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  • richardmitnick 4:58 pm on October 15, 2018 Permalink | Reply
    Tags: , , , , , , Fermi LAT, ,   

    From SLAC National Accelerator Lab: “Missing gamma-ray blobs shed new light on dark matter, cosmic magnetism” 

    From SLAC National Accelerator Lab

    October 15, 2018
    Manuel Gnida

    Astrophysicists use a catalog of extended gamma-ray sources spotted by Fermi spacecraft to home in on mysterious properties of deep space.

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    Extended gamma-ray sources (circled areas) identified in data taken with the Large Area Telescope on NASA’s Fermi spacecraft. (Matthew Wood/Fermi-LAT collaboration)

    NASA/Fermi LAT


    NASA/Fermi Gamma Ray Space Telescope

    When astrophysicists look at the gamma-ray glow from a galaxy outside our own, all they typically see is a small spot because the galaxy is extremely far away. So, when a galaxy appears as an extended blob, something extraordinary must be going on that could help researchers better understand the properties of deep space.

    Now, scientists, including researchers from the Department of Energy’s SLAC National Accelerator Laboratory, have compiled the most detailed catalog of such blobs using eight years of data collected with the Large Area Telescope (LAT) on NASA’s Fermi Gamma-Ray Space Telescope. The blobs, including 19 gamma-ray sources that weren’t known to be extended before, provide crucial information on how stars are born, how they die, and how galaxies spew out matter trillions of miles into space.

    Intriguingly, though, it was the cosmic regions where they didn’t find blobs that shed new light on two particularly mysterious ingredients of the universe: dark matter – an invisible form of matter six times more prevalent than regular matter – and the magnetic field that pervades the space between galaxies and whose origin is unknown.

    “These data are very exciting because they allow us to study some of the most fundamental processes in the universe, and they could potentially lead us to discover completely new physics,” says NASA scientist Regina Caputo, one of the leaders of the recent study by the international Fermi-LAT collaboration, which was published in The Astrophysical Journal.

    One of the things the researchers looked for were gamma-ray blobs associated with companion galaxies orbiting our Milky Way.

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    Researchers have discovered a set of possible dwarf satellite galaxies orbiting the Milky Way. The new objects (red dots) were detected in the new sky area (gray transparent area) covered by the Dark Energy Survey. Scientists have seen about two dozen dwarf galaxies (blue dots) before. They are the smallest known galaxy structures and may hold the key to understanding unseen dark matter, which accounts for about 85 percent of all matter in the universe but whose nature is unknown. The zoom-in region shows an image of the stars that likely belong to one of the dwarf galaxy candidates. (Kavli Institute for Particle Astrophysics and Cosmology/SLAC National Accelerator Laboratory/Fermi National Accelerator Laboratory/Dark Energy Survey/Infrared Processing and Analysis Center/California Institute of Technology/University of Massachusetts)

    Since the faintest of these satellites contain very few stars, they are thought to be held together by dark matter.

    Scientists believe dark matter could be made of particles called WIMPs, which would emit gamma rays when they collide and destroy each other. A gamma-ray blob signal coming from an ultrafaint satellite galaxy would be a strong hint that WIMPS exist.

    “Our simulations of galaxy formation predict that there should be more satellite galaxies than those we’ve been able to detect in optical surveys,” Caputo says. “Some of them could be so faint that we might only be able to see them if they produced gamma rays due to dark matter annihilation.”

    In the new study, the Fermi-LAT researchers searched for gamma-ray blobs associated with those predicted satellite galaxies. They didn’t find any. But even the fact that they came up empty-handed is an important result: It will allow them, in future studies, to define the distribution of dark matter in Milky Way satellites and the likelihood that WIMPs produce gamma rays. It also provides new input for models of galaxy evolution.

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    The Small Magellanic Cloud (SMC) 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. (Regina Caputo/NASA; Axel Mellinger/Central Michigan University)

    Small Magellanic Cloud. NASA/ESA Hubble and ESO/Digitized Sky Survey 2

    Faint cosmic magnetism

    The researchers also used their data to obtain more information on the strength of the magnetic field between galaxies, which they hope will be an important puzzle piece in determining the origin of the field.

