Publications by Aris Karastergiou

Initial results from a realtime FRB search with the GBT

Monthly Notices of the Royal Astronomical Society Oxford University Press 497 (2020) 352-360

D Agarwal, D Lorimer, MP Surnis, X Pei, A Karastergiou, G Golpayegani, D Werthimer, J Cobb, MA McLaughlin, S White, W Armour, DHE MacMahon, APV Siemion, G Foster

We present the data analysis pipeline, commissioning observations, and initial results from the GREENBURST fast radio burst (FRB) detection system on the Robert C. Byrd Green Bank Telescope (GBT) previously described by Surnis et al., which uses the 21-cm receiver observing commensally with other projects. The pipeline makes use of a state-of-the-art deep learning classifier to winnow down the very large number of false-positive single-pulse candidates that mostly result from radio frequency interference. In our observations, totalling 156.5 d so far, we have detected individual pulses from 20 known radio pulsars that provide an excellent verification of the system performance. We also demonstrate, through blind injection analyses, that our pipeline is complete down to a signal-to-noise threshold of 12. Depending on the observing mode, this translates into peak flux sensitivities in the range 0.14–0.89 Jy. Although no FRBs have been detected to date, we have used our results to update the analysis of Lawrence et al. to constrain the FRB all-sky rate to be 1150+200−180 per day above a peak flux density of 1 Jy. We also constrain the source count index α = 0.84 ± 0.06, which indicates that the source count distribution is substantially flatter than expected from a Euclidean distribution of standard candles (where α = 1.5). We discuss this result in the context of the FRB redshift and luminosity distributions. Finally, we make predictions for detection rates with GREENBURST, as well as other ongoing and planned FRB experiments.

Possible periodic activity in the repeating FRB 121102


KM Rajwade, MB Mickaliger, BW Stappers, V Morello, D Agarwal, CG Bassa, RP Breton, M Caleb, A Karastergiou, EF Keane, DR Lorimer

Limits on absorption from a 332-MHz survey for fast radio bursts


KM Rajwade, MB Mickaliger, BW Stappers, CG Bassa, RP Breton, A Karastergiou, EF Keane

The Thousand-Pulsar-Array programme on MeerKAT - I. Science objectives and first results


S Johnston, A Karastergiou, MJ Keith, X Song, P Weltevrede, F Abbate, M Bailes, S Buchner, F Camilo, M Geyer, B Hugo, A Jameson, M Kramer, A Parthasarathy, DJ Reardon, A Ridolfi, M Serylak, RM Shannon, R Spiewak, W van Straten, VV Krishnan, F Jankowski, BW Meyers, L Oswald, B Posselt, C Sobey, A Szary, J van Leeuwen

Understanding the radio beam of PSR J1136+1551 through its single pulses

Monthly Notices of the Royal Astronomical Society Oxford University Press 489 (2019) 310-324

L Oswald, A Karastergiou, S Johnston

The frequency widening of pulsar profiles is commonly attributed to lower frequencies being produced at greater heights above the surface of the pulsar; so-called radius-to-frequency mapping (RFM). The observer’s view of pulsar emission is a 1D cut through a 3D magnetosphere: we can only see that emission which points along our line of sight. However, by comparing the frequency evolution of many single pulses positioned at different phases, we can build up an understanding of the shape of the active emission region. We use single pulses observed with the Giant Metrewave Radio Telescope to investigate the emission region of PSR J1136+1551 and test RFM. Assuming that emission is produced tangential to the magnetic field lines and that each emission frequency corresponds to a single height, we simulate the single pulse profile evolution resulting from the canonical conal beam model and a fan beam model. Comparing the results of these simulations with the observations, we conclude that the emission region of PSR J1136+1551 is better described by the fan beam model. The diversity of profile widening behaviour observed for the single pulses can be explained by orthogonally polarized modes propagating along differing frequency-dependent paths in the magnetosphere.

Linking long- and short-term emission variability in pulsars


PR Brook, A Karastergiou, S Johnston

GREENBURST: A commensal Fast Radio Burst search back-end for the Green Bank Telescope

Publications of the Astronomical Society of Australia Cambridge University Press 36 (2019) e032

MP Surnis, D Agarwal, Lorimer, X Pei, G Foster, A Karastergiou, G Golpayegani, RJ Maddalena, S White, W Armour, J Cobb, MA McLaughlin, DHE Macmahon, APV Siemion, D Werthimer, CJ Williams

