NASA's Fermi Mission, Namibia's HESS Telescopes Explore a Blazar

March 19, 2009

An international team of astrophysicists using telescopes on the ground and in space have uncovered surprising changes in radiation emitted by an active galaxy. The picture that emerges from these first-ever simultaneous observations with optical, X-ray and new-generation gamma-ray telescopes is much more complex than scientists expected and challenges current theories of how the radiation is generated.

The galaxy in question is PKS 2155-304, a type of object known as a "blazar." Like many active galaxies, a blazar emits oppositely directed jets of particles traveling near the speed of light as matter falls into a central supermassive black hole; this process is not well understood. In the case of blazars, the galaxy is oriented such that we're looking right down the jet.

PKS 2155-304 is located 1.5 billion light-years away in the southern constellation of Piscis Austrinus and is usually a detectable but faint gamma-ray source. But when its jet undergoes a major outburst, as it did in 2006, the galaxy can become the brightest source in the sky at the highest gamma-ray energies scientists can detect -- up to 50 trillion times the energy of visible light. Even from strong sources, only about one gamma ray this energetic strikes a square yard at the top of Earth's atmosphere each month.

Atmospheric absorption of one of these gamma rays creates a short-lived shower of subatomic particles. As these fast-moving particles rush through the atmosphere, they produce a faint flash of blue light. The High Energy Stereoscopic System (H.E.S.S), an array of telescopes located in Namibia, captured these flashes from PKS 2155-304.

Gamma rays at lower energies were detected directly by the Large Area Telescope (LAT) aboard NASA's orbiting Fermi Gamma-ray Space Telescope. "The launch of Fermi gives us the opportunity to measure this powerful galaxy across as many wavelengths as possible for the first time," says Werner Hofmann, spokesperson for the H.E.S.S. team at the Max-Planck Institute for Nuclear Physics in Heidelberg, Germany.

With the gamma-ray regime fully covered, the team turned to NASA's Swift and Rossi X-ray Timing Explorer (RXTE) satellites to provide data on the galaxy's X-ray emissions. Rounding out the wavelength coverage was the H.E.S.S. Automatic Telescope for Optical Monitoring, which recorded the galaxy's activity in visible light.

Between August 25 and September 6, 2008, the telescopes monitored PKS 2155-304 in its quiet, non-flaring state. The results of the 12-day campaign are surprising. During flaring episodes of this and other blazars, the X- and gamma-ray emission rise and fall together. But it doesn't happen this way when PKS 2155-304 is in its quiet state -- and no one knows why.

What's even stranger is that the galaxy's visible light rises and falls with its gamma-ray emission. "It's like watching a blowtorch where the highest temperatures and the lowest temperatures change in step, but the middle temperatures do not," says Berrie Giebels, an astrophysicist at France's École Polytechnique who works with both the H.E.S.S. and Fermi LAT teams.

"Astronomers are learning that the various constituents of the jets in blazars interact in fairly complicated ways to produce the radiation that we observe," says Fermi team member Jim Chiang at Stanford University, Calif. "These observations may contain the first clues to help us untangle what's really going on deep in the heart of a blazar."

The findings have been submitted to The Astrophysical Journal.

The H.E.S.S. team includes scientists from Germany, France, the United Kingdom, Poland, the Czech Republic, Ireland, Armenia, South Africa and Namibia. The Fermi mission is an astrophysics and particle physics partnership, developed by NASA in collaboration with the U.S. Department of Energy, along with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden, and the United States.

