Interesting to see how quickly the story on high-energy galactic cosmic rays has shifted in the past week. Recent work at the Pierre Auger Observatory in Argentina pointed strongly to the centers of active galaxies, where supermassive black holes are found, as the likely source. These Active Galactic Nuclei (AGN) stood out in analysis of the 27 highest energy events recorded at the Auger site because known AGNs seemed to correlate (in terms of direction) with the incoming cosmic rays.
In any case, the idea that these tortured galactic centers could be the source made obvious and intuitive sense. But is the origin of these most powerful of cosmic rays — with energies up to 100 x 1018 electronvolts — now understood, or is it just a statistical correlation that won’t stand up to continued scrutiny? The University of Utah-based High Resolution Fly’s Eye (HiRes) collaboration has been trying to check the correlation based on events in northern hemisphere skies. And here’s the gist, as reported by Katherine Sanderson in an article on nature news:
[HiRes] has tried to check this conclusion against data from ultra-high-energy cosmic-ray events they detected in the northern sky. The researchers used the Auger team’s parameters for factors such as the maximum distance of the active galactic nuclei from Earth and the maximum angle the ray will be bent by interactions with magnetic fields, and looked to see whether the active galactic nuclei could also explain their events. Their results suggest that they don’t.
“They see correlations, we do not see correlations,” says Gordon Thomson, one of the HiRes collaborators. Only 2 of the 13 events looked at by the HiRes team correlated with active galactic nuclei.
Although this first check on the Auger findings hasn’t been published yet, we already seem to be in familiar territory. Cosmic rays have taken us down many a crooked path in the past. Whether HiRes is on to something may depend on whether their dataset and Auger’s are comparable, given that HiRes seems to have few events in the highest-energy range. But we won’t know more about the specifics until the paper appears. Even if Auger is eventually confirmed, the deeper question remains: How does even an AGN produce the accelerations needed to produce these cosmic rays? That question should continue to confound us no matter where in the sky we trace the origin of these mysterious high-energy particles.
If the AGN’s turn out not to be the engine then what other would suffice? Very interesting, as far as speculation at least.
Good question. The article quotes Trevor Weekes, a cosmic-ray researcher with the Harvard-Smithsonian Center for Astrophysics: “If it’s not active galactic nuclei, says Weekes, ‘we have no idea’ what the source is.”
Gregory Benford and Raymond Protheroe proposed that large persistent magnetic structures in intergalactic space could (as they decay) produce electric fields that accelerate particles to ultrarelativistic energies.
http://space.newscientist.com/article/dn12818
Benford and Protheroe’s ideas are fascinating. More about them here:
https://centauri-dreams.org/?p=1383
Gamma-ray Astronomy
Authors: Jim Hinton (University of Leeds)
(Submitted on 20 Dec 2007)
Abstract: The relevance of gamma-ray astronomy to the search for the origin of the galactic and, to a lesser extent, the ultra-high-energy cosmic rays has long been recognised. The current renaissance in the TeV gamma-ray field has resulted in a wealth of new data on galactic and extragalactic particle accelerators, and almost all the new results in this field were presented at the recent International Cosmic Ray Conference (ICRC). Here I summarise the 175 papers submitted on the topic of gamma-ray astronomy to the 30th ICRC in Merida, Mexico in July 2007.
Comments: 24 pages, 12 figures. Rapporteur talk at the 30th International Cosmic Ray Conference, Merida, Mexico
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:0712.3352v1 [astro-ph]
Submission history
From: Jim Hinton [view email]
[v1] Thu, 20 Dec 2007 09:40:55 GMT (1009kb)
http://arxiv.org/abs/0712.3352
Status and recent results from the Pierre Auger Observatory
Authors: J. R. T. de Mello Neto, for the Pierre Auger Collaboration
(Submitted on 21 Dec 2007)
Abstract: We present the status and the recent measurements from the Pierre Auger Observatory. The energy spectrum will be described and its steepening discussed. The mass composition is addressed with the measurements of the variation of the depth of shower maximum with energy. We also report on upper limits in the primary photon fraction. And finally, searches for anisotropies of cosmic rays arrival directions are reported.
Comments: 4 pages, 2 figures, prepared for the 37th International Symposium on Multiparticle Dynamics, Berkeley, USA, 2007
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:0712.3727v1 [astro-ph]
Submission history
From: Joao de Mello Neto [view email]
[v1] Fri, 21 Dec 2007 15:54:25 GMT (112kb)
http://arxiv.org/abs/0712.3727
Highlights from the Pierre Auger Obseervatory – the birth of the hybrid era
Authors: A. A. Watson
(Submitted on 15 Jan 2008)
Abstract: Highlights from the Pierre Auger Observatory are presented. In particular there is a detailed discussion of of the cosmic ray energy spectrum from 0.3 EeV to 100 EeV and of the mass composition above 1 EeV.
Comments: 12 pages. Based on Highlight Talk at ICRC in Merida, Mexico, July 2007
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:0801.2321v1 [astro-ph]
Submission history
From: Alan Watson [view email]
[v1] Tue, 15 Jan 2008 15:05:31 GMT (496kb)
http://arxiv.org/abs/0801.2321
Lecture notes on high energy cosmic rays
Authors: M. Kachelriess
(Submitted on 29 Jan 2008)
Abstract: I give a concise introduction into high energy cosmic ray physics, including also few related aspects of high energy gamma-ray and neutrino astrophysics. The main emphasis is placed on astrophysical questions, and the level of the presentation is kept basic.
