UT: Astronomy On Ice

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UT: Astronomy On Ice

Post by bystander » Sun May 02, 2010 4:55 pm

Astronomy Without A Telescope – Astronomy On Ice
Universe Today - 01 May 2010
Well, here's a bit of a first for AWAT, because this is a story about a telescope. But it's not your average telescope, being composed of a huge chunk of Antarctic ice with a very large cosmic ray muon filter attached to the back of it, which is called the Earth.

Commenced in 2005, the IceCube Neutrino Observatory is now approaching completion with recent installation of a key component DeepCore. With DeepCore, the Antarctic observatory is now able to observe the southern sky, as well as the northern sky.

Neutrinos have no charge and are weakly interactive with other kinds of matter, making them difficult to detect. The method employed by IceCube and by many other neutrino detectors is to look for Cherenkov radiation which, in the context of IceCube, is emitted when a neutrino interacts with an ice atom creating a highly energized charged particle, such as an electron or a muon – which shoots off at a speed greater than the speed of light, at least greater than the speed of light in ice.

The advantage of using Antarctic ice as a neutrino detector is that it is available in large volumes and thousands of years of sedimentary compression has squeezed most impurities out of it, making it a very dense, consistent and transparent medium. So, not only can you see the little flashes of Cherenkov radiation, but you can also make reliable predictions about the trajectory and energy level of the neutrino which caused each little flash
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UWM: IceCube spies unexplained pattern of cosmic rays

Post by bystander » Wed Jul 28, 2010 12:53 am

IceCube spies unexplained pattern of cosmic rays
University of Wisconsin, Madison | 27 July 2010
Though still under construction, the IceCube Neutrino Observatory at the South Pole is already delivering scientific results — including an early finding about a phenomenon the telescope was not even designed to study.
IceCubeSkyMap.PNG
This "skymap," generated in 2009 from data collected by the IceCube
Neutrino Observatory, shows the relative intensity of cosmic rays
directed toward the Earth’s Southern Hemisphere. Researchers from
UW-Madison and elsewhere identified an unusual pattern of cosmic
rays, with an excess (warmer colors) detected in one part of the sky
and a deficit (cooler colors) in another. Credit: IceCube Collaboration

IceCube captures signals of notoriously elusive but scientifically fascinating subatomic particles called neutrinos. The telescope focuses on high-energy neutrinos that travel through the Earth, providing information about faraway cosmic events such as supernovas and black holes in the part of space visible from the Northern Hemisphere.

However, one of the challenges of detecting these relatively rare particles is that the telescope is constantly bombarded by other particles, including many generated by cosmic rays interacting with the Earth's atmosphere over the southern half of the sky. For most IceCube neutrino physicists these particles are simply background noise, but University of Wisconsin-Madison researchers Rasha Abbasi and Paolo Desiati, with collaborator Juan Carlos Díaz-Vélez, recognized an opportunity in the cosmic ray data.

"IceCube was not built to look at cosmic rays. Cosmic rays are considered background," Abbasi says. "However, we have billions of events of background downward cosmic rays that ended up being very exciting."

Abbasi saw an unusual pattern when she looked at a "skymap" of the relative intensity of cosmic rays directed toward the Earth's Southern Hemisphere, with an excess of cosmic rays detected in one part of the sky and a deficit in another. A similar lopsidedness, called "anisotropy," has been seen from the Northern Hemisphere by previous experiments, she says, but its source is still a mystery.

"At the beginning, we didn't know what to expect. To see this anisotropy extending to the Southern Hemisphere sky is an additional piece of the puzzle around this enigmatic effect — whether it's due to the magnetic field surrounding us or to the effect of a nearby supernova remnant, we don't know," Abbasi says.

