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  • richardmitnick 12:38 pm on December 8, 2017 Permalink | Reply
    Tags: , , , , , ESO 580-49, GRB's,   

    From ESA: “Explosive tendencies” 

    ESA Space For Europe Banner

    European Space Agency

    08/12/2017

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    ESO 580-49. NASA/ESA Hubble. CC BY 4.0

    NASA/ESA Hubble Telescope

    Don’t be fooled! The subject of this Picture of the Week, ESO 580-49, may seem tranquil and unassuming, but this spiral galaxy actually displays some explosive tendencies.

    In October of 2011, a cataclysmic burst of high-energy gamma-ray radiation — known as a gamma-ray burst, or GRB — was detected coming from the region of sky containing ESO 580-49. Astronomers believe that the galaxy was the host of the GRB, given that the chance of a coincidental alignment between the two is roughly 1 in 10 million. At a distance of around 185 million light-years from Earth, it was the second-closest gamma-ray burst (GRB) ever detected.

    Gamma-ray bursts are among the brightest events in the cosmos, occasionally outshining the combined gamma-ray output of the entire observable Universe for a few seconds. The exact cause of the GRB that probably occurred within this galaxy, catalogued as GRB 111005A, remains a mystery. Several events are known to lead to GRBs, but none of these explanations appear to fit the bill in this case. Astronomers have therefore suggested that ESO 580-49 hosted a new type of GRB explosion — one that has not yet been characterised.

    See the full article here .

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    The European Space Agency (ESA), established in 1975, is an intergovernmental organization dedicated to the exploration of space, currently with 19 member states. Headquartered in Paris, ESA has a staff of more than 2,000. ESA’s space flight program includes human spaceflight, mainly through the participation in the International Space Station program, the launch and operations of unmanned exploration missions to other planets and the Moon, Earth observation, science, telecommunication as well as maintaining a major spaceport, the Guiana Space Centre at Kourou, French Guiana, and designing launch vehicles. ESA science missions are based at ESTEC in Noordwijk, Netherlands, Earth Observation missions at ESRIN in Frascati, Italy, ESA Mission Control (ESOC) is in Darmstadt, Germany, the European Astronaut Centre (EAC) that trains astronauts for future missions is situated in Cologne, Germany, and the European Space Astronomy Centre is located in Villanueva de la Cañada, Spain.

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  • richardmitnick 6:59 pm on November 27, 2017 Permalink | Reply
    Tags: , , , , , Extinction events from giant space explosions: a cosmological perspective, GRB's   

    From astrobites: “Extinction events from giant space explosions: a cosmological perspective” 

    Astrobites bloc

    astrobites

    Nov 27, 2017
    Christopher Lovell

    Title: Exploring the Cosmic Evolution of Habitability with Galaxy Merger Trees
    Authors: E. R. Stanway, M. J. Hoskin, M. A. Lane, G. C. Brown, H. J. T. Childs, S. M. L. Greis and A. J. Levan
    First Author’s Institution: University of Warwick

    Status: Submitted to MNRAS, Open Access

    We’re still unsure how life began, but we have plenty of ideas for how to snuff it out completely. From global warming to an asteroid collision, rogue AI to a supervolcano explosion, we have a morbid ability to imagine our own demise (and dramatic rescue, if you have a Bruce Willis with a thermonuclear weapon). But the cosmos has far more powerful means of sterilising planets beyond the solar system, and depending on how common they are, the chances of life lasting elsewhere in the cosmos could be slim indeed.

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    Figure 1: Illustration of a Gamma Ray Burst (GRB). Most of the energy is emitted along the jet axis. Courtesy of the Chandra X-ray Observatory.

    NASA/Chandra Telescope

    Explosions in the sky

    Massive stars end their lives in massive explosions known as a supernovae (SNe), and if they are rotating rapidly enough can lead to gamma ray bursts (GRBs). GRBs can also occur during the collision of two neutron stars. Both SNe and GRBs release massive amounts of hard, ionising radiation that can dissociate complex molecules, or strip the atmosphere of a planet completely, killing any complex life on the surface. Such extinction events are not purely hypothetical – at least one mass extinction event in the history of life on Earth, in the late Ordivician period, has been attributed to a GRB. The supermassive black holes at the center of every galaxy can also release huge amounts of radiation when they’re accreting matter (hence the name, Active Galactic Nuclei, or AGN), which can irradiate any nearby stellar system in a similar way to a SNe or GRB.