    For this part of the study, the team looked at blazars – active galaxies that spit high-speed jets of plasma far into space. The Fermi spacecraft can detect gamma rays associated with jets that point in the direction of the Earth.

    Blazars appear as point-like sources, but a mechanism involving the intergalactic magnetic field could potentially make them look like extended sources, says Manuel Meyer, a Humboldt fellow at the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) and another lead author of the study.


    Manuel Meyer, Humboldt fellow at the Kavli Institute for Particle Astrophysics and Cosmology, explains a process involving the intergalactic magnetic field that could potentially make active galaxies known as blazars appear as extended gamma-ray sources in data taken with the Large Area Telescope onboard NASA’s Fermi mission. (Manuel Meyer/Kavli Institute for Particle Astrophysics and Cosmology)

    The researchers didn’t find any blobs associated with blazars. Again, this no-show was valuable information: It allowed the team to calculate that the magnetic field is at least a tenth of a millionth billionth as strong as Earth’s magnetic field. The magnetic field’s upper limit – a billion times weaker than Earth’s field – was already known.

    The intergalactic field is stronger than the researchers had expected, Meyer says, and this new information might help them find out whether it stems from material spilled into space in recent times or whether it was created in processes that occurred in earlier cosmic history.

    The cosmic magnetism could also have ties to dark matter. In an alternative to the WIMP model, dark matter is proposed to be made of lighter particles called axions that could emerge from gamma rays (and convert back into them) in the presence of a magnetic field. “For that to occur, the field strength would need to be closer to its upper limit, though,” Meyer says. “It’s definitely interesting to take this mechanism into account in our dark matter studies, and we’re doing this right now within the Fermi-LAT collaboration.”

    NASA’s Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership, developed in collaboration with the U.S. Department of Energy Office of Science and with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States. The Fermi mission recently celebrated its 10th anniversary. A number of SLAC researchers are members of the international Fermi-LAT collaboration. SLAC assembled the LAT and hosts the operations center that processes LAT data. The new analysis benefitted from a data analysis package, initially developed by KIPAC researcher Matthew Wood, that automates common analysis tasks. KIPAC is a joint institute of SLAC and Stanford University.

    See the full article here .


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    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.

     
  • richardmitnick 5:34 pm on December 10, 2017 Permalink | Reply
    Tags: , , , , , Fermi LAT, , , NASA's SuperTIGER Balloon Flies Again to Study Heavy Cosmic Particles, ,   

    From Goddard: “NASA’s SuperTIGER Balloon Flies Again to Study Heavy Cosmic Particles” 

    NASA Goddard Banner
    NASA Goddard Space Flight Center

    Dec. 6, 2017
    Francis Reddy
    francis.j.reddy@nasa.gov
    NASA’s Goddard Space Flight Center, Greenbelt, Md.

    A science team in Antarctica is preparing to loft a balloon-borne instrument to collect information on cosmic rays, high-energy particles from beyond the solar system that enter Earth’s atmosphere every moment of every day. The instrument, called the Super Trans-Iron Galactic Element Recorder (SuperTIGER), is designed to study rare heavy nuclei, which hold clues about where and how cosmic rays attain speeds up to nearly the speed of light.

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    NASA’s Super-TIGER balloon

    The launch is expected by Dec. 10, weather permitting.

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    Explore this infographic [on the full article] to learn more about SuperTIGER, cosmic rays and scientific ballooning.
    Credits: NASA’s Goddard Space Flight Center

    Download infographic as PDF

    “The previous flight of SuperTIGER lasted 55 days, setting a record for the longest flight of any heavy-lift scientific balloon,” said Robert Binns, the principal investigator at Washington University in St. Louis, which leads the mission. “The time aloft translated into a long exposure, which is important because the particles we’re after make up only a tiny fraction of cosmic rays.”

