Featured Research

from universities, journals, and other organizations

Distant blazar is a high-energy astrophysics puzzle

Date:
April 18, 2013
Source:
University of California - Santa Cruz
Summary:
Blazars are the brightest of active galactic nuclei, and many emit very high-energy gamma rays. New observations of the 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 now appears highly unusual in light of the new data.

Artist's concept of the Hubble Space Telescope viewing ultraviolet light from the jet of the active galactic nucleus of PKS 1424+240. Clouds of hydrogen gas along the line of sight absorb the light at known frequencies, allowing the redshift and distance of each cloud to be determined. The most distant gas cloud determines the minimum distance to PKS 1424+240. Data from the Fermi Gamma-ray Space Telescope, shown on the horizon at the left, were also used for this study. (
Credit: Image composition by Nina McCurdy, component images courtesy of NASA

Blazars are the brightest of active galactic nuclei, and many emit very high-energy gamma rays. New observations of the 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 now appears highly unusual in light of the new data.

A team led by physicists at the University of California, Santa Cruz, used data from the Hubble Space Telescope to set a lower limit for the blazar's redshift (z ≥ 0.6035), which corresponds to a distance of at least 7.4 billion light-years. 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 which does not display the characteristic emission expected from a very high-energy blazar," said Amy Furniss, a graduate student at the Santa Cruz Institute for Particle Physics (SCIPP) at UCSC and first author of a paper describing the new findings. The paper has been accepted for publication in Astrophysical Journal Letters.

Coauthor David Williams, adjunct professor of physics at UC Santa Cruz, said 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.

"We're finding very high-energy gamma-ray sources at greater distances than we thought we might, and in doing so we're finding some things we don't entirely understand," Williams said. "Having a source at this distance will allow us to better understand how much background absorption there is and test the 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 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, Furniss derived an intrinsic gamma-ray emission spectrum for the blazar. The results, however, deviate from the expected emission based on current blazar models.

Blazar emission is 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. "There may be something going on in the emission mechanisms of the blazar that we don't understand," Williams said. "There are more exotic explanations as well, but it may be premature to speculate at this point."

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 data obtained by the Hubble Space Telescope's Cosmic Origins Spectrograph for another research program.

In addition to Furniss and Williams, the coauthors of the paper include J. Xavier Prochaska, professor of astronomy and astrophysics at UCSC; Joel Primack, professor of physics at UCSC; Michele Fumagalli, a former UCSC graduate student now at Carnegie Observatories and Princeton University; Charles Danforth and John Stocke at the University of Colorado; Meg Urry at Yale University; Alex Filippenko at UC Berkeley; and William Neely at the NF/ Observatory.


Story Source:

The above story is based on materials provided by University of California - Santa Cruz. The original article was written by Tim Stephens. Note: Materials may be edited for content and length.


Journal Reference:

  1. A. Furniss, D. A. Williams, C. Danforth, M. Fumagalli, J. X. Prochaska, J. Primack, C. M. Urry, J. Stocke, A. V. Filippenko, W. Neely. The Firm Redshift Lower Limit of the Most Distant TeV-Detected Blazar PKS 1424 240. Astrophysical Journal Letters, 2013 [link]

Cite This Page:

University of California - Santa Cruz. "Distant blazar is a high-energy astrophysics puzzle." ScienceDaily. ScienceDaily, 18 April 2013. <www.sciencedaily.com/releases/2013/04/130418125746.htm>.
University of California - Santa Cruz. (2013, April 18). Distant blazar is a high-energy astrophysics puzzle. ScienceDaily. Retrieved July 23, 2014 from www.sciencedaily.com/releases/2013/04/130418125746.htm
University of California - Santa Cruz. "Distant blazar is a high-energy astrophysics puzzle." ScienceDaily. www.sciencedaily.com/releases/2013/04/130418125746.htm (accessed July 23, 2014).

Share This




More Space & Time News

Wednesday, July 23, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Raw: Cargo Craft Undocks from Space Station

Raw: Cargo Craft Undocks from Space Station

AP (July 22, 2014) A Russian Soyuz cargo-carrying spacecraft undocked from the International Space Station on Monday. The craft is due to undergo about ten days of engineering tests before it burns up in the Earth's atmosphere. (July 22) Video provided by AP
Powered by NewsLook.com
NASA Ceremony Honors Moon Walker Neil Armstrong

NASA Ceremony Honors Moon Walker Neil Armstrong

AP (July 21, 2014) NASA honored one of its most famous astronauts Monday by renaming a historic building at the Kennedy Space Center in Florida. It now bears the name of Neil Armstrong, the first man to walk on the moon. (July 21) Video provided by AP
Powered by NewsLook.com
Neil Armstrong's Post-Apollo 11 Life

Neil Armstrong's Post-Apollo 11 Life

Newsy (July 19, 2014) Neil Armstrong gained international fame after becoming the first man to walk on the moon in 1969. But what was his life like after the historic trip? Video provided by Newsy
Powered by NewsLook.com
This Week @ NASA, July 18, 2014

This Week @ NASA, July 18, 2014

NASA (July 18, 2014) Apollo 11 yesterday, Next Giant Leap tomorrow, Science instruments for Europa mission, and more... Video provided by NASA
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins