Scientific workshop - Astrophysics with E-LOFAR
16 - 19 September 2008, Hamburg, Germany
Organised by Hamburger Sternwarte /
German
Long-Wavelength Consortium (GLOW)
Talk Abstracts
| Title: | Planck satellite: Complementary probe of reionisation |
| Name: | Nabila Aghanim |
| Abstract: | I will present the Planck satellite scientific programme focusing on the synergy with LOFAR for EoR studies. |
| Title: | Initial Observations with the LOFAR Effelsberg-Exloo Baseline |
| Name: | James Anderson |
| Abstract: | With the many international stations in preparation, E-LOFAR will
provide a new opportunity to map the low-frequency sky at very high
resolution. I will report on initial long-baseline observations with
the existing LOFAR stations at Effelsberg and Exloo. These stations
provide a baseline length of approximately 250 km. The main focus
of the initial observations is to measure the LOFAR instrumental
behavior on long baselines and to perform a search for bright
calibration sources. Fluctuations in the ionospheric delay at long
baselines at LOFAR frequencies will also be studied to determine the
calibratability of E-LOFAR. And although the number of available
baselines is still quite small, initial science is also possible. |
| Title: | Exploring weak magnetic fields with LOFAR |
| Name: | Tigran Arshakian |
| Abstract: | The density of polarized background sources at 1.4 GHz observable with
the SKA allows the reconstruction and recognition of regular magnetic
field structures in foreground galaxies from the Faraday rotation
measure (RM) of polarized sources. At lower frequencies (<200 MHz) the
polarimetry of radio sources with LOFAR will allow the investigation
of extremely small RM. All-sky RM survey will allow to detect and map
weak regular fields in halos and outer parts of spiral galaxies,
interstellar and intergalactic medium, if background sources are
still polarized at frequencies observable with LOFAR. Very little is
known yet about the number density of polarized sources at very low
frequencies. I will discuss about simulated and observed density of
polarized sources and perspectives to detect weak magnetic fields with
LOFAR. |
| Title: | LOFAR in Germany |
| Name: | Rainer Beck |
| Abstract: | A summary of LOFAR activies and of LOFAR stations in Germany is given. |
| Title: | Magnetic fields in clusters |
| Name: | Marcus Brüggen |
| Abstract: | LOFAR offers a unique opportunity to study cosmic magnetism by observing polarized radio synchrotron emission. Faraday screens and Faraday tomography will allow to study the 3D structure of local Galactic magnetic fields. The low-frequency bands of LOFAR will give access to objects with weak magnetic fields and/or less energetic cosmic-ray electrons, such as galaxy halos, galaxy clusters and intergalactic magnetic fields, by direct observation of diffuse polarized emission and by Faraday rotation of polarized background sources. I will review the recent work in this field. |
| Title: | Technical challenges of the LOFAR EoR project |
| Name: | Michiel Brentjens |
| Abstract: | The LOFAR Epoch of Reionization (EoR) projects attempts to detect
red-shifted 21 cm radio emission that originated at the time when the
light in the universe switched on. The signal is unfortunately very
weak. Because it is expected to be observable at frequencies below 200
MHz, where the Earth's ionosphere can behave very badly. Furthermore,
the high dynamic range that is necessary for the observations
requires one to accurately model the sky itself, the ionosphere, and
the entire instrument. Another issue is the postprocessing of the
calibrated data. Which algorithms allow one to extract the signal with
the smallest chance of false detections or non-detections? On what
kind of hardware should this run? Where and how does one store a
petabyte of data? |
| Title: | LOFAR and particle acceleration in extragalactic radio sources |
| Name: | Gianfranco Brunetti |
| Abstract: | A variety of mechanisms can accelerate relativistic particles in extragalactic radio sources. These mechanisms determine the properties of relativistic plasma in radio sources, their emitting properties and evolution.
Radio observations at low frequencies are crucial to address the origin of relativistic particles, their spectral properties and energy content in different classes of extragalactic objects. Radio Galaxies and the large scale synchrotron emission from Galaxy Clusters are ideal targets for observations with LOFAR.