    The most common cosmic ray particles are protons or hydrogen nuclei, making up roughly 90 percent, followed by helium nuclei (8 percent) and electrons (1 percent). The remainder contains the nuclei of other elements, with dwindling numbers of heavy nuclei as their mass rises. With SuperTIGER, researchers are looking for the rarest of the rare — so-called ultra-heavy cosmic ray nuclei beyond iron, from cobalt to barium.

    “Heavy elements, like the gold in your jewelry, are produced through special processes in stars, and SuperTIGER aims to help us understand how and where this happens,” said lead co-investigator John Mitchell at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “We’re all stardust, but figuring out where and how this stardust is made helps us better understand our galaxy and our place in it.”

    When a cosmic ray strikes the nucleus of a molecule of atmospheric gas, both explode in a shower of subatomic shrapnel that triggers a cascade of particle collisions. Some of these secondary particles reach detectors on the ground, providing information scientists can use to infer the properties of the original cosmic ray. But they also produce an interfering background that is greatly reduced by flying instruments on scientific balloons, which reach altitudes of nearly 130,000 feet (40,000 meters) and float above 99.5 percent of the atmosphere.

    The most massive stars forge elements up to iron in their cores and then explode as supernovas, dispersing the material into space. The explosions also create conditions that result in a brief, intense flood of subatomic particles called neutrons. Many of these neutrons can “stick” to iron nuclei. Some of them subsequently decay into protons, producing new elements heavier than iron.

    Supernova blast waves provide the boost that turns these particles into high-energy cosmic rays.

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    NASA’s Fermi Proves Supernova Remnants Produce Cosmic Rays. February 14, 2013.

    NASA/Fermi Telescope


    NASA/Fermi LAT


    As a shock wave expands into space, it entraps and accelerates particles until they reach energies so extreme they can no longer be contained.

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    On Dec. 1, SuperTIGER was brought onto the deck of Payload Building 2 at McMurdo Station, Antarctica, to test communications in preparation for its second flight. Mount Erebus, the southernmost active volcano on Earth, appears in the background.
    Credits: NASA/Jason Link

    Over the past two decades, evidence accumulated from detectors on NASA’s Advanced Composition Explorer satellite and SuperTIGER’s predecessor, the balloon-borne TIGER instrument, has allowed scientists to work out a general picture of cosmic ray sources. Roughly 20 percent of cosmic rays were thought to arise from massive stars and supernova debris, while 80 percent came from interstellar dust and gas with chemical quantities similar to what’s found in the solar system.

    “Within the last few years, it has become apparent that some or all of the very neutron-rich elements heavier than iron may be produced by neutron star mergers instead of supernovas,” said co-investigator Jason Link at Goddard.

    Neutron stars are the densest objects scientists can study directly, the crushed cores of massive stars that exploded as supernovas. Neutron stars orbiting each other in binary systems emit gravitational waves, which are ripples in space-time predicted by Einstein’s general theory of relativity. These waves remove orbital energy, causing the stars to draw ever closer until they eventually crash together and merge.

    Theorists calculated that these events would be so thick with neutrons they could be responsible for most of the very neutron-rich cosmic rays heavier than nickel. On Aug. 17, NASA’s Fermi Gamma-ray Space Telescope and the National Science Foundation’s Laser Interferometer Gravitational-wave Observatory detected the first light and gravitational waves from crashing neutron stars. Later observations by the Hubble and Spitzer space telescopes indicate that large amounts of heavy elements were formed in the event.

    “It’s possible neutron star mergers are the dominant source of heavy, neutron-rich cosmic rays, but different theoretical models produce different quantities of elements and their isotopes,” Binns said. “The only way to choose between them is to measure what’s really out there, and that’s what we’ll be doing with SuperTIGER.”

    SuperTIGER is funded by the NASA Headquarters Science Mission Directorate Astrophysics Division.

    The National Science Foundation (NSF) Office of Polar Programs manages the U.S. Antarctic Program and provides logistic support for all U.S. scientific operations in Antarctica. NSF’s Antarctic support contractor supports the launch and recovery operations for NASA’s Balloon Program in Antarctica. Mission data were downloaded using NASA’s Tracking and Data Relay Satellite System.

