A Framework for RFI Simulation and Performance Verification

The next generation interferometric radio telescope, the Square Kilometre Array (SKA), which will be the most sensitive and largest radio telescope ever constructed, could greatly contribute to the detection, survey and characterization of Gamma Ray Bursts (GRBs). By the SKA, it will be possible to perform the follow up of GRBs even for several months. This approach would be extremely useful to extend the Spectrum Energetic Distribution (SED) from the gamma to the to radio band and would increase the number of radio detectable GRBs. In principle, the SKA could help to understand the physics of GRBs by setting constraints on theoretical models. This goal could be achieved by taking into account multiple observations at different wavelengths in order to obtain a deeper insight of the sources. Here, we present an estimation of GRB radio detections, showing that the GRBs can really be observed by the SKA. The approach that we present consists in determining blind detection rates derived by a very large sample consisting of merging several GRB catalogues observed by current missions as Swift, Fermi, Agile and INTEGRAL and by previous missions as BeppoSAX, CGRO, GRANAT, HETE-2, Ulysses and Wind. The final catalogue counts 7516 distinct sources. We compute the fraction of GRBs that could be observed by the SKA at high and low frequencies, above its observable sky. Considering the planned SKA sensitivity and through an extrapolation based on previous works and observations, we deduce the minimum fluence in the range 15-150 keV. This is the energy interval where a GRB should emit to be detectable in the radio band by the SKA. Results seem consistent with observational capabilities.

Large scale radio astronomy (RA) activity, brought to focus in South Africa with the Square Kilometre Array (SKA) developments, only began to impact on local engineering teams from around 2004. The country's first demonstrator was ready for evaluation towards the end of 2007. It was at that point that my EMRIN group's engagement on radio frequency interference (RFI) began. After a review of a number of European RA sites, and doing some calculations of required electromagnetic quietness required for viable SKA observations, it became apparent that RFI management would be a major priority for any contemporary large radio research instruments. This talk will discuss components of site development that are now considered essential for any such instruments to be regarded as robust. The presentation will review: 1. Electromagnetic compatibility (EMC) principles illustrated with simple schematic experiments and computational electromagnetics. The pictorial material will emphasise an understanding of current paths, resistive, E and B-field coupling mechanisms and then the use of enclosures, interfaces and cabling structures [1-3]. Some suitable sensors and their calibration will be described [4-6]. 2. Various radio astronomy observatories (RAO's) that have been visited in Europe and South Africa which will be considered in the light of these principles. 3. Experience gained from the South African experimental demonstrator model (XDM), the Karoo Array Telescopes (KAT-7 and MeerKAT) and some Square Kilometre Array (SKA) precursor lower-frequency arrays [7-21]. 4. Requirements for designing robust large radio research instruments where challenges for these large science projects will be posed. The two primary purposes of the presentation will be to: a) promote the viewpoint that site and instrument construction must embrace EMC principles from the start, and b) encourage the interaction of engineers, scientists and astronomers throughout the development process.

On behalf of the ASKAP team, this paper reviews the goals and status of the Australian Square Kilometre Array Pathfinder (ASKAP). ASKAP demonstrates key concepts for the Square Kilometre Array (SKA) radio telescope including: phased array feeds, high performance computing, and a radio quiet site suitable for the most sensitive radio telescope. ASKAP is being deployed to the Murchison Radio-astronomy Observatory in Western Australia. Six antennas have been installed and a further 30 will be installed this year. At the time of writing, February 2011, the first phased array feed has been assembled and integration with downconversion and beamforming systems is about to commence.

