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  • richardmitnick 5:40 am on October 4, 2017 Permalink | Reply
    Tags: , , , , , , , ESA e-ASTROGAM, , , NASA Fermi   

    From astrobites: “Future Gamma-ray Telescopes and the Search for Dark Matter” 

    Astrobites bloc

    Astrobites

    Oct 3, 2017
    Nora Shipp

    Title: Resolving Dark Matter Subhalos With Future Sub-GeV Gamma-Ray Telescopes
    Authors: Ti-Lin Chou, Dimitrios Tanoglidis, and Dan Hooper
    First Author’s Institution: Dept. of Physics, University of Chicago, USA

    Status: Submitted to the Journal of Cosmology and Astroparticle Physics (open access)

    We are surrounded by undetected dark matter.

    Caterpillar Project A Milky-Way-size dark-matter halo and its subhalos circled, an enormous suite of simulations . Griffen et al. 2016

    In fact, our entire Galaxy is enveloped in a large halo of it, but because dark matter does not emit or reflect light, the halo is completely invisible.

    Dark matter halo Image credit: Virgo consortium / A. Amblard / ESA

    Milky Way NASA/JPL-Caltech /ESO R. Hurt

    Inside this halo, orbiting our galaxy, are hundreds of smaller, equally invisible dark matter halos (Figure 1).

    1
    Figure 1. Galaxies like the Milky Way are surrounded by small dark matter halos (blue blobs). Some of these halos contain no stars, but could still produce gamma-rays from dark matter annihilation! Source: ESO

    The larger ones contain their own dwarf galaxies, but the smallest halos are so tiny that they contain no stars at all. However, if the leading theory of WIMP (Weakly Interacting Massive Particle) dark matter is correct, there is one way that we could actually see these dark matter halos without the help of any stars. If dark matter particles are their own antiparticle, they would annihilate when they come into contact with each other, producing various particles, including highly energetic photons known as gamma-rays.

    Gamma-rays have millions of times more energy than the optical photons that human eyes can see, yet these energetic particles are quite difficult to detect. The current leader in gamma-ray detection is the Fermi Gamma-ray Space Telescope, a satellite that has been orbiting the Earth, searching the sky for gamma-rays, for almost 10 years.

    NASA/Fermi Telescope

    NASA/Fermi LAT

    Since Fermi was first launched, scientists have searched the gamma-ray sky for evidence of dark matter annihilation. What makes this search really tricky is that dark matter is not the only thing that produces gamma-rays. The sky is actually full of gamma-rays coming from all directions, produced by clouds of gas, pulsars, and active galactic nuclei, among many other sources (Figure 2 [not shown in article, replaced here).

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    Fermi’s Latest Gamma-ray Census Highlights Cosmic Mysteries

    However, those tiny dark matter halos that don’t contain stars or gas or any kind of non-dark matter should only be producing gamma-rays from dark matter annihilation. The catch is that we have no idea where these dark matter halos are. Scientists, therefore, have searched all across the sky for gamma-rays that might be coming from dark halos, and they just might have found a couple.

    Two sources of gamma-rays fit all the requirements – they are in the right part of the sky, do not emit any other kind of light (as you’d expect from a halo containing only dark matter), and appear to extend wider across the sky than the single point of a far away star. However, it’s impossible to tell whether these sources are really extended like a dark matter halo or whether they are just two star-like points so close to each other that they blur together, appearing to Fermi as a single blob. Today’s paper considers whether a proposed successor to Fermi called e-ASTROGAM (Figure 3) will be able to resolve the mystery of these gamma-ray blobs.

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    Figure 3. A model of e-Astrogam, one potential successor to the Fermi Gamma-ray Space Telescope. Source: ESA

    Are they in fact dark matter halos (in which case this would be the first confirmed detection of dark matter annihilation!) or are they simply two points blurred into one?

    e-ASTROGAM would be quite similar to Fermi, but with several important changes. The biggest difference is that it would be able to detect gamma-rays at a slightly lower energy than Fermi, giving us a brand new view of the gamma-ray sky. In the context of today’s paper, however, the most significant difference is the angular resolution. Angular resolution determines how close together two objects can get before they blur together into a single blob. The angular resolution of e-ASTROGAM will be about 4-6 times better than Fermi’s in the energy range of these mysterious gamma-ray sources. According to the authors of today’s paper, this should definitely be enough to tell whether they are single extended objects or two independent points that are just too close together for Fermi to see (Figure 4).

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    Figure 4. Simulated images of two point sources as seen by Fermi and e-ASTROGAM. On the left, Fermi is unable to distinguish between the two objects, seeing only a single blob of gamma-rays. On the right, e-ASTROGAM, with its superior angular resolution, can tell that the single blob is actually two individual objects. Source: Figure 3 of the paper.

    In order to see just how well e-ASTROGAM will be able to see these objects, the authors modeled fake observations of dark matter annihilation from an extended halo and from two point sources. They determined for different halo sizes and dark matter particles how well e-ASTROGAM will be able to tell whether an object is one extended source or two points. Figure 5 illustrates the difference e-ASTROGAM will make in confirming the nature of these gamma-ray sources. The green and red lines represent how easily Fermi and e-ASTROGAM can distinguish pairs of sources (x-axis) as a function of source brightness (y-axis). e-ASTROGAM reaches much farther along the x-axis, indicating that it can much more easily resolve two point sources. The precise numbers change for different dark matter halos and particles, but in all cases e-ASTROGAM shows a significant improvement over Fermi.

    6
    Figure 5. This plot illustrates how e-ASTROGAM will be able to help distinguish between extended dark matter halos and two nearby points. The y-axis shows how bright the object in question is, and the x-axis is related to how easily the telescope can distinguish between two nearby points and a single extended object. Even with really bright objects Fermi (green) has a hard time distinguishing between the two scenarios, while e-ASTROGAM (red) can more easily tell the difference. Source: Figure 5 of the paper.

    A future gamma-ray telescope like e-ASTROGAM will be an essential tool in determining whether Fermi has in fact detected dark matter annihilation from dark halos. In addition to determining whether the two potential halos detected by Fermi are actually just pairs of close-together point sources, e-ASTROGAM may be able to detect gamma-rays from even more dark matter halos that are too faint for Fermi to observe on its own. e-ASTROGAM with its superior angular resolution and lower energy range would provide a brand new view of the gamma-ray universe, giving us unexpected insight into known and unknown sources of gamma-rays, and perhaps finally revealing the nature of dark matter.

    See the full article here .

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    What do we do?

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

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

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  • richardmitnick 2:07 pm on June 27, 2017 Permalink | Reply
    Tags: , , , NASA Fermi, , ,   

    From Symmetry: “The rise of LIGO’s space-studying super-team” 

    Symmetry Mag

    Symmetry

    06/27/17
    Troy Rummler

    The era of multi-messenger astronomy promises rich rewards—and a steep learning curve.

    NASA/Fermi LAT

    Sometimes you need more than one perspective to get the full story.

    Scientists including astronomers working with the Fermi Large Area Telescope have recorded brief bursts of high-energy photons called gamma rays coming from distant reaches of space. They suspect such eruptions result from the merging of two neutron stars—the collapsed cores of dying stars—or from the collision of a neutron star and a black hole.

    But gamma rays alone can’t tell them that. The story of the dense, crashing cores would be more convincing if astronomers saw a second signal coming from the same event—for example, the release of ripples in space-time called gravitational waves.

    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

    “The Fermi Large Area Telescope detects a few short gamma ray bursts per year already, but detecting one in correspondence to a gravitational-wave event would be the first direct confirmation of this scenario,” says postdoctoral researcher Giacomo Vianello of the Kavli Institute for Particle Astrophysics and Cosmology, a joint institution of SLAC National Accelerator Laboratory and Stanford University.

    Scientists discovered gravitational waves in 2015 (announced in 2016). Using the Laser Interferometer Gravitational-Wave Observatory, or LIGO, they detected the coalescence of two massive black holes.


    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project


    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

    ESA/eLISA the future of gravitational wave research

    LIGO scientists are now sharing their data with a network of fellow space watchers to see if any of their signals match up. Combining multiple signals to create a more complete picture of astronomical events is called multi-messenger astronomy.​

    Looking for a match

    “We had this dream of finding astronomical events to match up with our gravitational wave triggers,” says LIGO scientist Peter Shawhan of the University of Maryland. ​

    But LIGO can only narrow down the source of its signals to a region large enough to contain roughly 100,000 galaxies.

