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  • richardmitnick 10:15 am on June 22, 2016 Permalink | Reply
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    From Goddard: “Astronomers Find the First ‘Wind Nebula’ Around a Magnetar” 

    NASA Goddard Banner
    NASA Goddard Space Flight Center

    June 21, 2016
    Francis Reddy
    NASA’s Goddard Space Flight Center, Greenbelt, Maryland

    Astronomers have discovered a vast cloud of high-energy particles called a wind nebula around a rare ultra-magnetic neutron star, or magnetar, for the first time. The find offers a unique window into the properties, environment and outburst history of magnetars, which are the strongest magnets in the universe.

    This X-ray image shows extended emission around a source known as Swift J1834.9-0846, a rare ultra-magnetic neutron star called a magnetar. The glow arises from a cloud of fast-moving particles produced by the neutron star and corralled around it. Color indicates X-ray energies, with 2,000-3,000 electron volts (eV) in red, 3,000-4,500 eV in green, and 5,000 to 10,000 eV in blue. The image combines observations by the European Space Agency’s XMM-Newton spacecraft taken on March 16 and Oct. 16, 2014. Credits: ESA/XMM-Newton/Younes et al. 2016

    ESA/XMM Newton
    ESA/XMM Newton

    A neutron star is the crushed core of a massive star that ran out of fuel, collapsed under its own weight, and exploded as a supernova. Each one compresses the equivalent mass of half a million Earths into a ball just 12 miles (20 kilometers) across, or about the length of New York’s Manhattan Island. Neutron stars are most commonly found as pulsars, which produce radio, visible light, X-rays and gamma rays at various locations in their surrounding magnetic fields. When a pulsar spins these regions in our direction, astronomers detect pulses of emission, hence the name.

    This illustration compares the size of a neutron star to Manhattan Island in New York, which is about 13 miles long. A neutron star is the crushed core left behind when a massive star explodes as a supernova and is the densest object astronomers can directly observe. Credits: NASA’s Goddard Space Flight Center

    Typical pulsar magnetic fields can be 100 billion to 10 trillion times stronger than Earth’s. Magnetar fields reach strengths a thousand times stronger still, and scientists don’t know the details of how they are created. Of about 2,600 neutron stars known, to date only 29 are classified as magnetars.

    The newfound nebula surrounds a magnetar known as Swift J1834.9-0846 — J1834.9 for short — which was discovered by NASA’s Swift satellite on Aug. 7, 2011, during a brief X-ray outburst.

    NASA/SWIFT Telescope
    NASA/SWIFT Telescope

    Astronomers suspect the object is associated with the W41 supernova remnant, located about 13,000 light-years away in the constellation Scutum toward the central part of our galaxy.

    “Right now, we don’t know how J1834.9 developed and continues to maintain a wind nebula, which until now was a structure only seen around young pulsars,” said lead researcher George Younes, a postdoctoral researcher at George Washington University in Washington. “If the process here is similar, then about 10 percent of the magnetar’s rotational energy loss is powering the nebula’s glow, which would be the highest efficiency ever measured in such a system.”

    A month after the Swift discovery, a team led by Younes took another look at J1834.9 using the European Space Agency’s (ESA) XMM-Newton X-ray observatory, which revealed an unusual lopsided glow about 15 light-years across centered on the magnetar. New XMM-Newton observations in March and October 2014, coupled with archival data from XMM-Newton and Swift, confirm this extended glow as the first wind nebula ever identified around a magnetar. A paper describing the analysis will be published by The Astrophysical Journal.

    “For me the most interesting question is, why is this the only magnetar with a nebula? Once we know the answer, we might be able to understand what makes a magnetar and what makes an ordinary pulsar,” said co-author Chryssa Kouveliotou, a professor in the Department of Physics at George Washington University’s Columbian College of Arts and Sciences.

    The most famous wind nebula, powered by a pulsar less than a thousand years old, lies at the heart of the Crab Nebula supernova remnant in the constellation Taurus. Young pulsars like this one rotate rapidly, often dozens of times a second. The pulsar’s fast rotation and strong magnetic field work together to accelerate electrons and other particles to very high energies. This creates an outflow astronomers call a pulsar wind that serves as the source of particles making up in a wind nebula.

    Supernova remnant Crab nebula. NASA/ESA Hubble
    The best-known wind nebula is the Crab Nebula, located about 6,500 light-years away in the constellation Taurus. At the center is a rapidly spinning neutron star that accelerates charged particles like electrons to nearly the speed of light. As they whirl around magnetic field lines, the particles emit a bluish glow. This image is a composite of Hubble observations taken in late 1999 and early 2000. The Crab Nebula spans about 11 light-years. Credits: NASA, ESA, J. Hester and A. Loll (Arizona State University)

    “Making a wind nebula requires large particle fluxes, as well as some way to bottle up the outflow so it doesn’t just stream into space,” said co-author Alice Harding, an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “We think the expanding shell of the supernova remnant serves as the bottle, confining the outflow for a few thousand years. When the shell has expanded enough, it becomes too weak to hold back the particles, which then leak out and the nebula fades away.” This naturally explains why wind nebulae are not found among older pulsars, even those driving strong outflows.

    A pulsar taps into its rotational energy to produce light and accelerate its pulsar wind. By contrast, a magnetar outburst is powered by energy stored in the super-strong magnetic field. When the field suddenly reconfigures to a lower-energy state, this energy is suddenly released in an outburst of X-rays and gamma rays. So while magnetars may not produce the steady breeze of a typical pulsar wind, during outbursts they are capable of generating brief gales of accelerated particles.

    “The nebula around J1834.9 stores the magnetar’s energetic outflows over its whole active history, starting many thousands of years ago,” said team member Jonathan Granot, an associate professor in the Department of Natural Sciences at the Open University in Ra’anana, Israel. “It represents a unique opportunity to study the magnetar’s historical activity, opening a whole new playground for theorists like me.”

    ESA’s XMM-Newton satellite was launched on Dec. 10, 1999, from Kourou, French Guiana, and continues to make observations. NASA funded elements of the XMM-Newton instrument package and provides the NASA Guest Observer Facility at Goddard, which supports use of the observatory by U.S. astronomers.

    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

    NASA/Goddard Campus

    NASA image

  • richardmitnick 5:13 pm on September 30, 2015 Permalink | Reply
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    From AAS NOVA: ” A Pulsar Eases Off the Brakes” 


    Amercan Astronomical Society

    30 September 2015
    Susanna Kohler

    This still from an animation shows an artist’s impression of a pulsar, surrounded by strong magnetic field lines (blue) and emitting a beam of radiation (purple). [NASA]

    In 2006, pulsar PSR 1846–0258 unexpectedly launched into a series of energetic X-ray outbursts. Now a study has determined that this event may have permanently changed the behavior of this pulsar, raising questions about our understanding of how pulsars evolve.

