Supernova Blast Provides Clues to Age of Binary Star System
Dec. 4, 2013
Data from NASA’s Chandra X-ray Observatory has revealed faint remnants of a supernova explosion and helped researchers determine Circinus X-1 — an X-ray binary — is the youngest of this class of astronomical objects found to date.
As the name suggests, X-ray binaries are star systems made up of two parts: a compact stellar remnant — either a neutron star or a black hole; and a companion star — a normal star like our sun. As they orbit one another, the neutron star or black hole pulls in gas from the companion star. This heats the gas to millions of degrees, producing intense X-ray radiation and making these star systems some of the brightest X-ray sources in the sky.
Sebastian Heinz and his team at the University of Wisconsin-Madison (UW) discovered Circinus X-1 is less than 4,600 years old, making it the youngest X-ray binary system ever seen. This discovery, made in parallel with a radio telescope in Australia, provides scientists unique insight into the formation of neutron stars and supernovas, and the effect of the supernova’s explosion on a nearby companion star.
“X-ray binaries provide us with opportunities to study matter under extreme conditions that would be impossible to recreate in a laboratory,” Heinz said. “For the first time, we can study a newly minted neutron star in an X-ray binary system.”
Astronomers have detected hundreds of X-ray binaries throughout the Milky Way and other nearby galaxies. However, these older X-ray binaries, with ages typically measured in millions of years, only reveal information about what happens much later in the evolution of these systems.
“It’s critical that we see what these X-ray binaries are doing at all stages of their lives,” said co-author Paul Sell, also of UW. “Circinus X-1 is showing us what happens in a cosmic blink of an eye after one of these objects is born.”
To determine the age of Circinus X-1, the team of astronomers needed to examine the material around the orbiting pair of stars. However, the overwhelming brightness of the neutron star made it too difficult for researchers to observe that interstellar gas. The team recently caught a break, when they observed the neutron star in a very faint state — dim enough for scientists to detect the X-rays from the supernova shock wave that plowed through the surrounding interstellar gas.
“Since the supernova was triggered by the formation of the neutron star, our limit on the age of the supernova remnant also limits the age of the neutron star in Circinus X-1,” said co-author Robert Fender of the University of Oxford in the U.K.
The youth of Circinus X-1 helps explain its wild swings in brightness and the highly unusual orbit of its two stars, which had puzzled astronomers for years. The orbit is very eccentric — non-circular — and the period during which the two stars orbit each other is decreasing by several minutes every year. This is exactly what is expected for a young X-ray binary disrupted by a supernova explosion before the gravitational pull of the stars on each other has had time to circularize and stabilize the orbit.
Previous observations with other telescopes indicated the magnetic field of the neutron star in Circinus X-1 is weak. That, in addition to the star system’s young age, has led to two possible theories: either a neutron star can be born with a weak magnetic field, or it can quickly become de-magnetized as it pulls material from its companion star onto itself. Neither conclusion was expected from existing theories of neutron star evolution.
In our galaxy, the only other established X-ray binary within a supernova remnant is SS 433, which is between 10,000 and 100,000 years old, and behaves in many ways like an older version of Circinus X-1. Two other candidate X-ray binaries in nearby galaxies have ages similar to SS 433.
In addition to the Chandra data, radio observations from the Australia Telescope Compact Array were critical in these findings. A paper describing these results is available online and appears in the Dec. 4 issue of The Astrophysical Journal.
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 in Cambridge, Mass., controls Chandra’s science and flight operations.
Chandra X-ray Center, Cambridge, Mass.
Marshall Space Flight Center, Huntsville, Ala.
Glimpsing the Infrastructure of a Gamma-ray Burst Jet
Dec. 4, 2013
A new study using observations from a novel instrument provides the best look to date at magnetic fields at the heart of gamma-ray bursts, the most energetic explosions in the universe. An international team of astronomers from Britain, Slovenia and Italy has glimpsed the infrastructure of a burst’s high-speed jet.