I will focus on the acceleration of relativistic particles in Radio Galaxies and Clusters, and discuss the potential impact of LOFAR observations on our understanding of the acceleration mechanisms and on the physics of these sources. |
| Title: | Cluster Radio Halos in the LOFAR era |
| Name: | Rossella Cassano |
| Abstract: | Radio Halos (RH) are the most spectacular examples of diffuse non-thermal emission in galaxy clusters. Observations at GHz frequencies show that RH are not common and always found in merging clusters, and this favors a scenario in which particles are re-accelerated by cluster turbulence. A critical expectation of this scenario is that presently known RH must result from rare, energetic events, while a new population of RH should emerge at lower frequencies (Cassano et al. 2006,08). These RH, not visible at GHz frequencies because of their ultra-steep spectra, should be associated with more common but less energetic mergers, and should represent the bulk of RH in the universe. In this contribution I will discuss our predictions on low frequency RH and report on their expected luminosity functions and number counts at the LOFAR frequencies. LOFAR is expected to unvail the bulk of RH in the universe and our expectations provide a powerful tool to interpret future LOFAR data. |
| Title: | The reionization process: theory and observations |
| Name: | Benedetta Ciardi |
| Abstract: | In this talk I will discuss simulations of the cosmic reionization process and its observability through the 21cm line from the hyperfine transition of the ground state of neutral hydrogen. I will also discuss the impact of different heating sources (Lyalpha photons, x-rays...) on the observability of the signal. |
| Title: | Swedish LOFAR |
| Name: | John Conway |
| Abstract: | A description of the Swedish LOFAR station to be constructed at Onsala space observatory will be given. Progress on construction and provision of internet links will be described as will the main science interests of the Swedish science community. |
| Title: | E-LOFAR in Italy |
| Name: | Daniele Dallacasa |
| Abstract: | I will describe the efforts of the Italian astronomical community to get involved in the e-Lofar development.
Activities and the main scientific interests will be discussed, together with some milestones to be achieved in the very near future, |
| Title: | Low frequency polarimetry and cosmic magnetism |
| Name: | Ger de Bruyn |
| Abstract: | Cosmic magnetic fields play a fundamental role in many fields of (radio) astrophysics. LOFAR and the Magnetism KSP aim to address many of these topics and this will be the subject of my review.
The quadratic wavelength dependence of Faraday rotation creates both opportunities and challenges at low frequencies. With LOFARs exquisite spectral resolution we can use Rotation Measure (RM) synthesis to unravel multiple Faraday screens (both Faraday 'thin' and 'thick') along the line of sight and measure RMs to accuracies well below 0.1 rad/m2. This allows extremely sensitive studies of the magneto-ionic media in our Galaxy, nearby galaxies, the cosmic web, clusters and the intergalactic medium. Both polarized probes (e.g. pulsars and radiogalaxies) and polarized diffuse emission will be used.
I will briefly discuss some instrumental challenges (e.g. ionospheric Faraday rotation and wide-field instrumental polarization) that have to be overcome to make this all happen. |
| Title: | LOFAR-UK |
| Name: | Rob Fender |
| Abstract: | I will review the status of LOFAR-UK, including the siting of the first UK station, the progress of bids to raise funds for further stations, and the technical and scientific areas of interest for the UK community. |
| Title: | Thermal and non-thermal emission from galaxy clusters: X-ray and LOFAR observations |
| Name: | Chiara Ferrari |
| Abstract: | Deep radio observations of galaxy clusters have revealed the existence of diffuse radio sources related to the presence of relativistic electrons and weak magnetic fields in the intracluster volume. The importance of combining X-ray and radio observations to characterise the origin and physics of the non-thermal cluster component has been proven in recent years. In this talk, I will present a joint radio and X-ray project based on galaxy cluster observations by LOFAR and current/future X-ray instruments, such as XMM, Chandra and Simbol-X. |
| Title: | SETI with LOFAR |
| Name: | Parisa Noorishad |
| Abstract: | SETI practically began in 1960 with Ozam project. Since then different projects were defined and done by targeting particular regions in the sky but no sign of Extra Terrestrial Intelligence (ETI) has been yet found. We still believe that we have not searched properly because all these projects covered small patches of sky and observed in the limited frequency range.
Furthermore the fact that LOFAR is able to see a large fraction of the sky makes a breakthrough the limitation of targeting a specific direction on the sky but this brings many signal processing challenges. Depends on what assumption we want to start with, we should bear in mind different technical constraints and capabilities of LOFAR. SETI was not taken into consideration at the time of designing LOFAR but now because of the flexibility of system for change in current modes of operation and the possibility of adding even new mode of operation motivate us to evaluate LOFAR for being a low frequency SETI tool. |
| Title: | The GMRT Radio Halo survey - Results and implications for LOFAR |
| Name: | Simona Giacintucci |
| Abstract: | Radio halos in galaxy clusters are known to be a rare phenomenon, whose origin is thought to be related to the hierarchical formation of clusters through massive merging events. I will present the results of a 610 MHz survey carried out with the GMRT on a sample of 50 clusters. The survey was designed to address the question of the occurrence of radio halos in clusters at z=0.2-0.4, for comparison with statistical expectations and to increase our knowledge on the connection between halos and mergers. Follow up observations at lower frequency on a number of clusters in the sample allowed us to discover a new population of halos, which shows up at frequencies \ltsim 610 MHz, and which is most likely related to less energetic merging events. By means of a comparison between the GMRT sensitivity and the expected sensitivity of LOFAR at 230 MHz, we expect that LOFAR will be very efficient in detecting such "new class" of radio halos. |
| Title: | Ground based study of Saturn Electrostatic Discharges |
| Name: | Jean-Mathias Griessmeier |
| Abstract: | Radio signatures of lightning discharges have been detected by the Voyager spacecraft near Saturn up to 40 MHz. They are usually denoted as SED (Saturn Electrostatic Discharges). At the distance of the Earth, the flux density can reach a few hundred Jansky, for event durations between 30 and 400 msec. Detection of SED allows to study electrification processes, atmospheric dynamics, geographical and seasonal variations. Ground-based detection of SED was first achieved in 2006 in a few narrow spectral channels at the UTR-2 radiotelescope in Kharkov (Ukraine). Using a new broadband digital receiver at UTR-2, SED were detected over the whole spectral range of the instrument (10-30 MHz) in December 2007, and for the first time spectra of individual events were recorded. SED properties measured at that occasion are compared to those obtained from space missions. The capabilites of LOFAR with respect to such observations are discussed. |
| Title: | Statistics to extract and analyze the cosmological signal from the Epoch of Reionization |
| Name: | Geraint Harker |
| Abstract: | The strength of 21cm emission from the Epoch of Reionization (EoR) at a
given position and redshift depends upon the density and the ionized fraction at that point. We therefore expect the pattern of emission to be complex, probably consisting of ionized bubbles, free of emission, superimposed on a fluctuating background. In particular, it is not expected to be characterized only by its power spectrum: other statistics can provide complementary information on the progress of reionization.