Comments: 82 pages, prepared for the 17th Jyvaskyla Summer School, comments welcome
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:0801.4376v1 [astro-ph]
Submission history
From: Michael Kachelrie{\ss} [view email]
[v1] Tue, 29 Jan 2008 16:44:54 GMT (1097kb)
http://arxiv.org/abs/0801.4376
Fighting to Launch Cosmic-Ray Detector
By Dennis Overbye
February 29, 2008, 8:54 am
Dennis Overbye is a science correspondent for The Times. His most recent book is ‘’Einstein in Love: A Scientific Romance.’’
The Alpha Magnetic Spectrometer. (Photo: Photographs by The AMS Collaboration) In a recent report to Congress (pdf), NASA offered two contradictory statements: a $1.5 billion physics experiment intended for the International Space Station was on track for a 2009 launch, but it had no intention of actually launching the device into space.
Once upon a time the Alpha Magnetic Spectrometer, as it is known, was to be the scientific centerpiece of the space station. By sifting cosmic rays from outer space, the 15,000 pound detector would look for evidence of antimatter or the mysterious dark matter that accounts for 25 percent of creation.
The brainchild of MIT physicist and Nobel laureate Sam Ting, the detector was built by a collaboration of scientists from 16 countries, including China and Taiwan, mostly with their own money. NASA agreed in 1995 to give it a ride to the space station and then reneged 10 years later after the loss of the space shuttle Columbia, saying the remaining flights between now and 2010 when the shuttles are to be retired were all spoken for. This dismayed many physicists who thought the space agency should keep its word and was being a bad international partner.
“It’s a pity that NASA is living up to its commitment to finish the Space Station, but not to its commitment to use it for something scientifically interesting,” said Steven Weinberg, himself a Nobel physicist at the University of Texas, in Austin.
But Dr. Ting has supporters in Congress, including Sen. Bill Nelson, the chairman of the Space, Aeronautics, and Related Sciences Subcommittee who rode the shuttle into space in 1986. In December, he vowed to file legislation adding a shuttle flight for the detector if Michael Griffin, NASA’s administrator did not change his mind.
In a speech on February 8, the day after Atlantis lifted off on the most recent mission to the space station, Sen. Nelson said of Dr. Ting’s experiment, “What it does is it identifies the origin of cosmic rays, and that means it can help us understand the origin of the universe. This is not just an American experiment; this is an international experiment of countries around the world. This is a part of us wanting to understand our beginnings. This is a part of our nature, as a people, to want to explore the heavens and understand the universe.”
Full article here:
http://thelede.blogs.nytimes.com/2008/02/29/fighting-to-launch-cosmic-ray-detector/?hp
Astronomy with ultra high-energy particles
Authors: Joerg R. Hoerandel
(Submitted on 20 Mar 2008)
Abstract: Recent measurements of the properties of cosmic rays above 10^17 eV are summarized and implications on our contemporary understanding of their origin are discussed. Cosmic rays with energies exceeding 10^20 eV have been measured, they are the highest-energy particles in the Universe. Particles at highest energies are expected to be only marginally deflected by magnetic fields and they should point towards their sources on the sky. Recent results of the Pierre Auger Observatory have opened a new window to the Universe – astronomy with ultra high-energy particles.
Comments: to appear in Reviews of Modern Astronomy
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:0803.3040v1 [astro-ph]
Submission history
From: Joerg R. Hoerandel [view email]
[v1] Thu, 20 Mar 2008 19:03:19 GMT (1482kb)
http://arxiv.org/abs/0803.3040
Testing the proposed link between cosmic rays and cloud cover
Authors: T. Sloan, A.W. Wolfendale
(Submitted on 15 Mar 2008)
Abstract: A decrease in the globally averaged low level cloud cover, deduced from the ISCCP infra red data, as the cosmic ray intensity decreased during the solar cycle 22 was observed by two groups. The groups went on to hypothesise that the decrease in ionization due to cosmic rays causes the decrease in cloud cover, thereby explaining a large part of the presently observed global warming. We have examined this hypothesis to look for evidence to corroborate it. None has been found and so our conclusions are to doubt it.
From the absence of corroborative evidence, we estimate that less than 23%, at the 95% confidence level, of the 11-year cycle change in the globally averaged cloud cover observed in solar cycle 22 is due to the change in the rate of ionization from the solar modulation of cosmic rays.
Subjects: Atmospheric and Oceanic Physics (physics.ao-ph); Astrophysics (astro-ph); Physics and Society (physics.soc-ph)
Report number: Lancs-HEP/080309
Cite as: arXiv:0803.2298v1 [physics.ao-ph]
Submission history
From: Terry Sloan [view email]
[v1] Sat, 15 Mar 2008 14:52:30 GMT (36kb)
http://arxiv.org/abs/0803.2298
Discovered: Cosmic Rays from a Mysterious, Nearby Object
11.19.2008
Nov. 19, 2008: An international team of researchers has discovered a puzzling surplus of high-energy electrons bombarding Earth from space. The source of these cosmic rays is unknown, but it must be close to the solar system and it could be made of dark matter. Their results are being reported in the Nov. 20th issue of the journal Nature.
Full article here:
http://science.nasa.gov/headlines/y2008/19nov_cosmicrays.htm