg., with sources located along the arm piling up…


    Composite image of the source C region of HESS J1843-033: in red the radio image (from the VLA survey) showing a radio-galaxy candidate and a small fraction of a putative supernova remnant shell at the left, in blue the Chandra image, showing the diffuse emission coincident with the northern lobe, which is likely to be a pulsar wind nebula because of its morphology and spectrum.

    Applying analysis techniques to optimize angular resolution, the extended gamma-ray emission of the source HESS J1843-033 can be resolved into three significant gamma ray sources labeled source A, B, C. Source A is an extended source, source B is consistent with a point source, and source C is marginally extended. Below source B another faint hotspot starts to emerge.

    Top: The Scutum arm tangent as seen in the H.E.S.S. Galactic Plane Survey (in Galactic coordinates). Bottom: Zoom into the HESS J1843-033 region, using a gamma-ray analysis optimized for best angular resolution, and applying minimal smoothing of the image (image in RA-Dec coordinates, rotated compared to the survey image). The three sources have significances in excess of 8 sigma (source C), and 10 sigma (sources A, B). Source A is extended with a size of 0.15 degr., source B is consistent with a point source, and source C is marginally extended.”

    See the full article with much more data here.

    The High Energy Stereoscopic System

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

    Crab nebula

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  • richardmitnick 12:50 pm on March 1, 2013 Permalink | Reply
    Tags: , , , Gamma Rays,   

    From Fermilab- “Frontier Science Result: Theoretical Astrophysics Gamma-ray bubbles and dark matter” 

    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    Friday, March 1, 2013
    Dan Hooper

    “Although it’s been two and a half years since a group of Harvard astrophysicists discovered a pair of bright “bubbles” in data from the Fermi Gamma-Ray Space Telescope, the origin of these gamma-rays is still not well understood. Last summer, Harvard’s Tracy Slater and I began to think about ways that we could test different scenarios for how the Fermi bubbles may have formed. We found a very different gamma-ray signal, with a possible connection to dark matter.
    NASA Fermi Telescope.
    NASA Fermi

    Scientists have seen evidence of gamma-ray bubbles extending tens of thousands of light-years north and south of the Galactic Center. A new study finds that some of this gamma-ray emission may be the result of annihilating dark-matter particles. Image: NASA

    The Fermi bubbles extend tens of thousands of light years north and south of the Galactic Center—the center of the Milky Way—and are likely the consequence of a very active period in the recent history of the galaxy, maybe having to do with the rate of star formation in the inner galaxy or with an eruption from a supermassive black hole

    The Galactic Centre as seen by one of the 2MASS infrared telescopes, is located in the bright upper left portion of the image. Wikipedia


    …Early in our investigation of the bubbles, we noticed that their spectrum varies a lot with galactic latitude. At high latitudes—far from the Galactic Plane—the spectrum looks much like we would expect and can be easily explained by cosmic-ray electrons interacting with radiation and the galactic magnetic field. Within ten thousand light-years or so of the plane, however, the spectrum looks very different, exhibiting a sharp and bright feature, peaking at a few GeV. No realistic spectrum of cosmic rays could account for this strange signal.

    So if not from cosmic rays, where does this extra GeV emission come from?

    There is another, more exciting, interpretation. If the dark matter is made up of particles that can annihilate with each other, then we should expect those annihilations to produce a sharply peaked spectrum of gamma-rays, very much like the observed from the low-latitude regions of the Fermi bubbles. The angular distribution of the observed gamma-rays is also in good agreement with what we expect from dark matter. Furthermore, the gamma-rays from the inner few degrees around the Galactic Center exhibit the same bump and overall distribution, just as predicted from dark matter annihilations.

    Are we finally seeing evidence of dark matter particles? According to the old adage, “If it looks like a duck, swims like a duck and quacks like a duck, then it is probably a duck.”

    See the full article here.

    Fermilab Campus

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics.

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  • richardmitnick 3:31 pm on January 8, 2013 Permalink | Reply
    Tags: , , , , Gamma Rays,   

    From NASA Fermi: “Galaxy’s Gamma-Ray Flares Erupted Far From its Black Hole” 


    In 2011, a months-long blast of energy launched by an enormous black hole almost 11 billion years ago swept past Earth. Using a combination of data from NASA’s Fermi Gamma-ray Space Telescope and the National Science Foundation’s Very Long Baseline Array (VLBA), the world’s largest radio telescope, astronomers have zeroed in on the source of this ancient outburst.

    Credit: NASA/DOE/Fermi LAT Collaboration

    Prior to its strong outbursts in 2011, blazar 4C +71.07 was a weak source for Fermi’s LAT. These images centered on 4C +71.07 show the rate at which the LAT detected gamma rays with energies above 100 million electron volts; lighter colors equal higher rates. The image at left covers 2.5 years, from the start of Fermi’s mission to 2011. The image at right shows 10 weeks of activity in late 2011, when 4C +71.07 produced its strongest outburst. A more frequently active blazar, S5 0716+71, appears in both images.

    Theorists expect gamma-ray outbursts occur only in close proximity to a galaxy’s central black hole, the powerhouse ultimately responsible for the activity. A few rare observations suggested this is not the case.

    The 2011 flares from a galaxy known as 4C +71.07 now give astronomers the clearest and most distant evidence that the theory still needs some work. The gamma-ray emission originated about 70 light-years away from the galaxy’s central black hole.

    The 4C +71.07 galaxy was discovered as a source of strong radio emission in the 1960s. NASA’s Compton Gamma-Ray Observatory, which operated in the 1990s, detected high-energy flares, but the galaxy was quiet during Fermi’s first two and a half years in orbit.

    In early November 2011, at the height of the outburst, the galaxy was more than 10,000 times brighter than the combined luminosity of all of the stars in our Milky Way galaxy.

    ‘This renewed activity came after a long slumber, and that’s important because it allows us to explicitly link the gamma-ray flares to the rising emission observed by radio telescopes,’ said David Thompson, a Fermi deputy project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md.

    Located in the constellation Ursa Major, 4C +71.07 is so far away that its light takes 10.6 billion years to reach Earth. Astronomers are seeing this galaxy as it existed when the universe was less than one-fourth of its present age.”

    See the full article here.

    J. D. Harrington
    NASA Headquarters, Washington

    Lynn Chandler
    NASA’s Goddard Space Flight Center, Greenbelt, Md.

    The Fermi Gamma-ray Space Telescope , formerly referred to as the Gamma-ray Large Area Space Telescope (GLAST), is a space observatory being used to perform gamma-ray astronomy observations from low Earth orbit. Its main instrument is the Large Area Telescope (LAT), with which astronomers mostly intend to perform an all-sky survey studying astrophysical and cosmological phenomena such as active galactic nuclei, pulsars, other high-energy sources and dark matter. Another instrument aboard Fermi, the Gamma-ray Burst Monitor (GBM; formerly GLAST Burst Monitor), is being used to study gamma-ray bursts. The mission is a joint venture of NASA, the United States Department of Energy, and government agencies in France, Germany, Italy, Japan, and Sweden.

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    • katesisco 9:50 am on February 2, 2013 Permalink | Reply

      Baffling, if that was an experiment on Earth, one would think that the energy had been lazed via magnetism (90 degree offset), and that speed 20x faster than light was possible.


    • richardmitnick 10:32 am on February 2, 2013 Permalink | Reply

      Thanks for your comment.


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