Fermi observatory makes first gamma-ray study of a gravitational lens

January 6, 2014
In the heart of an active galaxy, matter falling toward a supermassive black hole creates jets of particles traveling near the speed of light. For active galaxies classified as blazars, one of these jets beams almost directly toward Earth. Credit: NASA/Goddard Space Flight Center Conceptual Image Lab

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 . 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 at the Naval Research Laboratory in Washington.

In September 2012, Fermi's Large Area Telescope (LAT) 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.

This movie illustrates the components of a gravitational lens system known as B0218+357. Different sight lines to a background blazar result in two images that show outbursts at slightly different times. NASA's Fermi made the first gamma-ray measurements of this delay in a lens system. Credit: NASA's Goddard Space Flight Center

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 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.

This Hubble image of gravitational lens B0218+357 reveals two bright sources separated by about a third of an arcsecond, each an image of the background blazar. Spiral arms belonging to the lensing galaxy also can be seen. B0218+357 boasts the smallest separation of lensed images currently known. Credit: NASA/ESA and the Hubble Legacy Archive

"Over the course of a day, one of these flares can brighten the 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 in other wavelengths.

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

Explore further: Galaxy's gamma-ray flares erupted far from its black hole

More information: www.nasa.gov/externalflash/fer … avitational_lensing/

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2.6 / 5 (7) Jan 06, 2014
Physorg seems to have forgotten to report on the death of Halton Arp, so I'd like to take a moment to remind people that part of the legacy of the Internet has traditionally been to pass on the critiques associated with conventional theory which academia (shamelessly) refuses to teach its own students. His story is now in the hands of the public, for we can plainly see that academia likes to pretend like there are no controversies associated with our most popular theories.
3.6 / 5 (8) Jan 06, 2014
While I'm sad to hear of his passing as usual you accuse people of hiding facts while ignoring the ones that don't suit your claims. Arp's ideas were tested, and his "non-cosmological redshifts" didn't do well when compared to fuller observations, neither did periodic redshifts when systematic errors were better considered. His published work was not ignored. His "controversies" were not controversial to few but Arp. They were studied and standard cosmology survived.
1 / 5 (3) Jan 07, 2014
Sub: Request better Interaction-East West Cosmology Studies
Many times , I do observe that Comprehension of Base concepts are missing.
Source, Fields, Flows, reflectors add to protective Index
In a complex situation one has to take cognisance of Plasma Regulated elctromagnetic phenomena in a magnetic field environment.
unless the reference frame is clear, the derived knoledge becomes a shade - in a shaded universe concept.
however, the data is interesting to read.
see my recent Research inputs
1. NANDI introduces new concepts for flow-fields integration=Vidyardhi nanduri
2. Super-imposition of Visible -Invisile matrix mode over space based observations-by Vidyardhi Nanduri
COSPAR-2013 Conference- Thailand.
Protect Copyrights- Knowledge Base -Content-Author Vidyardhi Nanduri
Space Cosmology studies-origins
1 / 5 (2) Jan 07, 2014
Arp's ideas were tested, and his "non-cosmological redshifts" didn't do well when compared to fuller observations, neither did periodic redshifts when systematic errors were better considered.

No, not even close. Things such as omitting and not publishing pertinent information were used.

And intentionally modifying images while rebuttals were conveniently ignored....


In his death at least show the man the dignity and respect he deserves by not lying.

1 / 5 (2) Jan 07, 2014
Re: "you accuse people of hiding facts while ignoring the ones that don't suit your claims. Arp's ideas were tested ..."

Those of us who have spent time reading through transcripts of the Bad Astronomy and Universe Today forum have a good sense for the mindset with which Arp's findings were engaged. The point was to take the investigation down before it developed legs.

There is this antiquated ideal of "thinking like a scientist" that pretends that scientists would be happy to see the theory they've had to memorize and think about upended. And then there is the far more real and observable cultural reality that graduate students today are encouraged to seat their perspective firmly within the root of mainstream theory. Few people seem to contemplate either the psychological or sociological implications of professors encouraging such mindset within their students.

But, what it generally does in the long term is pit the interest of professors against that of society.
3.7 / 5 (3) Jan 07, 2014
omitting and not publishing pertinent information were used.

No, editing papers is what journals do. It's not hiding anything, they didn't want to publish it so they don't have to.

And intentionally modifying images

No again. That's not hiding things. When you arrange an image like that as a nice picture you are trying to not over saturate anything and leave it as nice as possible. That is an image for aesthetic purposes, it is not scientific publication. It's not modified. A "connecting stream" does not prove connection.
Note that the mainstream view is maintained. Standard cosmology demands that the higher redshift object be in the background and hence if there is any material on top of it from the lower redshift galaxy you will see absorption lines at the lower redshift, demonstrating it is not in front. That is what was observed. Standard cosmology made a prediction it was confirmed. Arp's claims of it being 90% in front are conjecture, not fact.
3.7 / 5 (3) Jan 07, 2014
Those of us who have spent time reading through transcripts of the Bad Astronomy and Universe Today forum...

Should actually pay attention to scientific literature, where the actual scientific debate is.

You claim people repeat dogma but you engage scientific criticism with completely unscientific criticisms which have nothing to do with astronomy. You choose not to engage in technical debate but instead opinion on the current state of mind.

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