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  • richardmitnick 9:07 am on October 8, 2016 Permalink | Reply
    Tags: , , , , , MAGIC Telescope, ,   

    From IceCube: “Neutrinos and gamma rays, a partnership to explore the extreme universe” 

    icecube
    IceCube South Pole Neutrino Observatory

    07 Oct 2016
    Sílvia Bravo

    Solving the mystery of the origin of cosmic rays will not happen with a “one-experiment show.” High-energy neutrinos might be produced by galactic supernova remnants or by active galactic nuclei as well as other potential sources that are being sought. And, if our models are right, gamma rays at lower energies could also help identify neutrino sources and, thus, cosmic-ray sources. It’s sort of a “catch one, get them all” opportunity.

    IceCube’s collaborative efforts with gamma-ray, X-ray, and optical telescopes started long ago. Now, the IceCube, MAGIC and VERITAS collaborations present updates to their follow-up programs that will allow the gamma-ray community to collect data from specific sources during periods when IceCube detects a higher number of neutrinos.

    MAGIC Cherenkov gamma ray telescope  on the Canary island of La Palma, Spain
    MAGIC Cherenkov gamma ray telescope on the Canary island of La Palma, Spain

    CfA/VERITAS, AZ, USA
    “CfA/VERITAS, AZ, USA

    Details of the very high energy gamma-ray follow-up program have been submitted to the Journal of Instrumentation.

    1
    Image: Juan Antonio Aguilar and Jamie Yang. IceCube/WIPAC

    From efforts begun by its predecessor AMANDA, IceCube initiated a gamma-ray follow-up program with MAGIC for sources of electromagnetic radiation emissions with large time variations. If we can identify periods of increased neutrino emission, then we can look for gamma-ray emission later on from the same direction.

    For short transient sources, such as gamma-ray bursts and core-collapse supernovas, X-ray and optical wavelength telescopes might also detect the associated electromagnetic radiation. In this case, follow-up observations are much more time sensitive, with electromagnetic radiation expected only a few hours after neutrino emission from a GRB or a few weeks after a core-collapse supernova.

    Updates to this transient follow-up system will use a multistep high-energy neutrino selection to send alerts to gamma-ray telescopes, such as MAGIC and VERITAS, if clusters of neutrinos are observed from a predefined list of potential sources. The combined observation of an increased neutrino and gamma-ray flux could point us to the first source of astrophysical neutrinos. Also, the information provided by both cosmic messengers will improve our understanding of the physical processes that power those sources.

    The initial selection used simple cuts on a number of variables to discriminate between neutrinos and the atmospheric muon background. IceCube, MAGIC, and VERITAS are currently testing a new event selection that uses learning machines and other sophisticated discrimination algorithms to take into account the geometry and time evolution of the hit pattern in IceCube events. Preliminary studies show that this advanced event selection has a sensitivity comparable to offline point-source samples, with a 30-40% sensitivity increase in the Northern Hemisphere with respect to the old selection. The new technique does not rely only on catalogues of sources and allows observing neutrino flares in the Southern Hemisphere. Thus, those alerts will also be forwarded to the H.E.S.S. collaboration, expanding the gamma-ray follow-up program to the entire sky.

    HESS Cherenko Array, located on the Cranz family farm, Göllschau, in Namibia, near the Gamsberg
    HESS Cherenko Array, located on the Cranz family farm, Göllschau, in Namibia, near the Gamsberg

    During the last few years, IceCube has sent several alerts to VERITAS and MAGIC that have not yet resulted in any significant correlation between neutrino and gamma-ray emission. For some of those, however, the source was not in the reach of the gamma-ray telescopes, either because it was out of the field of view or due to poor weather conditions. Follow-up studies have allowed setting new limits on high-energy gamma-ray emission.

    With the increased sensitivity in the Northern Hemisphere and new alerts to telescopes in the Southern Hemisphere, the discovery potential of these joint searches for neutrino and gamma-ray sources is greatly enhanced. Stay tuned for new results!

    See the full article here .

