The Iowa State High Energy Gamma Ray Astronomy group has been credited by the American Physical Society for a noteworthy discovery.

Last May, The group observed some of the highest energy gamma ray photons ever detected. They were in an unusually intense, extremely short duration flare coming from Markarian 421, an elliptical galaxy some 400 million light-years from Earth, according to a press release.

Markarian 421 contains an active galactic nucleus, presumed to be driven by a super-massive rotating black hole, the release stated.

The short duration of the flares seen in Markarian 421 implies “the emission region is very small, comparable in size to our solar system.”

“However,” the release also stated, “the energy it emitted is at levels normally associated with whole galaxies.”

But more impressive than the short duration of the Markarian 421 flares is the intensity of their gamma ray emissions and the character of the spectrum of those emissions.

David Carter-Lewis, professor of physics and astronomy and leader of the Iowa State gamma ray astronomy group, said, “The flare is of unprecedented magnitude; it’s a factor of 30 brighter than normal, and a factor of three larger than anything we’ve ever seen.”

Jeff Zweerink, Ph.D. candidate in the physics and astronomy department, was the group member who presented the results at the April 18 meeting of the American Physical Society in Washington D.C.

Zweerink characterized the novelty of their discovery: “What’s news is not only the high intensity, but the fact that we see a spectrum with no absorption.”

Normally, the spectra of intensity of radiation received across a broad range of frequencies for a natural radiation source shows distinct dips, representing frequencies that are absorbed at some point along the radiation’s path of propagation before it reaches the detector.

Zweerink said there are three factors that usually conspire to reduce the radiation flux that they receive from the sources they observe. These are a fall-off of the efficiency of the gamma ray production at high energies, absorption through various mechanisms at the source, and absorption of some kind along the path of travel, he said.

The third factor is particularly important when considering absorption in inter-galactic space, Zweerink said. Intergalactic space is supposed to be filled with infrared radiation, from the billions of thermal energy sources in the billions of galaxies.

“We don’t see any of the absorption in our spectrum,” Zweerink said. “What this means is that there’s not as many infrared photons in intergalactic space as we’ve always thought.”

Zweerink said their spectrum includes photons up to energies of six TeV, for Terra-, or trillion electron-volts. Translated into frequency, this implies photons of electromagnetic radiation representing frequencies of about 10 to the power 27 Hertz, or a million billion trillion cycles per second.

The international team which made the observations using the Whipple Observatory’s 10-meter optical telescope in southern Arizona, as well as the space-based Compton Gamma Ray Observatory, consists of the ISU gamma ray group, as well as researchers from the Smithsonian Astrophysical Observatory, Purdue University, and universities in Ireland and the United Kingdom.