The characteristics of astrophysical and instrumental foregrounds, and
of noise, are expected to be quite different. This raises the
possibility of using the particular features of the cosmological signal not only to study the physics of reionization, but also to detect and extract the signal in the first place.
We report on the prospects for doing this using the LOFAR EoR dataset, incorporating realistic models for the cosmological signal, astrophysical and instrumental foregrounds, and n |
| Title: | Radio Detection of Cosmic Ray Air Showers |
| Name: | Andreas Haungs |
| Abstract: |
A major topic in astroparticle physics is the measurement and the understanding of the source, acceleration and transport of the highest energy cosmic particles. The radio detection of extensive air showers generated by these cosmic particles in our atmosphere is a novel, promising technique to boost the energy reach and performance of future detectors for charged cosmic rays and also neutrinos. There are several experimental approaches to path the way for this technique. In particular, LOPES is set up at the location of the KASCADE-Grande extensive air shower experiment in Karlsruhe, Germany and aims to measure and calibrate radio pulses from Extensive Air Showers. LOPES is designed as a digital radio interferometer using high bandwidths and fast data processing and profits from the reconstructed air shower observables of KASCADE-Grande. A short introduction in the basic principles and the technique of the technique is given; status and results of the specific LOPES experiment is discussed. |
| Title: | E-LOFAR and the Magnetic Milky Way |
| Name: | Marijke Haverkorn |
| Abstract: | The magnetic field in the Milky Way is highly complex: it consists of a large-scale regular field which presumably follows the spiral arms, and small-scale field fluctuations on a huge range of scales. The morphology of the large-scale field is still unclear: no current models can satisfactorily explain all observations yet. Also, the characteristics of the turbulent field component and the halo magnetic field are largely unknown. Nevertheless knowledge of Milky Way magnetic fields is crucial for understanding the turbulent interstellar gas and the origin of galactic magnetism.
LOFAR promises to make unique contributions to Galactic
magnetic field studies. LOFAR's exquisite sensitivity to low rotation measures will allow precision measurements of the weakly magnetized sky. Furthermore, we can make a 3D picture of the cosmic ray distribution in the plane through low-frequency measurements of absorption through HII regions, which will be used to refine Galactic magnetic field models.
|
| Title: | Deep, targeted imaging of pulsar wind nebulae with E-LOFAR |
| Name: | Jason Hessels |
| Abstract: | Young pulsars create synchrotron-emitting "wind nebulae", which
provide important insights into the energetics and environments of
these objects. E-LOFAR will allow us to observe pulsar wind nebulae
in a mostly unexplored spectral window with unprecedented resolution
and sensitivity. I will discuss how such observations can help us
better understand the properties and evolution of pulsar winds. |
| Title: | Air Shower Measurements with LOFAR |
| Name: | Andreas Horneffer |
| Abstract: | High energetic cosmic rays that hit the Earth's atmosphere undergo nuclear
interactions and produce cascades of secondary particles, an extensive air
shower. These air showers emit radio pulses. With LOPES, an early LOFAR
prototype, we have demonstrated that theses radio pulses can be measured
by LOFAR.
Designed primarily as a radio interferometer, LOFAR will have a high density
of antennas in the core, and will be extremely well calibrated.
While this design would not be cost effective for a dedicated cosmic-ray
detector it makes LOFAR an unique tool for the study of the radio properties
of single air showers.