We report the first measurements of radio frequency spectrum occupancy performed at sites aimed to host the future radio astronomy observatory in Indonesia. The survey is intended to obtain the radio frequency interference (RFI) environment in a spectral range from low frequency 10 MHz up to 8 GHz. The measurements permit the identification of the spectral occupancy over those selected sites in reference to the allocated radio spectrum in Indonesia. The sites are in close proximity to Australia, the future host of Square Kilometre Array (SKA) at low frequency. Therefore, the survey was deliberately made to approximately adhere the SKA protocol for RFI measurements, but with lower sensitivity. The RFI environment at Bosscha Observatory in Lembang was also measured for comparison. Within the sensitivity limit of the measurement equipment, it is found that a location called Fatumonas in the surrounding of Mount Timau in West Timor has very low level of RFI, with a total spectrum occupancy in this measured frequency range being about 1 %, mostly found at low frequency below 20 MHz. More detailed measurements as well as a strategy for a radio quiet zone must be implemented in the near future.

This paper will report on the progress in the research field of radio astronomy in Malaysia and also in South-East Asia. Radio astronomy research can be said to have only started being done actively in Malaysia in 2005. Fundamental setup and some basic research were done in the early parts. Jupiter radio bursts as well as radio meteor counting were the first few projects. Currently a medium-sized radio telescope which was recently purchased is being used to undergo more advanced research such as observing spectrum of galaxy clusters in order to study Dark Matter. This paper will also report on the latest results on the survey of Radio Frequency Interference (RFI), which is currently done on chosen candidate sites in Malaysia in order to setup on it a large radio telescope in the future. The best site with the lowest averaged RFI level is found at Langkawi (−100.33 dBm or 4.4 × 106 Jy). The author is the chair for the Radio Astronomy Working Group for the South-East Asia Astronomy Network (SEAAN) and the Malaysian team is very much an important part of this group. This group will eventually be a research hub for the global projects of the Global-Very Long Baseline Interferometer (Global-VLBI) and the Square Kilometre Array (SKA).

In radio astronomy, radio frequency interference (RFI) refers to any signal captured by a radio telescope that did not originate from the observed target in the sky. As RFI corrupts observational data and may even damage radio telescope equipment, astronomers seek to store data on RFI, with the aim of mitigating or preventing future interference events. This is a concern for the MeerKAT telescope, precursor to the Square Kilometer Array and one of the largest and most sensitive radio telescope in the world to date. Currently, RFI data at MeerKAT is collected in many different file formats that do not fit into traditional database models created to store data in a fixed schema. Therefore, we have designed a scalable database model for RFI storage, that supports many databases and many data models. The database is deployed in a Dockerized environment. Preliminary testing of our design shows linearly scaling of data ingestion as data sizes increases, as well as fast query processing.

The Square Kilometre Array (SKA) will be the world's largest and most sensitive radio telescope. It will address fundamental unanswered questions about our Universe including how the first stars and galaxies formed after the big bang, how dark energy is accelerating the expansion of the Universe, the role of magnetism in the cosmos, the nature of gravity, and the search for life beyond Earth. In this paper we discuss the data transport challenge posed by this transformational instrument.

The Square Kilometre Array (SKA) project is responsible for developing the SKA Observatory, the world’s largest radio telescope, with eventually over a square kilometre of collecting area and including a general headquarters as well as two radio telescopes: SKA1-Mid in South Africa and SKA1-Low in Australia. The SKA project consists of a number of subsystems (elements) among which the Telescope Manager (TM) is the one involved in controlling and monitoring the SKA telescopes. The TM element has three primary responsibilities: management of astronomical observations, management of telescope hardware and software subsystems, management of data to support system operations and all stakeholders (operators, maintainers, engineers and science users) in achieving operational, maintenance and engineering goals. Operators, maintainers, engineers and science users will interact with TM via appropriate user interfaces (UI). The TM UI framework envisaged is a complete set of general technical solutions (components, technologies and design information) for implementing a generic computing system (UI platform). Such a system will enable UI components to be instantiated to allow for human interaction via screens, keyboards, mouse and to implement the necessary logic for acquiring or deriving the information needed for interaction. It will provide libraries and specific Application Programming Interfaces (APIs) to implement operator and engineer interactive interfaces. This paper will provide a status update of the TM UI framework, UI platform and UI components design effort, including the technology choices, and discuss key challenges in the TM UI architecture, as well as our approaches to addressing them.

