Tuesday, April 22, 2014

Arecibo Observatory Detects Mysterious, Energetic Radio Burst

by Nadia Drake

A brief, blazing burst of radio waves detected by the Arecibo Observatorycould herald a turning of the tide for a peculiar class of cosmic signals. Until recently, the signals had only ever been detected by a telescope in Australia, a pattern that fueled doubts about their origin.

Fewer than a dozen of these bursts, lasting for only a few thousandths of a second, have ever been reported. Called “fast radio bursts,” the signals are cosmic enigmas that appear to come from the very, very distant universe. But since the first burst discovery in 2007, scientists have not only wondered what kind of cosmic object could produce such a tremendously bright, short-lived radio pulse – but have disagreed about whether the bursts are even celestial.

“There are more theories than there are bursts,” says West Virginia University astronomer Duncan Lorimer, an author on the paper describing the burst, posted to the arXiv on April 10.

On November 2, 2012, a blast of radio waves collided with the Arecibo Observatory in Puerto Rico, where the world’s largest single-dish radio telescope lives. Rain or shine, day or night, the 305-meter dish collects radio waves from the cosmos, which are then processed into data for scientists to study.

The data gathered at 6:35 am UT revealed a massive, 3-millisecond spike. Unlike the radio blasts emitted by some pulsars, the burst did not recur. It briefly blazed and then disappeared. Called FRB 121102, the burst was very similar to six earlier events that constitute the entire reported population of ultrafast radio bursts – a population that until November 2012 had only been seen by one telescope, in Australia.

But transience is only part of what makes these signals so weird. Their chief peculiarity lies in just how dang far away they seem to be.

Normally, radio waves travel at the speed of light. This means that all the different wavelengths and frequencies of radio waves emitted by the same object – say, a pulsar – should arrive on Earth in one big batch.

But if something is sufficiently far away, that changes. Longer, lower frequency waves traveling through the cosmos have a trickier time getting to Earth. Clouds of ionized interstellar particles – electrons, primarily – form roadblocks that slow and redirect these longer waves, causing them to follow a more sinuous path. As a result, the longer waves arrive just a bit later than their shorter kin – sometimes, the difference is only a fraction of a second.

That delay in arrival times is called “dispersion,” and it lets astronomers estimate how far away the waves are coming from. The longer the delay, the more intergalactic junk that got in the way. And since scientists think they know how much junk there is, they can use the dispersion measurement to approximate a distance, or at least identify whether an object lives inside or outside the Milky Way.

If astronomers are interpreting the bursts’ dispersion measures correctly, then the bursts came from billions and billions of light-years away – in other words, they’re nowhere near our cosmic neighborhood. And nobody knows what they are.

“The sources of the bursts are undoubtedly exotic by normal standards,” Cornell University astronomer Jim Cordes wrote in Science.

The ultrafast pulses take their name from Lorimer, who spotted and described the first burst in 2007. That mysterious signal, estimated to have traveled roughly 3 billion light-years before colliding with Earth, stunned astronomers. Many of them questioned whether it was an artifact produced by the telescope that detected it, the Parkes Observatory’s 64-meter telescope in Australia.

Site of the first burst found, in 2007. Lorimer et al., NRAO/AUI/NSF)

In the years after the discovery, skepticism grew. A new class of terrestrial radio bursts detected by the Parkes telescope in 2010 cast more doubt on the original Lorimer burst. Those Earth-based signals, called perytons, opened the door to the possibility that even if real, the original burst was actually coming from much closer to home.

Another Parkes-detected burst, reported in 2012, didn’t do much to alleviate doubts.

But that summer, a third Lorimer burst was described at the International Astronomical Union’s general assembly in Beijing, China; as it turned out, this burst would be one member of a quartet that astronomers would announce the next year in Science. By the end of July, 2013, the total reported stood at six.