Gamma-ray bursts are the most luminous explosions in the cosmos. Most are thought to be triggered when the core of a massive star runs out of nuclear fuel, collapses under its own weight, and forms a black hole. The black hole then drives jets of particles that drill all the way through the collapsing star and erupt into space at nearly the speed of light.
On March 8, 2012, NASA’s Swift satellite detected a 100-second pulse of gamma rays from a source in the constellation Ursa Minor. The spacecraft immediately forwarded the location of the gamma-ray burst, dubbed GRB 120308A, to observatories around the globe.
The world’s largest fully autonomous robotic optical telescope, the 2-meter Liverpool Telescope located at Roque de los Muchachos Observatory on La Palma in the Canary Islands, automatically responded to Swift’s notification.
“Just four minutes after it received Swift’s trigger, the telescope found the burst’s visible afterglow and began making thousands of measurements,” said lead researcher Carole Mundell, who heads the gamma-ray burst team at the Astrophysics Research Institute at Liverpool John Moores University in the U.K.
The telescope was fitted with an instrument named RINGO2, which Mundell’s team designed to detect any preferred direction, called polarization, in the vibration of light waves from burst afterglows.
Mundell’s team built RINGO2 in order to probe the magnetic fields long postulated to drive and focus the jets of gamma-ray bursts. The shoe-box-sized instrument pairs a spinning polarizing filter with a super-fast camera.
Energy across the spectrum, from radio waves to gamma rays, is emitted when a jet slams into its surroundings and begins to decelerate. This results in the formation of an outward-moving shock wave. At the same time, a reverse shock wave drives back into the jet debris, also producing bright emission.
“One way to picture these different shocks is by imagining a traffic jam,” Mundell said. “Cars approaching the jam abruptly slow down, which is similar to what happens in the forward shock. Cars behind them slow in turn, resulting in a wave of brake lights that moves backward along the highway, much like the reverse shock.”
Theoretical models of gamma-ray bursts predict that light from the reverse shock should show strong and stable polarized emissions if the jet possesses a structured magnetic field originating from the environment around the newly-formed black hole, thought to be the “central engine” driving the burst.
Previous observations of optical afterglows detected polarizations of about 10 percent, but they provided no information about how this value changed with time. As a result, they could not be used to test competing jet models.
The Liverpool Telescope’s rapid targeting enabled the team to catch the explosion just four minutes after the initial outburst. Over the following 10 minutes, RINGO2 collected 5,600 photographs of the burst afterglow while the properties of the magnetic field were still encoded in its captured light.
The observations show that the initial afterglow light was polarized by 28 percent, the highest value ever recorded for a burst, and slowly declined to 16 percent, while the angle of the polarized light remained the same. This supports the presence of a large-scale organized magnetic field linked to the black hole, rather than a tangled magnetic field produced by instabilities within the jet itself.
A paper describing the team’s findings will appear in the Dec. 5 issue of the journal Nature.
“This is a remarkable discovery that could not have occurred without the lickety-split response times of the Swift satellite and the Liverpool Telescope,” said Neil Gehrels, the Swift principal investigator at NASA’s Goddard Space Flight Center in Greenbelt, Md.
› Download additional graphics from NASA Goddard’s Scientific Visualization Studio
› Paper: “Highly polarized light from stable ordered magnetic fields in GRB 120308A”
› “NASA Sees ‘Watershed’ Cosmic Blast in Unique Detail” (Nov. 21, 2013)
› “NASA’s Fermi, Swift See ‘Shockingly Bright’ Burst” (05.03.13)
› “NASA’s Fermi Telescope Sees Most Extreme Gamma-ray Blast Yet” (02.19.09)
› “‘Naked-Eye’ Gamma-Ray Burst Was Aimed Squarely At Earth” (09.10.08)
NASA’s Goddard Space Flight Center, Greenbelt, Md.
Powerful Gamma-Ray Burst Detected Close To Milky Way
November 21, 2013
Lee Rannals for redOrbit.com – Your Universe Online
Astronomers from around the world have compiled data from satellites and observatories to help explain the most powerful gamma-ray burst ever recorded, according to a study published in the journal Science.