    Between Categories

    A pulsar — a highly magnetized, rotating neutron star that emits a beam of electromagnetic radiation — can be powered by one of three mechanisms:

    Rotation-powered pulsars transform rotational energy into radiation, gradually slowing down in a predictable way.
    Accretion-powered pulsars convert the gravitational energy of accreting matter into radiation.
    Magnetars are powered by the decay of their extremely strong magnetic fields.

    Astronomical classification often results in one pesky object that doesn’t follow the rules. In this case, that object is PSR 1846–0258, a young pulsar categorized as rotation-powered. But in 2006, PSR 1846–0258 suddenly emitted a series of short, hard X-ray bursts and underwent a flux increase — behavior that is usually only exhibited by magnetars. After this outburst, it returned to normal, rotation-powered-pulsar behavior.

    Since the discovery of this event, scientists have been attempting to learn more about this strange pulsar that seems to straddle the line between rotation-powered pulsars and magnetars.

    Unprecedented Drop

    One way to examine what’s going on with PSR 1846–0258 is to evaluate what’s known as its “braking index,” a measure of how quickly the pulsar’s rotation slows down. For a rotation-powered pulsar, the braking index should be roughly constant. The pulsar then slows down according to a fixed power law, where the slower it rotates, the slower it slows down.

    In a recent study, Robert Archibald (McGill University) and collaborators report on 7 years’ worth of timing observations of PSR 1846–0258 after its odd magnetar-like outburst. They then compare these observations to 6.5 years of data from before the outburst. The team finds that the braking index for this bizarre pulsar dropped suddenly by 14.5σ after the outburst — a change that’s unprecedented both in how large and how long-lived it’s been.

    Why is this a problem? Many of the quoted properties of pulsars (like ages, magnetic fields, and luminosities) are determined based on models that envision pulsars as magnetic dipoles in a vacuum. But if this is the case, a pulsar’s braking index should be constant — or, in more realistic scenarios, we might expect it to change slightly over the span of thousands of years. The fact that PSR 1846–0258 underwent such a drastic change during its outburst poses a significant challenge to these models of pulsar behavior and evolution.


    R. F. Archibald et al 2015 ApJ 810 67. doi:10.1088/0004-637X/810/1/67

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  • richardmitnick 8:17 pm on August 10, 2015 Permalink | Reply
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    From BBC: “The Most Accurate Clocks in Space” 


    Aug 10, 2015
    Marcus Woo

    Fast-spinning pulsars can act as the universe’s timekeepers

    At first, Shri Kulkarni didn’t think it was a big deal. It was the middle of the night in September 1982, and he was at Arecibo Observatory in Puerto Rico, using the enormous radio dish to hunt for pulsars: the ultra-dense, rapidly spinning corpses of massive stars.

    Arecibo Observatory
    Arecibo Observatory

    He had just detected his first pulsar, and it was rotating really fast – once every 1.5 milliseconds – which was more than 20 times faster than any known at the time.

    Temp 1
    Credit: Detlev van Ravenswaay/SPL

    For Kulkarni, who was still a graduate student then, the rapid rotation didn’t mean much. It was just a fast pulsar, he thought. He called his project advisor, the late Don Backer, an astronomer at the University of California, Berkeley, US and delivered the news.

    “There was a long silence,” Kulkarni recalls. Probably because Backer knew this was big.

    He reminded Kulkarni what such a fast pulsar meant: this was an object spinning 641 times per second. “Many people thought that pulsars going at that speed would break apart,” says Kulkarni, now an astronomer at the California Institute of Technology in the US. Pulsars are as big as a city – about 20 km in diameter – and the assumption was that if it were rotating that fast, the centrifugal force would rip it to smithereens.

    Temp 2
    Neutron stars become extraordinarily dense (Credit: Jupe/Alamy)

    But now Kulkarni’s discovery upended that assumption. It changed not only his burgeoning career, but also an entire field. The pulsar, known as PSR B1937+21, became the first of a new class of remarkable objects called millisecond pulsars.

    Not only are they fast, but they also spin with such amazing regularity that they’re among the most accurate clocks in the universe. Using these celestial timekeepers, astronomers are answering questions about stars, matter – and even space and time itself – that would otherwise be impossible.

    Extreme objects

    Even ordinary pulsars are extraordinary. They’re some of the universe’s most extreme objects, the remains of stars between about eight and 20 times as massive as the sun. When such a star burns up its fuel and dies, it explodes in a supernova, blowing off its outer layers of gas.

    Temp 3
    Credit: Julian Baum/SPL

    What’s left is a core so dense that its electrons have fused with protons, forming a solid sphere of mostly neutrons. It’s become a neutron star. These objects squeeze between about 1.2 and 2 suns worth of mass into a ball no more than 20 km in diameter. Just a teaspoonful weighs a trillion kilograms – comparable to the mass of every person on Earth.

    Such density means the gravity on a neutron star’s surface is extremely strong – 100 billion times greater than Earth’s. If you tried standing on a neutron star (ignoring the million-degree temperatures, of course), you’d be squished, your atoms smeared across the surface. In fact, this overwhelming gravitational pull prevents the formation of any bumps greater than a few centimetres high, giving neutron stars some of the smoothest surfaces in space.

    And then there are the magnetic fields, the most powerful in the universe. Even the weakest is a hundred million times stronger than Earth’s – strong enough to warp the structure of an atom. At the poles, a neutron star’s magnetic field accelerates charged particles – positrons and electrons stripped off the surface by powerful electric fields – and blasts them into space in the form of jets. Those particles produce beams of radiation at radio frequencies, which eventually reach radio telescopes on Earth.

    It’s these beams that give pulsars their namesake. When a neutron star rotates rapidly, it swings these beams around like a lighthouse. From Earth, it appears as a steady, pulsating signal, sometimes as slow as once every 10 seconds.

    But they start out faster. They were cranking up the speed before they were pulsars, when they were stellar cores. As a star runs out of nuclear fuel, it can’t maintain the pressure needed to hold itself up, and the core contracts due to its own gravity.

    Like the way ice skaters spin faster when tucking their arms in, the core of a dying star rotates faster as it collapses. By the time the star dies and you’re left with a neutron star, it can be spinning as fast as 100 times a second. Over time, its rotating magnetic field loses energy, which slows the pulsar down.