In order to measure cosmic rays we need to trigger on air showers,
i.e., determine when an air shower has hit LOFAR. We then initiate a
dump of the recorded raw antenna signals. I will present the current status of
our efforts and the work that still needs to be done to enable LOFAR to measure
cosmic-ray air showers.
|
| Title: | The foregrounds simulations for the LOFAR-EoR Experiment |
| Name: | Vibor Jelic |
| Abstract: | The LOFAR-EoR experiment is set to detect and quantify the
differential brightness temperature fluctuations of 21-cm EoR signal (z~11-6) using LOFAR's high band antennae. However there are many challenges in this task: the existence of very prominent foregrounds in the same frequency range as the EoR signal, ionospheric effects and a very complex instrumental response.
In this work we will present the simulations of the foreground maps in total intensity (Galactic diffuse synchrotron and free-free emission and extragalactic emission from radio galaxies and clusters) and polarised intensity (Galactic diffuse synchrotron emission).
Moreover, we will show that with realistic noise level (~52mK, 150MHz), expected for the LOFAR-EoR experiment, a simple polynomial fitting allows for a statistical detection of the EoR signal. |
| Title: | Solar wind in the outer heliosphere: IPS observations at the decameter wavelengths. |
| Name: | Nikolay Kalinichenko |
| Abstract: | IPS observations are considered to be very useful for studying the solar wind parameters. At high frequencies, they allow one to obtain the solar wind parameters in the inner heliosphere. Unfortunately, at the large solar elongations (large distances from the sun), the high frequencies are weakly scattered due to decrease of electron density with radial distance while the IPS observations at the decameter wavelengths show measurable scintillations indexes here. This fact has allowed us to carry out the complex investigations of the solar wind in the outer heliosphere. They included the elaboration of the scintillations theory, as applied to low frequencies, the carrying out of the observations with the low-frequency URAN interferometer. The developed technique has allowed us to obtain the main parameters of the solar wind, to find and to track the high-speed solar wind flows in the outer heliosphere. The discussed investigations are important for the approbation of the LOFAR concepts. |
| Title: | Solar Physics & Space Weather Science with LOFAR: The UK Perspective |
| Name: | Joe Khan |
| Abstract: | As a key member of the LOFAR Key Science Project (KSP) "Solar Physics and Space Weather" the UK will have a prominent role in solar studies with LOFAR. In this talk I will discuss how the UK anticipates contributing to solar studies with LOFAR via hardware and software contributions as well as via scientific research efforts. I will also give an account of the status of our funding applications to UK bodies for solar studies with LOFAR. |
| Title: | Dwarf galaxies and the magnetisation of the IGM |
| Name: | Uli Klein |
| Abstract: | I will review the properties of the synchrotron radio
emission and magnetic fields in dwarf galaxies. Given
that these make up for the majority of the first building
blocks in the universe, they could have efficiently injected
relativistic particles and magnetic fields into the IGM
(Kronberg et al. 1999). With LOFAR there is an excellent
instrument to search for low-frequency radio halos around
dwarf galaxies in the local universe and beyond; such halos
would eflect pools of formerly highly relativistic particles
stemming from periods of intense star formation.
|
| Title: | Giant Ukrainian Radio Telescope as a Complimentary Part to the E-LOFAR Super Stations |
| Name: | Alexander Konovalenko |
| Abstract: | At the present time the new low-frequency Giant Ukrainian Radio Telescope (GURT) is creating on the UTR-2 observatory in according to Special Program of the National Academy of sciences of Ukraine. The frequency range is from 10 to 70 MHz with the exceeding of the antenna element temperature over pre-amplifier noise temperature of about 10 dB. Special attention was paid on the interference immunity of the system including the high requirements to the dynamic range of the pre-amplifiers, next stages of the amplification, and analog-to-digital conversation. The main goal of this approach is to reach the maximum effective area (> 100 000 sq. m). This is important for the resolving of many astrophysical tasks when the sensitivity is not limited by the confusion effect. The instrument will be also useful for the coordinated (synchronized) observations with the future E-LOFAR and E-LOFAR Super Stations as more distant (~ 2000 km) antenna and in VLBI mode for some tasks. |
| Title: | Computational Challenges of the LOFAR EoR Key-Science-Project |
| Name: | Leon Koopmans |
| Abstract: | The Epoch of Reionization (EoR) is one of the least and last studied phases in the history of the Universe and as such drives one of the Dutch Key-Science-Programmes (KSP) of LOFAR. To detect the feeble 21-cm HI emission line from the EoR at redshifts between 6 and 11 (freq. ~100-200 MHz), exceedingly deep (~1 million second!) integrations are planned on a number of selected "radio windows" that show the least foreground emission and polarisation. Still, to statistically quantify the EoR signal, a dynamic range of ~10,000 or more needs to be reached over these windows. This requires the development of new computational, calibration, analysis and signal-extraction techniques. As core-member of the EoR KSP, I will outline the challenges we are faced with in trying to extract the EoR signal from the ~1 Pbyte of raw data, the pipe-lines that we are developing to simulate data and test our algorithms, and how to implement this computational challenge on alternative hardware solutions.
|
| Title: | Synergies with other observational facilities: ALMA (invited) |
| Name: | Robert Laing |
| Abstract: | The Atacama Large Millimetre/Submillimetre Array (ALMA) will be an interferometric array consisting of 54 12m and 12 7m antennas optimized for millimetre and sub-millimetre observations in the frequency range 30 - 950 GHz. It is located on the high-altitude (5000m) Llano de Chajnantor site in the Chilean Andes and is expected to commence full operation around 2012. I will describe the science goals, anticipated performance and current progress of the project.
