Publications by Christopher Williams


ALFABURST: a commensal search for fast radio bursts with Arecibo

Monthly Notices of the Royal Astronomical Society Oxford University Pres 474 (2017) 3847-3856

GRIFFIN Foster, A Karastergiou, G Golpayegani, M Surnis, J Chennamangalam, M McLaughlin, W Armour, J Cobb, DHE MacMahon, X Pei, K Rajwade, APV Siemion, D Werthimer, C Williams

ALFABURST has been searching for fast radio bursts (FRBs) commensally with other projects using the Arecibo L-band Feed Array receiver at the Arecibo Observatory since 2015 July. We describe the observing system and report on the non-detection of any FRBs from that time until 2017 August for a total observing time of 518 h. With current FRB rate models, along with measurements of telescope sensitivity and beam size, we estimate that this survey probed redshifts out to about 3.4 with an effective survey volume of around 600 000 Mpc 3 . Based on this, we would expect, at the 99 per cent confidence level, to see at most two FRBs. We discuss the implications of this non-detection in the context of results from other telescopes and the limitation of our search pipeline. During the survey, single pulses from 17 known pulsars were detected. We also report the discovery of a Galactic radio transient with a pulse width of 3 ms and dispersion measure of 281 pc cm -3 , which was detected while the telescope was slewing between fields.


SETIBURST: A robotic, commensal, realtime multi-science backend for the Arecibo Telescope

Astrophysical Journal Supplement Series Institute of Physics 228 (2017) 21-21

J Chennamangalam, D MacMahon, J Cobb, A Karastergiou, APV Siemion, K Rajwade, W Armour, V Gajjar, MA McLaughlin, D Werthimer, C Williams

Radio astronomy has traditionally depended on observatories allocating time to observers for exclusive use of their telescopes. The disadvantage of this scheme is that the data thus collected is rarely used for other astronomy applications, and in many cases, is unsuitable. For example, properly calibrated pulsar search data can, with some reduction, be used for spectral line surveys. A backend that supports plugging in multiple applications to a telescope to perform commensal data analysis will vastly increase the science throughput of the facility. In this paper, we present "SETIBURST," a robotic, commensal, realtime multi-science backend for the 305 m Arecibo Telescope. The system uses the 1.4 GHz, seven-beam Arecibo L-band Feed Array (ALFA) receiver whenever it is operated. SETIBURST currently supports two applications: SERENDIP VI, a SETI spectrometer that is conducting a search for signs of technological life, and ALFABURST, a fast transient search system that is conducting a survey of fast radio bursts (FRBs). Based on the FRB event rate and the expected usage of ALFA, we expect 0-5 FRB detections over the coming year. SETIBURST also provides the option of plugging in more applications. We outline the motivation for our instrumentation scheme and the scientific motivation of the two surveys, along with their descriptions and related discussions.


Limits on fast radio bursts at 145 MHz with ARTEMIS, a real-time software backend

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 452 (2015) 1254-1262

A Karastergiou, J Chennamangalam, W Armour, C Williams, B Mort, F Dulwich, S Salvini, A Magro, S Roberts, M Serylak, A Doo, AV Bilous, RP Breton, H Falcke, J-M Griessmeier, JWT Hessels, EF Keane, VI Kondratiev, M Kramer, J van Leeuwen, A Noutsos, S Oslowski, C Sobey, BW Stappers, P Weltevrede


ARTEMIS: A Real-Time Data Processing Pipeline for the Detection of Fast Transients

2015 1st URSI Atlantic Radio Science Conference (URSI AT-RASC) (2015)

J Chennamangalam, A Karastergiou, W Armour, C Williams, M Giles, IEEE


Flexible services for the support of research.

Philos Trans A Math Phys Eng Sci 371 (2013) 20120067-

M Turilli, D Wallom, C Williams, S Gough, N Curran, R Tarrant, D Bretherton, A Powell, M Johnson, T Harmer, P Wright, J Gordon

Cloud computing has been increasingly adopted by users and providers to promote a flexible, scalable and tailored access to computing resources. Nonetheless, the consolidation of this paradigm has uncovered some of its limitations. Initially devised by corporations with direct control over large amounts of computational resources, cloud computing is now being endorsed by organizations with limited resources or with a more articulated, less direct control over these resources. The challenge for these organizations is to leverage the benefits of cloud computing while dealing with limited and often widely distributed computing resources. This study focuses on the adoption of cloud computing by higher education institutions and addresses two main issues: flexible and on-demand access to a large amount of storage resources, and scalability across a heterogeneous set of cloud infrastructures. The proposed solutions leverage a federated approach to cloud resources in which users access multiple and largely independent cloud infrastructures through a highly customizable broker layer. This approach allows for a uniform authentication and authorization infrastructure, a fine-grained policy specification and the aggregation of accounting and monitoring. Within a loosely coupled federation of cloud infrastructures, users can access vast amount of data without copying them across cloud infrastructures and can scale their resource provisions when the local cloud resources become insufficient.