    Which is why Kulkarni’s discovery of a pulsar going so much faster was so astounding. To whip it up to such speeds, astronomers realised, a pulsar must receive help from a companion star in orbit. As the companion exhausts its fuel, it swells – as all stars do eventually – and its outer layers start to spill onto the pulsar, forming a disk of hot gas spiraling inward like water circling a drain. The swirling disk spins up the pulsar.

    Temp 5
    Credit: Julian Baum/SPL

    The discovery of millisecond pulsars revitalized a moribund field, which started in 1967 when Jocelyn Bell discovered the first pulsar. The field’s landmark discovery came in 1974, when Russell Hulse and Joseph Taylor found two pulsars spiraling in toward each other. For that to happen, the energy of the pulsar’s orbits must be dissipating in the form of gravitational waves, ripples in the fabric of space-time.

    Their measurements were the clearest evidence yet that these waves exist, confirming a prediction of [Albert] Einstein’s theory of general relativity; they would later win the Nobel Prize in 1993. “That was the one highlight of the field,” Kulkarni says. It seemed all that was left to do was find more pulsars. “By 1982,” he says, “there was a sense that everything about pulsars had been discovered.”

    Cosmic laboratories

    That changed when Kulkarni found the first millisecond pulsar. Since then, astronomers have identified about 300 more. They estimate that the Milky Way Galaxy is home to 20,000 millisecond pulsars, and about an equal number of regular pulsars – a meagre number compared to the galaxy’s hundreds of billions of stars. PSR B1937+21 held the speed record until 2006, when Jason Hessels – who, like Kulkarni, was a graduate student at the time – discovered Terzan 5ad, a faint pulsar that spins 716 times per second.

    Temp 6
    Black holes may produce gravitational waves (Credit: Gl0ck/Alamy)

    With such high speeds and masses – lots of angular momentum, in physics-speak -millisecond pulsars are hard to slow down. That makes them incredibly consistent over a long period of time. When millisecond pulsars were first discovered, they rivaled the stability of atomic clocks. Today, atomic clocks have surpassed pulsars in accuracy. But if you were to compare them over a longer period of time – say, decades – pulsars can be just as good, says Hessels, who’s now at the University of Amsterdam in the Netherlands. Even after billions of years, a millisecond pulsar may slow down by only a few milliseconds. But because astronomers can precisely pin down its rate of deceleration, they can compensate and still use them as clocks.

    Millisecond pulsars are so stable that astronomers have measured their spin periods to an accuracy of one part in a million trillion (that’s 18 decimal places). They know when a pulse arrives on Earth to a precision of 100 nanoseconds. Because the pulses are so reliable, the tiniest deviations can reveal with great detail what’s going on in and around the pulsar – and in the space between the stars.

    In this space is dust and gas, called the interstellar medium, which obstructs and scatters a pulsar’s signals. By measuring the pulses’ delay, their intensity, and how sharp they are, astronomers can probe the properties of the interstellar medium, which plays a key role in how stars and galaxies form and evolve.

    Temp 7
    Credit: Claus Lunau/SPL

    Around the pulsar is the companion star that helped speed it up. The size of the star and how it evolves over time – for example, how changing magnetic activity can alter its shape – influences its orbit. Delays, modulations, or other variations in the pulses reveal what the companion star is like and how it interacts with the pulsar.

    Thanks to the precision of these pulses, astronomers can detect even the most subtle gravitational tugs. In 1992, astronomers discovered a planetary system orbiting a millisecond pulsar – the first planets found outside the solar system. The gravity of the planets were causing the pulsar to wobble ever so slightly, changing the arrival times of the pulses. In the case of Kulkarni’s pulsar, PSR B1937+21, these kinds of timing variations have recently suggested the presence of objects as small as asteroids.

    Detecting those pulses of radio waves – and, in some cases, X rays and gamma rays – is crucial because it’s often the only way for astronomers to observe and study these exotic pulsar systems. It’s also one of the only ways to study the weird structure and composition of the pulsar itself.

    Pulsars are essentially giant atomic nuclei. They can have a thin atmosphere not much more than 10 cm thick made of helium, hydrogen, and carbon, and an outer crust that’s mostly iron. As you go deeper, the matter becomes denser, full of neutrons (and some protons and electrons) in increasingly exotic forms, merging together to form strands and even sheets. But no one really knows what it’s like inside.

    Millisecond pulsars offer clues. The pulses allow scientists to precisely determine the pulsars’ orbits and thus their masses – crucial data that theorists need to constrain and devise new hypotheses. Nowhere in the universe can you find matter at such high densities and pressure. For physicists, pulsars are like laboratories for exploring such extremes – and maybe discovering entirely new types of matter.

    “It’s almost miraculous that there’s this type of star that’s so useful for testing areas of physics that would otherwise be inaccessible,” Hessels says.

    Testing Einstein

    Those areas include gravity itself. Einstein’s theory of general relativity describes gravity as bends and curves in the fabric of space-time, and so far, its predictions have been proven true again and again. But the theory may work differently in the enormous densities and strong gravity of pulsars—as strong as you can get without becoming a black hole. To find out whether that’s the case, researchers can look for discrepancies in the pulses.

    Temp 8
    Credit: Mark Garlick/SPL

    Recently, Hessels was part of a team that discovered a millisecond pulsar in a triple system with two white dwarfs—the remnants of stars not massive enough to form neutron stars. This rare configuration gives scientists a way to test one of the hallmarks of relativity: the equivalence principle.

    The principle says that gravity is the same for everyone and everything. Perhaps the most dramatic example is when astronaut Dave Scott dropped a hammer and a feather on the moon in 1971. Both hit the lunar surface at the same time, showing that the moon’s gravity pulled on both equally. Likewise, researchers want to see if the gravity of one of the white dwarfs pulls on the pulsar in the same way as the other white dwarf. They haven’t done the experiment yet, but the researchers say it could be the most accurate test ever of the equivalence principle.

    Of course, no one has found Einstein to be wrong just yet. One of the most successful confirmations of relativity was the Hulse-Taylor binary pulsar system, the big pre-millisecond-pulsar discovery that proved gravitational waves were real. Still, the evidence was indirect, based on measurements of orbits that allowed Hulse and Taylor to infer the existence of gravitational waves. To this day, a direct detection remains elusive.

    Temp 9
    A pulsar radiating light (Credit: Stocktrek Images Inc/Alamy)

    That’s despite the efforts of ground-based experiments such as LIGO, the Laser Interferometer Gravitational-Wave Observatory, which is designed to detect gravitational waves from colliding neutron stars or black holes. Its first observing run between 2002 and 2010 turned up nothing. After significant upgrades, it’s set to start up again in the fall of 2015.