    Searching for contemporaneous signals within that gigantic volume of space is extremely challenging, especially since most telescopes only view a small part of the sky at a time. So Shawhan and his colleagues developed a plan to send out an automatic alert to other observatories whenever LIGO detected an interesting signal of its own. The alert would contain preliminary calculations and the estimated location of the source of the potential gravitational waves.

    “Our early efforts were pretty crude and only involved a small number of partners with telescopes, but it kind of got this idea started,” Shawhan says. The LIGO Collaboration and the Virgo Collaboration, its European partner, revamped and expanded the program while upgrading their detectors. Since 2014, 92 groups have signed up to receive alerts from LIGO, and the number is growing.

    LIGO is not alone in latching onto the promise of multi-messenger astronomy. The Supernova Early Warning System (SNEWS) also unites multiple experiments to look at the same event in different ways.

    Neutral, rarely interacting particles called neutrinos escape more quickly from collapsing stars than optical light, so a network of neutrino experiments is prepared to alert optical observatories as soon as they get the first warning of a nearby supernova in the form of a burst of neutrinos.

    National Science Foundation Director France Córdova has lauded multi-messenger astronomy, calling it in 2016 a bold research idea that would lead to transformative discoveries.​

    The learning curve

    Catching gamma ray bursts alongside gravitational waves is no simple feat.

    The Fermi Large Area Telescope orbits the earth as the primary instrument on the Fermi Gamma-ray Space Telescope.

    NASA/Fermi Telescope

    The telescope is constantly in motion and has a large field of view that surveys the entire sky multiple times per day.

    But a gamma-ray burst lasts just a few seconds, and it takes about three hours for LAT to complete its sweep. So even if an event that releases gravitational waves also produces a gamma-ray burst, LAT might not be looking in the right direction at the right time. It would need to catch the afterglow of the event.

    Fermi LAT scientist Nicola Omodei of Stanford University acknowledges another challenge: The window to see the burst alongside gravitational waves might not line up with the theoretical predictions. It’s never been done before, so the signal could look different or come at a different time than expected.

    That doesn’t stop him and his colleagues from trying, though. “We want to cover all bases, and we adopt different strategies,” he says. “To make sure we are not missing any preceding or delayed signal, we also look on much longer time scales, analyzing the days before and after the trigger.”

    Scientists using the second instrument on the Fermi Gamma-ray Space Telescope have already found an unconfirmed signal that aligned with the first gravitational waves LIGO detected, says scientist Valerie Connaughton of the Universities Space Research Association, who works on the Gamma-Ray Burst Monitor. “We were surprised to find a transient event 0.4 seconds after the first GW seen by LIGO.”

    While the event is theoretically unlikely to be connected to the gravitational wave, she says the timing and location “are enough for us to be interested and to challenge the theorists to explain how something that was not expected to produce gamma rays might have done so.”

    From the ground up

    It’s not just space-based experiments looking for signals that align with LIGO alerts. A working group called DESgw, members of the Dark Energy Survey with independent collaborators, have found a way to use the Dark Energy Camera, a 570-Megapixel digital camera mounted on a telescope in the Chilean Andes, to follow up on gravitational wave detections.​


    Dark Energy Camera [DECam], built at FNAL


    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam

    “We have developed a rapid response system to interrupt the planned observations when a trigger occurs,” says DES scientist Marcelle Soares-Santos of Fermi National Accelerator Laboratory. “The DES is a cosmological survey; following up gravitational wave sources was not originally part of the DES scientific program.”

    Once they receive a signal, the DESgw collaborators meet to evaluate the alert and weigh the cost of changing the planned telescope observations against what scientific data they could expect to see—most often how much of the LIGO source location could be covered by DECam observations.

    “We could, in principle, put the telescope onto the sky for every event as soon as night falls,” says DES scientist Jim Annis, also of Fermilab. “In practice, our telescope is large and the demand for its time is high, so we wait for the right events in the right part of the sky before we open up and start imaging.”

    At an even lower elevation, scientists at the IceCube neutrino experiment—made up of detectors drilled down into Antarctic ice—are following LIGO’s exploits as well.

    U Wisconsin ICECUBE neutrino detector at the South Pole

    Lunar Icecube

    IceCube DeepCore

    IceCube PINGU

    DM-Ice II at IceCube

    “The neutrinos IceCube is looking for originate from the most extreme environment in the cosmos,” says IceCube scientist Imre Bartos of Columbia University. “We don’t know what these environments are for sure, but we strongly suspect that they are related to black holes.”

    LIGO and IceCube are natural partners. Both gravitational waves and neutrinos travel for the most part unimpeded through space. Thus, they carry pure information about where they originate, and the two signals can be monitored together nearly in real time to help refine the calculated location of the source.

    The ability to do this is new, Bartos says. Neither gravitational waves nor high-energy neutrinos had been detected from the cosmos when he started working on IceCube in 2008. “During the past few years, both of them were discovered, putting the field on a whole new footing.”

    Shawhan and the LIGO collaboration are similarly optimistic about the future of their program and multi-messenger astronomy. More gravitational wave detectors are planned or under construction, including an upgrade to the European detector Virgo, the KAGRA detector in Japan, and a third LIGO detector in India, and that means scientists will home in closer and closer on their targets.​


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    KAGRA gravitational wave detector, Kamioka mine in Kamioka-cho, Hida-city, Gifu-prefecture, Japan

    IndIGO LIGO in India

    IndIGO in India

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 4:45 pm on March 8, 2017 Permalink | Reply
    Tags: , , , , , NASA Fermi, The Discovery of Five Early Gamma-Ray Blazars   

    From AAS NOVA: “The Discovery of Five Early Gamma-Ray Blazars” 

    AASNOVA

    American Astronomical Society

    8 March 2017
    Susanna Kohler

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    An artist’s impression of a quasar, in which accretion onto a supermassive black hole powers a high-speed jet. A new study has discovered five such galactic nuclei from the early universe that are pointed toward us. [NASA/Dana Berry (SkyWorks Digital)]

    Due to a recent software improvement, the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope has discovered five gamma-ray blazars at high redshifts, opening a window to the early universe.


    NASA/Fermi LAT


    NASA Fermi Telescope

    Spotting Pointed Activity

    Quasars, the active centers of some distant galaxies, shine brightly across the electromagnetic spectrum. These luminous objects are fueled by material accreting onto a supermassive black hole, and the release of energy in this accretion launches powerful jets that, in the case of a type of quasar called a “blazar”, point along our line of sight — causing them to be relativistically boosted to look especially bright. The jet radiation dominates blazar broadband emission, especially at gamma-ray wavelengths.

    Fermi-LAT has detected thousands of blazars in gamma rays; in fact, blazars have been found to be the most numerous gamma-ray population in our sky. In spite of this, Fermi hasn’t found any gamma-ray blazars at a redshift greater than z = 3.1 — likely because at this distance, the blazars’ gamma-ray emission is redshifted to lower frequencies at which the LAT is less sensitive.

    A recent, spectacular set of improvements to Fermi data analysis, however, known as Pass 8, has substantially enhanced the sensitivity of LAT to gamma rays across the spectrum — with particular improvement at lower frequencies. Motivated by this increased sensitivity, a team of Fermi scientists has used the data from Pass 8 to search for especially distant gamma-ray-bright blazars.

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    Maps of the five high-redshift blazars detected by Fermi-LAT. [Ackermann et al. 2017]

    Window to the Early Universe

    The Fermi team began by selecting high-redshift radio-loud blazars from a known catalog of over a million quasars. They then searched for these ~1100 sources within the 92 months of LAT data produced by Pass 8.

    This systematic search led to the detection of five new gamma-ray sources consistent with the positions of blazars at redshifts greater than z = 3.1 — including NVSS J151002+570243, which now qualifies as the most distant gamma-ray blazar known, at a redshift of z = 4.31.

