Space

January 6, 2014

NASA’s Fermi makes first gamma-ray study of a gravitational lens

An international team of astronomers, using NASA’s Fermi observatory, has made the first-ever gamma-ray measurements of a gravitational lens, a kind of natural telescope formed when a rare cosmic alignment allows the gravity of a massive object to bend and amplify light from a more distant source.

This accomplishment opens new avenues for research, including a novel way to probe emission regions near supermassive black holes. It may even be possible to find other gravitational lenses with data from the Fermi Gamma-ray Space Telescope.

“We began thinking about the possibility of making this observation a couple of years after Fermi launched, and all of the pieces finally came together in late 2012,” said Teddy Cheung, lead scientist for the finding and an astrophysicist at the Naval Research Laboratory in Washington.

In September 2012, Fermi’s Large Area Telescope detected a series of bright gamma-ray flares from a source known as B0218+357, located 4.35 billion light-years from Earth in the direction of a constellation called Triangulum. These powerful flares, in a known gravitational lens system, provided the key to making the lens measurement.

Astronomers classify B0218+357 as a blazar – a type of active galaxy noted for its intense emissions and unpredictable behavior. At the blazar’s heart is a supersized black hole with a mass millions to billions of times that of the sun. As matter spirals toward the black hole, some of it blasts outward as jets of particles traveling near the speed of light in opposite directions.

The extreme brightness and variability of blazars result from a chance orientation that brings one jet almost directly in line with Earth. Astronomers effectively look down the barrel of the jet, which greatly enhances its apparent emission.

Long before light from B0218+357 reaches us, it passes directly through a face-on spiral galaxy — one very much like our own – about 4 billion light-years away.

The galaxy’s gravity bends the light into different paths, so astronomers see the background blazar as dual images. With just a third of an arcsecond (less than 0.0001 degree) between them, the B0218+357 images hold the record for the smallest separation of any lensed system known.

While radio and optical telescopes can resolve and monitor the individual blazar images, Fermi’s LAT cannot. Instead, the Fermi team exploited a “delayed playback” effect.

“One light path is slightly longer than the other, so when we detect flares in one image we can try to catch them days later when they replay in the other image,” said team member Jeff Scargle, an astrophysicist at NASA’s Ames Research Center in Moffett Field, Calif.

In September 2012, when the blazar’s flaring activity made it the brightest gamma-ray source outside of our own galaxy, Cheung realized it was a golden opportunity. He was granted a week of LAT target-of-opportunity observing time, from Sept. 24 to Oct. 1, to hunt for delayed flares.

At the American Astronomical Society meeting in National Harbor, Md., Cheung said the team had identified three episodes of flares showing playback delays of 11.46 days, with the strongest evidence found in a sequence of flares captured during the week-long LAT observations.

Intriguingly, the gamma-ray delay is about a day longer than radio observations report for this system. And while the flares and their playback show similar gamma-ray brightness, in radio wavelengths one blazar image is about four times brighter than the other.

Astronomers don’t think the gamma rays arise from the same regions as the radio waves, so these emissions likely take slightly different paths, with correspondingly different delays and amplifications, as they travel through the lens.

“Over the course of a day, one of these flares can brighten the blazar by 10 times in gamma rays but only 10 percent in visible light and radio, which tells us that the region emitting gamma rays is very small compared to those emitting at lower energies,” said team member Stefan Larsson, an astrophysicist at Stockholm University in Sweden.

As a result, the gravity of small concentrations of matter in the lensing galaxy may deflect and amplify gamma rays more significantly than lower-energy light. Disentangling these so-called microlensing effects poses a challenge to taking further advantage of high-energy lens observations.

The scientists say that comparing radio and gamma-ray observations of additional lens systems could help provide new insights into the workings of powerful black-hole jets and establish new constraints on important cosmological quantities like the Hubble constant, which describes the universe’s rate of expansion.

The most exciting result, the team said, would be the LAT’s detection of a playback delay in a flaring gamma-ray source not yet identified as a gravitational lens in other wavelengths.

A paper describing the research will appear in a future edition of The Astrophysical Journal Letters.

NASA’s Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership. Fermi is managed by NASA’s Goddard Space Flight Center in Greenbelt, Md. It was developed in collaboration with the U.S. Department of Energy, with contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

Click here to watch on YouTube




All of this week's top headlines to your email every Friday.


 
 

 

Headlines October 24, 2014

News: U.S., South Korea delay transfer of wartime control - The U.S. and South Korea have delayed transferring wartime operational control of allied forces by taking on a “conditions-based approach” and scrapping the previously set deadline of 2015.   Business: Exclusive: Lockheed, Pentagon reach $4 billion deal for more F-35 jets - Lockheed Martin and U.S. defense...
 
 

News Briefs October 24, 2014

French moving troops toward Libyan border A top French military official says the country is moving troops toward the Libyan border within weeks and, along with U.S. intelligence, is monitoring al Qaeda arms shipments to Africa’s Sahel region. A French base will go up within weeks in a desert outpost just a hundred kilometers (60...
 
 
Navy photograph

Navy to commission submarine North Dakota

Navy photograph The PCU North Dakota (SSN 784) during bravo sea trials. The crew performed exceptionally well on both alpha and bravo sea trials. The submarine North Dakota is the 11th ship of the Virginia class, the first U.S....
 

 

Boeing announces SF Airlines order for Boeing converted freighters

Boeing announced Oct. 23 that SF Airlines has placed an order for an undisclosed number of 767-300ER passenger-to-freighter conversions (Boeing Converted Freighters). SF Airlines, a subsidiary of Shenzhen, China-based delivery services company SF Express, will accept its first redelivered 767 in the second half of 2015. “SF Express aims to become China’s most respected and...
 
 
LM-C130

Another Super Herc Little Rock Rollin’

  Lockheed Martin delivered another C-130J Super Hercules to the 61st Airlift Squadron at Little Rock Air Force Base, Ark., Oct. 23. Little Rock AFB’s new C-130J was ferried from the Lockheed Martin Aeronautics facility ...
 
 

United Technologies beats third quarter profit expectations

United Technologies Corp. Oct. 23 reported third-quarter profit of $1.85 billion as sales increased across all its businesses and the aerospace giant reported favorable tax settlements. The Hartford, Conn.,-based company said it had profit of $2.04 per share and earnings, adjusted for non-recurring gains, came to $1.82 per share. The results topped Wall Street expectations,...
 




0 Comments


Be the first to comment!


Leave a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>