    For more information about NASA’s Balloon Program, visit:

    http://www.nasa.gov/balloons

    See the full article here.

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    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

     
  • richardmitnick 2:54 pm on September 5, 2017 Permalink | Reply
    Tags: ASAS-SN, ASASSN-16ma, , , , , Fermi LAT, , Novas   

    From NASA blueshift: “Shock Waves Power an Exploding Star” 

    NASA Blueshift

    NASA Blueshift

    September 5, 2017
    Raleigh McElvery

    Roughly 50 times each year, a star nearing the end of its life accretes too much material from a close companion star and erupts in a violent display of light — shedding its outer surface and propelling shock waves into our galaxy — only to recover and smolder as it did before. This event is called a ‘nova.’

    This ability to “reprocess” sets novae apart from their rare supernovae counterparts, which occur only several times per century and self-destruct amid an even greater celestial outburst. And yet, it’s the more common novae that could hold the answers to essential questions regarding our universe.

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    As this nova illustration shows, when a white dwarf accretes too much material from its companion star, it ejects material in two district winds. Shock waves are created as the two winds collide, producing gamma rays (magenta). Research now suggests this may be the primary source of visible light as well. Credit: NASA’s Goddard Space Flight Center/S. Wiessinger

    Given that these events usually occur thousands of light years away, I went to discuss their significance with two more accessible sources: Laura Chomiuk and Kwan Lok Li of Michigan State University. Both scientists recently allied with Columbia University and the ASAS-SN project (of which Chomiuk is a key member) in hopes of untangling the fundamental processes underlying the lifecycle of stars.

    2
    ASAS-SN OSU

    3
    ASAS-SN Cerro Tololo

    3
    ASASSN-14li: Destroyed Star Rains onto Black Hole, Winds Blow it Back. NASA/Chandra

    They have turned their attention to one classical nova in particular, ASASSN-16ma, located within the “archer” constellation Sagittarius.

    Their paper, recently published in Nature Astronomy, suggests a novel source for the nova’s post-outburst glow — offering insight into other outer-space explosions.

    The authors explained that ASASSN-16ma is among the brightest novae ever detected by the Fermi Large Area Telescope — a satellite instrument built to observe cosmic events releasing a high-energy form of light called gamma rays. The Fermi Mission, spearheaded by NASA’s Goddard Space Flight Center, also discovered back in 2010 that novae generate these high-energy rays.

    Gamma rays are emitted as material is ejected from the star in two distinct winds or “outflows.” A slow burst is followed by a faster one, which then crashes into the first and creates a shock wave. Visible light also radiates from the same explosion, although until now most scientists believed it stemmed from nuclear reactions on the surface of the star.

    But something wasn’t right about the traditional explanation. Novae shouldn’t have enough power to produce gamma rays — nor release as much visible light as they do given their calculated luminosity limit.

    This inherent contradiction confounded astrophysicists and theorists alike, until last year when Chomiuk requested that Fermi focus on ASASSN-16ma for an extended duration to collect more sensitive data. As luck would have it, Fermi was already observing another nova in the same neighborhood, so Goddard’s team was more than happy to oblige, tilting their telescope slightly. When scientists began to sift through the data transmitted from the cosmos to Earth, one specific trend became abundantly clear.

    “Our results were telling us our previous assumption that all the luminosity comes from the surface of the star was flawed,” Chomiuk explained to me from her office in East Lansing. “A lot of it actually comes from the same place as the gamma rays,” she continued. That is, the colliding shock waves.

    Seeking an outsider’s perspective, I made my way to the second floor of Goddard’s astrophysics building to chat with one of the center’s Fermi aficionados, David Thompson. Eager to lend guidance, Thompson presented his miniature replica of the spacecraft, and indicated the boxy Large Area Telescope seated atop the winged satellite. “We’ve been seeing similar novae for years, but this was unexpected,” he said. “The authors have enough detail in their data to challenge the conventional wisdom about what makes novae bright.”

    But I soon learned these ideas weren’t entirely unprecedented. During every interview I conducted, one name kept coming up: collaborator and lead theorist, Brian Metzger of Columbia University. Metzger had been crunching the numbers on novae for several years, but lacked substantive data to bolster his hypotheses. That is, until now.

