As we learn more about cosmic rays, it becomes clear that these incoming particles — protons and electrons accelerated to high energy levels — do not reach us uniformly. Just a few days ago we saw that the ATIC (Advanced Thin Ionization Calorimeter) experiment had revealed a source of cosmic rays relatively close to the Earth. Now the Milagro Gamma-Ray Observatory, based at Los Alamos National Laboratory, has found two such cosmic ray ‘hot spots.’ Again we are looking at a source of high energy cosmic rays not terribly far (in galactic terms) from our planet.
Jordan Goodman (University of Maryland) is principal investigator for Milagro:
“These two results may be due to the same, or different, astrophysical phenomenon. However, they both suggest the presence of high-energy particle acceleration in the vicinity of the earth. Our new findings point to general locations for the localized excesses of cosmic-ray protons observed with the Milagro observatory.”
Milagro has been monitoring the entire northern hemisphere sky since 2000, recording over 200 billion cosmic ray collisions with the atmosphere. Such collisions create a shower of secondary particles that reach the surface, collisions now observed in sufficient numbers for the Milagro collaboration to see statistical peaks like the two most recently observed. The results are intriguing because the magnetic field of the Milky Way deflects cosmic rays, making it difficult to pin down their source. Now we see peaks that imply sources closer to our planet.
Image: An international team of researchers, using Los Alamos National Laboratory’s Milagro observatory, has seen for the first time two distinct hot spots that appear to be bombarding Earth with an excess of cosmic rays. The hot spots were identified in the two red-colored regions near the constellation Orion. Credit: John Pretz.
So what is the source of these phenomena? And why are these peaks found to be stronger in winter than in summer? All we can say at present is that they raise more questions than they answer, including the issue of how cosmic rays originate, and the more immediate question of whether the Solar System’s movements through the interstellar medium may have something to do with how they arrive. That latter issue points out how little we know about the heliosphere, and how much we could use a dedicated mission to this distant region. Note this, which I’m drawing from an article on the American Physical Society site by Karl-Heinz Kampert (University of Wuppertal, Germany):
Some clues may come from the actual sky position of the hot spots… The Milagro team noticed a directional coincidence of the stronger of the two hot spots with the heliotail. The heliotail is located in the direction opposite to the motion of the solar system with respect to the local interstellar medium (ISM), but there is no model of cosmic-ray acceleration in this region, so it may be purely coincidental.
Yes, and there’s also the fact that the hot spots encompass the Geminga pulsar that resulted from a relatively nearby supernova. Are the hot spots related to the supernova event, or is there some other acceleration mechanism nearby that can account for the high energies of these cosmic rays? We need more data. The Tibet Air Shower Gamma Array experiment has collected a huge amount of data (more than Milagro), within which are clues to what may be another cosmic ray ‘hot spot’ near Cygnus. As Kampert notes, getting the data from these teams together for refinement is a logical next step.
The paper is Abdo et al., “Discovery of localized regions of excess 10-TeV cosmic rays,” Physical Review Letters 101, 221101 (24 November, 2008). Abstract available. The Kampert article is “Puzzling Hot Spots in the Cosmic-Ray Sky,” Physics 1, 37 (2008), available online.
Addendum: Dennis Overbye discusses the ATIC findings, among other results, in this New York Times article, looking at them in the context of a possible dark matter signature.
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Hmm. Considering the angular size of those hot spots I have to wonder if the distance isn’t at the low end of estimates. Imagine if they are at a sub-stellar distance. Resolution is poor but if they were less than 1 ly from us the distance may be determinable using parallax. Now that would be exciting. It would also be a particularly worthwhile target for a solar sail test mission since the travel time becomes almost reasonable.
Researchers find evidence for the origin of cosmic rays
June 30, 2009 | 7:00 am
Studies of supernova remnant RCW 86 have revealed the origin of cosmic rays.
(Image courtesy of ESO/E. Helder and NASA/Chandra.)
An international team of researchers has discovered strong evidence that extremely energetic cosmic rays are born in supernova remnants.
“Cosmic rays constantly bombard the earth’s atmosphere but, until now, we didn’t have proof of where in our galaxy they originated,” said co-author Stefan Funk of the Kavli Institute for Particle Astrophysics and Cosmology at SLAC National Accelerator Laboratory.
“That’s because cosmic rays are almost entirely made of protons, which as charged particles are bent by magnetic forces as they travel to Earth. So we can’t just trace a straight line back to know where they originated, like we can with light.”
Instead, the researchers traced the sources of cosmic rays by indirect means.
Full article here:
A Galactic Cosmic-Ray Database
Authors: A. W. Strong, I. V. Moskalenko
(Submitted on 3 Jul 2009)
Abstract: Despite a century of cosmic-ray measurements there seems to have been no attempt to collect these data systematically for use by the CR community. The result is that everyone makes their own collection as required, a large duplication of effort.
Therefore we have started a project to place published Galactic CR measurements in a database available online. It currently addresses energies up to 100 TeV, including elemental spectra, secondary/primary nuclei ratios, antiprotons, electrons and positrons.
It is updated regularly as data appears in the literature. It is supported by access software. The community is encouraged to participate by providing data, pointing out errors or omissions, and suggestions for improvements.
Comments: Contribution to the 31st ICRC, Lodz, Poland, July 2009. Paper ID 0626
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:0907.0565v1 [astro-ph.HE]
From: Andrew Strong [view email]
[v1] Fri, 3 Jul 2009 08:58:42 GMT (55kb)
Simulation of the Cosmic Ray Moon Shadow in the Geomagnetic field
Authors: G. Di Sciascio, R. Iuppa (INFN, Sezione Roma Tor Vergata and Dipartimento di Fisica, Universita’ Roma Tor Vergata, Rome – Italy)
(Submitted on 7 Jul 2009)
Abstract: An accurate MonteCarlo simulation of the deficit of primary cosmic rays in the direction of the Moon has been developed to interpret the observations reported in the TeV energy region until now. Primary particles are propagated trough the geomagnetic field in the Earth-Moon system. The algorithm is described and the contributions of the detector resolution and of the geomagnetic field are disentangled.
Comments: 4 pages, 5 figures, Contribution to the 31st ICRC, Lodz, Poland, July 2009
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)
Cite as: arXiv:0907.1173v1 [astro-ph.HE]
From: Giuseppe Di Sciascio [view email]
[v1] Tue, 7 Jul 2009 09:37:46 GMT (203kb)
Desperatly need cumulative energy absorbed by this earth,
data by date , but cumulative
OK to split data out by convenient energy levels,
but need a total.
And I really don’t think that putting H2O and CO2 in upper atmosphere is going to
accomplidh anything good , unless you can remove with it
to some other planet immediately, if not sooner