Fermi telescope finds gamma-ray galaxy surprises

Jul 14, 2009
This artist's concept shows the core of an active galaxy, where a feeding supermassive black hole drives oppositely directed particle jets. Credit: ESA/NASA/AVO/Paolo Padovani

Back in June 1991, just before the launch of NASA's Compton Gamma-Ray Observatory, astronomers knew of gamma rays from exactly one galaxy beyond our own. To their surprise and delight, the satellite captured similar emissions from dozens of other galaxies. Now its successor, the Fermi Gamma-ray Space Telescope, is filling in the picture with new finds of its own.

"Compton showed us that two classes of active galaxies emitted gamma rays -- blazars and radio galaxies," said Luigi Foschini at Brera Observatory of the National Institute for Astrophysics in Merate, Italy. "With Fermi, we've found a third -- and opened a new window in the field."

In the Beam

Active galaxies are those with unusually bright centers that show evidence of particle acceleration to speeds approaching that of light itself. In 1943, astronomer Carl Seyfert described the first two types of active galaxy based on the width of spectral lines, a tell-tale sign of rapid gas motion in their cores. Today, astronomers recognize many additional classes, but they now believe these types represent the same essential phenomenon seen at different viewing angles.

At the center of each active galaxy sits a feeding black hole weighing upwards of a million times the sun's mass. Through processes not yet understood, some of the matter headed for the black hole blasts outward in fast, oppositely directed particle jets. For the most luminous active-galaxy classes -- blazars -- astronomers are looking right down the particle beam.

Using Fermi's Large Area Telescope (LAT), Foschini and his colleagues detected gamma rays from a Seyfert 1 galaxy cataloged as PMN J0948+0022, which lies 5.5 billion light-years away in the constellation Sextans. Splitting the light from this source into its component colors shows a spectrum with narrow lines, which indicates slower gas motions and argues against the presence of particle jet.

"But, unlike ninety percent of narrow-line Seyfert 1 galaxies, PMN J0948 also produces strong and variable radio emission," said Gino Tosti, who leads the Fermi LAT science group studying active galaxies at the University and National Institute of Nuclear Physics in Perugia, Italy. "This suggested the galaxy was indeed producing such a jet."

"The gamma rays seen by Fermi's LAT seal the deal," said team member Gabriele Ghisellini, a theorist at Brera Observatory. "They confirm the existence of particle acceleration near the speed of light in these types of galaxies." The findings will appear in the July 10 issue of The Astrophysical Journal.

"We are sifting through Fermi LAT data for gamma rays from more sources of this type," Foschini said. "And we've begun a multiwavelength campaign to monitor PMN J0948 across the spectrum, from radio to gamma rays."

Flare Up

Another case where Fermi sees something new involves NGC 1275, a massive Seyfert galaxy much closer to home. Also known as Perseus A, one of the sky's loudest radio sources, NGC 1275 lies at the center of the Perseus cluster of about 225 million light-years away.

The Compton observatory's high-energy EGRET instrument never detected gamma rays from NGC 1275, although it was detected by another instrument sensitive to lower-energy gamma rays. But Fermi's LAT clearly shows the galaxy to be a gamma-ray source at the higher energies for which EGRET was designed. "Fermi sees this galaxy shining with gamma rays at a flux about seven times higher than the upper limit of EGRET," said Jun Kataoka at Waseda University in Tokyo. "If NGC 1275 had been this bright when EGRET was operating, it would have been seen."

This change in the galaxy's output suggests that its particle beam was either inactive or much weaker a decade ago. Such changes clue astronomers into the size of the emitting region. "The in NGC 1275 must arise from a source no more than two light-years across," said Teddy Cheung at NASA's Goddard Space Flight Center in Greenbelt, Md. "That means we're seeing radiation from the heart of the galaxy -- near its black hole -- as opposed to emission by hot gas throughout the cluster."

The Fermi team plans to monitor the galaxy to watch for further changes. The results of the study will appear in the July 1 issue of The Astrophysical Journal.

Source: NASA/Goddard Space Flight Center

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yyz
5 / 5 (1) Jul 15, 2009
Fascinating story, especially the inferred size limit of the supermassive black hole at the center of NGC 1275. My guess is that Fermi may further constrain the size of this relatively nearby SMBH (~400 million l.y.)!
omatumr
1 / 5 (5) Jul 15, 2009
STILL MORE MYSTERIES?

Astronomical observation will always be a "mystery" to astrophysicists who refuse to consider the information recorded in nuclear rest mass data. See bottom photo in http://tinyurl.com/m8rxdb

Repulsive interactions between neutrons:
a.) Prevent the formation of Black Holes, and
b.) Energize galactic and stellar centers.

[Journal of Fusion Energy 25 (2006) 107-114]
http://arxiv.org/.../0511051

With kind regards,
Oliver K. Manuel
http://www.omatumr.com
yyz
5 / 5 (1) Jul 15, 2009
It will be interesting in studying these radio loud NLS1 galaxies and will hopefully add to our understanding of SMBHs and NLS1 galaxies.
yyz
5 / 5 (4) Jul 15, 2009
@ omatumr, Once again you present references to your own paper in a vain attempt to 'educate' readers at this site of your 'unique' take on the astrophysics of highly condensed matter (black holes) and neutron stars. Most of your posts repeat similar links to your body of work with few credible papers by other authors that reference your papers!I can't figure out your fanatical adherence to your theories other than that you, among with several others, developed this unsubstantiated theory. Why not submit your work to peer-reviewed astrophysical publications than try to peddle this thing to mostly unknowing readers? I'm talking about peer-reviewed, published papers in relevant astrophysical journals(like ApJ, AJ, A&A, MNRAS or at least Science or Nature). What do you hope to accomplish?
BuckeyeKeel
2.4 / 5 (5) Jul 15, 2009
This passage from the article is a tad concerning:
" '"If NGC 1275 had been this bright when EGRET was operating, it would have been seen."' This change in the galaxy's output suggests that its particle beam was either inactive or much weaker a decade ago."(sorry for the crazy quotation marks)
**Anyways, the (slightly) concerning notion I get from this is that maybe we're, I dunno....coming closer to an 'alignment' of sorts with the main source/direction of these gamma rays? I know this is even more of a stretch, but what would be the result/impact of Earth possibly centering itself relative to this GRsource-in conjunction with our pending centering over the Milky Way center? Could it possibly (God forbid) result in a double-time exposure-to/amount-of GR's? I don't like thinking in such doom-tastic ways, so I'll leave it at that. But I still think my initial comment holds merit, would much appreciate any input on that at least...thanks!
yyz
5 / 5 (2) Jul 16, 2009
@ BuckeyeKeel: I wouldn't fret about being bombarded by gamma-rays if we were directly in line with a jet source. AFAIK, NGC 1275 doesn't exhibit jet activity of any sort. Even if it did, NGC 1275's distance of over 400 million l.y. and the Earth's ozone layer are more than sufficient to shield life here on earth. Blazars (with VHE beams pointed right at us!) exist with a much higher frequency luminosity than that found in NGC 1275. I think you're confusing the high energy of these sources with their extreme distance (neutral hydrogen in the IGM also attenuates gamma-rays from across the universe). Hope some of this makes sense :)