    Caltech LIGO
    Caltech LIGO

    Meanwhile, an international effort has been racing to beat LIGO using – you guessed it – millisecond pulsars. “The idea is to use them as a galactic GPS,” says Hessels, who is part of the European contingent. When gravitational waves pass through Earth, the planet bobs like a buoy on the water. Those tiny motions alter the arrival times of the pulses.

    Over the last few years, astronomers have continued to refine their techniques, meticulously timing a few dozen of the best cosmic clocks known. And they hope to see something soon. “There’s a reasonable prospect of detecting gravitational waves in this way in the next five years or so,” says Ingrid Stairs, an astronomer at the University of British Columbia in Canada and member of the North American team.

    Temp 10
    The ultimate cosmic clock (Credit: Stocktrek Images Inc/Alamy)

    Still, Stairs thinks LIGO probably will beat them to it. But while LIGO is designed to detect waves from merging neutron stars and black holes several times as massive as the sun, the pulsar method is sensitive to collisions between supermassive black holes, which are millions to billions of times heftier than the sun. “It’s looking at a totally different source of gravitational waves,” she says. “Even if we’re later than LIGO, it doesn’t mean they’ve totally scooped us.”

    Regardless of who wins the race, the millisecond pulsar has been vital for understanding a range of cosmic phenomena. “It’s nature’s gift to us,” Kulkarni says. “It’s a precise, physical laboratory – but in the heavens.” It was a gift received more than three decades ago, and if it didn’t seem like a big deal then, it certainly does now.

    See the full article here.

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  • richardmitnick 8:07 pm on May 19, 2015 Permalink | Reply
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    From CAASTRO: “Where are all the pulsars at the Galactic Centre?” 

    CAASTRO bloc

    CAASTRO ARC Centre of Excellence for All Sky Astrophysics

    19 May 2015
    No Writer Credit

    As stable, regularly pulsing rotators, pulsars are superb instruments for testing theories of gravity. An important test of General Relativity is the behaviour of bodies in extremely strong gravitational fields. The detection of a pulsar in the gravitational field of a black hole therefore potentially constitutes an exceptional test of theories of gravity in the strong field regime.

    Astronomers have long sought to find pulsar-black hole binary systems by conducting large surveys of the Galactic pulsar population. But there is another way to find such systems: find a supermassive black hole and then search for orbiting pulsars. For this reason, the region immediately surrounding the four million solar mass black hole at the Galactic Centre, Sgr A* has been the site for a number of deep pulsar surveys over the past several decades.

    Sagittarius A*. This image was taken with NASA’s Chandra X-Ray Observatory. Ellipses indicate light echoes.

    NASA Chandra Telescope

    Yet, despite these searches, none of these searches has uncovered a single regular pulsar.


    Where are all the pulsars at the Galactic Centre? In their current paper, CAASTRO Associate Investigator Jean-Pierre Macquart (Curtin University) and colleague Nissim Kanekar (National Centre for Radio Astrophysics, Pune / India) argue that the high stellar density in the central parsec around the Galactic Centre is likely to result in a pulsar population dominated by millisecond pulsars (MSPs). Earlier pulsar searches have been largely insensitive to such an MSP population, accounting for the lack of pulsar detections. We estimate the best search frequency for such an MSP population, taking into account new information on the scattering environment towards Sgr A* provided by the recently-detected magnetar near the Galactic Centre. The optimal search frequency is near 8 GHz for pulsars with periods 1-20ms, assuming that the pulsars have a luminosity distribution similar to those in the rest of the Milky Way. We find that 10-30 hour integrations with the Green Bank Telescope or the Very Large Array would be sufficient to detect MSPs at the Galactic Centre.

    Interestingly, observations of the Galactic Centre at X-ray and GeV energies have, just within the last few months, independently suggested evidence for such an MSP population (Perez et al. 2015, O’Leary et al. 2015).

    Publication details:
    J.-P. Macquart and N. Kanekar in the Astrophysical Journal (2015) On Detecting Millisecond Pulsars at the Galactic Center

    See the full article here.

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    Astronomy is entering a golden age, in which we seek to understand the complete evolution of the Universe and its constituents. But the key unsolved questions in astronomy demand entirely new approaches that require enormous data sets covering the entire sky.

    In the last few years, Australia has invested more than $400 million both in innovative wide-field telescopes and in the powerful computers needed to process the resulting torrents of data. Using these new tools, Australia now has the chance to establish itself at the vanguard of the upcoming information revolution centred on all-sky astrophysics.

    CAASTRO has assembled the world-class team who will now lead the flagship scientific experiments on these new wide-field facilities. We will deliver transformational new science by bringing together unique expertise in radio astronomy, optical astronomy, theoretical astrophysics and computation and by coupling all these capabilities to the powerful technology in which Australia has recently invested.


    The University of Sydney
    The University of Western Australia
    The University of Melbourne
    Swinburne University of Technology
    The Australian National University
    Curtin University
    University of Queensland

  • richardmitnick 10:14 am on April 10, 2015 Permalink | Reply
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    From ASTRON: “LOFAR Discovers its First RRAT” 

    ASTRON bloc

    Netherlands Institute for Radio Astronomy

    Daniele Michilli


    Rotating RAdio Transients (RRATs; McLaughlin et al. 2006) are sporadically emitting pulsars. Finding more RRATs is important in order to have a complete picture of the radio-emitting neutron star population. Also, understanding why their behavior is in some cases quite different compared to “steady” pulsars is important for understanding the pulsar radio-emission mechanism.

    The bottom panel of the plot shows all the significant pulses detected in beam 56 of sub-array pointing 2 of observation L202425. These are plotted as a function of dispersion measure and time. The discovered RRAT has a dispersion measure close to 78 pc/cm3 and a period of 2.23 s (or some integer fraction of this). About ten bright single pulses have been detected from the source in the one-hour discovery observation.

    LOFAR’s first RRAT discovery is shown in this plot, where the pulses from the neutron star are highlighted in blue.

    LOFAR map

    ASTRON LOFAR Radio Antenna Bank
    ASTRON LOFAR Radio Antenna Bank

    The discovery has been made as part of the LOFAR Tied-Array All-Sky Survey (LOTAAS), an ongoing survey for pulsars and fast radio transients, which has previously discovered another 13 new pulsars (www.astron.nl/lotaas). The irregular emission of RRATs makes them difficult to detect in periodicity searches. For my PhD I am developing new techniques to sift through the LOTAAS data in order to find more individual dispersed pulses. This is a very challenging task because each LOTAAS pointing contains 222 beams, each with thousands of frequency channels, and millions of time samples!

    See the full article here.

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    ASTRON-Westerbork Synthesis Radio Telescope
    Westerbork Synthesis Radio Telescope (WSRT)

    ASTRON was founded in 1949, as the Foundation for Radio radiation from the Sun and Milky Way (SRZM). Its original charge was to develop and operate radio telescopes, the first being systems using surplus wartime radar dishes. The organisation has grown from twenty employees in the early 1960’s to about 180 staff members today.

  • richardmitnick 4:38 pm on December 5, 2014 Permalink | Reply
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    From Daily Galaxy: “Discovery of a Pulsar and Supermassive Black Hole Pairing Could Help Unlock the Enigma of Gravity” 

    Daily Galaxy
    The Daily Galaxy

    Last year, the very rare presence of a pulsar (named SGR J1745-2900) was also detected in the proximity of a supermassive black hole (Sgr A**, made up of millions of solar masses), but there is a combination that is still yet to be discovered: that of a pulsar orbiting a ‘normal’ black hole; that is, one with a similar mass to that of stars.



    Supermassive Black Hole Sagittarius A*

    The center of the Milky Way galaxy, with the supermassive black hole Sagittarius A* (Sgr A*), located in the middle, is revealed in these images. As described in our press release, astronomers have used NASA’s Chandra X-ray Observatory to take a major step in understanding why material around Sgr A* is extraordinarily faint in X-rays.

    NASA Chandra Telescope

    The large image contains X-rays from Chandra in blue and infrared emission from the Hubble Space Telescope in red and yellow. The inset shows a close-up view of Sgr A* in X-rays only, covering a region half a light year wide. The diffuse X-ray emission is from hot gas captured by the black hole and being pulled inwards. This hot gas originates from winds produced by a disk-shaped distribution of young massive stars observed in infrared observations.

    NASA Hubble Telescope
    NASA/ESA Hubble

    These new findings are the result of one of the biggest observing campaigns ever performed by Chandra. During 2012, Chandra collected about five weeks worth of observations to capture unprecedented X-ray images and energy signatures of multi-million degree gas swirling around Sgr A*, a black hole with about 4 million times the mass of the Sun. At just 26,000 light years from Earth, Sgr A* is one of very few black holes in the universe where we can actually witness the flow of matter nearby.

    The authors infer that less than 1% of the material initially within the black hole’s gravitational influence reaches the event horizon, or point of no return, because much of it is ejected. Consequently, the X-ray emission from material near Sgr A* is remarkably faint, like that of most of the giant black holes in galaxies in the nearby Universe.

    The captured material needs to lose heat and angular momentum before being able to plunge into the black hole. The ejection of matter allows this loss to occur.

    This work should impact efforts using radio telescopes to observe and understand the “shadow” cast by the event horizon of Sgr A* against the background of surrounding, glowing matter. It will also be useful for understanding the impact that orbiting stars and gas clouds might make with the matter flowing towards and away from the black hole.

    The paper is available online and is published in the journal Science. The first author is Q.Daniel Wang from University of Massachusetts at Amherst, MA; and the co-authors are Michael Nowak from Massachusetts Institute of Technology (MIT) in Cambridge, MA; Sera Markoff from University of Amsterdam in The Netherlands, Fred Baganoff from MIT; Sergei Nayakshin from University of Leicester in the UK; Feng Yuan from Shanghai Astronomical Observatory in China; Jorge Cuadra from Pontificia Universidad de Catolica de Chile in Chile; John Davis from MIT; Jason Dexter from University of California, Berkeley, CA; Andrew Fabian from University of Cambridge in the UK; Nicolas Grosso from Universite de Strasbourg in France; Daryl Haggard from Northwestern University in Evanston, IL; John Houck from MIT; Li Ji from Purple Mountain Observatory in Nanjing, China; Zhiyuan Li from Nanjing University in China; Joseph Neilsen from Boston University in Boston, MA; Delphine Porquet from Universite de Strasbourg in France; Frank Ripple from University of Massachusetts at Amherst, MA and Roman Shcherbakov from University of Maryland, in College Park, MD. Image credit: X-ray: NASA/UMass/D.Wang et al., IR: NASA/STScI

    This image was taken with NASA’s Chandra X-Ray Observatory.

    The intermittent light emitted by pulsars, the most precise timekeepers in the universe, allows scientists to verify Einstein’s theory of relativity, especially when these objects are paired up with another neutron star or white dwarf that interferes with their gravity. However, this theory could be analysed much more effectively if a pulsar with a black hole were found, except in two particular cases, according to researchers from Spain and India.

    Pulsars are very dense neutron stars that are the size of a city (their radius approaches ten kilometres), which, like lighthouses for the universe, emit gamma radiation beams or X-rays when they rotate up to hundreds of times per second. These characteristics make them ideal for testing the validity of the theory of general relativity, published by Einstein between 1915 and 1916.

    “Pulsars act as very precise timekeepers, such that any deviation in their pulses can be detected,” Diego F. Torres, ICREA researcher from the Institute of Space Sciences (IEEC-CSIC), explains to SINC. “If we compare the actual measurements with the corrections to the model that we have to use in order for the predictions to be correct, we can set limits or directly detect the deviation from the base theory.”

    These deviations can occur if there is a massive object close to the pulsar, such as another neutron star or a white dwarf. A white dwarf can be defined as the stellar remnant left when stars such as our Sun use up all of their nuclear fuel. The binary systems, comprised of a pulsar and a neutron star (including double pulsar systems) or a white dwarf, have been very successfully used to verify the theory of gravity.

    Until now scientists had considered the strange pulsar/black hole pairing to be an authentic ‘holy grail’ for examining gravity, but there exist at least two cases where other pairings can be more effective. This is what is stated in the study that Torres and the physicist Manjari Bagchi, from the International Centre of Theoretical Sciences (India) and now postdoc at the IEEC-CSIC, have published in the Journal of Cosmology and Astroparticle Physics. The work also received an Honourable Mention in the 2014 Essays of Gravitation prize.

    The first case occurs when the so-called principle of strong equivalence is violated. This principle of the theory of relativity indicates that the gravitational movement of a body that we test only depends on its position in space-time and not on what it is made up of, which means that the result of any experiment in a free fall laboratory is independent of the speed of the laboratory and where it is found in space and time.

    The other possibility is if one considers a potential variation in the gravitational constant that determines the intensity of the gravitational pull between bodies. Its value is G = 6.67384(80) x 10-11 N m2/kg2. Despite it being a constant, it is one of those that is known with the least accuracy, with a precision of only one in 10,000.