The goal of the Square Kilometre Array is to increase the sensitivity of radio telescopes a hundred-fold in the frequency range of ∼70 MHz to 10 GHz. In order to exploit its tremendous scientific capabilities it should be made as robust as possible against unwanted man-made Radio Frequency Interference (RFI). An essential part in this RFI protection scheme is the establishment of Radio Quiet Zones around the instrument, in which regulatory and other legislative measures will ensure acceptable levels of unwanted emissions that could degrade the quality of the astronomical data. An overview will be given of the principles underlying the establishment of Radio Quiet Zones in general, and their application to the Square Kilometre Array case.

This decade, the Square Kilometre Array (SKA) will perform its first observations. Preparations for building dishes, antennas, correlators and infrastructure are well underway. Concurrently, software for the processing of SKA observations is developed at a number of levels. At a more basic level there are the telescope monitoring and control systems and also the correlator software. On top of that, in order to deliver science ready data products, software pipelines are needed for radio frequency interference (RFI) mitigation, averaging, calibration and imaging. Here, we focus on the SAGECal calibration package, in particular on the times needed to obtain calibration solutions. This is an important aspect, since this package is now used for the Epoch of Reionization (EoR) Key Science Project of LOFAR, but will also have to run optimally on SKAI LOW. In terms of number of stations used for observing this amounts to a factor 10 increase, from 51 to 512 stations. Consequentially, the disk space needed to store an observation will increase by a factor 100, provided the number of frequency channels remains the same. In this paper we investigate the scaling behaviour of SAGECal, whose runtimes should ideally scale linearly with the number of stations. We also explain the algorithms inside SAGECal and use them to explain its scaling behaviour.

Radio Telescopes are inevitably exposed to undesirable radio frequency interference (RFI) signals from terrestrial human activity and are becoming stronger with time and with increasing population density, urbanisation and modernisation of communication system degrading the quality of astronomical observations. The problem is aggravated with highly sensitive radio telescope at low frequency and further gets affected with broadband radio astronomy receivers.An additional threat comes from self-generated RFI produced by the increasingly computer controlled and data intensive operations of a typical radio telescope. All these aspects of RFI significantly affect the highly sensitive upgraded Giant Metrewave Radio Telescope (uGMRT), working at low frequency with a seamless frequency coverage from 50MHz to 1.5GHz having an instantaneous bandwidth of 400MHz.

We consider a decaying scalar dark matter (DM) with mass $m_\chi$ in the range 10 GeV - 10 TeV and vary the branching ratios of all possible two-body SM final states (excluding and including $\nu\bar{\nu}$) in the range $0\%-100\%$ to derive constraints on the total decay width $\Gamma$ using the data collected by several astrophysical and cosmological observations. We find that, $\Gamma \lesssim 10^{-26} - 10^{-27}\,{\rm s}^{-1}$ (excluding $\nu\bar{\nu}$) and $\Gamma \lesssim 10^{-24} - 10^{-26}\,{\rm s}^{-1}$ (including $\nu\bar{\nu}$) are allowed, depending on the values of $m_\chi$, which are most robust upper limits on $\Gamma$ for a generic decaying scalar DM. We then investigate the prospect of the upcoming Square Kilometre Array (SKA) radio telescope in detecting the DM decay induced radio signals originating inside the dwarf spheroidal (dSph) galaxies. We have classified the DM parameter space, allowed by the existing observations, independently of the branching ratio of each individual two-body SM final state, based on the detectability at the SKA. Excluding the $\nu\bar{\nu}$ decay mode, we find that, throughout the DM mass range considered, $\Gamma \gtrsim 10^{-30}\,{\rm s}^{-1} - 10^{-29}\,{\rm s}^{-1}$ is detectable for all possible branching ratio combinations at the SKA (assuming 100 hours of observation time), with conservative choices for the relevant astrophysical parameters. On the other hand, when arbitrary branching ratios are allowed also for the $\nu\bar{\nu}$ decay mode, DM decays can be probed independently of the branching ratio of each SM final state for $\Gamma \gtrsim 2 \times 10^{-29}\,{\rm s}^{-1}$, provided DM masses are greater than a few hundreds of GeV.