I will then outline a number of science projects which will benefit from ALMA and E-LOFAR observations, concentrating on high-redshift galaxies and the epoch of reionization. |
| Title: | Low frequency results from the GMRT and the role of the E-LOFAR |
| Name: | Dharam Vir Lal |
| Abstract: | We have studied several radio sources at low radio frequencies using GMRT. Our prime motivation to study these fields is to detect faint radio emission at very low frequencies due to low energy electrons.
Our results provide evidence that the spectra of low-surface-brightness features are flatter than the spectra of high-surface-brightness features in several radio galaxies. In addition, the low frequency radio images show morphologies that are similar to the morphologies at high frequencies. This suggests that low-frequency synchrotron emission fades (nearly) as rapidly as high-frequency synchrotron emission. These results suggest that the simple picture of spectral electron ageing needs revision or we need to re-examine the formation mechanism of such sources.
In the talk, I will present the images and statistics, and will discuss the relevance of these results and the role of E-LOFAR in exploring several unknowns. |
| Title: | Searching for Transients with LOFAR/CS1 |
| Name: | Casey Law |
| Abstract: | Variability in the low-frequency radio sky has been largely unstudied. Observational extrapolations and theoretical predictions suggest that some variable and transient sources are best studied at low frequencies. Furthermore, some physical processes, such as cyclotron emission or dispersion, are only accessible at low frequencies. The wide field of view and flexible design of LOFAR makes it well-suited to the study of this new world.
I will present the results of an initial search for transients with the first LOFAR station, called Core Station 1 (CS1). This talk will also summarize the search strategy and software used by the LOFAR Transients Key Project. |
| Title: | Search for radio emission from exoplanets: dynamic spectra from GMRT observations |
| Name: | Walid Majid |
| Abstract: | Massive extrasolar planets are expected to emit, in analogy with Jupiter and Saturn, detectable radio emission at low frequencies. We have carried out a series of observations of known extrasolar planetary systems at 150 MHz with the Giant Meterwave Radio Telescope (GMRT) in both interferometric and phased array modes. We will describe our observing campaign, target list, and preliminary results from studies of dynamic spectra. As low frequency observations are plagued with RFI, we will focus on observing strategies and analysis techniques to minimize, identify and remove RFI effects from dynamic spectra. We will also briefly discuss prospects for similar searches with future instruments such as LOFAR, the LWA, and the SKA instruments. |
| Title: | Solar Physics and Space Weather with LOFAR |
| Name: | Gottfried Mann |
| Abstract: | The Sun is an active star and an intense radio source on the sky. That manifests not only in terms of the 11-year Sun spot cycle but also in flares. During flares a huge amount of energy is suddenly released. They are accompanied by enhanced emissions of radio waves. Consequently, the radio emission of the Sun is a sensitive indicator of solar activity. The solar radio radiation in LOFAR's frequency range (20-240 MHz) is emitted from the upper corona. Thus, observations of the Sun by LOFAR will provide new results for a better understanding of the processes related with energetic electrons in the corona during flares.
