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

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

    Symmetry Mag


    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 .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 2:21 pm on March 7, 2014 Permalink | Reply
    Tags: , , SNEWS,   

    From Symmetry: “Start spreading the SNEWS” 

    March 07, 2014
    Andre Salles

    When it comes to studying supernovae, if you don’t SNEWS, you lose.

    SNEWS, the Supernova Early Warning System, is a worldwide network designed to do just what the name implies: let astronomers and physicists know when a nearby supernova appears. This can be a tricky business, since supernovae appear in our galaxy roughly once every 30 years, and the window for studying them can vary—anywhere from a few weeks down to a few hours.

    Courtesy of NASA

    Seeing a supernova in action is certainly a great chance to learn about how supernovae work. But it’s the burst of neutrinos released in a supernova that most interests Kate Scholberg and Alec Habig, the two physicists who spearheaded SNEWS. Scholberg and Habig were post-doctoral researchers on the Super-Kamiokande neutrino experiment when the idea was first discussed in the late 1990s.

    “There is enormous potential to learn about neutrinos from supernovae,” says Scholberg, now a professor at Duke University. “We can learn about their properties, like their mass, their ability to oscillate, and potentially exotic effects. Furthermore, with supernova neutrinos, we get the complete story of the stellar core collapse, a story that is of great interest to a lot of theorists.”

    The trick is to catch them. Neutrinos are the most abundant particles in the universe, and physicists know very little about them. That’s because they’re notoriously elusive—they rarely interact with matter and have miniscule masses. Terrestrial neutrino experiments fire billions of the tiny particles at massive detectors every few seconds and see only a few interactions a week.

    Supernova neutrinos are even more difficult to pin down. As Habig, now a professor at the University of Minnesota, Duluth, explains, neutrinos are often the first sign of a supernova, arriving before anyone knows what’s happening.

    “You get the neutrinos before you get the light,” Habig says. “It takes hours before you see the photons. Depending on the type of star, it could take up to 12 hours for the photons to blast their way out of the dying star, but the neutrinos escape immediately.”

    It’s that very principle that allows SNEWS to work. It starts with five of the biggest neutrino experiments in the world: Super-Kamiokande and KamLAND in Japan, the Large Volume Detector and Borexino in Italy, and IceCube in Antarctica. Each experiment can detect supernova neutrinos.

    Once potential supernova neutrinos are detected in one of these experiments, a datagram is sent to the SNEWS computer, housed at Brookhaven National Laboratory in New York. If multiple datagrams indicate that two bursts of neutrinos arrived within ten seconds of each other, the computer automatically alerts the SNEWS mailing list. According to Habig, there are nearly 2700 email addresses on the list, although some of those addresses send to lists themselves. (Sky & Telescope magazine’s AstroAlert list receives SNEWS alerts, for example.)

    The entire process is automated, and its purpose is to get as many eyes trained on the sky as possible, and quickly. The network includes just about every operational neutrino experiment (and some that are not yet operational, like Fermilab’s upgraded MicroBooNE experiment), all of which will be ready to view and study supernova neutrinos.

    “Our best estimate is one supernova in our galaxy every 30 years or so,” Scholberg says. “But there could be two in the next 10 years, we don’t know. They’re so rare that we have to be sure to get every possible piece of information from them, so we need to be properly prepared.”

    As Scholberg points out, we’re due for one. The last supernova that sent detectable neutrinos to Earth occurred in 1987, on the edge of the Tarantula Nebula in the Large Magellanic Cloud, a nearby galaxy. About three hours before the visible light from that supernova reached earth, three neutrino experiments detected a grand total of 24 neutrino interactions from the wave of particles emitted.

    SNEWS was first discussed in earnest in 1998, Habig says, at the 17th Conference on Neutrino Physics and Astrophysics in Takayema, Japan. With Scholberg as the driving and organizational force behind the project, Habig and Scholberg wrote the code in the late 1990s. (The design was based on an old multiplayer e-sports game, Netrek, which Habig helped develop in the 1990s.)

    The SNEWS team held a workshop in 1998 at Boston University and, as Habig says, they’ve been running ever since. They have only done one full test of the system, in February of 2003, sending an alert out to the mailing list. Since then, members of the SNEWS team have taken weekly shifts, testing the computer network twice a day, making sure everything is ready.

    Of course, the fact that no supernova has exploded in our galaxy in decades means that the SNEWS system has never sent out an actual alert. (“It’s not a very busy computer,” Scholberg jokes.) That’s also a testament to the checks and balances built into the system, to prevent mistakes.

    “When we started, the astronomy community was clear: no false alarms or you’re dead,” Habig says with a laugh.

    As more large neutrino experiments come online, they will add their supernova-sensing abilities to the SNEWS network. Fermilab’s NOvA experiment, which has just seen its first neutrino interactions, will soon launch its supernova trigger. And when the Long-Baseline Neutrino Experiment starts taking data sometime in the next 10 years, it will also feed into the network.

    While studying supernova neutrinos may not teach us everything about these tiny, mysterious particles, we’re likely to find out more than we expect, Scholberg says.

    “Theorists are confident that these signals could help us infer information about neutrino properties that are hard to predict in advance,” she says. “It’s a very rich signal, which means a rich field for surprises.”

    See the full article here.

    Symmetry is a joint Fermilab/SLAC publication.

    ScienceSprings is powered by MAINGEAR computers

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