    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.

     
  • richardmitnick 3:37 pm on November 13, 2017 Permalink | Reply
    Tags: , , , , , GRB's   

    From astrobites- “GRB Afterglows: Coming out of a Cocoon, and Doing Just Fine?” 

    Astrobites bloc

    astrobites

    Nov 13, 2017
    Mia de los Reyes

    Title: Thermal components in the early X-ray afterglows of GRBs: likely cocoon emission and constraints on the progenitors
    https://arxiv.org/abs/1711.02948
    Authors: Vlasta Valan, Josefin Larsson, Björn Ahlgren
    First Author’s Institution: KTH, Department of Physics, and the Oskar Klein Centre, Stockholm, Sweden
    1
    Status: Accepted to MNRAS, open access on arXiv

    Introduction

    Today’s paper uses X-ray observations to study gamma ray bursts (GRBs) with strange components in their spectra.

    Wait, real quick, what’s a GRB again?

    For once, astronomers didn’t pick a catchy-but-ultimately-confusing name for an astrophysical phenomenon! Gamma ray bursts are exactly what they sound like: bursts of gamma rays. To be fair, they’re a bit more than mere bursts. GRBs are tremendously energetic; a typical GRB could release as much energy as the entire mass of our Sun converted into radiation (try plugging a solar mass into E=mc^{2} to get a sense of how much energy that is!).

    What’s more, all that energy is released in just a short period of time. As this previous Astrobite explains, GRBs are classified by their duration. Short GRBs, which are thought to be produced by neutron star mergers (like the one recently observed by LIGO), last for just a few seconds. Long GRBs last longer and are thought to be produced by core-collapse supernovae.

    As shown in Figure 1, both kinds of GRBs are likely the result of relativistic jets—beams of radiation and charged particles moving close to the speed of light. Some GRBs are also accompanied by an afterglow of longer-wavelength emission (i.e., any emission that isn’t gamma rays). This afterglow can last for up to years after the prompt emission from the relativistic jet.

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    Figure 1. Parts of a gamma ray burst. Note the prompt emission produced by the jet, and the afterglow produced when the jet interacts with the surrounding medium.

    See the full article here .

    Please help promote STEM in your local schools.

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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.

     
  • richardmitnick 11:38 am on February 16, 2017 Permalink | Reply
    Tags: , , , GRB's   

    From astrobites: “Neutron Star Mergers May Help Short GRBs Go ‘Boom’ “ 

    Astrobites bloc

    Astrobites

    Title: Binary neutron star mergers: a jet engine for short gamma-ray bursts
    Authors: Milton Ruiz, Ryan N. Lang, Vasileios Paschalidis, & Stuart L. Shapiro
    First Author’s Institution: University of Illinois at Urbana-Champaign; Universidad Industrial de Santander, Colombia
    U Illinois bloc
    2
    Status: Published in ApJ Letters, Volume 824, Number 1 (2016 June 3) [open access]

    The LIGO Scientific Collaboration‘s direct detection of gravitational waves (GWs) is the first whisper from an era of so-called “multimessenger astronomy,” of which astronomers have thus far only been able to dream.
    LIGO bloc new

    The ability to probe an astrophysical event in both the electromagnetic spectrum and in gravitational waves would allow for groundbreaking scientific activities, such as unique tests of general relativity (GR) and understanding the interior properties of neutron stars (NSs). Among the transient events able to produce a strong signal simultaneously in GWs and the EM spectrum are black hole-black hole (BH-BH) mergers, NS-BH mergers, and NS-NS mergers. Intriguingly, NS-BH and NS-NS mergers are strongly favored progenitors of gamma-ray bursts (GRBs), making them ideal multimessenger candidates.

    Do Neutron Star Mergers Actually Produce GRBs?

    GRBs are the brightest events in our universe.

    Gamma-ray burst credit NASA SWIFT Cruz Dewilde
    Gamma-ray burst credit NASA SWIFT Cruz Dewilde

    They’re known to fall into two (fairly) distinct categories: short-duration, “hard” GRBs and long-duration, “soft” GRBs. Short GRBs last ∼0.1 seconds and are spectrally hard, meaning they have a high ratio of high-frequency to low-frequency emission. These make up about 20-30% of the total GRB population. Long GRBs last ∼10-30 seconds and are associated with type Ic supernovae. The short variety may be powered by the coalescence of compact binaries (like double NSs), but this is still an active area of research.