    Analysis of the sources’ spectral energy distributions verifies that they have all the properties expected of especially powerful blazars, confirming their identity. Modeling of their spectra suggests they harbor massive black holes in the range of hundreds of millions to tens of billions of solar masses. The properties of these sources allow the authors to estimate the space density of massive black holes hosted in jetted systems: roughly 70 per cubic gigaparsec.

    Though these five new gamma-ray blazars may constitute a small sample, they provide information that can be used to begin to constrain our models of how supermassive black holes formed in the early universe. They’re also a shining example of the remarkable benefit possible with clever software improvements!

    Citation

    M. Ackermann et al 2017 ApJL 837 L5. doi:10.3847/2041-8213/aa5fff

    See the full article here .

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  • richardmitnick 2:37 pm on February 22, 2017 Permalink | Reply
    Tags: , , , , NASA Fermi   

    From Fermi: “NASA’s Fermi Finds Possible Dark Matter Ties in Andromeda Galaxy” 

    NASA Fermi Banner


    Fermi

    Feb. 21, 2017
    Claire Saravia
    NASA’s Goddard Space Flight Center, Greenbelt, Md.

    NASA’s Fermi Gamma-ray Space Telescope has found a signal at the center of the neighboring Andromeda galaxy that could indicate the presence of the mysterious stuff known as dark matter. The gamma-ray signal is similar to one seen by Fermi at the center of our own Milky Way galaxy.

    1

    Gamma rays are the highest-energy form of light, produced by the universe’s most energetic phenomena. They’re common in galaxies like the Milky Way because cosmic rays, particles moving near the speed of light, produce gamma rays when they interact with interstellar gas clouds and starlight.

    Surprisingly, the latest Fermi data shows the gamma rays in Andromeda — also known as M31 — are confined to the galaxy’s center instead of spread throughout. To explain this unusual distribution, scientists are proposing that the emission may come from several undetermined sources. One of them could be dark matter, an unknown substance that makes up most of the universe.


    NASA’s Fermi telescope has detected a gamma-ray excess at the center of the Andromeda galaxy that’s similar to a signature Fermi previously detected at the center of our own Milky Way. Watch to learn more.
    Credits: NASA’s Goddard Space Flight Center/Scott Wiessinger, producer

    2
    The gamma-ray excess (shown in yellow-white) at the heart of M31 hints at unexpected goings-on in the galaxy’s central region. Scientists think the signal could be produced by a variety of processes, including a population of pulsars or even dark matter.
    Credits: NASA/DOE/Fermi LAT Collaboration and Bill Schoening, Vanessa Harvey/REU program/NOAO/AURA/NSF

    “We expect dark matter to accumulate in the innermost regions of the Milky Way and other galaxies, which is why finding such a compact signal is very exciting,” said lead scientist Pierrick Martin, an astrophysicist at the National Center for Scientific Research and the Research Institute in Astrophysics and Planetology in Toulouse, France. “M31 will be a key to understanding what this means for both Andromeda and the Milky Way.”

    A paper describing the results will appear in an upcoming issue of The Astrophysical Journal.

    Another possible source for this emission could be a rich concentration of pulsars in M31’s center. These spinning neutron stars weigh as much as twice the mass of the sun and are among the densest objects in the universe. One teaspoon of neutron star matter would weigh a billion tons on Earth. Some pulsars emit most of their energy in gamma rays. Because M31 is 2.5 million light-years away, it’s difficult to find individual pulsars. To test whether the gamma rays are coming from these objects, scientists can apply what they know about pulsars from observations in the Milky Way to new X-ray and radio observations of Andromeda.

    Now that Fermi has detected a similar gamma-ray signature in both M31 and the Milky Way, scientists can use this information to solve mysteries within both galaxies. For example, M31 emits few gamma rays from its large disk, where most stars form, indicating fewer cosmic rays roaming there. Because cosmic rays are usually thought to be related to star formation, the absence of gamma rays in the outer parts of M31 suggests either that the galaxy produces cosmic rays differently, or that they can escape the galaxy more rapidly. Studying Andromeda may help scientists understand the life cycle of cosmic rays and how it is connected to star formation.

    “We don’t fully understand the roles cosmic rays play in galaxies, or how they travel through them,” said Xian Hou, an astrophysicist at Yunnan Observatories, Chinese Academy of Sciences in Kunming, China, also a lead scientist in this work. “M31 lets us see how cosmic rays behave under conditions different from those in our own galaxy.”

    The similar discovery in both the Milky Way and M31 means scientists can use the galaxies as models for each other when making difficult observations. While Fermi can make more sensitive and detailed observations of the Milky Way’s center, its view is partially obscured by emission from the galaxy’s disk. But telescopes view Andromeda from an outside vantage point impossible to attain in the Milky Way.

    “Our galaxy is so similar to Andromeda, it really helps us to be able to study it, because we can learn more about our galaxy and its formation,” said co-author Regina Caputo, a research scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “It’s like living in a world where there’s no mirrors but you have a twin, and you can see everything physical about the twin.”

    While more observations are necessary to determine the source of the gamma-ray excess, the discovery provides an exciting starting point to learn more about both galaxies, and perhaps about the still elusive nature of dark matter.

    “We still have a lot to learn about the gamma-ray sky,” Caputo said. “The more information we have, the more information we can put into models of our own galaxy.”

    NASA’s Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership, developed in collaboration with the U.S. Department of Energy and with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

    For more information on Fermi, visit:

    http://www.nasa.gov/fermi

    See the full article here .

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    NASA’s Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership, developed in collaboration with the U.S. Department of Energy and with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

     
  • richardmitnick 12:51 pm on January 31, 2017 Permalink | Reply
    Tags: , , , , Gamma rays from solar storms, NASA Fermi,   

    From Fermi: “NASA’s Fermi Sees Gamma Rays from ‘Hidden’ Solar Flares” 

    NASA Fermi Banner


    Fermi

    Jan. 30, 2017
    Francis Reddy
    NASA’s Goddard Space Flight Center, Greenbelt, Md.

    An international science team says NASA’s Fermi Gamma-ray Space Telescope has observed high-energy light from solar eruptions located on the far side of the sun, which should block direct light from these events. This apparent paradox is providing solar scientists with a unique tool for exploring how charged particles are accelerated to nearly the speed of light and move across the sun during solar flares.

    “Fermi is seeing gamma rays from the side of the sun we’re facing, but the emission is produced by streams of particles blasted out of solar flares on the far side of the sun,” said Nicola Omodei, a researcher at Stanford University in California. “These particles must travel some 300,000 miles within about five minutes of the eruption to produce this light.”

    Omodei presented the findings on Monday, Jan. 30, at the American Physical Society meeting in Washington, and a paper describing the results will be published online in The Astrophysical Journal on Jan. 31.


    Access mp4 video here .
    On three occasions, NASA’s Fermi Gamma-ray Space Telescope has detected gamma rays from solar storms on the far side of the sun, emission the Earth-orbiting satellite shouldn’t be able to detect. Particles accelerated by these eruptions somehow reach around to produce a gamma-ray glow on the side of the sun facing Earth and Fermi. Watch to learn more. Credits: NASA’s Goddard Space Flight Center/Scott Wiessinger, producer

    Fermi has doubled the number of these rare events, called behind-the-limb flares, since it began scanning the sky in 2008. Its Large Area Telescope (LAT) has captured gamma rays with energies reaching 3 billion electron volts, some 30 times greater than the most energetic light previously associated with these “hidden” flares.

    NASA/Fermi LAT
    NASA/Fermi LAT

    Thanks to NASA’s Solar Terrestrial Relations Observatory (STEREO) spacecraft, which were monitoring the solar far side when the eruptions occurred, the Fermi events mark the first time scientists have direct imaging of beyond-the-limb solar flares associated with high-energy gamma rays.