The new result publishes Aug. 1 in The Astrophysical Journal Letters, published by the American Astronomical Society.
Measurement of the Anisotropy of Cosmic-ray Arrival Directions with IceCube - RU Abbasi et al Analysis of Large-scale Anisotropy of Ultra-high Energy Cosmic Rays in HiRes Data - RU Abbasi et al Galactic Cosmic Ray Anisotropy Origin, Implications and the Role of IceCube | 12 Nov 2009 | P Desiati
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NSF/UWM: World's Largest Neutrino Observatory Completed

Post by bystander » Sun Dec 19, 2010 3:33 pm

NSF / UWM Complete Construction of the World's Largest Neutrino Observatory
National Science Foundation | 17 Dec 2010
Antarctica's IceCube is among the most ambitious scientific construction projects ever attempted.
Culminating a decade of planning, innovation and testing, construction of the world's largest neutrino observatory, installed in the ice of the Antarctic plateau at the geographic South Pole, was successfully completed December 18, 2010, New Zealand time.

The last of 86 holes had been drilled and a total of 5,160 optical sensors are now installed to form the main detector--a cubic kilometer of instrumented ice--of the IceCube Neutrino Observatory, located at the National Science Foundation's Amundsen-Scott South Pole Station.

From its vantage point at the end of the world, IceCube provides an innovative means to investigate the properties of fundamental particles that originate in some of the most spectacular phenomena in the universe.

In the deep, dark, stillness of the Antarctic ice, IceCube records the rare collisions of neutrinos--elusive sub-atomic particles--with the atomic nuclei of the water molecules of the ice. Some neutrinos come from the sun, while others come from cosmic rays interacting with the Earth's atmosphere and dramatic astronomical sources such as exploding stars in the Milky Way and other distant galaxies. Trillions of neutrinos stream through the human body at any given moment, but they rarely interact with regular matter, and researchers want to know more about them and where they come from.

The size of the observatory is important because it increases the number of potential collisions that can be observed, making neutrino astrophysics a reality.
World's largest neutrino observatory completed at South Pole
University of Wisconsin, Madison | 17 Dec 2010
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Re: UT: Astronomy On Ice

Post by neufer » Wed Feb 09, 2011 10:32 pm

http://www.scientificamerican.com/article.cfm?id=ice-cube-antarctica wrote: World's Largest Neutrino Detector Completed at South Pole
With 86 strings of detectors reaching down 2.5 kilometers into Antarctic ice,
the IceCube observatory is now finished
By John Matson | December 23, 2010 | 4

<<Thousands of meters below the ice near the South Pole lies one of the most unusual observatories ever constructed. The instrument's nervous system comprises 86 strands of light detectors, stretching down into the ice sheet like oversize strings of pearls. Each strand features 60 basketball-size detectors, spanning the depths from 1,450 to 2,450 meters below the surface. And the body of the observatory is the ice itself, an abundant medium with an astonishing natural clarity.

Altogether, the instrument, known as IceCube, spans a cubic kilometer of ice. Scientists have for years been taking data using the partially built observatory, but on December 18 the 86th and final string of detectors was lowered into place, marking the completion of construction on the estimated $270-million project. The observatory will likely start running at full strength in April, according to communications manager Laurel Bacqué.

IceCube's task is to watch for energetic neutrinos emanating from violent cosmic events such as supernovae and gamma-ray bursts. Much as gamma-ray and x-ray observatories have already done, IceCube should provide a new layer of observational insight to the highest-energy processes in the universe. For instance, catching the trace of neutrinos from core-collapse supernovae, some of which emit more than 99 percent of their energy in neutrino form, would allow astrophysicists a clearer look into the mechanism by which stars die.

IceCube takes advantage of neutrinos' slipperiness, using Earth as a filter of more interactive particles. From the South Pole the observatory hunts out particles that come barreling out of the northern sky; some strike atoms at Earth, some pass straight through the planet, and a critical few pass nearly all the way through, striking an atom in the last few kilometers of Antarctic ice instead.