Led by researchers from the Niels Bohr Institute and the University of Leicester, the international team said this gamma-ray burst occurred relatively close to the Milky Way. Gamma-ray bursts (GRBs) are violent bursts of gamma radiation typically associated with an exploding massive star.
When a star explodes as a supernova it releases the gamma-ray bursts, which are so bright that they can be seen from across the universe. Telescopes underneath Earth’s atmosphere are unable to detect this light, however; so astronomers rely on space-based observatories such as the Swift satellite to pick up on them.
Swift monitors the skies and typically discovers about 100 gamma-ray bursts each year, but the one they found this past April was particularly unusual.
Continue Learning: http://www.redorbit.com/news/space/1113010268/supernova-unleashes-monster-gamma-ray-burst-112113/
Intense gamma-ray burst spells doom—for our models of gamma-ray bursts
Closest, most intense one we’ve observed yet.
by John Timmer – Nov 22 2013, 12:30pm EST
Back in April, orbiting observatories started picking up the first indications of a gamma-ray burst. By the time observations wrapped up, the event (GRB 130427A) produced the largest outpouring of photons of any yet detected, and it set a record for the highest energy photon we’ve seen from these events. And because it was unusually close to Earth, GRB 130427A provided a wealth of information about these extreme events—and told us that we don’t really understand how they produce the gamma-rays that are their signature.
Yesterday’s issue of Science contains four papers that describe the event, partly because it was unusually well-documented. The enormous stars that produce gamma-ray bursts were much more common in the early Universe and, as a result, most of them occur out at the edge of the observable Universe. But GRB 130427A is an exception; the Universe was already about 10 billion years old when it happened, meaning the supernova that produced the gamma rays occurred less than four billion light years from Earth. As a result, ground-based instruments that were directed to the right area of the sky by the orbiting instruments were quickly able to identify the supernova involved (SN 2013cq).
Continue Learning: http://arstechnica.com/science/2013/11/intense-gamma-ray-burst-spells-doomfor-our-models-of-gamma-ray-bursts/
NASA sees ‘watershed’ cosmic blast in unique detail
Posted: Nov 21, 2013 by Francis Reddy
(Phys.org) —On April 27, a blast of light from a dying star in a distant galaxy became the focus of astronomers around the world. The explosion, known as a gamma-ray burst and designated GRB 130427A, tops the charts as one of the brightest ever seen
A trio of NASA satellites, working in concert with ground-based robotic telescopes, captured never-before-seen details that challenge current theoretical understandings of how gamma-ray bursts work.
“We expect to see an event like this only once or twice a century, so we’re fortunate it happened when we had the appropriate collection of sensitive space telescopes with complementary capabilities available to see it,” said Paul Hertz, director of NASA’s Astrophysics Division in Washington.
Gamma-ray bursts are the most luminous explosions in the cosmos, thought to be triggered when the core of a massive star runs out of nuclear fuel, collapses under its own weight, and forms a black hole. The black hole then drives jets of particles that drill all the way through the collapsing star and erupt into space at nearly the speed of light.
Gamma-rays are the most energetic form of light. Hot matter surrounding a new black hole and internal shock waves produced by collisions within the jet are thought to emit gamma-rays with energies in the million-electron-volt (MeV) range, or roughly 500,000 times the energy of visible light. The most energetic emission, with billion-electron-volt (GeV) gamma rays, is thought to arise when the jet slams into its surroundings, forming an external shock wave.
The Gamma-ray Burst Monitor (GBM) aboard NASA’s Fermi Gamma-ray Space Telescope captured the initial wave of gamma rays from GRB 130427A shortly after 3:47 a.m. EDT April 27. In its first three seconds alone, the “monster burst” proved brighter than almost any burst previously observed.
Continue Learning: http://phys.org/news/2013-11-nasa-watershed-cosmic-blast-unique.html