    NASA/STEREO spacecraft
    NASA/STEREO spacecraft

    3
    These solar flares were imaged in extreme ultraviolet light by NASA’s STEREO satellites, which at the time were viewing the side of the sun facing away from Earth. All three events launched fast coronal mass ejections (CMEs). Although NASA’s Fermi Gamma-ray Space Telescope couldn’t see the eruptions directly, it detected high-energy gamma rays from all of them. Scientists think particles accelerated by the CMEs rained onto the Earth-facing side of the sun and produced the gamma rays. The central image was returned by the STEREO A spacecraft, all others are from STEREO B.
    Credits: NASA/STEREO

    4
    Combined images from NASA’s Solar Dynamics Observatory (center) and the NASA/ESA Solar and Heliospheric Observatory (red and blue) show an impressive coronal mass ejection departing the far side of the sun on Sept. 1, 2014. This massive cloud raced away at about 5 million mph and likely accelerated particles that later produced gamma rays Fermi detected. Credits: NASA/SDO and NASA/ESA/SOHO

    NASA/SDO
    NASA/SDO

    ESA/NASA SOHO
    ESA/NASA SOHO

    “Observations by Fermi’s LAT continue to have a significant impact on the solar physics community in their own right, but the addition of STEREO observations provides extremely valuable information of how they mesh with the big picture of solar activity,” said Melissa Pesce-Rollins, a researcher at the National Institute of Nuclear Physics in Pisa, Italy, and a co-author of the paper.

    The hidden flares occurred Oct. 11, 2013, and Jan. 6 and Sept. 1, 2014. All three events were associated with fast coronal mass ejections (CMEs), where billion-ton clouds of solar plasma were launched into space. The CME from the most recent event was moving at nearly 5 million miles an hour as it left the sun. Researchers suspect particles accelerated at the leading edge of the CMEs were responsible for the gamma-ray emission.

    Large magnetic field structures can connect the acceleration site with distant part of the solar surface. Because charged particles must remain attached to magnetic field lines, the research team thinks particles accelerated at the CME traveled to the sun’s visible side along magnetic field lines connecting both locations. As the particles impacted the surface, they generated gamma-ray emission through a variety of processes. One prominent mechanism is thought to be proton collisions that result in a particle called a pion, which quickly decays into gamma rays.

    In its first eight years, Fermi has detected high-energy emission from more than 40 solar flares. More than half of these are ranked as moderate, or M class, events. In 2012, Fermi caught the highest-energy emission ever detected from the sun during a powerful X-class flare, from which the LAT detected high­energy gamma rays for more than 20 record-setting hours.

    NASA’s Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership, developed in collaboration with the U.S. Department of Energy and with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

    For more information on Fermi, visit:

    https://www.nasa.gov/fermi

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    NASA’s Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership, developed in collaboration with the U.S. Department of Energy and with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

     
  • richardmitnick 6:29 am on December 27, 2016 Permalink | Reply
    Tags: , , , , NASA Fermi, NASA's Fermi Finds Record-breaking Binary in Galaxy Next Door,   

    From NASA Goddard: “NASA’s Fermi Finds Record-breaking Binary in Galaxy Next Door” 

    NASA Goddard Banner

    NASA Goddard Space Flight Center

    Sept. 29, 2016
    Francis Reddy
    francis.j.reddy@nasa.gov
    NASA’s Goddard Space Flight Center, Greenbelt, Md.

    Using data from NASA’s Fermi Gamma-ray Space Telescope and other facilities, an international team of scientists has found the first gamma-ray binary in another galaxy and the most luminous one ever seen.

    NASA/Fermi Telescope
    NASA/Fermi Telescope

    The dual-star system, dubbed LMC P3, contains a massive star and a crushed stellar core that interact to produce a cyclic flood of gamma rays, the highest-energy form of light.

    “Fermi has detected only five of these systems in our own galaxy, so finding one so luminous and distant is quite exciting,” said lead researcher Robin Corbet at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Gamma-ray binaries are prized because the gamma-ray output changes significantly during each orbit and sometimes over longer time scales. This variation lets us study many of the emission processes common to other gamma-ray sources in unique detail.”

    These rare systems contain either a neutron star or a black hole and radiate most of their energy in the form of gamma rays. Remarkably, LMC P3 is the most luminous such system known in gamma rays, X-rays, radio waves and visible light, and it’s only the second one discovered with Fermi.


    Dive into the Large Magellanic Cloud and see a visualization of LMC P3, an extraordinary gamma-ray binary system discovered by NASA’s Fermi Gamma-ray Space Telescope.
    Credits: NASA’s Goddard Space Flight Center/Scott Wiessinger, producer
    Access mp4 video here .

    A paper describing the discovery will appear in the Oct. 1 issue of The Astrophysical Journal and is now available online.

    LMC P3 lies within the expanding debris of a supernova explosion located in the Large Magellanic Cloud (LMC), a small nearby galaxy about 163,000 light-years away.

    Large Magellanic Cloud. Adrian Pingstone  December 2003
    Large Magellanic Cloud. Adrian Pingstone December 2003

    In 2012, scientists using NASA’s Chandra X-ray Observatory found a strong X-ray source within the supernova remnant and showed that it was orbiting a hot, young star many times the sun’s mass.

    NASA/Chandra Telescope
    NASA/Chandra Telescope

    The researchers concluded the compact object was either a neutron star or a black hole and classified the system as a high-mass X-ray binary (HMXB).

    In 2015, Corbet’s team began looking for new gamma-ray binaries in Fermi data by searching for the periodic changes characteristic of these systems. The scientists discovered a 10.3-day cyclic change centered near one of several gamma-ray point sources recently identified in the LMC. One of them, called P3, was not linked to objects seen at any other wavelengths but was located near the HMXB. Were they the same object?

    1
    Observations from Fermi’s Large Area Telescope (magenta line) show that gamma rays from LMC P3 rise and fall over the course of 10.3 days. The companion is thought to be a neutron star. Illustrations across the top show how the changing position of the neutron star relates to the gamma-ray cycle.
    Credits: NASA’s Goddard Space Flight Center

    NASA/Fermi LAT
    NASA/Fermi LAT

    To find out, Corbet’s team observed the binary in X-rays using NASA’s Swift satellite, at radio wavelengths with the Australia Telescope Compact Array [ATCA] near Narrabri and in visible light using the 4.1-meter Southern Astrophysical Research Telescope on Cerro Pachón in Chile and the 1.9-meter telescope at the South African Astronomical Observatory [SAAO]near Cape Town.

    NASA/SWIFT Telescope
    NASA/SWIFT Telescope

    CSIRO ATCA at the Paul Wild Observatory, about 25 km west of the town of Narrabri in rural NSW about 500 km north-west of Sydney, AU
    CSIRO ATCA at the Paul Wild Observatory, about 25 km west of the town of Narrabri in rural NSW about 500 km north-west of Sydney, AU

    NOAO/ Southern Astrophysical Research Telescope (SOAR)telescope situated on Cerro Pachón - IV Región - Chile, at 2,700 meters (8,775 feet)
    NOAO/ Southern Astrophysical Research Telescope (SOAR)telescope situated on Cerro Pachón – IV Región – Chile, at 2,700 meters (8,775 feet)

    SAAO 1.9 meterTelescope, at the SAAO observation station 15Kms from the small Karoo town of Sutherland in the Northern Cape, a 4-hour drive from Cape Town.
    SAAO 1.9 meterTelescope, at the SAAO observation station 15Kms from the small Karoo town of Sutherland in the Northern Cape, a 4-hour drive from Cape Town.

    The Swift observations clearly reveal the same 10.3-day emission cycle seen in gamma rays by Fermi. They also indicate that the brightest X-ray emission occurs opposite the gamma-ray peak, so when one reaches maximum the other is at minimum. Radio data exhibit the same period and out-of-phase relationship with the gamma-ray peak, confirming that LMC P3 is indeed the same system investigated by Chandra.

    The Swift observations clearly reveal the same 10.3-day emission cycle seen in gamma rays by Fermi. They also indicate that the brightest X-ray emission occurs opposite the gamma-ray peak, so when one reaches maximum the other is at minimum. Radio data exhibit the same period and out-of-phase relationship with the gamma-ray peak, confirming that LMC P3 is indeed the same system investigated by Chandra.

    3
    LMC P3 (circled) is located in a supernova remnant called DEM L241 in the Large Magellanic Cloud, a small galaxy about 163,000 light-years away. The system is the first gamma-ray binary discovered in another galaxy and is the most luminous known in gamma rays, X-rays, radio waves and visible light.

    Both objects form when a massive star runs out of fuel, collapses under its own weight and explodes as a supernova. The star’s crushed core may become a neutron star, with the mass of half a million Earths squeezed into a ball no larger than Washington, D.C. Or it may be further compacted into a black hole, with a gravitational field so strong not even light can escape it.

