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MAGNETIC VISIONS: MAPPING COSMIC MAGNETISM WITH LOFAR AND SKA
R. Beck
Revista mexicana de astronomía y astrofísica , 2009,
Abstract: The origin of magnetic fields in the Universe is an open problem in astrophysics and fundamental physics. "Cosmic Magnetism" has been accepted as Key Science Project both for the Low Frequency Array (LOFAR, under construction) and the planned Square Kilometre Array (SKA). At low frequencies LOFAR and SKA will allow to map the structure of weak magnetic fields in the outer regions and halos of galaxies, in galaxy clusters and in the Milky Way. High-resolution polarization observations at high frequencies with the SKA will trace magnetic fields in the disks and central regions of galaxies in unprecedented detail. All-sky surveys of Faraday rotation measures (RM) towards polarized background sources will be used to model the structure and strength of the magnetic fields in the Milky Way, the interstellar medium of galaxies and the intergalactic medium. The new method of "RM Synthesis", applied to spectro-polarimetric data cubes, will separate RM components from different distances and allow 3-D "Faraday tomography". Magnetic fields in distant galaxies and clusters and in intergalactic filaments will be searched for by deep imaging of weak synchrotron emission and of RM towards background sources. This will open a new era in the observation of cosmic magnetic fields.
The LOFAR View of Cosmic Magnetism  [PDF]
Rainer Beck,James Anderson,George Heald,Andreas Horneffer,Marco Iacobelli,Jana Koehler,David Mulcahy,Roberto Pizzo,Anna Scaife,Olaf Wucknitz,the team of the LOFAR Magnetism Key Science Project
Physics , 2013, DOI: 10.1002/asna.201311894
Abstract: The origin of magnetic fields in the Universe is an open problem in astrophysics and fundamental physics. Polarization observations with the forthcoming large radio telescopes will open a new era in the observation of magnetic fields and should help to understand their origin. At low frequencies, LOFAR (10-240 MHz) will allow us to map the structure of weak magnetic fields in the outer regions and halos of galaxies, in galaxy clusters and in the Milky Way via their synchrotron emission. Even weaker magnetic fields can be measured at low frequencies with help of Faraday rotation measures. A detailed view of the magnetic fields in the local Milky Way will be derived by Faraday rotation measures from pulsars. First promising images with LOFAR have been obtained for the Crab pulsar-wind nebula, the spiral galaxy M51, the radio galaxy M87 and the galaxy clusters A2255 and A2256. With help of the polarimetric technique of "Rotation Measure Synthesis", diffuse polarized emission has been detected from a magnetic bubble in the local Milky Way. Polarized emission and rotation measures were measured for more than 20 pulsars so far.
Stacking for Cosmic Magnetism with SKA Surveys  [PDF]
J. M. Stil,B. W. Keller
Physics , 2015,
Abstract: Stacking polarized radio emission in SKA surveys provides statistical information on large samples that is not accessible otherwise due to limitations in sensitivity, source statistics in small fields, and averaging over frequency (including Faraday synthesis). Polarization is a special case because one obvious source of stacking targets is the Stokes I source catalog, possibly in combination with external catalogs, for example an SKA HI survey or a non-radio survey. We point out the significance of stacking sub-samples selected by additional observable parameters to investigate relations that reveal more about the physics of the source. Applications of stacking polarization include, but are not limited to, obtaining in a statistical sense polarization information to the detection limit in total intensity, depolarization as a function of cosmic time at consistent source-frame wavelengths, magnetic field properties in objects with a low radio luminosity such as dwarf and low-surface-brightness galaxies, and investigating potential correlations of observable parameters with the average magnetic field direction in a sample. We also point out the potential use of stacking in validating the polarization calibration of a survey. While stacking is flexible in terms of survey definition, we discuss optimal survey parameters for the science experiments presented, as well as computing and archiving requirements.