A GPU-based survey for millisecond radio transients using ARTEMIS

ArXiv (0)

W Armour, A Karastergiou, M Giles, C Williams, A Magro, K Zagkouris, S Roberts, S Salvini, F Dulwich, B Mort

Astrophysical radio transients are excellent probes of extreme physical processes originating from compact sources within our Galaxy and beyond. Radio frequency signals emitted from these objects provide a means to study the intervening medium through which they travel. Next generation radio telescopes are designed to explore the vast unexplored parameter space of high time resolution astronomy, but require High Performance Computing (HPC) solutions to process the enormous volumes of data that are produced by these telescopes. We have developed a combined software /hardware solution (code named ARTEMIS) for real-time searches for millisecond radio transients, which uses GPU technology to remove interstellar dispersion and detect millisecond radio bursts from astronomical sources in real-time. Here we present an introduction to ARTEMIS. We give a brief overview of the software pipeline, then focus specifically on the intricacies of performing incoherent de-dispersion. We present results from two brute-force algorithms. The first is a GPU based algorithm, designed to exploit the L1 cache of the NVIDIA Fermi GPU. Our second algorithm is CPU based and exploits the new AVX units in Intel Sandy Bridge CPUs.


Observations of transients and pulsars with LOFAR international stations

ArXiv (0)

M Serylak, A Karastergiou, C Williams, W Armour, LOFARPW Group

The LOw FRequency ARray - LOFAR is a new radio telescope that is moving the science of radio pulsars and transients into a new phase. Its design places emphasis on digital hardware and flexible software instead of mechanical solutions. LOFAR observes at radio frequencies between 10 and 240 MHz where radio pulsars and many transients are expected to be brightest. Radio frequency signals emitted from these objects allow us to study the intrinsic pulsar emission and phenomena such as propagation effects through the interstellar medium. The design of LOFAR allows independent use of its stations to conduct observations of known bright objects, or wide field monitoring of transient events. One such combined software/hardware solution is called the Advanced Radio Transient Event Monitor and Identification System (ARTEMIS). It is a backend for both targeted observations and real-time searches for millisecond radio transients which uses Graphical Processing Unit (GPU) technology to remove interstellar dispersion and detect millisecond radio bursts from astronomical sources in real-time using a single LOFAR station.


Observations of Transients and Pulsars with LOFAR International Stations

ELECTROMAGNETIC RADIATION FROM PULSARS AND MAGNETARS 466 (2012) 83-+

M Serylak, A Karastergiou, C Williams, W Armour, LOFARPW Grp


GridPP: Development of the UK computing Grid for particle physics

Journal of Physics G: Nuclear and Particle Physics 32 (2006)

PJW Faulkner, LS Lowe, CLA Tan, PM Watkins, DS Bailey, TA Barrass, NH Brook, RJH Croft, MP Kelly, CK Mackay, S Metson, OJE Maroney, DM Newbold, FF Wilson, PR Hobson, A Khan, P Kyberd, JJ Nebrensky, M Bly, C Brew, S Burke, R Byrom, J Coles, LA Cornwall, A Djaoui, L Field, SM Fisher, GT Folkes, NI Geddes, JC Gordon, SJC Hicks, JG Jensen, G Johnson, D Kant, DP Kelsey, G Kuznetsov, J Leake, RP Middleton, GN Patrick, G Prassas, BJ Saunders, D Ross, RA Sansum, T Shah, B Strong, O Synge, R Tam, M Thorpe, S Traylen, JF Wheeler, NGH White, AJ Wilson, I Antcheva, E Artiaga, J Beringer, IG Bird, J Casey, AJ Cass, R Chytracek, MV Gallas Torreira, J Generowicz, M Girone, G Govi, F Harris, M Heikkurinen, A Horvath, E Knezo, M Litmaath, M Lubeck, J Moscicki, I Neilson, E Poinsignon, W Pokorski, A Ribon, Z Sekera, DH Smith, WL Tomlin, JE van Eldik, J Wojcieszuk, FM Brochu, S Das, K Harrison, M Hayes, JC Hill, CG Lester, MJ Palmer, MA Parker, M Nelson, MR Whalley, EWN Glover, P Anderson, PJ Clark, AD Earl, A Holt, A Jackson, B Joo, RD Kenway, CM Maynard, J Perry, L Smith

The GridPP Collaboration is building a UK computing Grid for particle physics, as part of the international effort towards computing for the Large Hadron Collider. The project, funded by the UK Particle Physics and Astronomy Research Council (PPARC), began in September 2001 and completed its first phase 3 years later. GridPP is a collaboration of approximately 100 researchers in 19 UK university particle physics groups, the Council for the Central Laboratory of the Research Councils and CERN, reflecting the strategic importance of the project. In collaboration with other European and US efforts, the first phase of the project demonstrated the feasibility of developing, deploying and operating a Grid-based computing system to meet the UK needs of the Large Hadron Collider experiments. This note describes the work undertaken to achieve this goal. © 2006 IOP Publishing Ltd.


Optical spectra and Auger recombination in SiGe/Si heterostructures in 10 μm range of wavelengths

Superlattices and Microstructures Elsevier BV 19 (1996) 25-32

E Corbin, CJ Williams, KB Wong, RJ Turton, M Jaros