When a neutrino does strike an atom in IceCube's cubic-kilometer expanse, it gives off a high-speed burst of charged secondary particles, such as muons, that illuminate the transparent ice with a brief flash of light. IceCube's array of detectors, more than 5,000 in total, can then determine the origin of the neutrino based on the trajectory of the secondary particles. (Northern-sky neutrinos come streaking upward through the detector, from the bedrock toward the surface of the ice.) The beauty of neutrino astronomy is that, being neutral, the particles trace a straight line back to their point of origin.

IceCube can also detect more local neutrinos and muons that originate from cosmic rays striking Earth's atmosphere. Those particles essentially constitute the background that scientists will have to filter out to find distant astrophysical neutrino sources, but they are providing some surprises in their own right. "We already made the totally puzzling observation that an excess of galactic cosmic rays reaches Earth from a spot pointing at Vela, the strongest gamma-ray emitter in the sky," says University of Wisconsin–Madison physicist Francis Halzen, the project's principal investigator. Because cosmic rays are charged, their inbound trajectory should be jumbled by the Milky Way's magnetic field, so any hot spot on the cosmic ray map demands an explanation.

With a full-power observatory in place, that explanation, as well as a better explanation of high-energy astrophysical phenomena throughout the universe, may be available in the years to come. "A great asset of IceCube so far is that we took data as the detector increased in size," Halzen said as the final hole was being drilled. "It will, however, be great to finally have a stable instrument that we can calibrate and fine-tune without any further major changes. So, as soon as the celebration stops, we will start preparing for a long, stable, uninterrupted period of data taking.">>
http://en.wikipedia.org/wiki/IceCube_Neutrino_Observatory wrote:
<<The IceCube Neutrino Observatory (or simply IceCube) is a neutrino telescope constructed at the Amundsen-Scott South Pole Station. Similar to its predecessor, the Antarctic Muon And Neutrino Detector Array (AMANDA), IceCube is being constructed in the deep Antarctic ice by deploying thousands of spherical optical sensors called Digital Optical Modules (DOMs), each with a photomultiplier tube (PMT) and a single board data acquisition computer which sends digital data to the counting house on the surface above the array. IceCube was completed on the 18th December, 2010, New Zealand time.

DOMs are deployed on "strings" of sixty modules each at depths ranging from 1,450 to 2,450 meters, into holes melted in the ice using a hot water drill. IceCube is designed to look for point sources of neutrinos in the TeV range to explore the highest-energy astrophysical processes.

The IceCube project is part of the University of Wisconsin–Madison projects developed and supervised by the same institution, while collaboration and funding is provided by numerous other universities and research institutions worldwide. Construction of IceCube is only possible during the Antarctic austral summer from November to February, when permanent sunlight allows for 24 hour drilling. Construction began in 2005, when the first IceCube string was deployed and collected enough data to verify that the optical sensors worked correctly. In the 2005–2006 season, an additional eight strings were deployed, making IceCube the largest neutrino telescope in the world.

The IceCube Neutrino Observatory is made up of several sub-detectors in addition to the main in-ice array.
  • * AMANDA, the Antarctic Muon And Neutrino Detector Array, was the first part built, and it served as a proof-of-concept for IceCube. AMANDA was turned off in April 2009.

    * The IceTop array is a series of Cherenkov detectors on the surface of the glacier, two detectors approximately above each IceCube string. IceTop is used as a cosmic ray shower detector, for cosmic ray composition studies and coincident event tests: if a muon is observed going through IceTop, it cannot be from a neutrino interacting in the ice.