We describe the design and deployment of GREENBURST, a commensal Fast Radio Burst (FRB) search system at the Green Bank Telescope. GREENBURST uses the dedicated L-band receiver tap to search over the 960$-$1920 MHz frequency range for pulses with dispersion measures out to $10^4$ pc cm$^{-3}$. Due to its unique design, GREENBURST will obtain data even when the L-band receiver is not being used for scheduled observing. This makes it a sensitive single pixel detector capable of reaching deeper in the radio sky. While single pulses from Galactic pulsars and rotating radio transients will be detectable in our observations, and will form part of the database we archive, the primary goal is to detect and study FRBs. Based on recent determinations of the all-sky rate, we predict that the system will detect approximately one FRB for every 2$-$3 months of continuous operation. The high sensitivity of GREENBURST means that it will also be able to probe the slope of the FRB source function, which is currently uncertain in this observing band.

A fast radio burst with frequency-dependent polarization detected during Breakthrough Listen observations


DC Price, G Foster, M Geyer, W van Straten, V Gajjar, G Hellbourg, A Karastergiou, EF Keane, APV Siemion, I Arcavi, R Bhat, M Caleb, S-W Chang, S Croft, D DeBoer, I de Pater, J Drew, JE Enriquez, W Farah, N Gizani, JA Green, H Isaacson, J Hickish, A Jameson, M Lebofsky, DHE MacMahon, A Moller, CA Onken, E Petroff, D Werthimer, C Wolf, SP Worden, YG Zhang

The LOFAR Tied-Array All-Sky Survey (LOTAAS): Survey overview and initial pulsar discoveries


S Sanidas, S Cooper, CG Bassa, JWT Hessels, VI Kondratiev, D Michilli, BW Stappers, CM Tan, J van Leeuwen, L Cerrigone, RA Fallows, M Iacobelli, E Orru, RF Pizzo, A Shulevski, MC Toribio, S ter Veen, P Zucca, L Bondonneau, J-M Griessmeier, A Karastergiou, M Kramer, C Sobey

The period-width relationship for radio pulsars revisited


S Johnston, A Karastergiou

Low-frequency Faraday rotation measures towards pulsars using LOFAR: probing the 3D Galactic halo magnetic field


C Sobey, AV Bilous, J-M Griessmeier, JWT Hessels, A Karastergiou, EF Keane, VI Kondratiev, M Kramer, D Michilli, A Noutsos, M Pilia, EJ Polzin, BW Stappers, CM Tan, J van Leeuwen, JPW Verbiest, P Weltevrede, G Heald, MIR Alves, E Carretti, T Ensslin, M Haverkorn, M Iacobelli, W Reich, C Van Eck

A GPU implementation of the correlation technique for real-time Fourier domain pulsar acceleration searches

Astrophysical Journal Supplement Series American Astronomical Society 239 (2018) 28

S Dimoudi, K Adamek, P Thiagaraj, SM Ransom, A Karastergiou, W Armour

The study of binary pulsars enables tests of general relativity. Orbital motion in binary systems causes the apparent pulsar spin frequency to drift, reducing the sensitivity of periodicity searches. Acceleration searches are methods that account for the effect of orbital acceleration. Existing methods are currently computationally expensive, and the vast amount of data that will be produced by next-generation instruments such as the Square Kilometre Array necessitates real-time acceleration searches, which in turn requires the use of high-performance computing (HPC) platforms. We present our implementation of the correlation technique for the Fourier Domain Acceleration Search (FDAS) algorithm on Graphics Processor Units (GPUs). The correlation technique is applied as a convolution with multiple finite impulse response (FIR) filters in the Fourier domain. Two approaches are compared: the first uses the NVIDIA cuFFT library for applying Fast Fourier transforms (FFTs) on the GPU, and the second contains a custom FFT implementation in GPU shared memory. We find that the FFT shared-memory implementation performs between 1.5 and 3.2 times faster than our cuFFT-based application for smaller but sufficient filter sizes. It is also 4–6 times faster than the existing GPU and OpenMP implementations of FDAS. This work is part of the AstroAccelerate project, a many-core accelerated time-domain signal-processing library for radio astronomy.