“The discovery of fast radio bursts at the Parkes Observatory, if confirmed at other observatories, would be a monumental discovery, comparable to that of cosmological gamma-ray bursts and even pulsars,” Shrinivas Kulkarni, an astronomer at Caltech, told Scientific American at the time.

Strength in numbers was helping the bursts achieve legitimacy, but there was no escaping that they’d all been detected by the same telescope. And until another observatory saw something similar, skeptics could easily question whether the signals were a product of the telescope and its location, rather than the cosmos.

“In fairness, it’s not a bad question to ask at all,” Lorimer says. “Whenever you make a new discovery, it’s very important to have it confirmed by different groups, using different equipment.”

Now, the Arecibo detection of FRB 121102 strongly suggests the signals are not a Parkes artifact, and furthermore, that they’re not terrestrial in origin.

“I’m certainly very excited to see such a convincing result from another team using a different observatory,” says astronomer Michael Keith of the University of Manchester, who was not involved in the current study.

So the questions astronomers are asking are: How far have the bursts traveled? And what, exactly, are they?

“My hunch has always been that they’re extragalactic,” Lorimer says. “But that’s really nothing more than a hypothesis at this point.”

Overall, the dispersion measures do seem to suggest an extragalactic origin. There are many more electrons between Earth and the bursts than can be explained by the Milky Way’s interstellar electrons; but it’s still possible that intervening nebulas could be clouding the measurement, Kulkarni says. He suggests the signals could be coming from spinning neutron stars known as radio rotating transients, or RRATs, that live in our galaxy and also emit a single pulse.

Because the signals are so brief and bright, they must be coming from a rather dense source, says astronomer Scott Ransom of the National Radio Astronomy Observatory. “That means a compact object – i.e., a neutron star or a black hole – is likely somehow to blame,” he says.

Just what that compact object is has yet to be explained. One theory suggests that giant flares erupting from highly magnetic neutron stars, known as magnetars, cause the bursts. Others suggest the bursts result from colliding neutron stars or black holes, evaporating primordial black holes, large magnetic stars, or are the death spasms produced when massive, slowly spinning neutron stars collapse into black holes. That last object, proposed in 2013, is known as a blitzar.

More observations should help teams pinpoint the bursts’ origin. Already, more detections from Parkes are coming down the pipeline, and Ransom says he’s looking through the Green Bank Telescope’s data for similar signals. But what astronomers are really hoping for is a way to find the bursts in real-time – then, they might be able to identify an optical source, like a host galaxy. In addition to supporting an extragalactic origin, that would also allow scientists to use the bursts to probe the characteristics of the intervening intergalactic medium and its ions.

“We really need to get their precise positions,” Ransom says. “That will let us see where they originate – hopefully in or near other galaxies where we can get their distances.”

North Korea may be close to nuke test.

INSIDE KOREA: North Korea has stepped up activity at its nuclear site, Seoul’s Defense Ministry said Tuesday, in a fresh sign that the communist country may push ahead with a fourth atomic test in breach of international resolutions.

Concerns have been growing since Pyongyang threatened a “new form of nuclear test” late last month in protest against the U.N. Security Council’s condemnation of its test-firing of ballistic missiles.

Though no signs were spotted of an impending underground explosion, the ministry said it set up an “integrated crisis management” task force Monday to prepare for any possibilities.

“We’re detecting lots of activity in North Korea’s nuclear site in the (northeast) town of Punggye,” ministry spokesperson Kim Min-seok told a news briefing.

“North Korea could suddenly carry out a nuclear test in the short term.”

But he suggested that the signs may mark another attempt by the Kim Jong-un regime to “deceive” the outside world, rather than actual preparations.

Other officials and analysts also raised the possibility that the increased activities are meant to be a flexing of military muscles in the run-up to U.S. President Barack Obama’s Asia tour this week. He is due to arrive in Seoul on Friday.

The South Korean military is believed to have perceived an increase in vehicle and personnel movement, as well as a screen to cover a tunnel.