The solar activity can influence our Earth's environment and technical civilization. That is usually called Space Weather. Therefore, monitoring the solar activity by LOFAR is not only of astrophysical but also of social interest. |
| Title: | Properties of the redshifted 21cm signal from reionization |
| Name: | Garrelt Mellema |
| Abstract: | The redshifted 21cm signal is probably the most powerful observable for pinning down the when and how of the reionization of the Universe. Using the results of large scale simulations of reionization, I will present an overview of the specific properties of the 21cm signal that should help us to confirm its detection from among foregrounds and instrumental effects, and how these properties can be used to derive the properties of the reionization process, the responsible sources, and the cosmological density field. |
| Title: | Decameter Type IV bursts: Properties of Fiber Bursts |
| Name: | Valentin Melnik |
| Abstract: | Type IV bursts at 10-30 MHz were observed for the first time at radio telescope UTR-2 in 2003-2006. All of them have the fine structure in the form of sub-bursts (fiber bursts) in emission and absorption, and zebra structures. In this paper we study properties of fiber bursts in emission on the example of 4 Type IV bursts happened on July, 2005. More than 800 fiber bursts were analyzed. These sub-bursts have both positive and negative frequency drift rates with values 1-3 MHz/s. These rates are a little smaller than those for usual Type III bursts. Their durations mainly change from 3 s to 10 s and approximately equal to the durations of Type III bursts. The most of fiber bursts have frequency band 3-12 MHz. The fluxes of these bursts are in wide ranges from some s.f.u. to hundreds and even thousands s.f.u. and defined by power of parent Type IV bursts. For detailed study of fine structure of Type IV bursts needs prolonged observations at radio telescopes with high effective square. |
| Title: | Studying the cosmological evolution of Supermassive Black Holes with LOFAR |
| Name: | Andrea Merloni |
| Abstract: | I will discuss the role played by radio AGN in our current synthetic models for the Cosmological evolution of supermassive black holes. In particular, I will concentrate on the differences, both in physical and evolutionary terms, between 'classical' radio loud Quasars and low luminosity radio AGN, which likely dominate the kinetic energy feedback in the most massive galaxies at low redshifts. Finally, I will outline the specific topics where LOFAR has the chance to make a substantial contribution towards our understanding of the cosmological co-evolution of galaxies and black holes. |
| Title: | Radio halos: spectral index analysis. |
| Name: | Emanuela Orru |
| Abstract: | Radio halos are diffuse radio sources hosted in the center of
massive merging clusters of galaxies. These synchrotron sources are the evidence of the presence of magnetic fields and relativistic particles on large scale. Two classes of models were proposed to understand the origin of radio halos. Spectral index maps allow to discriminate between these two classes of models. Primary models predict a radial spectral steepening in the spectral index distribution, while secondary models expect alpha < 1.5 and a constant trend of the radial spectral index. We observed that although there are significant variations of the spectral index from point-to-point, on average the radio spectrum does not change with radius. We will discuss this dual behaviour. E-LOFAR will provide images at high sensitivity and resolution in a range of frequencies almost unexplored. It will be possible to obtain a more accurate analysis of the spectral index behavior, thereby a sharp-cut between the models. |
| Title: | Polish contribution to E-LOFAR |
| Name: | Katarzyna Otmianowska-Mazur |
| Abstract: | I will present plans of the Polish astronomical society to take part in the E-LOFAR progress, our main scientific interests and the current situation of POLFAR in Poland. |
| Title: | Non-thermal radio spectral index study of spiral galaxies |
| Name: | Rosita Paladino |
| Abstract: | The study of the correlation between thermal and non thermal
emissions from interstellar medium is a fascinating and promising
research field that possesses potential for the enhancement of
our knowledge on past and present star formation processes in galaxies.
New observing facilities now available have completely changed the way
we can address these issues.
Infrared and millimetric emissions (tracers of the star-formation
activity) are observed with the necessary resolution to extend these
studies to local scales in many external galaxies.
LOFAR will provide high resolution low-frequency observations which
will enable us to compare the spatially resolved distribution of
non-thermal radio spectral index in galaxies with their infrared and
millimetric distributions. This is a promising way to understand the cosmic
ray propagation mechanisms, and their correlation with star-formation on
local scales.
|
| Title: | A view of the sub-mJy population: The AGN component |
| Name: | Isabella Prandoni |
| Abstract: | We are studying a complete sample of 131 radio sources with S>0.4 mJy, observed at 1.4 and 5 GHz as part of the ATESP radio survey. The available deep multi-color optical information is exploited to infer the physical properties of the faint
radio population. We find that AGNs largely dominate our sub-mJy sample. Radio/optical analysis of such AGN component has revealed a somewhat unexpected class of compact, flat/inverted--spectrum sources identified with early--type galaxies. We are following up such sources at other radio frequencies in order to assess whether such class of faint AGNs is more related to efficiently accreting systems (eg radio-quiet quasars) - or to systems with very low accretion rates (e.g. FRI radio galaxies). We will discuss the observational and modeling results obtained so far and the possible implications for deep surveys with E-LOFAR. |
| Title: | Galactic magnetic field research with LOFAR |
| Name: | Wolfgang Reich |
| Abstract: | Low-frequency observations of polarized Galactic emission
with LOFAR will clarify a number of open issues related to
Galactic magnetic field research. Our recent Galactic magnetic
field modeling indicates a close spatial relationship between
the warm thermal matter and the turbulent magnetic field component.
At low frequencies, depolarization effects caused by Faraday
rotation can be studied best. However, high angular resolution
polarization data as provided by a European LOFAR are needed to
avoid beam averaging effects as much as possible.
|
| Title: | Ram pressure stripping of disk galaxies in clusters |
| Name: | Elke Roediger |
| Abstract: | Ram pressure stripping in galaxy clusters is believed to play a significant
role for the evolution of disk galaxies. Although this process has been
studied for some decades, only recently realistic, full 3D hydrodynamical
simulations were performed. We present the results of such simulations, where
the model galaxy orbits through a galaxy cluster and thus experiences a
variable ram pressure. We study the gas loss from the galaxy and the
resulting tails of stripped gas.
