The Fermi Gamma-ray Telescope has found a new class of active galaxies with some of the fastest particles jets ever detected, accelerating particles near the speed of light. Using Fermi’s Large Area Telescope (LAT), astronomers 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. Previously, it was know that two classes of active galaxies emitted gamma rays – blazars and radio galaxies. “With Fermi, we’ve found a third — and opened a new window in the field, “said Luigi Foschini at Brera Observatory of the National Institute for Astrophysics in Merate, Italy.
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.
Foschini and his team split the light from PMN J0948 into its component colors, showing a spectrum with narrow lines, which indicated slower gas motions, arguing 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.”