SKA Deep Polarization and Cosmic Magnetism  [PDF]
A. R. Taylor,Ivan Agudo,Takuya Akahori,Rainer Beck,Bryan Gaensler,George Heald,Melanie Johnston-Hollitt,Mathieu Langer,Lawrence Rudnick,Dongsu Ryu,Anna Scaife,Dominik Schleicher,Jeroen Stil
Physics , 2015,
Abstract: Deep surveys with the SKA1-MID array offer for the first time the opportunity to systematically explore the polarization properties of the microJy source population. Our knowledge of the polarized sky approaching these levels is still very limited. In total intensity the population will be dominated by star-forming and normal galaxies to intermediate redshifts ($z \sim1-2$), and low-luminosity AGN to high redshift. The polarized emission from these objects is a powerful probe of their intrinsic magnetic fields and of their magnetic environments. For redshift of order 1 and above the broad bandwidth of the mid-bands span the Faraday thick and thin regimes allowing study of the intrinsic polarization properties of these objects as well as depolarization from embedded and foreground plasmas. The deep field polarization images will provide Rotation Measures data with very high solid angle density allowing a sensitive statistical analysis of the angular variation of RM on critical arc-minute scales from a magnetic component of Large Scale Structure of the Universe.
Future Observations of Cosmic Magnetic Fields with the SKA and its Precursors  [PDF]
Rainer Beck
Physics , 2011,
Abstract: The origin of magnetic fields in the Universe is an open problem in astrophysics and fundamental physics. Polarization observations with the forthcoming large radio telescopes, especially the Square Kilometre Array (SKA), will open a new era in the observation of magnetic fields and should help to understand their origin. Low-frequency radio synchrotron emission, to be observed with LOFAR, MWA and the SKA, traces low-energy cosmic ray electrons and allows us to map the structure of weak magnetic fields in the outer regions and halos of galaxies, in halos and relics of galaxy clusters and in the Milky Way. Polarization at higher frequencies (1-10 GHz), to be observed with the SKA and its precursors ASKAP and MeerKAT, will trace magnetic fields in the disks and central regions of galaxies and in cluster relics in unprecedented detail. All-sky surveys of Faraday rotation measures towards a dense grid of polarized background sources with ASKAP (project POSSUM) and the SKA are dedicated to measure magnetic fields in intervening galaxies, clusters and intergalactic filaments, and will be used to model the overall structure and strength of magnetic fields in the Milky Way. "Cosmic Magnetism" is key science for LOFAR, ASKAP and the SKA.
Precision measurements of cosmic ray air showers with the SKA  [PDF]
T. Huege,J. D. Bray,S. Buitink,R. Dallier,R. D. Ekers,H. Falcke,C. W. James,L. Martin,B. Revenu,O. Scholten,F. G. Schr?der
Physics , 2014,
Abstract: Supplemented with suitable buffering techniques, the low-frequency part of the SKA can be used as an ultra-precise detector for cosmic-ray air showers at very high energies. This would enable a wealth of scientific applications: the physics of the transition from Galactic to extragalactic cosmic rays could be probed with very high precision mass measurements, hadronic interactions could be studied up to energies well beyond the reach of man-made particle accelerators, air shower tomography could be performed with very high spatial resolution exploiting the large instantaneous bandwidth and very uniform instantaneous $u$-$v$ coverage of SKA1-LOW, and the physics of thunderstorms and possible connections between cosmic rays and lightning initiation could be studied in unprecedented levels of detail. In this article, we describe the potential of the SKA as an air shower radio detector from the perspective of existing radio detection efforts and discuss the associated technical requirements.
Cosmic Magnetism with the Square Kilometre Array and its Pathfinders  [PDF]
Bryan M. Gaensler
Physics , 2009, DOI: 10.1017/S1743921309031470
Abstract: One of the five key science projects for the Square Kilometre Array (SKA) is "The Origin and Evolution of Cosmic Magnetism", in which radio polarimetry will be used to reveal what cosmic magnets look like and what role they have played in the evolving Universe. Many of the SKA prototypes now being built are also targeting magnetic fields and polarimetry as key science areas. Here I review the prospects for innovative new polarimetry and Faraday rotation experiments with forthcoming facilities such as ASKAP, LOFAR, the ATA, the EVLA, and ultimately the SKA. Sensitive wide-field polarisation surveys with these telescopes will provide a dramatic new view of magnetic fields in the Milky Way, in nearby galaxies and clusters, and in the high-redshift Universe.
