Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

High-energy astrophysics puzzle

24.04.2013
Blazars are the brightest of active galactic nuclei, and many emit very high-energy gamma rays. New observations of a blazar known as PKS 1424+240 show that it is the most-distant known source of very high-energy gamma rays. But its emission spectrum appears highly unusual.

A team including Carnegie's Michele Fumagalli used data from the Hubble Space Telescope to set a lower limit for the blazar's redshift (z ¡Ý 0.6035). An object's redshift value is a measurement of how much the wavelength of the light from it that reaches Earth is stretched by the expansion of the Universe.

Thus, it reveals the object's age and distance. This blazar's redshift corresponds to a distance of at least 7.4 billion light-years. Their work will be published by The Astrophysical Journal and is available online.

Over such a great distance, a substantial proportion of the gamma rays should be absorbed by the extragalactic background light, but calculations that account for the expected absorption yield an unexpected emission spectrum for the blazar.

"We're seeing an extraordinarily bright source that does not display the characteristic emission expected from a very high-energy blazar," said lead author Amy Furniss, University of California Santa Cruz.

The findings may indicate something new about the emission mechanisms of blazars, the extragalactic background light, or the propagation of gamma-ray photons over long distances. It was not thought that such high-energy gamma-ray sources could be seen at such great distances. The research should allow scientists to better understand cosmological models that predict the extragalactic background light.

The extragalactic background light (EBL) is the diffuse radiation from all stars and galaxies, a dim but pervasive glow that fills the universe. When a high-energy gamma-ray photon collides with a lower-energy EBL photon, they annihilate and create an electron-positron pair. The farther gamma rays have to travel, the more likely they are to be absorbed by this mechanism. This limits the distance to which sources of very high-energy gamma rays can be detected.

Measuring the EBL directly is extremely difficult because there are so many bright sources of light in our immediate neighborhood. In addition to estimates based on cosmological models, astronomers have used galaxy counts to set a lower limit for the EBL. Using a model close to this lower limit to calculate the expected absorption of very high-energy gamma rays from PKS 1424+240, the team derived an intrinsic gamma-ray emission spectrum for the blazar. The results, however, deviate from the expected emission based on current blazar models, which are thought to result from a relativistic jet of particles powered by matter falling onto a supermassive black hole at the center of the host galaxy.

Gamma rays from PKS 1424+240 were first detected by the Fermi Gamma-ray Space Telescope and subsequently by the ground-based instrument VERITAS (Very Energetic Radiation Imaging Telescope Array System), which is sensitive to gamma-rays in the very high-energy (VHE) band from about 100 GeV to more than 10 TeV. To determine the redshift of the blazar--a measure of how much the light from an object has been stretched to longer wavelengths by the expansion of the universe--the researchers used archival data obtained by the Hubble Space Telescope.

The other co-authors on the paper are David Williams, J. Xavier Prochaska, Joel Primack, also of UCSC; Charles Danforth and John Stocke of the University of Colorado; Meg Urry of Yale University; Alex Filippenko of UC Berkeley; and William Neely of the NF/ Observatory.

Support was provided by NASA awarded through grants from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA; the National Science Foundation award PHY-0970134; NASA grants NNX08AC146 and NAS5-98043 to the University of Colorado at Boulder ; NASA/Fermi grants GO-31089 and NNX12AF12GA; NSF grant AST-1211916; the Christopher R. Redlich Fund; the TABASGO Foundation; and NASA Hubble Fellowship grant HF-51305.01-A.

KAIT and its ongoing operation were made possible by donations from Sun Microsystems, Inc., the Hewlett-Packard Company, AutoScope Corporation, Lick Observatory, the NSF, the University of California, the Sylvia & Jim Katzman Foundation and the TABASGO Foundation.

The Carnegie Institution for Science is a private, nonprofit organization headquartered in Washington, D.C., with six research departments throughout the U.S. Since its founding in 1902, the Carnegie Institution has been a pioneering force in basic scientific research. Carnegie scientists are leaders in plant biology, developmental biology, astronomy, materials science, global ecology, and Earth and planetary science.

Michele Fumagalli | EurekAlert!
Further information:
http://www.carnegiescience.edu

More articles from Physics and Astronomy:

nachricht Breakthrough with a chain of gold atoms
17.02.2017 | Universität Konstanz

nachricht New functional principle to generate the „third harmonic“
16.02.2017 | Laser Zentrum Hannover e.V.

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

Switched-on DNA

20.02.2017 | Materials Sciences

Second cause of hidden hearing loss identified

20.02.2017 | Health and Medicine

Prospect for more effective treatment of nerve pain

20.02.2017 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>