    The surface of the star at the heart of LMC P3 has a temperature exceeding 60,000 degrees Fahrenheit (33,000 degrees Celsius), or more than six times hotter than the sun’s. The star is so luminous that pressure from the light it emits actually drives material from the surface, creating particle outflows with speeds of several million miles an hour.

    In gamma-ray binaries, the compact companion is thought to produce a “wind” of its own, one consisting of electrons accelerated to near the speed of light. The interacting outflows produce X-rays and radio waves throughout the orbit, but these emissions are detected most strongly when the compact companion travels along the part of its orbit closest to Earth.

    Through a different mechanism, the electron wind also emits gamma rays. When light from the star collides with high-energy electrons, it receives a boost to gamma-ray levels. Called inverse Compton scattering, this process produces more gamma rays when the compact companion passes near the star on the far side of its orbit as seen from our perspective.

    Prior to Fermi’s launch, gamma-ray binaries were expected to be more numerous than they’ve turned out to be. Hundreds of HMXBs are cataloged, and these systems are thought to have originated as gamma-ray binaries following the supernova that formed the compact object.

    “It is certainly a surprise to detect a gamma-ray binary in another galaxy before we find more of them in our own,” said Guillaume Dubus, a team member at the Institute of Planetology and Astrophysics of Grenoble in France. “One possibility is that the gamma-ray binaries Fermi has found are rare cases where a supernova formed a neutron star with exceptionally rapid spin, which would enhance how it produces accelerated particles and gamma rays.”

    NASA’s Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership, developed in collaboration with the U.S. Department of Energy and with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    NASA’s Goddard Space Flight Center is home to the nation’s largest organization of combined scientists, engineers and technologists that build spacecraft, instruments and new technology to study the Earth, the sun, our solar system, and the universe.

    Named for American rocketry pioneer Dr. Robert H. Goddard, the center was established in 1959 as NASA’s first space flight complex. Goddard and its several facilities are critical in carrying out NASA’s missions of space exploration and scientific discovery.

    NASA Goddard campus
    NASA/Goddard Campus
    NASA image

     
  • richardmitnick 4:17 pm on September 29, 2016 Permalink | Reply
    Tags: , , LMC P3, NASA Fermi, , Record-breaking Binary in Galaxy Next Door   

    From NASA Goddard and Fermi: “NASA’s Fermi Finds Record-breaking Binary in Galaxy Next Door” 

    NASA Goddard Banner

    NASA Goddard Space Flight Center

    NASA Fermi Banner


    Fermi

    Sept. 29, 2016
    Francis Reddy
    francis.j.reddy@nasa.gov
    NASA’s Goddard Space Flight Center, Greenbelt, Md.

    Using data from NASA’s Fermi Gamma-ray Space Telescope and other facilities, an international team of scientists has found the first gamma-ray binary in another galaxy and the most luminous one ever seen. The dual-star system, dubbed LMC P3, contains a massive star and a crushed stellar core that interact to produce a cyclic flood of gamma rays, the highest-energy form of light.

    “Fermi has detected only five of these systems in our own galaxy, so finding one so luminous and distant is quite exciting,” said lead researcher Robin Corbet at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Gamma-ray binaries are prized because the gamma-ray output changes significantly during each orbit and sometimes over longer time scales. This variation lets us study many of the emission processes common to other gamma-ray sources in unique detail.”

    These rare systems contain either a neutron star or a black hole and radiate most of their energy in the form of gamma rays. Remarkably, LMC P3 is the most luminous such system known in gamma rays, X-rays, radio waves and visible light, and it’s only the second one discovered with Fermi.


    Access mp4 video here .
    Dive into the Large Magellanic Cloud and see a visualization of LMC P3, an extraordinary gamma-ray binary system discovered by NASA’s Fermi Gamma-ray Space Telescope. Credits: NASA’s Goddard Space Flight Center/Scott Wiessinger, producer

    A paper describing the discovery will appear in the Oct. 1 issue of The Astrophysical Journal and is now available online, and you an see the full science team.

    LMC P3 lies within the expanding debris of a supernova explosion located in the Large Magellanic Cloud (LMC), a small nearby galaxy about 163,000 light-years away.

    Large Magellanic Cloud. Adrian Pingstone  December 2003
    Large Magellanic Cloud. Adrian Pingstone December 2003

    In 2012, scientists using NASA’s Chandra X-ray Observatory found a strong X-ray source within the supernova remnant and showed that it was orbiting a hot, young star many times the sun’s mass.

    NASA/Chandra Telescope
    NASA/Chandra Telescope

    The researchers concluded the compact object was either a neutron star or a black hole and classified the system as a high-mass X-ray binary (HMXB).

    In 2015, Corbet’s team began looking for new gamma-ray binaries in Fermi data by searching for the periodic changes characteristic of these systems. The scientists discovered a 10.3-day cyclic change centered near one of several gamma-ray point sources recently identified in the LMC. One of them, called P3, was not linked to objects seen at any other wavelengths but was located near the HMXB. Were they the same object?

    3
    Observations from Fermi’s Large Area Telescope (magenta line) show that gamma rays from LMC P3 rise and fall over the course of 10.3 days. The companion is thought to be a neutron star. Illustrations across the top show how the changing position of the neutron star relates to the gamma-ray cycle. Credits: NASA’s Goddard Space Flight Center

    To find out, Corbet’s team observed the binary in X-rays using NASA’s Swift satellite, at radio wavelengths with the Australia Telescope Compact Array near Narrabri and in visible light using the 4.1-meter Southern Astrophysical Research Telescope on Cerro Pachón in Chile and the 1.9-meter telescope at the South African Astronomical Observatory near Cape Town.

    NASA/SWIFT Telescope
    NASA/SWIFT Telescope

    CSIRO Australian Telescope Compact Array at the Paul Wild Observatory, about 25 km west of the town of Narrabri in rural NSW about 500 km north-west of Sydney
    CSIRO Australian Telescope Compact Array at the Paul Wild Observatory, about 25 km west of the town of Narrabri in rural NSW about 500 km north-west of Sydney, AU

    NOAO/ Southern Astrophysical Research Telescope (SOAR)telescope situated on Cerro Pachón - IV Región - Chile, at 2,700 meters (8,775 feet)
    NOAO/ Southern Astrophysical Research Telescope (SOAR)telescope situated on Cerro Pachón – IV Región – Chile

    4
    1.9-meter Radcliffe telescope at the South African Astronomical Observatory near Cape Town

    The Swift observations clearly reveal the same 10.3-day emission cycle seen in gamma rays by Fermi. They also indicate that the brightest X-ray emission occurs opposite the gamma-ray peak, so when one reaches maximum the other is at minimum. Radio data exhibit the same period and out-of-phase relationship with the gamma-ray peak, confirming that LMC P3 is indeed the same system investigated by Chandra.

    “The optical observations show changes due to binary orbital motion, but because we don’t know how the orbit is tilted into our line of sight, we can only estimate the individual masses,” said team member Jay Strader, an astrophysicist at Michigan State University in East Lansing. “The star is between 25 and 40 times the sun’s mass, and if we’re viewing the system at an angle midway between face-on and edge-on, which seems most likely, its companion is a neutron star about twice the sun’s mass.” If, however, we view the binary nearly face-on, then the companion must be significantly more massive and a black hole.

    5
    LMC P3 (circled) is located in a supernova remnant called DEM L241 in the Large Magellanic Cloud, a small galaxy about 163,000 light-years away. The system is the first gamma-ray binary discovered in another galaxy and is the most luminous known in gamma rays, X-rays, radio waves and visible light.

    Both objects form when a massive star runs out of fuel, collapses under its own weight and explodes as a supernova. The star’s crushed core may become a neutron star, with the mass of half a million Earths squeezed into a ball no larger than Washington, D.C. Or it may be further compacted into a black hole, with a gravitational field so strong not even light can escape it.

    The surface of the star at the heart of LMC P3 has a temperature exceeding 60,000 degrees Fahrenheit (33,000 degrees Celsius), or more than six times hotter than the sun’s. The star is so luminous that pressure from the light it emits actually drives material from the surface, creating particle outflows with speeds of several million miles an hour.

