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 Seeing the quantum future... literally
16.01.2017 | University of Sydney

nachricht Airborne thermometer to measure Arctic temperatures
11.01.2017 | Moscow Institute of Physics and Technology

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: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

Im Focus: How to inflate a hardened concrete shell with a weight of 80 t

At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).

Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...

Im Focus: Bacterial Pac Man molecule snaps at sugar

Many pathogens use certain sugar compounds from their host to help conceal themselves against the immune system. Scientists at the University of Bonn have now, in cooperation with researchers at the University of York in the United Kingdom, analyzed the dynamics of a bacterial molecule that is involved in this process. They demonstrate that the protein grabs onto the sugar molecule with a Pac Man-like chewing motion and holds it until it can be used. Their results could help design therapeutics that could make the protein poorer at grabbing and holding and hence compromise the pathogen in the host. The study has now been published in “Biophysical Journal”.

The cells of the mouth, nose and intestinal mucosa produce large quantities of a chemical called sialic acid. Many bacteria possess a special transport system...

Im Focus: Newly proposed reference datasets improve weather satellite data quality

UMD, NOAA collaboration demonstrates suitability of in-orbit datasets for weather satellite calibration

"Traffic and weather, together on the hour!" blasts your local radio station, while your smartphone knows the weather halfway across the world. A network of...

Im Focus: Repairing defects in fiber-reinforced plastics more efficiently

Fiber-reinforced plastics (FRP) are frequently used in the aeronautic and automobile industry. However, the repair of workpieces made of these composite materials is often less profitable than exchanging the part. In order to increase the lifetime of FRP parts and to make them more eco-efficient, the Laser Zentrum Hannover e.V. (LZH) and the Apodius GmbH want to combine a new measuring device for fiber layer orientation with an innovative laser-based repair process.

Defects in FRP pieces may be production or operation-related. Whether or not repair is cost-effective depends on the geometry of the defective area, the tools...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

Nothing will happen without batteries making it happen!

05.01.2017 | Event News

 
Latest News

Multiregional brain on a chip

16.01.2017 | Power and Electrical Engineering

New technology enables 5-D imaging in live animals, humans

16.01.2017 | Information Technology

Researchers develop environmentally friendly soy air filter

16.01.2017 | Power and Electrical Engineering

VideoLinks
B2B-VideoLinks
More VideoLinks >>>