    In these two specific cases, the pulsar-black hole combination would not be the perfect ‘holy grail’, but in any case scientists are anxious to find this pair, because it could be used to analyse the majority of deviations. In fact, it is one of the desired objectives of X-ray and gamma ray space telescopes (such as Chandra, NuStar or Swift), as well as that of large radio telescopes that are currently being built, such as the enormous ‘Square Kilometre Array’ (SKA) in Australia and South Africa.


    NASA SWIFT Telescope

    SKA Square Kilometer Array

    The image at the top of the page shows dynamic rings, wisps and jets of matter and antimatter around the pulsar in the Crab Nebula as observed in X-ray light by Chandra Space Observatory in 2001.

    Manjari Bagchi y Diego F. Torres. “In what sense a neutron star−black hole binary is the holy grail for testing gravity?”. Journal of Cosmology and Astroparticle Physics, 2014. Doi:10.1088/1475-7516/2014/08/055.

    See the full article here.

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  • richardmitnick 12:07 pm on November 18, 2014 Permalink | Reply
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    From SPACE.com: ” Dark Matter Murder Mystery: Is Weird Substance Destroying Neutron Stars?” 

    space-dot-com logo


    November 18, 2014
    Charles Q. Choi

    This illustration shows a dark matter annihilation map. Credit: Illustris Collaboration

    The mysterious substance that makes up most of the matter in the universe may be destroying neutron stars by turning them into black holes in the center of the Milky Way, new research suggests.

    When an image from NASA’s Chandra X-ray Observatory of PSR B1509-58 — a spinning neutron star surrounded by a cloud of energetic particles –was released in 2009, it quickly gained attention because many saw a hand-like structure in the X-ray emission. In a new image of the system, X-rays from Chandra in gold are seen along with infrared data from NASA’s Wide-field Infrared Survey Explorer (WISE) telescope in red, green and blue. NASA’s Nuclear Spectroscopic Telescope Array, or NuSTAR, also took a picture of the neutron star nebula in 2014, using higher-energy X-rays than Chandra. PSR B1509-58 is about 17,000 light-years from Earth.
    JPL, a division of the California Institute of Technology in Pasadena, manages the WISE mission for NASA. NASA’s Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for the NASA Science Mission Directorate. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra’s science and flight operations.

    If astronomers successfully detect a neutron star dying at the metaphorical hands of dark matter, such a finding could yield critical insights on the elusive properties of material, scientists added.

    Dark matter — an invisible substance thought to make up five-sixths of all matter in the universe — is currently one of the greatest mysteries in science. The consensus among researchers suggests that dark matter is composed of a new type of particle, one that interacts very weakly at best with all the known forces of the universe. As such, dark matter is invisible and nearly completely intangible, mostly detectable only via the gravitational pull it exerts.

    A number of ongoing experiments based on massive sensor arrays buried underground are attempting to identify the weak signals dark matter is expected to give off when it makes a rare encounter with other particles. In addition, the most powerful particle accelerator on Earth, the Large Hadron Collider (LHC), is attempting to create particles that might be dark matter. So far, none of these studies have confirmed any signs of dark matter, leaving much uncertain about its properties.

    CERN LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC at CERN

    Now, physicists suggest answers to the mystery of dark matter might lie in another puzzle, known as the missing pulsar problem.

    A pulsar is a kind of neutron star, which is a super-dense remnant of a massive star left behind after dying in a gigantic explosion known as a supernova. Neutron stars can devour matter from companion stars, acts of cannibalization that make neutron stars give off pulses of radiation, earning such neutron stars the name pulsar.

    According to current astrophysical and cosmological models, several hundred pulsars should be orbiting the supermassive black hole at the heart of the Milky Way. However, searches for these pulsars by looking for the radio waves they emit have so far come up empty-handed.

    Now researchers suggest dark matter could destroy these neutron stars, transforming them into black holes.

    Dark matter, like ordinary matter, is drawn to the gravity of other matter. The greatest concentration of normal matter in the Milky Way is at its center, so the greatest concentration of dark matter is there as well.

    In a region of high dark matter density such as the heart of the Milky Way, an enormous amount of dark matter particles could accumulate in a pulsar, causing it to grow massive enough to collapse and form a black hole.

    “It is possible that pulsars imploding into black holes may provide the first concrete signal of particulate dark matter,” said study co-author Joseph Bramante, a physicist at the University of Notre Dame.

    The models of dark matter that are most consistent with this idea, and with observations of pulsars seen outside the galactic center, are ones that suggest dark matter is asymmetric, meaning there is more of one kind of dark matter particle than its antiparticle counterpart. Normal matter is asymmetric as well — there are far more protons in the universe than anti-protons. (When a particle and its antimatter counterpart meet, they annihilate each other, releasing a burst of energy — a proof of Einstein’s famous equation, E=mc2, which revealed mass can be converted to energy and vice versa.)

    “For me, the most surprising result is that already existing models of dark matter could cause pulsars at the galactic center to collapse into black holes,” Bramante told Space.com.

    If dark matter is asymmetric, this would be consistent with “why there is more matter than antimatter in the universe, and why there is five times more dark matter than visible matter,” Bramante added.

    The mass of the dark matter particle responsible for imploding pulsars in the galactic core might be 100 times lighter than an electron or heavier than 100 million protons. If dark matter is as massive as 100 million protons, it would take more than 1,000 times the energies capable at the LHC to create them, Bramante noted. This suggests that looking for an imploding pulsar in the centers of galaxies might be a more feasible way to learn about dark matter.

    There might be other explanations for the missing pulsar problem. For instance, massive stars may form short-lived, highly magnetic pulsars known as magnetars in the galactic center rather than ordinary long-lived pulsars, perhaps because stars in the galactic core might be highly magnetized. The researchers are exploring how astronomers might identify whether a pulsar in the galactic core died because of dark matter, supporting their idea.

    Bramante and his colleague Tim Linden detailed their findings Oct. 10 in the journal Physical Review Letters.

    See the full article here.

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  • richardmitnick 1:43 pm on September 17, 2014 Permalink | Reply
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    From NASA: “Pulse of a Dead Star Powers Intense Gamma Rays” 



    September 16, 2014
    Whitney Clavin 818-354-4673
    Jet Propulsion Laboratory, Pasadena, California

    Our Milky Way galaxy is littered with the still-sizzling remains of exploded stars.

    The blue dot in this image marks the spot of an energetic pulsar — the magnetic, spinning core of star that blew up in a supernova explosion. NASA’s Nuclear Spectroscopic Telescope Array, or NuSTAR, discovered the pulsar by identifying its telltale pulse — a rotating beam of X-rays, that like a cosmic lighthouse, intersects Earth every 0.2 seconds.