The purely hydrodynamical treatment can explain basic observed features,
but not all. Thus, we intend to model ram pressure stripping with a
magneto-hydrodynamics (MHD) code. We summarize features in the magnetic
fields of observed ram pressure galaxies and line out our future MHD
simulations. |
| Title: | LOFAR surveys of the low frequency sky |
| Name: | Huub Rottgering |
| Abstract: | LOFAR surveys at the key frequencies 15, 30, 60, 120 and 200 MHz will provide a goldmine for investigating several fundamental questions in astrophysics, including the formation of massive black holes, galaxies and clusters of galaxies. The design of the surveys will be discussed during this presentation. It has been driven by 3 important topics:
1. Forming massive galaxies at z>6
2. Diffuse synchrotron emission associated with the first bound clusters of galaxies.
3. Star formation processes in galaxies.
Since these large surveys will probe unexplored parameter space, they will not only be an important new tool for the study of a broad range of astrophysical problems, but it is likely that they will lead to the discovery of new phenomena. |
| Title: | Detection of Ultra-High Energy Cosmic rays and Neutrinos using the Moon. |
| Name: | Olaf Scholten |
| Abstract: | When high-energy cosmic rays impinge on a dielectric medium, radio waves are produced through the Askaryan effect. It will be shown why, at wavelengths comparable to the length of the shower produced by an Ultra-High Energy (UHE) cosmic ray or neutrino, radio signals of 100-200 MHz are an extremely efficient way to detect these particles. First results of observations obtained with the Westerbork Synthesis Radio Telescope will be reported, already showing improved flux limits for neutrinos with energies in excess of 3 10^22 eV. The status of the planning of the NuMoon experiment for LOFAR will be presented.
|
| Title: | Pulsars with E-LOFAR |
| Name: | Ben Stappers |
| Abstract: | The core of LOFAR has huge potential for the study of pulsars. It is likely that it will be able to find many hundreds of new pulsars and to study the known population with unprecedented sensitvitiy. However there is also signifcant collecting area on the international baselines as well. I will discuss ways in which the E-LOFAR stations can be used for a range of different pulsar studies. This includes combining E-LOFAR stations for sensitive and rapid searches of the sky and the use of individual E-LOFAR stations for the monitoring of known sources. |
| Title: | Observation of Carbon Radio Recombination Lines Towards Dust Cloud L1407 at decameter wavelengths |
| Name: | Sergiy Stepkin |
| Abstract: | Extremely low frequency RRLs could be used as effective means of the low density partially ionized interstellar medium diagnostic. Nevertheless, low intensities of the features and high level of interferences makes such investigations difficult. The best-studied object with extremely low frequency carbon RRLs is the medium in the direction of Cassiopeia A, and positive detections of such phenomena are still not too numerous. It is possible to improve efficiency of the low frequency RRLs studies by increasing frequency band of experiments. In our case of very high atom quantum states n is much bigger than delta n. So adjacent lines can be considered as equivalent and we could fold individual transitions in order to improve measurement sensitivity. Such approach have been used in the course of observations towards dust cloud L1407 with radio telescope UTR-2 near 26 MHz that have yielded the detection of carbon radio recombination lines (RRLs) C627alpha %G–%@ C636 alpha. |
| Title: | On the use of electromagnetic angular momentum for better characterization and calibration of radio signals from space |
| Name: | Bo Thidé |
| Abstract: | Wide-area radio telescopes such as LOFAR and SKA, which use many antennas distributed over large areas, can be used to measure the angular momentum and other topological degrees of freedom of the radio beams received. This will enable a more detailed characterization of the sources of the radio emission as well as better ways of calibration the signals against plasma vorticity and turbulence.
An overview of this new technique, its theoretical foundation and its use in radio studies of space will be presented. |
| Title: | Simulating Various Reionization Scenarios for the LOFAR-EoR Experiment |
| Name: | Rajat Thomas |
| Abstract: | The sensitive dependence of the history of reionization on numerous factors including the types of sources (stars/qsos) and their spectra, clustering properties, lifetimes and so on., urges us to recreate as many scenarios for reionization as possible. It is also imperative that each of these models do flow through the LOFAR pipeline of the instrumental response and signal retrival to establish a working mode and algorithm for the LOFAR-EoR experiment. Given the computational expenses of a full 3D radiative transfer code, it becomes impossible to test all the given scenarios. Therefore, we have developed a semi-analytical model in which any given N-body simulation is coupled to a 1-D radiative transfer code to mimic various reionization scenarios. We will present the basic LOFAR-EoR pipeline and the algorithm mentioned. |
| Title: | En Route to SKA |
| Name: | Stephen Torchinsky |
| Abstract: | The Square Kilometre Array will be an enormous radio astronomy facility with first-light of the completed array expected by 2020, and initial operations beginning in 2015. The SKA will be a massive array of many receiving elements, and it will thus have both exquisite sensitivity and angular resolution, as well as an ultra wide field of view. The fully sampled field-of-view, of the order of 200 square degrees, makes the SKA effectively a 10-gigapixel ultra wide field spectroscopic radio camera. Survey science will especially benefit from this instrument. For example, a billion galaxy redshift survey out to z=2 will be used to detect Baryonic Acoustic Oscillations leading directly to a measure of the Dark Energy equation of state parameter. I will review the key science projects of the SKA, and give an overview of the planned implementation, in particular with a focus on the technology developments currently underway in Europe as part of the FP6 funded project SKADS. |
| Title: | Solar observations with LOFAR |
| Name: | Christian Vocks |
| Abstract: | The Sun is a strong radio source that mainly emits plasma emission, whose frequency depends on the electron density at the source. LOFAR's frequency range covers the middle and upper corona, making the instrument ideally suited for studies of the solar activity and Space Weather.