This followed an analysis of satellite imagery last month by the U.S.-Korea Institute at Johns Hopkins University that concluded that recent excavation activities at the Punggye site may indicate that the North is building a tunnel complex to conduct multiple tests or explosions on a “much more regular basis.”

Kim also mentioned that North Korean officials have spoken of a “next step that is unimaginable to enemies,” a “big event before April 30,” and “one big shot,” citing intelligence.

“North Korea is currently at the stage where it is capable of conducting a nuclear test unexpectedly if it decides so,” he added.

As tension escalates, Seoul has been ratcheting up diplomatic efforts with Washington, Beijing and other partners to dissuade its wayward neighbor from another atomic blast. Foreign Minister Yun Byung-se has warned Pyongyang of “unimaginable consequences.”

The chief nuclear negotiators of South Korea, the U.S. and Japan gathered in Washington early this month, sending a strong warning to North Korea against a fourth nuclear test and vowed to step up cooperation to preclude further provocations.

Hwang Joon-kook, Seoul’s new special representative for Korean peninsular peace and security affairs and top envoy to the six-party talks, also met with his Chinese counterpart Wu Dawei, China’s special representative for Korean affairs, in Beijing. Wu then traveled to the U.S. for consultations with Special Representative for North Korea Policy Glyn Davies last week.

By Shin Hyon-hee | The Korea Herald

US to conduct small ground force exercise in Europe

File photo
WASHINGTON — The United States plans to carry out small ground-force exercises in Poland and Estonia in an attempt to reassure NATO’s Eastern European members worried aboutRussia’s military operations in and near Ukraine, Western officials said Friday.

The moves are part of a broader effort by NATO to strengthen the alliance’s air, sea and land presence in Eastern Europe in response to Russia’s new assertiveness in the region.

It is not yet clear what additional troop deployments the United States and other NATO nations might undertake in Eastern Europe after the exercises and to what extent the moves would ease anxieties there.

The land-force exercises the Obama administration is planning are extremely modest.

The exercise in Poland, which is expected to be announced next week, would involve a United States Army company and would last about two weeks, officials said. A company consists of about 150 soldiers.

The exercise in Estonia would be similar, said a Western official who declined to be identified because he was talking about internal planning.

Although the exercises would be short, the United States is considering other ways to maintain a regular ground-force presence in Eastern Europe by rotating troops and conducting training there.

“There’s an entire range of possibilities and measures that are being considered,” Defense Secretary Chuck Hagel said on Thursday in a joint news conference with Poland’s defense minister, Tomasz Siemoniak. “Rotational basis of training and exercises are always part of that.”

The company-size Army exercise that is planned is far from the sort of NATO deployment that Poland’s foreign minister, Radoslaw Sikorski, suggested this month when he told reporters that he wanted the alliance to deploy two combat brigades with as many as 5,000 troops each in Poland.

This week, NATO’s top military commander, Gen. Philip M. Breedlove, gave members of the alliance a range of options for strengthening its military posture in response to Russia’s annexation of Crimea, along with his own recommendations.

The measures include immediate, midterm and long-term steps. One option, General Breedlove said in an interview this month, is to move the 4,500-member American combat brigade from Fort Hood, Tex., to Europe. But Obama administration officials have not publicly supported such a step.

The first hint that the Obama administration plans to announce that American troops would be sent to Poland was provided on Friday by The Washington Post, which noted that Mr. Siemoniak had said that the move had been agreed to on a political level but provided no details.

The United States has already sent 12 F-16 fighter jets and 200 support personnel to Poland.

NATO’s secretary general, Anders Fogh Rasmussen, said this week that the alliance would fly more air patrols over the Baltic region and that allied ships would deploy to the Baltic Sea.

Mr. Rasmussen left open the possibility for additional deployments, including on land.

“More will follow, if needed, in the weeks and months to come,” he said.


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