    * The Deep Core Low-Energy Extension is a densely instrumented region of the IceCube array which extends the observable energies below 100 GeV. The Deep Core strings are deployed at the center (in the surface plane) of the larger array, deep in the clearest ice at the bottom of the array (between 1760 and 2450 m deep). There are no Deep Core DOMs between 1850 m and 2107 m depth, as the ice is not as clear in those layers.
____ Experimental mechanism

Neutrinos are electrically neutral leptons, and interact very rarely with matter. When they do react with the molecules of water in the ice, they can create charged leptons (electrons, muons, or taus). These charged leptons can, if they are energetic enough, emit Cherenkov radiation. This happens when the charged particle travels through the ice faster than the speed of light in the ice, similar to the bow shock of a boat traveling faster than the waves it crosses. This light can then be detected by photomultiplier tubes (PMTs) within the digital optical modules (or DOMs) making up IceCube.

The signals from the PMTs are digitized and then sent to the surface of the glacier on a cable. These signals are collected in a surface counting house, and some of them are sent north via satellite for further analysis. More of the data is kept on tape and sent north once a year via ship. Once the data reach experimenters, they can reconstruct kinematical parameters of the incoming neutrino. High-energy neutrinos may leave a large signal in the detector, pointing back to their origin. Clusters of such neutrino directions indicate point sources of neutrinos.

Each of the above steps requires a certain minimum energy, and thus IceCube is sensitive mostly to high energy neutrinos, in the range of 1011 to about 1021 eV. Current estimates predict a neutrino event about every 20 minutes in the fully constructed IceCube detector.

IceCube is more sensitive to muons than other charged leptons, because they are the most penetrating and thus have the longest tracks in the detector. Thus, of the neutrino flavors, IceCube is most sensitive to muon neutrinos. Electrons typically scatter several times before losing enough energy to fall below the Cherenkov threshold; this means that they cannot typically be used to point back to sources, but they are more likely to be fully contained in the detector, and thus they can be useful for energy studies. These events are more spherical, or "cascade"-like, than "track"-like; muons are more track-like. Taus can also create cascade events; but are short-lived and cannot travel very far before decaying, and are thus usually indistinguishable from electron cascades.

A tau could be distinguished from an electron with a "double bang" event, where a cascade is seen both at the tau creation and decay. This is only possible with very high energy taus. Hypothetically, to resolve a tau track, the tau would need to travel at least from one DOM to an adjacent DOM (17 m) before decaying. As the average lifetime of a tau is 2.9×10−13 s, a tau traveling at near the speed of light would requires an energy of 20 TeV for every meter traveled. Realistically, an experimenter would need more space than just one DOM to the next to distinguish two cascades, so double bang searches are centered at PeV scale energies. Such searches are under way but have not so far isolated a double bang event from background events.

However, there is a large background of muons created not by neutrinos from astrophysical sources but by cosmic rays impacting the atmosphere above the detector. There are about 106 times more cosmic ray muons than neutrino-induced muons observed in IceCube. Most of these can be rejected using the fact that they are traveling downwards. Most of the remaining (up-going) events are from neutrinos, but most of these neutrinos are from cosmic rays hitting the far side of the Earth; some unknown fraction may come from astronomical sources, and these neutrinos are the key to IceCube point source searches. Current estimates predict the detection of about 75 upgoing neutrinos per day in the fully-constructed IceCube detector. The arrival directions of these astrophysical neutrinos are the points with which the IceCube telescope maps the sky. To distinguish these two types of neutrinos statistically, the direction and energy of the incoming neutrino is estimated from its collision by-products. Unexpected excesses in energy or excesses from a given spatial direction indicate an extraterrestrial source.

____ Point sources of high energy neutrinos

A point source of neutrinos could help explain the mystery of the origin of the highest energy cosmic rays. These cosmic rays have energies high enough that they cannot be contained by galactic magnetic fields (their gyroradii are larger than the radius of the galaxy), so they are believed to come from extra-galactic sources. Astrophysical events which are cataclysmic enough to create such high energy particles would probably also create high energy neutrinos, which could travel to the Earth with very little deflection, because neutrinos interact so rarely. IceCube could observe these neutrinos: its observable energy range is about 100 GeV (0.1 TeV) to several PeV. The more energetic an event is, the larger volume IceCube may detect it in; in this sense, IceCube is more similar to Cherenkov telescopes like the Pierre Auger Observatory (an array of Cherenkov detecting tanks) than it is to other neutrino experiments, such as Super-K (with inward-facing PMTs fixing the fiducial volume).