    In gamma-ray binaries, the compact companion is thought to produce a “wind” of its own, one consisting of electrons accelerated to near the speed of light. The interacting outflows produce X-rays and radio waves throughout the orbit, but these emissions are detected most strongly when the compact companion travels along the part of its orbit closest to Earth.

    Through a different mechanism, the electron wind also emits gamma rays. When light from the star collides with high-energy electrons, it receives a boost to gamma-ray levels. Called inverse Compton scattering, this process produces more gamma rays when the compact companion passes near the star on the far side of its orbit as seen from our perspective.

    Prior to Fermi’s launch, gamma-ray binaries were expected to be more numerous than they’ve turned out to be. Hundreds of HMXBs are cataloged, and these systems are thought to have originated as gamma-ray binaries following the supernova that formed the compact object.

    “It is certainly a surprise to detect a gamma-ray binary in another galaxy before we find more of them in our own,” said Guillaume Dubus, a team member at the Institute of Planetology and Astrophysics of Grenoble in France. “One possibility is that the gamma-ray binaries Fermi has found are rare cases where a supernova formed a neutron star with exceptionally rapid spin, which would enhance how it produces accelerated particles and gamma rays.”

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    NASA’s Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership, developed in collaboration with the U.S. Department of Energy and with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

    NASA’s Goddard Space Flight Center is home to the nation’s largest organization of combined scientists, engineers and technologists that build spacecraft, instruments and new technology to study the Earth, the sun, our solar system, and the universe.

    Named for American rocketry pioneer Dr. Robert H. Goddard, the center was established in 1959 as NASA’s first space flight complex. Goddard and its several facilities are critical in carrying out NASA’s missions of space exploration and scientific discovery.

    NASA Goddard campus
    NASA/Goddard Campus

    NASA image

     
  • richardmitnick 2:23 pm on August 12, 2016 Permalink | Reply
    Tags: , , Fermi Researchers Explore New Ways of Searching for Dark Matter, NASA Fermi, , Three Studies Expand the Hunt for Unexplained Cosmic Gamma-ray Signals   

    From SLAC: “Fermi Researchers Explore New Ways of Searching for Dark Matter” 


    SLAC Lab

    August 12, 2016

    Three Studies Expand the Hunt for Unexplained Cosmic Gamma-ray Signals

    Researchers working with more than six years of data from NASA’s Fermi Gamma-ray Space Telescope have used novel approaches to search for cosmic signals that could reveal what mysterious dark matter is made of.

    NASA/Fermi Telescope
    NASA/Fermi Telescope

    The scientists looked for hypothetical axion particles, studied the gamma-ray emissions from a large satellite galaxy of our Milky Way and analyzed the faint glow of gamma rays that covers the entire sky.

    Although none of these studies identified signals clearly attributable to dark matter, the results help scientists determine what dark matter cannot be by ruling out numerous theoretical dark matter models.

    “The new approaches have set tight limits on the properties of dark matter, complementing and extending previous results,” says Seth Digel, who leads the Fermi team at the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), a joint institute of Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory.

    2

    The nature of invisible dark matter remains one of the biggest mysteries of modern science. Because dark matter makes up 85 percent of all matter in the universe, it affects how galaxies rotate and how light passes through massive galaxy clusters. But what exactly is dark matter, and what are its constituents?

    Astrophysicists do not know the answers, but they believe that dark matter might be composed of hypothetical particles. Gamma rays as detected by the Fermi telescope can potentially help reveal their existence. Previously, Fermi has searched for telltale gamma-ray signals associated with dark matter in the center of our galaxy and in small dwarf galaxies orbiting our own. The new studies take this search to the next level.

    Gamma Rays Turning into Axions and Vice Versa

    The first study investigated the possibility that dark matter consists of hypothetical particles called axions or other contenders with similar properties. An intriguing aspect of axion-like particles is their ability to convert into gamma rays and back again when they interact with strong magnetic fields. These conversions would leave behind characteristic traces, like gaps or steps, in the spectrum of a bright gamma-ray source.

    A team led by Manuel Meyer at Stockholm University searched for these effects in the gamma rays from the central galaxy of the Perseus galaxy cluster, whose high-energy emissions are thought to be associated with a supermassive black hole at its center. Like all galaxy clusters, the Perseus cluster is filled with hot gas threaded with magnetic fields, potentially enabling the switch from gamma rays to axion-like particles and vice versa.

    3
    Top: Gamma rays (magenta) coming from a bright source such as the central galaxy (at left) of the Perseus galaxy cluster have a particular type of spectrum that is detected by the Fermi telescope (at right). Bottom: Gamma rays could potentially convert into hypothetical axion-like particles (green) and back again in the presence of the cluster’s magnetic field (gray lines). This would lead to steps and gaps in the spectrum (lower curve at right). (SLAC National Accelerator Laboratory). (T. Wistisen/Aarhus University)

    Meyer’s team collected observations from Fermi’s Large Area Telescope (LAT) but didn’t find any axion-related distortions in the gamma-ray signal.

    NASA/Fermi LAT
    NASA/Fermi LAT

    The findings, published April 20 in Physical Review Letters, exclude a small range of axion-like particles that could have comprised about 4 percent of dark matter.

    “While we don’t yet know what dark matter is, our results show we can probe axion-like models and provide the strongest constraints to date for certain masses,” Meyer says. “Remarkably, we reached a sensitivity we thought would only be possible in a dedicated laboratory experiment, which is quite a testament to Fermi.”

    WIMPs Decaying or Annihilating Each Other in Space

    Other dark matter candidates are so-called weakly interacting massive particles (WIMPs). In some theoretical models, colliding WIMPs either annihilate each other or decay in space; both scenarios should result in gamma rays that could be detected by the LAT.

    In the second study, scientists sought these signals from the Small Magellanic Cloud (SMC), the second-largest of the satellite galaxies orbiting our Milky Way. The SMC’s conventional sources of gamma rays, such as pulsars and processes related to the formation of massive stars, are well established, and its dark matter content is known from the galaxy’s well-measured rotation.

    “These properties make the SMC a great object for searches for any unexplained gamma-ray excess, which could potentially be a WIMP signature,” says KIPAC researcher Eric Charles, co-author of a paper published on March 22 in Physical Review D.

    4
    The Small Magellanic Cloud (SMC, at center) is the second-largest satellite galaxy orbiting our Milky Way. The image superimposes a photograph of the SMC with one-half of a model of its dark matter. Lighter colors indicate greater density and show a strong concentration of dark matter toward the SMC’s center. Ninety-five percent of the dark matter is contained within a circle tracing the outer edge of the model shown here. (R. Caputo; A. Mellinger/Central Michigan University)

    The researchers modeled the dark matter content of the satellite galaxy, showing it possesses enough dark matter to theoretically produce detectable signals for two WIMP types.

    However, “no signal from dark matter annihilation was found to be statistically significant,” says lead author Regina Caputo from the University of California, Santa Cruz. “The LAT definitely sees gamma rays from the SMC, but we can explain them all through conventional sources.”

    An Extragalactic Glow of Gamma Rays

    In the third study, a research team led by Clemson University’s Marco Ajello and KIPAC’s Mattia Di Mauro took the search in a different direction. Instead of looking at specific astronomical targets, the team analyzed the background glow of gamma rays seen all over the sky.

    The nature of this light, called the extragalactic gamma-ray background (EGB), has been debated since it was first measured by NASA’s Small Astronomy Satellite 2 in the early 1970s.

    5
    This view of the gamma-ray sky is constructed from one year of Fermi Large Area Telescope (LAT) observations. The blue color includes the extragalactic gamma-ray background. The map shows the rate at which the LAT detects gamma rays with energies above 300 million electron volts — about 120 million times the energy of visible light — from different sky directions. Brighter colors represent higher rates. Credit: NASA/DOE/Fermi LAT Collaboration

    Fermi has shown that much of this light arises from gamma-ray sources that cannot be identified as individual sources, particularly galaxies called blazars that are powered by material falling toward gigantic black holes.

    Some models predict that EGB gamma rays could also arise from distant interactions of dark matter particles, such as the annihilation or decay of WIMPs.