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    ICECUBE neutrino detector

    IceCube neutrino detector interior

    IceCube is a particle detector at the South Pole that records the interactions of a nearly massless sub-atomic particle called the neutrino. IceCube searches for neutrinos from the most violent astrophysical sources: events like exploding stars, gamma ray bursts, and cataclysmic phenomena involving black holes and neutron stars. The IceCube telescope is a powerful tool to search for dark matter, and could reveal the new physical processes associated with the enigmatic origin of the highest energy particles in nature. In addition, exploring the background of neutrinos produced in the atmosphere, IceCube studies the neutrinos themselves; their energies far exceed those produced by accelerator beams. IceCube is the world’s largest neutrino detector, encompassing a cubic kilometer of ice.

     
  • richardmitnick 9:09 am on November 7, 2014 Permalink | Reply
    Tags: , , , , MAGIC Telescope,   

    From SPACE.com: “Rare Flickering Black Hole Jet Challenges Theories” 

    space-dot-com logo

    SPACE.com

    November 06, 2014
    Calla Cofield

    A close-up view of a rare, flickering black hole jet has scientist rethinking how these enormous eruptions form.

    flare
    The artist’s illustration shows a close-up view of jets erupting away from the supermassive black hole at the center of a galaxy. Scientists have now observers a rare flickering black hole jet that has them revisiting theories on the phenomenon.
    Credit: CXC/M. Weiss

    Black holes are mostly known for gobbling up everything that gets near them, including light. But there are also jets of matter rushing away from many black holes — like cosmic fire hoses. Two years ago, the MAGIC telescope, located in the Canary Islands, happened to catch a black hole jet doing something very rare: It was flickering.

    MAGIC Telescope
    MAGIC Telescope

    Radiating from a black hole in a galaxy called IC 310, the jet was emitting bright flashes of gamma rays — the highest-energy light in the universe. The flashes would reach 10 to 100 times the normal brightness of the jet in a matter of minutes. The light show lasted just over three hours.

    Switching a flashlight on and off doesn’t take much effort, but at this cosmic scale the flickering would require a massive amount of energy, according to the authors of a new research paper that uses the data from the MAGIC-II observation. The best explanation scientists have given for how such flares might occur is called shock acceleration. But that would require a very large area to create those brilliant flashes, the researchers say, and there’s no way it could make them as quickly.

    “But we have found something very, very fast, and very, very small,” said Dorit Eisenacher, a doctoral candidate at the University of Würzburg in Germany, and an author on the new paper.

    The new research shows that the portion of the jet responsible for generating the flares is five times smaller than what shock acceleration would require.

    In other words, say the researchers, the current theory doesn’t cut it.

    “For most sources [the shock acceleration model] was working nicely. It looks like for IC 310 it does not work,” said Julian Sitarek, an astrophysicist at the Institute for High Energy Physics (IFAE) near Barcelona, Spain, and an author on the new study.

    The researchers have an alternative proposal. When a star dies and collapses in on itself, it may become a pulsar: an incredibly dense, rapidly spinning nugget. Pulsars emit two bright beams of light, not unlike black hole jets. As the pulsar spins, the beams sometimes flash toward earth, and so the pulsar looks like it is blinking on and off.

    In 2011, another group of researchers proposed that a similar mechanism that drives pulsar beams could also generate flare events like the one seen in IC 310. Shock acceleration, as its name implies, would move particles with the physical force of a shock wave. Accelerating particles will radiate, so a sudden shockwave pushing particles up and out could also create gamma-ray flashes. Alternatively, particles are accelerated in pulsar beams by an electric field. This requires a much smaller area to get the particles moving.

    “We tried a few other scenarios, but each of them had some problems,” said Sitarek. “The pulsar theory is a plausible explanation for what we saw.”

    The details of how this mechanism might work in black holes will be difficult to sort out. Ideally, the team would like to have more data, from more black hole flares. But because the flaring events are short and unpredictable, it is extremely difficult to get telescope observations of them. For now, the researchers can only wait, but Sitarek is hopeful that black hole IC 310 has more to show them.

    “With this source, every time we look at it we get some surprise,” he said. “Next time we look at this, maybe we get even bigger surprises.”

    The new research is detailed in the Nov. 7 issue of the journal Science.

    See the full article here.

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