IceCube is sensitive to point sources more in the northern hemisphere than the southern. It can observe astrophysical neutrino signals from any direction, but in the southern hemisphere these neutrinos are swamped by the downgoing cosmic-ray muon background. Thus, early IceCube point source searches focus on the northern hemisphere, and the extension to southern hemisphere point sources takes extra work.

Although IceCube is expected to detect very few neutrinos (relative to the number of photons detected by more traditional telescopes), it should have very high resolution with the ones that it does find. Over several years of operation, it could produce a flux map of the northern hemisphere similar to existing maps like that of the cosmic microwave background, or gamma ray telescopes, which use particle terminology more like IceCube. Likewise, KM3NeT could complete the map for the southern hemisphere.

____ Gamma ray bursts coincident with neutrinos

When protons collide with one another or with photons, the result is usually pions. Charged pions decay into muons and muon neutrinos whereas neutral pions decay into gamma rays. Potentially, the neutrino flux and the gamma ray flux may coincide in certain sources such as gamma ray bursts and supernova remnants, indicating the elusive nature of their origin. Data from IceCube is being used in conjunction with cosmic ray detectors like HESS or MAGIC for this goal. The 22 string setup, "IC22," did not observe any neutrinos in coincidence with GRBs, but was able to use this search to constrain neutrino flux models from GRBs.

____ Indirect dark matter searches

Weakly interacting massive particle (WIMP) dark matter could be attracted by the mass of the Sun and collect gravitationally in the core of the Sun. When it reaches a critical mass, it could start annihilating with itself. The decay products of this annihilation could decay into neutrinos, which could be observed by IceCube as an excess of neutrinos from the direction of the Sun. This technique of looking for the decay products of WIMP annihilation is called indirect, as opposed to direct searches which look for dark matter interacting within a contained, instrumented volume. Solar WIMP searches are more sensitive to spin-dependent WIMP models than many direct searches, because the Sun is made of lighter elements than direct search detectors (e.g. xenon or germanium).

____ Galactic supernovae

Despite the fact that individual neutrinos expected from supernovae have energies well below the IceCube energy cutoff, IceCube could detect a local supernova. It would appear as a detector-wide, brief, correlated rise in noise rates. The supernova would have to be relatively close (within our galaxy) to get enough neutrinos before the 1/r2 distance dependence took over. IceCube is a member of the Supernova Early Warning System (SNEWS).

____ String theory

The described detection strategy, along with its South Pole position, could allow the detector to provide the first robust experimental evidence of extra dimensions predicted in string theory. Many extensions of the Standard Model of particle physics, including string theory, propose a sterile neutrino; in string theory this is made from a closed string. These could leak into extra dimensions before returning, making them appear to travel faster than the speed of light. An experiment to test this may be possible in the near future. Furthermore, if high energy neutrinos create microscopic black holes (as predicted by some aspects of string theory) it would create a shower of particles; resulting in an increase of "down" neutrinos while reducing "up" neutrinos.

The IceCube collaboration has published flux limits for neutrinos from point sources, Gamma-ray bursts, and neutralino annihilation in the Sun, with implications for weakly interacting massive particle- (WIMP-) proton cross sections. A shadowing effect from the Moon has been observed. Cosmic ray protons are blocked by the Moon, creating a deficit of cosmic ray shower muons in the direction of the Moon. A small (under 1%) but robust anisotropy has been observed in cosmic ray muons.>>
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Re: UT: Astronomy On Ice

Post by rstevenson » Thu Feb 10, 2011 2:36 am

Obviously, these astronomers were able to Get Down.
Click to play embedded YouTube video.
Rob