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.


 
 

 

Boeing concludes commercial crew space act agreement for CST-100/Atlas V

Boeing has successfully completed the final milestone of its Commercial Crew Integrated Capability Space Act Agreement with NASA. The work and testing completed under the agreement resulted in significant maturation of Boeing’s crew transportation system, including the CST-100 spacecraft and Atlas V rocket. NASA in July approved the Critical Design Review Board milestone for Boeing’...
 
 

NASA partners with leading technology innovators to enable future exploration

Recognizing that technology drives exploration, NASA has selected four teams of agency technologists for participation in the Early Career Initiative pilot program. The program encourages creativity and innovation among early career NASA technologists by engaging them in hands-on technology development opportunities needed for future missions. NASA’s Space Technology Mission Directorate c...
 
 

New commercial rocket descent data may help NASA with future Mars landings

NASA successfully captured thermal images of a SpaceX Falcon 9 rocket on its descent after it launched in September from Cape Canaveral Air Force Station, Fla. The data from these thermal images may provide critical engineering information for future missions to the surface of Mars. “Because the technologies required to land large payloads on Mars...
 

 
Image courtesy of NASA, J. Lotz, (STScI

NASA’s Hubble finds extremely distant galaxy through cosmic magnifying glass

Image courtesy of NASA, J. Lotz, (STScI The mammoth galaxy cluster Abell 2744 is so massive that its powerful gravity bends the light from galaxies far behind it, making these otherwise unseen background objects appear larger a...
 
 
NASA photograph

NASA TV to air Russian spacewalk from International Space Station

NASA photograph Expedition 41 Commander Max Suraev and Flight Engineer Alexander Samokutyaev of the Russian Federal Space Agency will don Orlan spacesuits and step outside the International Space Station Oct. 22, to perform wor...
 
 
Ball Aerospace photograph

Ball Aerospace green propellant infusion mission to host three DOD space experiments

Ball Aerospace photograph The NASA and Ball Aerospace & Technologies Corp. Green Propellant Infusion Mission (GPIM) will fly three Defense Department experimental hosted payloads when it launches in 2016. The NASA and Ball ...
 




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>