Different LOFAR observation modes are proposed. Beside using single stations as spectrometers, these modes are based on image synthesis on a number of frequencies. The special properties of the Sun as a radio source need to be considered here. One of the two main modes is solar monitoring, i.e. imaging with a 1-minute cadence, in combination with other patrol observations, like in H\alpha. The other one is a burst mode with imaging with a rapid sequence, e.g. 0.1 s. This mode can be triggered externally, e.g. from the AIP's radio spectrometer at Tremsdorf. Furthermore, joint observation campaigns with other ground- and space-based instruments (Gregor, RHESSI, SDO, Solar Orbiter, ...) are suggested. |
| Title: | LOFAR - As it is built |
| Name: | Corina Vogt |
| Abstract: | I will present LOFAR as it is built at the moment within the Netherlands and throughout Europe. I will also mention LOFAR's capabilities, the station layout and array configuration. |
| Title: | The potential for Galactic Plane Surveys with LOFAR |
| Name: | Glenn White |
| Abstract: | Low frequency radio surveys of the Galactic Plane will provide a new window to view a diverse range of astrophysical phenomena in the galactic plane. In this review, the importance of LOFAR to studies of star formation, supernova remnants, and large scale phenomena such as supershells and outflows will be examined, and an overview will be presented for kind of surveys that will uniquely become accessible. |
| Title: | The Transients KSP: Aims and Means |
| Name: | Ralph Wijers |
| Abstract: | I will outline the plans of the Transients KSP as they stand today and give a brief progress report on the implementation of the project. Emphasis will be placed on expected science highlights and needed capabilities, as well as open issues in the project. |
| Title: | X-WiN, a Network Infrastructure for Research Projects |
| Name: | Martin Wilhelm |
| Abstract: | Many international resarch projects like LOFAR are dependent on reliable and highly productive networks. In nearly all countries, National Research and Education Networks (NRENs) provide such a basis. In addition, the NRENs in Europe are interconnected by GÉANT 2, a powerfull backbone for researchers in Europe. This presentation will give an overview of the German network X-WiN and will show, how X-WiN is embedded in the worldwide community of NRENs.
The presentation will also show how projects like LOFAR can benefit from such an infrastructure. |
| Title: | Status Update on the LOFAR Science Processing Pipelines |
| Name: | Michael Wise |
| Abstract: | From its inception, the LOFAR project has been designed to provide a wide range of scientific capabilities to its astronomical users. These capabilities include not only traditional interferometric imaging but also the ability to detect radio transients on short timescales, radio emission from cosmic ray-induced particle showers, and efficient surveys for pulsars to name a few. The definition of LOFAR's observing capabilities has largely been driven by the scientific goals of the Key Science Projects (KSPs). Taken together the ambitions of these KSPs span a broad range of astrophysical studies. Supporting this scientific diversity requires an innovative and extremely flexible system capable of dynamic scheduling, real-time response, and multiple concurrent observations. In this talk, we will provide an overview of the scientific observing modes currently planned for LOFAR as well as provide an update on the capabilities of the system now and in the coming months.
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| Title: | Difference imaging in radio interferometry |
| Name: | Olaf Wucknitz |
| Abstract: | A promising approach to find gravitational lenses is to select objects with time-variable extended emission. Since intrinsic variability (but also scintillation) is generally only possible for compact sources, the signature of extended variability provides evidence for several compact components with small separations. In a good fraction of these objects, the multiple images will just be an illusion caused by a gravitational lens.
I discuss the development of difference imaging algorithms in radio interferometry. Independent deconvolution with subsequent subtraction is not an option, because difference images produced in this way would be dominated by deconvolution errors.
A multi-channel adaption of CLEAN is a viable alternative. The availability of powerful deconvolution techniques for variable sources may also be of relevance for other fields of research. |
| Title: | The Epoch of Reionization with LOFAR |
| Name: | Saleem Zaroubi |
| Abstract: | I'll review the status of the LOFAR Epoch of Reionization key science project. |