As the most sensitive single-dish radio telescope, the Five-hundred Aperture Spherical radio Telescope (FAST) is very susceptive to radio frequency interference (RFI) from active radio services. Moreover, due to the rapid development of space applications and research, satellite interference has become one of the main RFI sources for FAST, particularly at the L band. Therefore, we have developed several measures to mitigate satellite RFI. On the one hand, an antenna with 4.5-meter diameter has been constructed and installed at the FAST site to detect the satellite interference in the frequency band between 1 to 5 GHz. Meanwhile, we have developed a satellite RFI database based on the FAST sky coverage, the observing frequency bands, and known satellite systems. By combining the satellite RFI monitoring antenna and the database, we have established a satellite RFI mitigation system. With this system, we can not only track satellites to collect their characteristics and update the database but also help the observer to program the observing plan by predicting satellite interference. During the practical observation of FAST at the L band, the feasibility of this system to mitigate satellite RFI has been proved. In particular, the system effectively avoids strong satellite interference from entering the main beam of the telescope and causing receiver saturation.

The Square Kilometre Array (SKA) Project is a global science and engineering project realizing the next-generation radio telescopes operating in the metre and centimetre wavelengths regions. This paper addresses design concepts of the broadband, exceptionally sensitive receivers and reflector antennas deployed in the SKA1-Mid radio telescope to be located in South Africa. SKA1-Mid (350 MHz -13.8 GHz with an option for an upper limit of similar to 24 GHz) will consist of 133 reflector antennas using an unblocked aperture, offset Gregorian configuration with an effective diameter of 15 m. Details on the unblocked aperture Gregorian antennas, low noise front ends and advanced direct digitization receivers, are provided from a system design perspective. The unblocked aperture results in increased aperture efficiency and lower side-lobe levels compared to a traditional on-axis configuration. The low side-lobe level reduces the noise contribution due to ground pick-up but also makes the antenna less susceptible to ground-based RFI sources. The addition of extra shielding on the sub-reflector provides a further reduction of ground pick-up. The optical design of the SKA1-Mid reflector antenna has been tweaked using advanced EM simulation tools in combination with sophisticated models for sky, atmospheric and ground noise contributions. This optimal antenna design in combination with very low noise, partially cryogenic, receivers and wide instantaneous bandwidth provide excellent receiving sensitivity in combination with instrumental flexibility to accommodate a wide range of astronomical observation modes.

The first Search for Extra-Terrestrial Intelligence (SETI) conducted with very long baseline interferometry (VLBI) is presented. By consideration of the basic principles of interferometry, we show that VLBI is efficient at discriminating between SETI signals and human generated radio frequency interference (RFI). The target for this study was the star Gliese 581, thought to have two planets within its habitable zone. On 2007 June 19, Gliese 581 was observed for 8 hr at 1230-1544 MHz with the Australian Long Baseline Array. The data set was searched for signals appearing on all interferometer baselines above five times the noise limit. A total of 222 potential SETI signals were detected and by using automated data analysis techniques were ruled out as originating from the Gliese 581 system. From our results we place an upper limit of 7 MW Hz–1 on the power output of any isotropic emitter located in the Gliese 581 system within this frequency range. This study shows that VLBI is ideal for targeted SETI including follow-up observations. The techniques presented are equally applicable to next-generation interferometers, such as the long baselines of the Square Kilometre Array.