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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.

    https://www6.slac.stanford.edu/sites/www6.slac.stanford.edu/files/styles/lightbox_large_image/public/images/Fermi_bubbles-ST.jpg
    This artist’s representation shows the Fermi bubbles towering above and below the galaxy. (NASA’s Goddard Space Flight Center)

    NASA Fermi Telescope
    NASA/Fermi

    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.

    two
    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.

    SLAC Campus
    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.
    i1


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  • richardmitnick 4:10 pm on July 31, 2014 Permalink | Reply
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    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.

    novae
    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

    image
    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.

    shock
    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.

    gb
    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
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    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…

    scu

    scu
    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.

    he
    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
    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

    gray
    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

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

    2mSS

    …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” 

    01.07.13

    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.

    blast
    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
    202-358-5241
    j.d.harrington@nasa.gov

    Lynn Chandler
    NASA’s Goddard Space Flight Center, Greenbelt, Md.
    301-286-2806
    lynn.chandler-1@nasa.gov

    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.

      Like

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

      Thanks for your comment.

      Like

  • richardmitnick 10:18 am on December 14, 2012 Permalink | Reply
    Tags: , , , , Gamma Rays,   

    From CERN COURIER: HESS II is officially inaugurated The world’s largest Cherenkov telescope 

    Nov 27, 2012

    HESS II, located in the Khomas Highlands of Namibia, was officially inaugurated on 28 September, two months after it saw first light (CERN Courier October 2012 p39). Werner Hofmann of the Max Planck Institute for Nuclear Physics, Heidelberg, and spokesperson of the HESS collaboration, opened the ceremony with a brief presentation on HESS II, which was followed by messages from representatives of key collaborating institutes and agencies. HESS II has a 28-meter mirror and weighs in at almost 600 tons. Originally, H.E.S.S. had four telescopes, each with a mirror just under 12 meters in diameter

    HESS II

    HESS Cherenko Array

    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.

    The H.E.S.S. observatory is operated by the collaboration of more than 170 scientists, from 32 scientific institutions and 12 different countries: Namibia and South Africa, Germany, France, the UK, Ireland, Austria, Poland, the Czech Republic, Sweden, Armenia, and Australia. To date, the H.E.S.S. Collaboration has published over 100 articles in high-impact scientific journals, including the top-ranked Nature and Science journals.”

    See the full article here.


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  • richardmitnick 9:21 pm on December 13, 2012 Permalink | Reply
    Tags: , , , , , Gamma Rays, , , ,   

    From NASA Swift and Fermi – “Study Reveals a Remarkable Symmetry in Black Hole Jets” 

    NASA Fermi Small
    Fermi

    NASA SWIFT Telescope
    Swift

    Black holes range from modest objects formed when individual stars end their lives to behemoths billions of times more massive that rule the centers of galaxies. A new study using data from NASA’s Swift satellite and Fermi Gamma-ray Space Telescope shows that high-speed jets launched from active black holes possess fundamental similarities regardless of mass, age or environment. The result provides a tantalizing hint that common physical processes are at work.

    tri image
    Astronomers examining the properties of black hole jets compared 54 gamma-ray bursts (GRB’s) with 234 active galaxies classified as blazars and quasars. Surprisingly, the power and brightness of the jets share striking similarities despite a wide range of black hole mass, age and environment. Regardless of these differences, the jets produce light by tapping into similar percentages of the kinetic energy of particles moving along the jet, suggesting a common underlying physical cause.

    Credit: NASA’s Goddard Space Flight Center

    The particles in some GRB jets have been clocked at speeds exceeding 99.9 percent the speed of light. When the jet breaches the star’s surface, it produces a pulse of gamma rays typically lasting a few seconds. Satellites like Swift and Fermi can detect this emission if the jet is approximately directed toward us.

    To search for a trend across a wide range of masses, the scientists looked at the galactic-scale equivalent of GRB jets. These come from the brightest classes of active galaxies, blazars and quasars, which sport jets that likewise happen to point our way.

    To match the amount of energy given off by a typical blazar in one second, the sun must shine for 317,000 years. To equal the energy a run-of-the-mill GRB puts out in one second, the sun would need to shine for another 3 billion years.

    The finding simplifies astronomers’ understanding of black holes by showing that their activity is governed by the same set of rules — whatever they happen to be — independent of mass, age, or the jet’s brightness and power. The jets tap into similar fractions — between 3 and 15 percent — of the energy wrapped up in the motion of their accelerated particles to power the emission of gamma rays and other forms of light.”

    See the full article here.

    NASA Fermi Banner

    Fermi Space Telescope: Exploring the Extreme Universe
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  • richardmitnick 4:36 pm on November 28, 2012 Permalink | Reply
    Tags: , , , Gamma Rays, ,   

    From Symmetry: “Stellar black widows entrap companion stars” 

    Of the hundreds of objects in the universe emitting gamma rays, two look to be “black widows,” ancient stars extending their lives by sucking in material from companion stars. Stanford physicist Roger Romani is hot on the trail of these extreme stars.

    November 27, 2012
    Lori Ann White

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    Roger Romani

    “In its four years in orbit, the Fermi Gamma-ray Space Telescope has found a cosmos teeming with points of gamma-ray light. Newly discovered gamma-ray sources run the gamut from the expected, like supernova remnants and active galactic nuclei, to the surprising, like gamma rays from the sun or Earth-bound lightning strikes.


    Fermi

    But a considerable percentage of the gamma-ray sources discovered by Fermi can’t be matched up with any type of object, expected or not. Of the more than 1800 sources found by Fermi’s main instrument, the Large Area Telescope, in its first two years of operation, almost a third fell into this category.

    These “unassociated objects,” as they’re called, are the ones Stanford physics professor Roger Romani likes to study. Romani, a member of the Kavli Institute for Particle Astrophysics and Cosmology, an institute run jointly by Stanford and SLAC National Accelerator Laboratory, has spent the past few years identifying these sources. He’s found most of them to be common astronomical objects that, for one reason or another, were just a bit more difficult to recognize. Two of them, however, appear to be “black widows,” ancient stars extending their lives by sucking in material from companion stars. And there may be more….”

    Read on. It gets very interesting.

    See the full article here.

    Symmetry is a joint Fermilab/SLAC publication.

     
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