    “We performed a statistical analysis of the EGB, in which we looked at very dim objects and asked whether we can account for all detected gamma-ray photons with known astrophysical sources,” says Di Mauro.

    6
    This animation switches between two images of the gamma-ray sky: one using the first three months of data from Fermi’s Large Area Telescope (LAT), the other showing an exposure over seven years. The background glow of gamma rays seen all over the sky (blue contours) is mostly caused by blazars, galaxies that are powered by material falling toward gigantic black holes. With increasing exposure, Fermi reveals more and more of them. (NASA/SLAC National Accelerator Laboratory/Fermi-LAT collaboration)

    The detailed analysis, published April 14 in Physical Review Letters, shows that the researchers can in fact explain nearly all of this emission.

    “There is very little room left for signals from exotic sources in the EGB, which in turn means that any contribution from these sources must be quite small,” Ajello says. “This information may help us place limits on how often WIMP particles collide or decay.”

    NASA’s Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership, developed in collaboration with the U.S. Department of Energy and with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States. A number of researchers from SLAC are members of the international Fermi-LAT collaboration. SLAC assembled the LAT and hosts the operations center that processes LAT data.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    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

     
  • richardmitnick 8:27 pm on June 27, 2016 Permalink | Reply
    Tags: , , , NASA Fermi,   

    From particlebites: “The Fermi LAT Data Depicting Dark Matter Detection” 

    particlebites bloc

    particlebites

    June 27, 2016
    Chris Karwin

    The center of the galaxy is brighter than astrophysicists expected. Could this be the result of the self-annihilation of dark matter? Chris Karwin, a graduate student from the University of California, Irvine presents the Fermi collaboration’s analysis.

    Presenting: Fermi-LAT Observations of High-Energy Gamma-Ray Emission Toward the Galactic Center
    Authors: The Fermi-LAT Collaboration (ParticleBites blogger is a co-author)
    Reference: 1511.02938, Astrophys.J. 819 (2016) no.1, 44

    NASA/Fermi Telescope
    NASA/Fermi

    Introduction

    Like other telescopes, the Fermi Gamma-Ray Space Telescope is a satellite that scans the sky collecting light. Unlike many telescopes, it searches for very high energy light: gamma-rays. The satellite’s main component is the Large Area Telescope (LAT).

    NASA/Fermi LAT
    NASA/Fermi LAT

    When this detector is hit with a high-energy gamma-ray, it measures the the energy and the direction in the sky from where it originated. The data provided by the LAT is an all-sky photon counts map:

    1
    All-sky counts map of gamma-rays. The color scale correspond to the number of detected photons. Image from NASA

    In 2009, researchers noticed that there appeared to be an excess of gamma-rays coming from the galactic center. This excess is found by making a model of the known astrophysical gamma-ray sources and then comparing it to the data.

    What makes the excess so interesting is that its features seem consistent with predictions from models of dark matter annihilation. Dark matter theory and simulations predict:

    The distribution of dark matter in space. The gamma rays coming from dark matter annihilation should follow this distribution, or spatial morphology.
    The particles to which dark matter directly annihilates. This gives a prediction for the expected energy spectrum of the gamma-rays.

    Although a dark matter interpretation of the excess is a very exciting scenario that would tell us new things about particle physics, there are also other possible astrophysical explanations. For example, many physicists argue that the excess may be due to an unresolved population of milli-second pulsars. Another possible explanation is that it is simply due to the mis-modeling of the background. Regardless of the physical interpretation, the primary objective of the Fermi analysis is to characterize the excess.

    The main systematic uncertainty of the experiment is our limited understanding of the backgrounds: the gamma rays produced by known astrophysical sources. In order to include this uncertainty in the analysis, four different background models are constructed. Although these models are methodically chosen so as to account for our lack of understanding, it should be noted that they do not necessarily span the entire range of possible error. For each of the background models, a gamma-ray excess is found. With the objective of characterizing the excess, additional components are then added to the model. Among the different components tested, it is found that the fit is most improved when dark matter is added. This is an indication that the signal may be coming from dark matter annihilation.
    Analysis

    This analysis is interested in the gamma rays coming from the galactic center. However, when looking towards the galactic center the telescope detects all of the gamma-rays coming from both the foreground and the background. The main challenge is to accurately model the gamma-rays coming from known astrophysical sources.

    2
    Schematic of the experiment. We are interested in gamma-rays coming from the galactic center, represented by the red circle. However, the LAT detects all of the gamma-rays coming from the foreground and background, represented by the blue region. The main challenge is to accurately model the gamma-rays coming from known astrophysical sources. Image adapted from Universe Today.

    An overview of the analysis chain is as follows. The model of the observed region comes from performing a likelihood fit of the parameters for the known astrophysical sources. A likelihood fit is a statistical procedure that calculates the probability of observing the data given a set of parameters. In general there are two types of sources:

    1. Point sources such as known pulsars
    2. Diffuse sources due to the interaction of cosmic rays with the interstellar gas and radiation field

    Parameters for these two types of sources are fit at the same time. One of the main uncertainties in the background is the cosmic ray source distribution. This is the number of cosmic ray sources as a function of distance from the center of the galaxy. It is believed that cosmic rays come from supernovae. However, the source distribution of supernova remnants is not well determined. Therefore, other tracers must be used. In this context a tracer refers to a measurement that can be made to infer the distribution of supernova remnants. This analysis uses both the distribution of OB stars and the distribution of pulsars as tracers. The former refers to OB associations, which are regions of O-type and B-type stars. These hot massive stars are progenitors of supernovae. In contrast to these progenitors, the distribution of pulsars is also used since pulsars are the end state of supernovae. These two extremes serve to encompass the uncertainty in the cosmic ray source distribution, although, as mentioned earlier, this uncertainty is by no means bracketing. Two of the four background model variants come from these distributions.

    3
    An overview of the analysis chain. In general there are two types of sources: point sources and diffuse source. The diffuse sources are due to the interaction of cosmic rays with interstellar gas and radiation fields. Spectral parameters for the diffuse sources are fit concurrently with the point sources using a likelihood fit. The question mark represents the possibility of an additional component possibly missing from the model, such as dark matter.

    The information pertaining to the cosmic rays, gas, and radiation fields is input into a propagation code called GALPROP. This produces an all-sky gamma-ray intensity map for each of the physical processes that produce gamma-rays. These processes include the production of neutral pions due to the interaction of cosmic ray protons with the interstellar gas, which quickly decay into gamma-rays, cosmic ray electrons up-scattering low-energy photons of the radiation field via inverse Compton, and cosmic ray electrons interacting with the gas producing gamma-rays via Bremsstrahlung radiation.

    4
    Residual map for one of the background models. Image from 1511.02938

    The maps of all the processes are then tuned to the data. In general, tuning is a procedure by which the background models are optimized for the particular data set being used. This is done using a likelihood analysis. There are two different tuning procedures used for this analysis. One tunes the normalization of the maps, and the other tunes both the normalization and the extra degrees of freedom related to the gas emission interior to the solar circle. These two tuning procedures, performed for the the two cosmic ray source models, make up the four different background models.

    Point source models are then determined for each background model, and the spectral parameters for both diffuse sources and point sources are simultaneously fit using a likelihood analysis.

    Results and Conclusion

    6
    Best fit dark matter spectra for the four different background models. Image: 1511.02938

    In the plot of the best fit dark matter spectra for the four background models, the hatching of each curve corresponds to the statistical uncertainty of the fit. The systematic uncertainty can be interpreted as the region enclosed by the four curves. Results from other analyses of the galactic center are overlaid on the plot. This result shows that the galactic center analysis performed by the Fermi collaboration allows a broad range of possible dark matter spectra.

    The Fermi analysis has shown that within systematic uncertainties a gamma-ray excess coming from the galactic center is detected. In order to try to explain this excess additional components were added to the model. Among the additional components tested it was found that the fit is most improved with that addition of a dark matter component. However, this does not establish that a dark matter signal has been detected. There is still a good chance that the excess can be due to something else, such as an unresolved population of millisecond pulsars or mis-modeling of the background. Further work must be done to better understand the background and better characterize the excess. Nevertheless, it remains an exciting prospect that the gamma-ray excess could be a signal of dark matter.

    See the full article here .

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    What is ParticleBites?