    The pulsar, called PSR J1640-4631, lies in our inner Milky Way galaxy about 42,000 light-years away. It was originally identified by as an intense source of gamma rays by the High Energy Stereoscopic System (H.E.S.S.) in Namibia. NuSTAR helped pin down the source of the gamma rays to a pulsar.
    HESS Cherenko Array
    H.E.S.S. Array
    The other pink dots in this picture show low-energy X-rays detected by NASA’s Chandra X-ray Observatory.
    NASA Chandra Telescope
    In this image, NuSTAR data is blue and shows high-energy X-rays with 3 to 79 kiloelectron volts; Chandra data is pink and shows X-rays with 0.5 to 10 kiloeletron volts.
    The background image shows infrared light and was captured by NASA’s Spitzer Space Telescope.

    NASA Spitzer Telescope
    NASA Spitzer

    Image credit: NASA/JPL-Caltech/SAO

    When the most massive stars explode as supernovas, they don’t fade into the night, but sometimes glow ferociously with high-energy gamma rays. What powers these energetic stellar remains?

    NASA’s Nuclear Spectroscopic Telescope Array, or NuSTAR, is helping to untangle the mystery. The observatory’s high-energy X-ray eyes were able to peer into a particular site of powerful gamma rays and confirm the source: A spinning, dead star called a pulsar. Pulsars are one of several types of stellar remnants that are left over when stars blow up in supernova explosions.

    This is not the first time pulsars have been discovered to be the culprits behind intense gamma rays, but NuSTAR has helped in a case that was tougher to crack due to the distance of the object in question. NuSTAR joins NASA’s Chandra X-ray Observatory and Fermi Gamma-ray Space Telescope, and the High Energy Stereoscopic System (H.E.S.S.) in Namibia, each with its own unique strengths, to better understand the evolution of these not-so-peaceful dead stars.

    NASA Fermi Telescope

    “The energy from this corpse of a star is enough to power the gamma-ray luminosity we are seeing,” said Eric Gotthelf of Columbia University, New York. Gotthelf explained that while pulsars are often behind these gamma rays in our galaxy, other sources can be as well, including the outer shells of the supernova remnants, X-ray binary stars and star-formation regions. Gotthelf is lead author of a new paper describing the findings in the Astrophysical Journal.

    In recent years, the Max-Planck Institute for Astronomy’s H.E.S.S. experiment has identified more than 80 incredibly powerful sites of gamma rays, called high-energy gamma-ray sources, in our Milky Way. Most of these have been associated with prior supernova explosions, but for many, the primary source of observed gamma rays remains unknown.

    The gamma-ray source pinpointed in this new study, caled HESS J1640-465, is one of the most luminous discovered so far. It was already known to be linked with a supernova remnant, but the source of its power was unclear. While data from Chandra and the European Space Agency’s XMM-Newton telescopes hinted that the power source was a pulsar, intervening clouds of gas blocked the view, making it difficult to see.

    ESA XMM Newton

    NuSTAR complements Chandra and XMM-Newton in its capability to detect higher-energy range of X-rays that can, in fact, penetrate through this intervening gas. In addition, the NuSTAR telescope can measure rapid X-ray pulsations with fine precision. In this particular case, NuSTAR was able to capture high-energy X-rays coming at regular fast-paced pulses from HESS J1640-465. These data led to the discovery of PSR J1640-4631, a pulsar spinning five times per second — and the ultimate power source of both the high-energy X-rays and gamma rays.

    How does the pulsar produce the high-energy rays? The pulsar’s strong magnetic fields generate powerful electric fields that accelerate charged particles near the surface to incredible speeds approaching that of light. The fast-moving particles then interact with the magnetic fields to produce the powerful beams of high-energy gamma rays and X-rays.

    “The discovery of a pulsar engine powering HESS J1640-465 allows astronomers to test models for the underlying physics that result in the extraordinary energies generated by these rare gamma-rays sources,” said Gotthelf.

    “Perhaps other luminous gamma-ray sources harbor pulsars that we can’t detect,” said Victoria Kaspi of McGill University, Montreal, Canada, a co-author on the study. “With NuSTAR, we may be able to find more hidden pulsars.”

    The new data also allowed astronomers to measure the rate at which the pulsar slows, or spins down (about 30 microseconds per year), as well as how this spin-down rate varies over time. The answers will help researchers understand how these spinning magnets — the cores of dead stars — can be the source of such extreme radiation in our galaxy.

    See the full article here.

    The National Aeronautics and Space Administration (NASA) is the agency of the United States government that is responsible for the nation’s civilian space program and for aeronautics and aerospace research.

    President Dwight D. Eisenhower established the National Aeronautics and Space Administration (NASA) in 1958 with a distinctly civilian (rather than military) orientation encouraging peaceful applications in space science. The National Aeronautics and Space Act was passed on July 29, 1958, disestablishing NASA’s predecessor, the National Advisory Committee for Aeronautics (NACA). The new agency became operational on October 1, 1958.

    Since that time, most U.S. space exploration efforts have been led by NASA, including the Apollo moon-landing missions, the Skylab space station, and later the Space Shuttle. Currently, NASA is supporting the International Space Station and is overseeing the development of the Orion Multi-Purpose Crew Vehicle and Commercial Crew vehicles. The agency is also responsible for the Launch Services Program (LSP) which provides oversight of launch operations and countdown management for unmanned NASA launches. Most recently, NASA announced a new Space Launch System that it said would take the agency’s astronauts farther into space than ever before and lay the cornerstone for future human space exploration efforts by the U.S.

    NASA science is focused on better understanding Earth through the Earth Observing System, advancing heliophysics through the efforts of the Science Mission Directorate’s Heliophysics Research Program, exploring bodies throughout the Solar System with advanced robotic missions such as New Horizons, and researching astrophysics topics, such as the Big Bang, through the Great Observatories [Hubble,
    Chandra, Spitzer ]and associated programs. NASA shares data with various national and international organizations such as from the Greenhouse Gases Observing Satellite.
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  • richardmitnick 5:00 pm on January 13, 2014 Permalink | Reply
    Tags: , , , , , Pulsars,   

    From Symmetry: “Scientists pinpoint ‘very peculiar’ pulsar” 

    Scientists studying five years of data from the Fermi Gamma-ray Space Telescope have found the first gamma-ray variable pulsar. But is it really what it seems?

    NASA Fermi Telescope

    January 13, 2014
    Lori Ann White

    Astrophysicists studying the gamma-ray sky have gone back over five years of survey data from the Fermi Gamma-ray Space Telescope and discovered something new: a pulsar that varies in the amount of gamma-ray radiation it emits.