The LOFAR Magnetism Key Science Project  [PDF]
James Anderson,Rainer Beck,Michael Bell,Ger de Bruyn,Krzysztof Chyzy,Jochen Eisl?ffel,Torsten En?lin,Andrew Fletcher,Marijke Haverkorn,George Heald,Andreas Horneffer,Aris Noutsos,Wolfgang Reich,Anna Scaife,the LOFAR collaboration
Physics , 2012,
Abstract: Measuring radio waves at low frequencies offers a new window to study cosmic magnetism, and LOFAR is the ideal radio telescope to open this window widely. The LOFAR Magnetism Key Science Project (MKSP) draws together expertise from multiple fields of magnetism science and intends to use LOFAR to tackle fundamental questions on cosmic magnetism by exploiting a variety of observational techniques. Surveys will provide diffuse emission from the Milky Way and from nearby galaxies, tracking the propagation of long-lived cosmic-ray electrons through magnetic field structures, to search for radio halos around spiral and dwarf galaxies and for magnetic fields in intergalactic space. Targeted deep-field observations of selected nearby galaxies and suspected intergalactic filaments allow sensitive mapping of weak magnetic fields through Rotation Measure (RM) grids. High-resolution observations of protostellar jets and giant radio galaxies reveal structures on small physical scales and at high redshifts, whilst pulsar RMs map large-scale magnetic structures of the Galactic disk and halo in revolutionary detail. The MKSP is responsible for the development of polarization calibration and processing, thus widening the scientific power of LOFAR.
Simulating the 21cm forest detectable with LOFAR and SKA in the spectra of high-z GRBs  [PDF]
B. Ciardi,S. Inoue,F. B. Abdalla,K. Asad,G. Bernardi,J. S. Bolton,M. Brentjens,A. G. de Bruyn,E. Chapman,S. Daiboo,E. R. Fernandez,A. Ghosh,L. Graziani,G. J. A. Harker,I. T. Iliev,V. Jelic,H. Jensen,S. Kazemi,L. V. E. Koopmans,O. Martinez,A. Maselli,G. Mellema,A. R. Offringa,V. N. Pandey,J. Schaye,R. Thomas,H. Vedantham,S. Yatawatta,S. Zaroubi
Physics , 2015, DOI: 10.1093/mnras/stv1640
Abstract: We investigate the feasibility of detecting 21cm absorption features in the afterglow spectra of high redshift long Gamma Ray Bursts (GRBs). This is done employing simulations of cosmic reionization, together with the instrumental characteristics of the LOw Frequency ARray (LOFAR). We find that absorption features could be marginally (with a S/N larger than a few) detected by LOFAR at z>7 if the GRB originated from PopIII stars, while the detection would be easier if the noise were reduced by one order of magnitude, i.e. similar to what is expected for the first phase of the Square Kilometer Array (SKA1-low). On the other hand, more standard GRBs are too dim to be detected even with ten times the sensitivity of SKA1-low, and only in the most optimistic case can a S/N larger than a few be reached at z>9.
Exploring weak magnetic fields with LOFAR and SKA  [PDF]
Tigran G. Arshakian,Rainer Beck
Physics , 2009,
Abstract: Regular magnetic field structures can be derived from the Faraday rotation measures (RM) of polarized background sources observable at 1.4 GHz with the SKA. At lower frequencies ($<250$ MHz) polarimetry of radio sources with the Low Frequency Array (LOFAR) will allow the investigation of extremely small RM, to detect and map weak regular fields in halos and outer parts of spiral galaxies, and in the interstellar and intergalactic medium. Very little is known yet about the number density of polarized sources at low frequencies. Observed distributions of polarized sources at 350 MHz and 1.4 GHz and perspectives to detect weak magnetic fields with LOFAR are presented. Test observations of polarized radio sources with the Westerbork Synthesis Radio Telescope (WSRT) and the Giant Metrewave Radio Telescope (GMRT) are discussed.
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