    ParticleBites is an online particle physics journal club written by graduate students and postdocs. Each post presents an interesting paper in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.

    The papers are accessible on the arXiv preprint server. Most of our posts are based on papers from hep-ph (high energy phenomenology) and hep-ex (high energy experiment).

    Why read ParticleBites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.

    Our goal is to solve this problem, one paper at a time. With each brief ParticleBite, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in particle physics.

    Who writes ParticleBites?

    ParticleBites is written and edited by graduate students and postdocs working in high energy physics. Feel free to contact us if you’re interested in applying to write for ParticleBites.

    ParticleBites was founded in 2013 by Flip Tanedo following the Communicating Science (ComSciCon) 2013 workshop.

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    Flip Tanedo UCI Chancellor’s ADVANCE postdoctoral scholar in theoretical physics. As of July 2016, I will be an assistant professor of physics at the University of California, Riverside

    It is now organized and directed by Flip and Julia Gonski, with ongoing guidance from Nathan Sanders.

     
  • richardmitnick 6:32 am on May 13, 2016 Permalink | Reply
    Tags: , , NASA Fermi,   

    From NASA Fermi: “NASA’s Fermi Telescope Helps Link Cosmic Neutrino to Blazar Blast” 

    NASA Fermi Banner

    NASA/Fermi Telescope
    Fermi

    April 28, 2016
    By Francis Reddy
    NASA’s Goddard Space Flight Center, Greenbelt, Md.

    Nearly 10 billion years ago, the black hole at the center of a galaxy known as PKS B1424-418 produced a powerful outburst. Light from this blast began arriving at Earth in 2012. Now astronomers using data from NASA’s Fermi Gamma-ray Space Telescope and other space- and ground-based observatories have shown that a record-breaking neutrino seen around the same time likely was born in the same event.


    Access mp4 video here.
    NASA Goddard scientist Roopesh Ojha explains how Fermi and TANAMI uncovered the first plausible link between a blazar eruption and a neutrino from deep space. Credits: NASA’s Goddard Space Flight Center

    “Neutrinos are the fastest, lightest, most unsociable and least understood fundamental particles, and we are just now capable of detecting high-energy ones arriving from beyond our galaxy,” said Roopesh Ojha, a Fermi team member at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and a coauthor of the study. “Our work provides the first plausible association between a single extragalactic object and one of these cosmic neutrinos.”

    Although neutrinos far outnumber all the atoms in the universe, they rarely interact with matter, which makes detecting them quite a challenge. But this same property lets neutrinos make a fast exit from places where light cannot easily escape — such as the core of a collapsing star — and zip across the universe almost completely unimpeded. Neutrinos can provide information about processes and environments that simply aren’t available through a study of light alone.

    The IceCube Neutrino Observatory, built into a cubic kilometer of clear glacial ice at the South Pole, detects neutrinos when they interact with atoms in the ice.

    U Wisconsin ICECUBE neutrino detector
    IceCube neutrino detector interior
    U Wisconsin ICECUBE neutrino detector

    This triggers a cascade of fast-moving charged particles that emit a faint glow, called Cerenkov light, as they travel, which is picked up by thousands of optical sensors strung throughout IceCube. Scientists determine the energy of an incoming neutrino by the amount of light its particle cascade emits.

    To date, the IceCube science team has detected about a hundred very high-energy neutrinos and nicknamed some of the most extreme events after characters on the children’s TV series “Sesame Street.” On Dec. 4, 2012, IceCube detected an event known as Big Bird, a neutrino with an energy exceeding 2 quadrillion electron volts (PeV). To put that in perspective, it’s more than a million million times greater than the energy of a dental X-ray packed into a single particle thought to possess less than a millionth the mass of an electron. Big Bird was the highest-energy neutrino ever detected at the time and still ranks second.

    Where did it come from? The best IceCube position only narrowed the source to a patch of the southern sky about 32 degrees across, equivalent to the apparent size of 64 full moons.

    Enter Fermi. Starting in the summer of 2012, the satellite’s Large Area Telescope (LAT) witnessed a dramatic brightening of PKS B1424-418, an active galaxy classified as a gamma-ray blazar.

    NASA/Fermi LAT
    NASA/Fermi LAT

    An active galaxy is an otherwise typical galaxy with a compact and unusually bright core. The excess luminosity of the central region is produced by matter falling toward a supermassive black hole weighing millions of times the mass of our sun. As it approaches the black hole, some of the material becomes channeled into particle jets moving outward in opposite directions at nearly the speed of light. In blazars, one of these jets happens to point almost directly toward Earth.

    l
    Left
    r
    Right

    Fermi LAT images showing the gamma-ray sky around the blazar PKS B1424-418. Brighter colors indicate greater numbers of gamma rays. The dashed arc marks part of the source region established by IceCube for the Big Bird neutrino (50-percent confidence level). Left: An average of LAT data centered on July 8, 2011, and covering 300 days when the blazar was inactive. Right: An average of 300 active days centered on Feb. 27, 2013, when PKS B1424-418 was the brightest blazar in this part of the sky. Credits: NASA/DOE/LAT Collaboration

    During the year-long outburst, PKS B1424-418 shone between 15 and 30 times brighter in gamma rays than its average before the eruption. The blazar is located within the Big Bird source region, but then so are many other active galaxies detected by Fermi.

    The scientists searching for the neutrino source then turned to data from a long-term observing program named TANAMI. Since 2007, TANAMI has routinely monitored nearly 100 active galaxies in the southern sky, including many flaring sources detected by Fermi. The program includes regular radio observations using the Australian Long Baseline Array (LBA) and associated telescopes in Chile, South Africa, New Zealand and Antarctica. When networked together, they operate as a single radio telescope more than 6,000 miles across and provide a unique high-resolution look into the jets of active galaxies.

    Australian Long Baseline Array
    Australian Long Baseline Array map

    ATNF TANAMI array Australia
    ATNF TANAMI array Australia

    3
    Radio images from the TANAMI project reveal the 2012-2013 eruption of PKS B1424-418 at a wavelength of 8.4 GHz. The core of the blazar’s jet brightened by four times, producing the most dramatic blazar outburst TANAMI has observed to date. Credits: TANAMI

    Three radio observations of PKS B1424-418 between 2011 and 2013 cover the period of the Fermi outburst. They reveal that the core of the galaxy’s jet had brightened by about four times. No other galaxy observed by TANAMI over the life of the program has exhibited such a dramatic change.

    “We combed through the field where Big Bird must have originated looking for astrophysical objects capable of producing high-energy particles and light,” said coauthor Felicia Krauss, a doctoral student at the University of Erlangen-Nuremberg in Germany. “There was a moment of wonder and awe when we realized that the most dramatic outburst we had ever seen in a blazar happened in just the right place at just the right time.”

    In a paper* published Monday, April 18, in Nature Physics, the team suggests the PKS B1424-418 outburst and Big Bird are linked, calculating only a 5-percent probability the two events occurred by chance alone. Using data from Fermi, NASA’s Swift and WISE satellites, the LBA and other facilities, the researchers determined how the energy of the eruption was distributed across the electromagnetic spectrum and showed that it was sufficiently powerful to produce a neutrino at PeV energies.

    NASA/SWIFT Telescope
    NASA/SWIFT Telescope

    NASA/Wise Telescope
    NASA/Wise Telescope

    “Taking into account all of the observations, the blazar seems to have had means, motive and opportunity to fire off the Big Bird neutrino, which makes it our prime suspect,” said lead author Matthias Kadler, a professor of astrophysics at the University of Wuerzburg in Germany.

    Francis Halzen, the principal investigator of IceCube at the University of Wisconsin–Madison, and not involved in this study, thinks the result is an exciting hint of things to come. “IceCube is about to send out real-time alerts when it records a neutrino that can be localized to an area a little more than half a degree across, or slightly larger than the apparent size of a full moon,” he said. “We’re slowly opening a neutrino window onto the cosmos.”

    For more information about NASA’s Fermi, visit:

    http://www.nasa.gov/fermi

    *Science paper:
    Coincidence of a high-fluence blazar outburst with a PeV-energy neutrino event

    See the full article here .

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    NASA’s Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership, developed in collaboration with the U.S. Department of Energy and with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

     
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