    “Novae have been observed by the naked eye since well before the modern era,” Metzger told me, “and yet our view of what is producing these bright outbursts continues to change.”

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    The Fermi LAT 60-month image, constructed from front-converting gamma rays with energies greater than 1 GeV. The most prominent feature is the bright band of diffuse glow along the map’s center, which marks the central plane of our Milky Way galaxy. Image credit: NASA/DOE/Fermi LAT Collaboration

    NASA/Fermi LAT


    NASA/Fermi Telescope

    Fermi’s Deputy Project Scientist, Elizabeth Hays, said Metzger’s paradigm had already garnered some buzz throughout the scientific community, although at the time the universe had yet to reveal an event that clearly reflected his calculations. Now, thanks to ASASSN-16ma, she affirmed his conjectures may expose what powers these nova outbursts — processes which might also extend to other kinds of stellar explosions, like dazzling supernovae as well as star mergers.

    “We’ve been ignoring this whole piece of the puzzle,” she said. “When we come across high-energy processes like these novae, it becomes clear just how much more work we have left to do.”

    Understanding novae shock and gamma ray production could also explain certain properties of accelerating particles traveling close to the speed of light, as well as the subsequent magnetic fields.

    When I asked Li what was next, he said he plans to continue using Fermi data to monitor nearby novae. Ultimately, he hopes to pinpoint similarly strong correlations between gamma ray and visible light emissions within additional novae. “We’re always looking for new sources to test our model, and ensure it truly and accurately describes gamma-ray phenomena in classical novae,” he added.

    Back at Goddard, Thompson repositioned his Fermi model on the shelf among his books, and agreed a single example alone does not constitute proof. But it’s certainly a good place to start. “These results prompt us to think about things in a new way,” he said, “and that’s what science is about.”

    See the full article here .

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

    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 8:32 pm on May 2, 2017 Permalink | Reply
    Tags: , , , , , Fermi LAT, Mystery glow of Milky Way likely not dark matter, ,   

    From Symmetry: “Mystery glow of Milky Way likely not dark matter” 


    Symmetry

    05/02/17
    Manuel Gnida

    1
    NASA/CXC/University of Massachusetts/D. Wang et al.; Greg Stewart, SLAC National Accelerator Laboratory

    According to the Fermi LAT collaboration, the galaxy’s excessive gamma-ray glow likely comes from pulsars, the remains of collapsed ancient stars.

    NASA/Fermi LAT

    A mysterious gamma-ray glow at the center of the Milky Way is most likely caused by pulsars, the incredibly dense, rapidly spinning cores of collapsed ancient stars that were up to 30 times more massive than the sun.

    That’s the conclusion of a new analysis by an international team of astrophysicists on the Fermi LAT collaboration. The findings cast doubt on previous interpretations of the signal as a potential sign of dark matter, a form of matter that accounts for 85 percent of all matter in the universe but that so far has evaded detection.

    “Our study shows that we don’t need dark matter to understand the gamma-ray emissions of our galaxy,” says Mattia Di Mauro from the Kavli Institute for Particle Astrophysics and Cosmology, a joint institute of Stanford University and the US Department of Energy’s SLAC National Accelerator Laboratory. “Instead, we have identified a population of pulsars in the region around the galactic center, which sheds new light on the formation history of the Milky Way.”

    Di Mauro led the analysis, which looked at the glow with the Large Area Telescope on NASA’s Fermi Gamma-ray Space Telescope, which has been orbiting Earth since 2008. The LAT, a sensitive “eye” for gamma rays, the most energetic form of light, was conceived of and assembled at SLAC, which also hosts its operations center.

    The collaboration’s findings, submitted to The Astrophysical Journal for publication, are available as a preprint.

    A mysterious glow

    Dark matter is one of the biggest mysteries of modern physics. Researchers know that dark matter exists because it bends light from distant galaxies and affects how galaxies rotate. But they don’t know what the substance is made of. Most scientists believe it’s composed of yet-to-be-discovered particles that almost never interact with regular matter other than through gravity, making it very hard to detect them.