    Previous studies have simulated the merging of a BH-NS system, and found that they are able to power short GRB jets when the dipole magnetic field (think: bar magnet) of the neutron star extends all the way from its interior to exterior, as in a pulsar. However, the BH-NS merger did not produce jets when the dipole field was confined to the interior of the neutron star. Similar simulations of NS-NS mergers produced conflicting, unclear results. The authors therefore made a new attempt at trying to simulate a NS-NS merger in order to determine if they are also capable of producing short GRB jets, and if the magnetic field arrangement mattered (like in the BH-NS case). In other words, is the BH necessary for a short GRB to occur?

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    Figure 1: This series of images from the Ruiz et al. publication shows the stages of NS merging. Colors indicate rest mass density (for example, the NSs are shown in purple in the first panel). The process starts from two separate, orbiting NSs with dipole magnetic fields (white lines). Their orbit shrinks as energy is lost to gravitational radiation, and tidal forces cause them to become oblate as they draw nearer. Eventually a high-mass NS is formed, which collapses into a black hole. Helical jets with twisted magnetic fields are finally formed with energies comparable to observed short GRBs. Figure 1 in the paper.

    For their simulations, it was necessary to include a combination of general relativistic and magnetohydrodynamic (relating to the electrical conductivity of fluids) parameters. The NSs were given astrophysically plausible but intentionally strong magnetic fields of ∼1015 G. The simulation of two nonrotating NSs is initialized at a separation distance prior to merging (see Figure 1). Both the “pulsar” case, in which the magnetic field extends outside the NS, and the interior-only case were studied. The authors found that both of these scenarios prompted the formation of short GRB jets, unlike the BH-NS case. The collimated jets that form are consistent with an effect called the “Blandford-Znajek Process” in which jets are formed from the twisting of magnetic field lines above and below a BH (see bottom-middle panel of Figure 1). In addition to the simulations producing mildly relativistic jets, the observed accretion timescales and energy outputs match expected values for short GRBs. In short, NS-NS mergers can probably power short GRBs, no matter if their magnetic fields are pulsar-like or not.

    Is the Era of Multimessenger Astronomy Here?

    Studies such as this are a boon to the new era of GW astronomy. Though electromagnetic followup and localization of GW sources was difficult for the first LIGO detections, we should feel encouraged that such a powerful phenomenon — that of the GRB — might coincide with a detectable GW event. These capabilities will almost definitely yield answers to questions about fundamental physics that can’t be found in the lab.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    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.

     
  • richardmitnick 5:16 pm on July 14, 2016 Permalink | Reply
    Tags: , , GRB's,   

    From Chandra: “GRB 140903A: Chandra Finds Evidence for Violent Stellar Merger” 

    NASA Chandra Banner
    NASA Chandra Telescope

    NASA Chandra

    July 14, 2016

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    Credit X-ray: NASA/CXC/Univ. of Maryland/E. Troja et al, Optical: Lowell Observatory’s Discovery Channel Telescope/E.Troja et al.
    Illustration: NASA/CXC/M.Weiss
    Release Date July 14, 2016

    Astronomers have the strongest evidence to date that violent stellar mergers produce pencil-thin jets.

    This means that a majority of these events will not be detected because they will not be pointed where telescopes can detect them.

    This result has implications for estimating the number of such mergers that may detected with gravitational wave observatories.

    Chandra was used to study X-ray emission from the gamma-ray burst, allowing the width of the jet to be estimated.

    Gamma-ray bursts, or GRBs, are some of the most violent and energetic events in the Universe. Although these events are the most luminous explosions in the universe, a new study using NASA’s Chandra X-ray Observatory, NASA’s Swift satellite and other telescopes suggests that scientists may be missing a majority of these powerful cosmic detonations.

    NASA/SWIFT Telescope
    NASA/SWIFT Telescope

    Astronomers think that some GRBs are the product of the collision and merger of two neutron stars or a neutron star and a black hole. The new research gives the best evidence to date that such collisions will generate a very narrow beam, or jet, of gamma rays. If such a narrow jet is not pointed toward Earth, the GRB produced by the collision will not be detected.

    Collisions between two neutron stars or a neutron star and black hole are expected to be strong sources of gravitational waves that could be detected whether or not the jet is pointed towards the Earth. Therefore, this result has important implications for the number of events that will be detectable by the Laser Interferometry Gravitational-Wave Observatory (LIGO) and other gravitational wave observatories.