NASA's Goddard Space Flight Center

---

---

	The Effect of Gamma Rays on Man-in-the-Moon Marigolds by Paul Zindel (Author) The old, converted vegetable shop where Tillie lives is more like a madhouse than a home. Tillie's mother, Beatrice, is bitter and cruel, yet desperate for her daughters' love. Her sister, Ruth, suffers epileptic fits and sneaks cigarettes every chance she gets. In the midst of chaos, Tillie struggles to keep her focus and dreams alive. Tillie -- keeper of rabbits, dreamer of atoms, true believer in life, hope, and the effect of gamma rays on man-in-the-moon marigolds.
	Milkshakes and Gamma Rays Milkshakes and Gamma Rays is a humorous tale centered around a dramatic week in the lives of Brie Gable and her spirited new friend Naomi "Star Flower" Minami. They are intelligent, opinionated high school juniors who divide their free time between chilling out, flirting with trouble, and philosophizing about the issues of the day. Each is a new transfer student to St. Margaret's, a private school in California. They are living in present day America, but in a divergent timeline, where public education has been eliminated, there's a civil war in Nevada, privacy is on the decline, peculiar brands of moralism are taking hold, and things are getting a little crazy all around. The book is a little over 50,000 words long, and contains occasional adult language. A sequel...
	What Are Gamma-Ray Bursts? (Princeton Frontiers in Physics) by Joshua S. Bloom (Author) Gamma-ray bursts are the brightest--and, until recently, among the least understood--cosmic events in the universe. Discovered by chance during the cold war, these evanescent high-energy explosions confounded astronomers for decades. But a rapid series of startling breakthroughs beginning in 1997 revealed that the majority of gamma-ray bursts are caused by the explosions of young and massive stars in the vast star-forming cauldrons of distant galaxies. New findings also point to very different origins for some events, serving to complicate but enrich our understanding of the exotic and violent universe. What Are Gamma-Ray Bursts? is a succinct introduction to this fast-growing subject, written by an astrophysicist who is at the forefront of today's research into these incredible cosmic...
	Practical Gamma-ray Spectroscopy by Gordon Gilmore (Author) The Second Edition of Practical Gamma-Ray Spectrometry has been completely revised and updated, providing comprehensive coverage of the whole gamma-ray detection and spectrum analysis processes. Drawn on many years of teaching experience to produce this uniquely practical volume, issues discussed include the origin of gamma-rays and the issue of quality assurance in gamma-ray spectrometry. This new edition also covers the analysis of decommissioned nuclear plants, computer modelling systems for calibration, uncertainty measurements in QA, and many more topics.
	Technology and Law Enforcement: From Gumshoe to Gamma Rays by Robert L. Snow (Author) Although for much of the mid-20th century police departments across the U.S. had been reluctant to embrace new technology, depending instead on traditional police techniques, detectives in Los Angeles finally departed from this practice when they found themselves stymied in their attempts to solve the infamous Night Stalker serial murder case. This murderer and rapist had gone on a deadly rampage during the spring and summer of 1985, and though the police used every traditional police technique, they could not solve the crime. Finally, in desperation, they decided to do something different: use what was then the latest, cutting edge-technology. This new technology, the laser print finder, worked perfectly and the police arrested the Night Stalker the next day. Following this astonishing...
	Exploding Superstars: Understanding Supernovae and Gamma-Ray Bursts (Springer Praxis Books / Popular Astronomy) by Alain Mazure (Author), Stéphane Basa (Author) The exceptional cosmic history and the fabulous destinies of exploding stars – supernovae and gamma-ray bursters – are highly fertile areas of research and are also very special tools to further our understanding of the universe. In this book, cosmologists Dr Alain Mazure and Dr Stéphane Basa throw light on the assemblage of facts, hypotheses and cosmological conclusions and show how these ‘beacons’ illuminate their immediate surroundings and allow us to study the vast cosmos, like searchlights revealing the matter comprising our universe.
	The Effect of Gamma Rays on Man in the Moon Marigolds : A Unit Plan (LitPlans) by Marion B. Hoffman (Author) LitPlans are manuals full of materials for teaching specific novels and plays. Each LitPlan is written to go with a particular book title and contains study questions, quizzes, writing assignments, discussion questions, unit tests, vocabulary worksheets, daily lesson plans, group and individual assignments and activities, worksheets, games, puzzles, bulletin board ideas, written objectives for the guide and each lesson, and more. The lessons can be used as planned or teachers may use the materials provided in other ways. Number of pages in the LitPlans varies depending on the length and complexity of the book being taught, but ranges from 100-250 pages.
	Gamma-Ray Bursts: The brightest explosions in the Universe (Springer Praxis Books / Astronomy and Planetary Sciences) by Gilbert Vedrenne (Author), Jean-Luc Atteia (Author) Since their discovery was first announced in 1973, gamma-ray bursts (GRBs) have been among the most fascination objects in the universe. While the initial mystery has gone, the fascination continues, sustained by the close connection linking GRBs with some of the most fundamental topics in modern astrophysics and cosmology. Both authors have been active in GRB observations for over two decades and have produced an outstanding account on both the history and the perspectives of GRB research.
	Gamma-Ray and Electron Spectroscopy in Nuclear Physics (Oxford Studies in Nuclear Physics) by H. Ejiri (Author), M. J. A. de Voigt (Author) This book introduces graduate students to the gamma-ray and conversion-electron spectroscopic methods, which have shed new light on nuclear structure and reaction mechanisms. The simplicity and familiarity of the electromagnetic interaction involved gives accurate values for many nuclear quantities, and both static and dynamic properties can be investigated over a wide range of excitation energies. More experienced nuclear physicists will benefit by the book's review of recent developments in the field, including the development of new experimental techniques such as gamma-detector assemblies, electron spectrometers, and measurements of electromagnetic moments. The book is distinguished by a careful balance between the presentation of theoretical concepts and experimental methods.
	The Effect of Gamma Rays on Man-in-the-Moon Marigolds by Paul Zindel (Author)