    One way scientific instruments might catch a glimpse of dark matter particles is when the particles either decay or collide and destroy each other. “Widely studied theories predict that these processes would produce gamma rays,” says Seth Digel, head of KIPAC’s Fermi group. “We search for this radiation with the LAT in regions of the universe that are rich in dark matter, such as the center of our galaxy.”

    Previous studies have indeed shown that there are more gamma rays coming from the galactic center than expected, fueling some scientific papers and media reports that suggest the signal might hint at long-sought dark matter particles. However, gamma rays are produced in a number of other cosmic processes, which must be ruled out before any conclusion about dark matter can be drawn. This is particularly challenging because the galactic center is extremely complex, and astrophysicists don’t know all the details of what’s going on in that region.

    Most of the Milky Way’s gamma rays originate in gas between the stars that is lit up by cosmic rays, charged particles produced in powerful star explosions called supernovae. This creates a diffuse gamma-ray glow that extends throughout the galaxy. Gamma rays are also produced by supernova remnants, pulsars—collapsed stars that emit “beams” of gamma rays like cosmic lighthouses—and more exotic objects that appear as points of light.

    “Two recent studies by teams in the US and the Netherlands have shown that the gamma-ray excess at the galactic center is speckled, not smooth as we would expect for a dark matter signal,” says KIPAC’s Eric Charles, who contributed to the new analysis. “Those results suggest the speckles may be due to point sources that we can’t see as individual sources with the LAT because the density of gamma-ray sources is very high and the diffuse glow is brightest at the galactic center.”

    Remains of ancient stars

    The new study takes the earlier analyses to the next level, demonstrating that the speckled gamma-ray signal is consistent with pulsars.

    “Considering that about 70 percent of all point sources in the Milky Way are pulsars, they were the most likely candidates,” Di Mauro says. “But we used one of their physical properties to come to our conclusion. Pulsars have very distinct spectra—that is, their emissions vary in a specific way with the energy of the gamma rays they emit. Using the shape of these spectra, we were able to model the glow of the galactic center correctly with a population of about 1,000 pulsars and without introducing processes that involve dark matter particles.”

    The team is now planning follow-up studies with radio telescopes to determine whether the identified sources are emitting their light as a series of brief light pulses—the trademark that gives pulsars their name.

    Discoveries in the halo of stars around the center of the galaxy, the oldest part of the Milky Way, also reveal details about the evolution of our galactic home, just as ancient remains teach archaeologists about human history.

    “Isolated pulsars have a typical lifetime of 10 million years, which is much shorter than the age of the oldest stars near the galactic center,” Charles says. “The fact that we can still see gamma rays from the identified pulsar population today suggests that the pulsars are in binary systems with companion stars, from which they leach energy. This extends the life of the pulsars tremendously.”

    Dark matter remains elusive

    The new results add to other data that are challenging the interpretation of the gamma-ray excess as a dark matter signal.

    “If the signal were due to dark matter, we would expect to see it also at the centers of other galaxies,” Digel says. “The signal should be particularly clear in dwarf galaxies orbiting the Milky Way. These galaxies have very few stars, typically don’t have pulsars and are held together because they have a lot of dark matter. However, we don’t see any significant gamma-ray emissions from them.”

    The researchers believe that a recently discovered strong gamma-ray glow at the center of the Andromeda galaxy, the major galaxy closest to the Milky Way, may also be caused by pulsars rather than dark matter.

    But the last word may not have been spoken. Although the Fermi-LAT team studied a large area of 40 degrees by 40 degrees around the Milky Way’s galactic center (the diameter of the full moon is about half a degree), the extremely high density of sources in the innermost four degrees makes it very difficult to see individual ones and rule out a smooth, dark matter-like gamma-ray distribution, leaving limited room for dark matter signals to hide.

    This work was funded by NASA and the DOE Office of Science, as well as agencies and institutes in France, Italy, Japan and Sweden.

    See the full article here .

    Please help promote STEM in your local schools.

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    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.


     
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