    MIT Advanced Ligo
    VIRGO Collaboration bloc

    On September 3, 2014, NASA’s Swift observatory picked up a GRB – dubbed GRB 140903A due to the date it was detected. Scientists used optical observations with the Gemini Observatory telescope in Hawaii to determine that GRB 140903A was located in a galaxy about 3.9 billion light years away, relatively nearby for a GRB.

    Gemini/North telescope
    Gemini/North telescope at Mauna Kea, Hawaii, USA

    The large panel in the graphic is an illustration showing the aftermath of a neutron star merger, including the generation of a GRB. In the center is a compact object – either a black hole or a massive neutron star – and in red is a disk of material left over from the merger, containing material falling towards the compact object. Energy from this infalling material drives the GRB jet shown in yellow. In orange is a wind of particles blowing away from the disk and in blue is material ejected from the compact object and expanding at very high speeds of about one tenth the speed of light.

    The image on the left of the two smaller panels shows an optical view from the Discovery Channel Telescope (DCT) with GRB 140903A in the middle of the square and a close-up X-ray view from Chandra on the right.

    Discovery Channel Telescope at Happy Jack AZ
    Discovery Channel Telescope at Happy Jack AZ, USA

    The bright star in the optical image is unrelated to the GRB.

    The gamma-ray blast lasted less than two seconds. This placed it into the “short GRB” category, which astronomers think are the output from neutron star-neutron star or black hole-neutron star collisions eventually forming either a black hole or a neutron star with a strong magnetic field. (The scientific consensus is that GRBs that last longer than two seconds result from the collapse of a massive star.)

    About three weeks after the Swift discovery of GRB 140903A, a team of researchers led by Eleonora Troja of the University of Maryland, College Park (UMD), observed the aftermath of the GRB in X-rays with Chandra. Chandra observations of how the X-ray emission from this GRB decreases over time provide important information about the properties of the jet.

    Specifically, the researchers found that the jet is beamed into an angle of only about five degrees based on the X-ray observations, plus optical observations with the Gemini Observatory and the DCT and radio observations with the National Science Foundation’s Karl G. Jansky Very Large Array.

    NRAO/VLA, on the Plains of San Agustin fifty miles west of Socorro, NM, USA
    NRAO/VLA, on the Plains of San Agustin fifty miles west of Socorro, NM, USA

    This is roughly equivalent to a circle with the diameter of your three middle fingers held at arms length. This means that astronomers are detecting only about 0.4% of this type of GRB when it goes off, since in most cases the jet will not be pointed directly at us.

    Previous studies by other astronomers had suggested that these mergers could produce narrow jets. However, the evidence in those cases was not as strong because the rapid decline in light was not observed at multiple wavelengths, allowing for explanations not involving jets.

    Several pieces of evidence link this event to the merger of two neutron stars, or between a neutron star and black hole. These include the properties of the gamma ray emission, the old age and the low rate of stars forming in the GRB’s host galaxy and the lack of a bright supernova. In some previous cases strong evidence for this connection was not found.

    New studies have suggested that such mergers could be the production site of elements heavier than iron, such as gold. Therefore, the rate of these events is also important to estimate the total amount of heavy elements produced by these mergers and compare it with the amounts observed in the Milky Way galaxy.

    A paper describing these results was recently accepted for publication in The Astrophysical Journal and is available online. The first author of this paper is Eleonora Troja and the co-authors are T. Sakamoto (Aoyama Gakuin University, Japan), S.Cenko (GSFC), A. Lien (University of Maryland, Baltimore), N. Gehrels (GSFC), A. Castro-Tirado (IAA-CSIC, Spain), R. Ricci (INAF-Istituto di Radioastronomia, Italy), J. Capone, V. Toy, & A. Kutyrev (UMD), N. Kawai (Tokyo Institute of Technology, Japan), A. Cucchiara (GSFC), A. Fruchter (STScI), J.Gorosabel (UMD), S. Jeong (IAA-CSIC), A. Levan (University of Warwick, UK), D. Perley (University of Copenhagen, Denmark), R.Sanchez-Ramirez (Instituto de Astrof ́ısica de Andaluc ́ıa, Spain), N.Tanvir (University of Leicester, UK), S. Veilleux (UMD).

    See the full article here .

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    NASA’s Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA’s Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra’s science and flight operations from Cambridge, Mass.

     
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