    Courtesy of NASA/DOE/Fermi LAT Collaboration

    Pulsars have a reputation as the cosmic versions of lighthouses: These neutron stars emit beams of electromagnetic energy. The beams sweep across the sky with the pulsar’s rotations, like beacons sweeping across space. Astrophysicists have known for some time, though, that the clockwork precision of pulsars is an illusion; not only do they rotate more and more slowly as they lose energy over millennia, the amount of energy they emit in radio waves and X-rays at any one time can change too.

    But the knowledge that pulsars also vary in gamma rays is a bit surprising, says Fermi scientist Luigi Tibaldo. “The X-rays and radio waves emitted by pulsars are generated through different processes than the gamma waves,” he says. When the Energetic Gamma Ray Experiment Telescope, or EGRET, the predecessor to Fermi’s main instrument, the Large Area Telescope, saw no signs of variability, astrophysicists considered the stability of pulsars in gamma rays to be an axiom—”No, more than an axiom. A motivated conclusion. We just didn’t think they varied,” Tibaldo says.

    The pulsar, known as PSR J2021+4026, is one of the first previously unknown pulsars found by Fermi after its launch in 2008. It resides in the Gamma Cygni region—the very heart of the Swan constellation. At first, it seemed like a perfectly ordinary pulsar. Yet as Tibaldo and his colleague Massimiliano Razzano reviewed the data, they saw hints of a small, steady increase in gamma rays from the beginning of Fermi’s mission in 2008 until mid-October 2011. Then, in less than a week, gamma-ray energies dropped by almost 20 percent, while the pulsar’s rotational speed got slower and slower.

    This was “very peculiar,” Tibaldo says. A pulsar slows down because it emits energy. “Think about it,” he continues. If the rotational speed continues to drop, “the pulsar should be emitting more energy, but we weren’t seeing it. Where was the energy going?”

    Their theory, which Tibaldo presented last month at the 27th Texas Symposium on Relativistic Astrophysics, is that a violent upheaval in the intense magnetic fields surrounding the pulsar caused the variability.

    “Here we are dealing with magnetic fields trillions of times more intense than Earth’s magnetic field,” says Razzano, who presented their results at the American Astronomical Society meeting in Washington, DC, earlier this month. “Fields of that strength are currently impossible to reproduce in the laboratory.”

    These magnetic fields essentially aim the pulsar’s energy beams, and, says Tibaldo, “the field lines broke and reconfigured in less than a week. This moved the beam slightly off our line of sight. It only looks like the gamma ray flux went down because we’re no longer directly in its path.”

    In other words, researchers can only see pulsars whose beams sweep across Earth. If the pulsar’s beams were to redirect away from Earth, the signal would drop—just what the Fermi telescope observed.

    PSR J2021+4026 remains the only known pulsar that’s variable in gamma rays. With a sample set of one, Tibaldo can’t say if his team’s theory is correct or not. “Having more cases is important to understanding what’s going on,” he says.

    As the Fermi mission continues, Tibaldo and Razzano—working with a team at laboratories and universities including SLAC National Accelerator Laboratory, the University of Pisa and Italy’s National Institute of Nuclear Physics—hope to gather data on additional gamma-ray-variable pulsars. With these, they may be able to determine if this new type of pulsars really stands apart from the rest, or if the only difference is in perspective.

    This work recently appeared in The Astrophysical Journal Letters.

    See the full article here.

    Symmetry is a joint Fermilab/SLAC publication.

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  • richardmitnick 12:41 pm on September 25, 2013 Permalink | Reply
    Tags: , , , , , Pulsars   

    From ESA: “Missing link found between X-ray and radio pulsars” 

    European Space Agency

    25 September 2013
    Markus Bauer
    ESA Science and Robotic Exploration Communication Officer
    Tel: +31 71 565 6799
    Mob: +31 61 594 3 954
    Email: markus.bauer@esa.int

    Alessandro Papitto
    Institut de Ciències de l’Espai (ICE), CSIC-IEEC (Spanish National Research Council – Institute for Space Studies of Catalonia)
    Barcelona, Spain
    Tel: +34 935 868355
    Email: papitto@ice.csic.es

    Enrico Bozzo
    ISDC Data Centre for Astrophysics
    University of Geneva, Switzerland
    Tel: +41 79 3129209
    Email: Enrico.Bozzo@unige.ch

    Erik Kuulkers
    ESA Integral Project Scientist
    Tel: +34 918131358
    Email: Erik.Kuulkers@esa.int

    Norbert Schartel
    ESA XMM-Newton Project Scientist
    Tel: +34 91 8131 184
    Email: Norbert.Schartel@esa.int

    Astronomers using ESA’s Integral and XMM-Newton space observatories have caught a fast-spinning ‘millisecond pulsar’ in a crucial evolutionary phase for the first time, as it swings between emitting pulses of X-rays and radio waves.

    Pulsar in the Crab Nebula

    Pulsars are spinning, magnetised neutron stars, the dead cores of massive stars that exploded as a dramatic supernova after having burned up their fuel. As they spin, they sweep out pulses of electromagnetic radiation hundreds of times per second, like beams from a lighthouse. This tells us that the spin period of the neutron stars can be as short as a few milliseconds.

    neutron star
    Neutron star

    Pulsars are classified according to how their emission is generated. For example, radio pulsars are powered by the rotation of their magnetic field, while X-ray pulsars are fuelled by the accretion of material siphoned off from a companion star.

    Theory holds that initially slowly rotating neutron stars with a low-mass companion are spun up as matter accretes onto them from a surrounding disc fed by the companion. X-rays are emitted as the accreting material heats up as it falls onto the neutron star.

    After a billion years or so, the rate of accretion drops and the pulsars are thought to switch on again as a radio-emitting millisecond pulsar.

    There is thought to be an intermediate phase during which they swing back and forth between the two states several times, but until now, there has been no direct and conclusive evidence for this transitional phase.

    Thanks to the combined forces of ESA’s Integral and XMM-Newton space observatories, along with follow-up observations by NASA’s Swift and Chandra satellites and by ground-based radio telescopes, scientists have finally caught a pulsar in the act of changing between the two evolutionary steps.

    “The search is finally over: with our discovery of a millisecond pulsar that, within only a few weeks, switched from being accretion-powered and X-ray-bright to rotation-powered and bright in radio waves, we finally have the missing link in pulsar evolution,” says Alessandro Papitto from the Institute of Space Sciences in Barcelona, Spain, who led the research published this week in Nature .

    The object, identified as IGR J18245-2452, was first detected in X-rays on 28 March 2013 by Integral in the globular cluster M28, which lies in the constellation Sagittarius.

    M28 by Hubble

    See the full article here.

    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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