Verifying and reporting Fast Radio Bursts


G Foster, A Karastergiou, M Geyer, M Surnis, G Golpayegani, K Lee, D Lorimer, DC Price, K Rajwade

The NANOGrav 11-year Data Set: Pulse Profile Variability


PR Brook, A Karastergiou, MA McLaughlin, MT Lam, Z Arzoumanian, S Chatterjee, JM Cordes, K Crowter, M DeCesar, PB Demorest, T Dolch, JA Ellis, RD Ferdman, E Ferrara, E Fonseca, PA Gentile, G Jones, ML Jones, TJW Lazio, L Levin, DR Lorimer, RS Lynch, C Ng, DJ Nice, TT Pennucci, SM Ransom, PS Ray, R Spiewak, IH Stairs, DR Stinebring, K Stovall, JK Swiggum, WW Zhu

LOFAR Discovery of a 23.5 s Radio Pulsar


CM Tan, CG Bassa, S Cooper, TJ Dijkema, P Esposito, JWT Hessels, VI Kondratiev, M Kramer, D Michilli, S Sanidas, TW Shimwell, BW Stappers, J van Leeuwen, I Cognard, J-M Griessmeier, A Karastergiou, EF Keane, C Sobey, P Weltevrede

The galactic halo pulsar population

Monthly Notices of the Royal Astronomical Society Oxford University Press 479 (2018) 3094-3100

K Rajwade, J Chennamangalam, D Lorimer, A Karastergiou

Most population studies of pulsars have hitherto focused on the disc of the Galaxy, the Galactic centre, globular clusters, and nearby galaxies. It is expected that pulsars, by virtue of their natal kicks, are also to be found in the Galactic halo. We investigate the possible population of canonical (i.e. non-recycled) radio pulsars in the halo, estimating the number of such pulsars, and the fraction that is detectable via single pulse and periodicity searches. Additionally, we explore the distributions of flux densities and dispersion measures (DMs) of this population. We also consider the effects of different velocity models and the evolution of inclination angle and magnetic field on our results. We show that ∼33  % of all pulsars beaming towards the Earth are in the halo but the fraction reduces to ∼1.5  % if we let the inclination angle and the magnetic field evolve as a falling exponential. Moreover, the fraction that is detectable is significantly limited by the sensitivity of surveys. This population would be most effectively probed by surveys using time-domain periodicity search algorithms. The current non-detections of pulsars in the halo can be explained if we assume that the inclination angle and magnetic field of pulsars evolve with time. We also highlight a possible confusion between bright pulses from halo pulsars and fast radio bursts with low DMs where further follow-up is warranted.

Shock location and CME 3D reconstruction of a solar type II radio burst with LOFAR


P Zucca, DE Morosan, AP Rouillard, R Fallows, PT Gallagher, J Magdalenic, K-L Klein, G Mann, C Vocks, EP Carley, MM Bisi, EP Kontar, H Rothkaehl, B Dabrowski, A Krankowski, J Anderson, A Asgekar, ME Bell, MJ Bentum, P Best, R Blaauw, F Breitling, JW Broderick, WN Brouw, M Brueggen, HR Butcher, B Ciardi, E de Geus, A Deller, S Duscha, J Eisloeffel, MA Garrett, JM Griessmeier, AW Gunst, G Heald, M Hoeft, J Horandel, M Iacobelli, E Juette, A Karastergiou, J van Leeuwen, D McKay-Bukowski, H Mulder, H Munk, A Nelles, E Orru, H Paas, VN Pandey, R Pekal, R Pizzo, AG Polatidis, W Reich, A Rowlinson, DJ Schwarz, A Shulevski, J Sluman, O Smirnov, C Sobey, M Soida, S Thoudam, MC Toribio, R Vermeulen, RJ van Weeren, O Wucknitz, P Zarka

Initial results from the ALFABURST survey

Proceedings of the International Astronomical Union Cambridge University Press 13 (2018) 414-415

M Surnis, R Foster, G Golpayegani, A Karastergiou, D Lorimer, J Chennamangalam, K Rajwade, M McLaughlin, D Agarwal, W Armour, D Werthimer, J Cobb, A Siemion, D MacMahon, D Gorthi, P Xin

Here, we present initial results from the ALFABURST radio transient survey, which is currently running in a commensal mode with the ALFA receiver at the Arecibo telescope. We observed for a total of 1400 hours and have detected single pulses from known pulsars but did not detect any FRBs. The non-detection of FRBs is consistent with the current FRB sky rates.

Revival of the Magnetar PSR J1622-4950: Observations with MeerKAT, Parkes, XMM-Newton, Swift, Chandra, and NuSTAR


F Camilo, P Scholz, M Serylak, S Buchner, M Merryfield, VM Kaspi, RF Archibald, M Bailes, A Jameson, W van Straten, J Sarkissian, JE Reynolds, S Johnston, G Hobbs, TD Abbott, RM Adam, GB Adams, T Alberts, R Andreas, KMB Asad, DE Baker, T Baloyi, EF Bauermeister, T Baxana, TGH Bennett, G Bernardi, D Booisen, RS Booth, DH Bothar, L Boyana, LRS Brederode, JP Burger, T Cheetham, J Conradie, JP Conradie, DB Davidson, G De Bruin, B de Swardt, C de Villiers, DIL de Villiers, MS de Villiers, W de Villiers, C De Waal, MA Dikgale, G du Toit, LJ du Toit, SWP Esterhuysel, B Fanaroff, S Fataari, AR Foley, G Foster, D Fourier, R Gamatham, T Gatsi, R Geschke, S Goedhart, TL Grobler, SC Gumede, MJ Hlakola, A Hokwana, DH Hoorn, D Horn, J Horrell, B Hugo, A Isaacson, O Jacobs, JPJ van Rensburg, JL Jonas, B Jordaan, A Joubert, F Joubert, GIG Jozsa, R Julie, CC Julius, F Kapp, A Karastergiou, F Karels, M Kariseb, R Karuppusamy, V Kasper, EC Knox-Davies, D Koch, PPA Kotze, A Krebs, N Krick, H Kriel, T Kusel, S Lamoor, R Lehmensiek, D Liebenberg, I Liebenberg, RT Lord, B Lunsky, N Mabombo, T Macdonald, P Macfarlane, K Madisa, L Mafhungo, LG Magnus, C Magozore, O Mahgoub, JPL Main, S Makhathini, JA Malan, P Malgas, JR Manley, M Manzini, L Marais, N Marais, SJ Marais, M Maree, A Martens, SD Matshawule, N Matthysen, T Mauch, LD Mc Nally, B Merry, RP Millenaar, C Mjikelo, N Mikhabela, N Mnyandu, IT Moeng, OJ Mokone, TE Monama, K Montshiwa, V Moss, M Mphego, W New, B Ngcebetsha, K Ngoasheng, H Niehaus, P Ntuli, A Nzama, F Obies, M Obrocka, MT Ockards, C Olyn, N Oozeer, AJ Otto, Y Padayachee, S Passmoor, AA Patel, S Paula, A Peens-Hough, B Pholoholo, P Prozesky, S Rakoma, AJT Ramaila, I Rammala, ZR Ramudzuli, M Rasivhaga, S Ratcliffe, HC Reader, R Renil, L Richter, A Robyntjies, D Rosekrans, A Rust, S Salle, N Sambu, CTG Schollar, L Schwardt, S Seranyane, G Sethosa, C Sharper, R Siebrits, SK Sirothia, MJ Slabber, O Smirnov, S Smith, L Sofeya, N Songqumase, R Spann, B Stappers, D Steyn, TJ Steyn, R Strong, A Struthers, C Stuart, P Sunnylall, PS Swart, B Taljaard, C Tasse, G Taylor, IP Theron, V Thondikulam, K Thorat, A Tiplady, O Toruvanda, J van Aardt, T van Balla, L van den Heever, A van der Byl, C van der Merwe, P van der Merwe, PC van Niekerk, R van Rooyen, JP van Staden, V van Tonder, R van Wyk, I Wait, AL Walker, B Wallace, M Welz, LP Williams, B Xaia, N Young, S Zitha

Tracking of an electron beam through the solar corona with LOFAR


G Mann, F Breitling, C Vocks, H Aurass, M Steinmetz, KG Strassmeier, MM Bisi, RA Fallows, P Gallagher, A Kerdraon, A Mackinnon, J Magdalenic, H Rucker, J Anderson, A Asgekar, IM Avruch, ME Bell, MJ Bentum, G Bernardi, P Best, L Birzan, A Bonafede, JW Broderick, M Brueggen, HR Butcher, B Ciardi, A Corstanje, F de Gasperin, E de Geus, A Deller, S Duscha, J Eisloeffel, D Engels, H Falcke, R Fender, C Ferrari, W Frieswijk, MA Garrett, J Griessmeier, AW Gunst, M van Haarlem, TE Hassall, G Heald, JWT Hessels, M Hoeft, J Horandel, A Horneffer, E Juette, A Karastergiou, WFA Klijn, VI Kondratiev, M Kramer, M Kuniyoshi, G Kuper, P Maat, S Markoff, R McFadden, D McKay-Bukowski, JP McKean, DD Mulcahy, H Munk, A Nelles, MJ Norden, E Orru, H Paas, M Pandey-Pommier, VN Pandey, R Pizzo, AG Polatidis, D Rafferty, W Reich, H Rottgering, AMM Scaife, DJ Schwarz, M Serylak, J Sluman, O Smirnov, BW Stappers, M Tagger, Y Tang, C Tasse, S ter Veen, S Thoudam, MC Toribio, R Vermeulen, RJ van Weeren, MW Wise, O Wucknitz, S Yatawatta, P Zarka, JA Zensus