Publications by Aris Karastergiou


framework for assessing the performance of pulsar search pipelines

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 467 (2017) 1661-1677

E van Heerden, A Karastergiou, SJ Roberts


Pulsar braking and the P–$\dot{P}$ diagram

Monthly Notices of the Royal Astronomical Society 467 (2017) 3493-3499

S Johnston, A Karastergiou


SETIBURST: A Robotic, Commensal, Realtime Multi-science Backend for the Arecibo Telescope

ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES 228 (2017) ARTN 21

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


Scattering analysis of LOFAR pulsar observations

Monthly Notices of the Royal Astronomical Society 470 (2017) 2659-2679

M Geyer, A Karastergiou, VI Kondratiev, K Zagkouris, M Kramer, BW Stappers, JM Grießmeier, JWT Hessels, D Michilli, M Pilia, C Sobey

© 2017 The Authors Published by Oxford University Press. We measure the effects of interstellar scattering on average pulse profiles from 13 radio pulsars with simple pulse shapes. We use data from the LOFAR High Band Antennas, at frequencies between 110 and 190 MHz.We apply a forward fitting technique, and simultaneously determine the intrinsic pulse shape, assuming single Gaussian component profiles. We find that the constant τ , associated with scattering by a single thin screen, has a power-law dependence on frequency τ ∝ ν -a , with indices ranging from α = 1.50 to 4.0, despite simplest theoretical models predicting α =4.0 or 4.4. Modelling the screen as an isotropic or extremely anisotropic scatterer, we find anisotropic scattering fits lead to larger power-law indices, often in better agreement with theoretically expected values.We compare the scattering models based on the inferred, frequency-dependent parameters of the intrinsic pulse, and the resulting correction to the dispersion measure (DM). We highlight the cases in which fits of extreme anisotropic scattering are appealing, while stressing that the data do not strictly favour either model for any of the 13 pulsars. The pulsars show anomalous scattering properties that are consistent with finite scattering screens and/or anisotropy, but these data alone do not provide the means for an unambiguous characterization of the screens. We revisit the empirical t versus DM relation and consider how our results support a frequency dependence of a. Very long baseline interferometry, and observations of the scattering and scintillation properties of these sources at higher frequencies, will provide further evidence.


Simultaneous radio and X-ray observations of PSR B0611+22

Monthly Notices of the Royal Astronomical Society 462 (2016) 2518-2526

K Rajwade, A Seymour, DR Lorimer, A Karastergiou, M Serylak, MA McLaughlin, JM Griessmeier

© 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. We report results from simultaneous radio and X-ray observations of PSR B0611+22 which is known to exhibit bursting in its single-pulse emission. The pulse phase of the bursts vary with radio frequency. The bursts are correlated in 327/150 MHz data sets while they are anti-correlated, with bursts at one frequency associated with normal emission at the other, in 820/150 MHz data sets. Also, the flux density of this pulsar is lower than expected at 327 MHz assuming a power law. We attribute this unusual behaviour to the pulsar itself rather than absorption by external astrophysical sources. Using this data set over an extensive frequency range, we show that the bursting phenomenon in this pulsar exhibits temporal variance over a span of few hours. We also show that the bursting is quasi-periodic over the observed band. The anti-correlation in the phase offset of the burst mode at different frequencies suggests that the mechanisms responsible for phase offset and flux enhancement have different dependencies on the frequency. We did not detect the pulsar with XMM-Newton and place a 99 per cent confidence upper limit on the X-ray efficiency of 10 -5 .


LOFAR MSSS: detection of a low-frequency radio transient in 400 h of monitoring of the North Celestial Pole

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 456 (2016) 2321-2342

AJ Stewart, RP Fender, JW Broderick, TE Hassall, T Munoz-Darias, A Rowlinson, JD Swinbank, TD Staley, GJ Molenaar, B Scheers, TL Grobler, M Pietka, G Heald, JP McKean, ME Bell, A Bonafede, RP Breton, D Carbone, Y Cendes, AO Clarke, S Corbel, F de Gasperin, J Eisloeffel, H Falcke, C Ferrari, J-M Griemeier, MJ Hardcastle, V Heesen, JWT Hessels, A Horneffer, M Iacobelli, P Jonker, A Karastergiou, G Kokotanekov, VI Kondratiev, M Kuniyoshi, CJ Law, J van Leeuwen, S Markoff, JCA Miller-Jones, D Mulcahy, E Orru, M Pandey-Pommier, L Pratley, E Rol, HJA Rottgering, AMM Scaife, A Shulevski, CA Sobey, BW Stappers, C Tasse, AJ van der Horst, S van Velzen, RJ van Weeren, RAMJ Wijers, R Wijnands, M Wise, P Zarka, A Alexov, J Anderson, A Asgekar, IM Avruch, MJ Bentum, G Bernardi, P Best, F Breitling, M Bruggen, HR Butcher, B Ciardi, JE Conway, A Corstanje, E de Geus, A Deller, S Duscha, W Frieswijk, MA Garrett, AW Gunst, MP van Haarlem, M Hoeft, J Horandel, E Juette, G Kuper, M Loose, P Maat, R McFadden, D McKay-Bukowski, J Moldon, H Munk, MJ Norden, H Paas, AG Polatidis, D Schwarz, J Sluman, O Smirnov, M Steinmetz, S Thoudam, MC Toribio, R Vermeulen, C Vocks, SJ Wijnholds, O Wucknitz, S Yatawatta


Characterization of a dense aperture array for radio astronomy

Astronomy and Astrophysics 589 (2016)

SA Torchinsky, AOH Olofsson, B Censier, A Karastergiou, M Serylak, P Picard, P Renaud, C Taffoureau

© 2016 ESO. EMBRACE@Nancąy is a prototype instrument consisting of an array of 4608 densely packed antenna elements creating a fully sampled, unblocked aperture. This technology is proposed for the Square Kilometre Array and has the potential of providing an extremely large field of view making it the ideal survey instrument. We describe the system, calibration procedures, and results from the prototype.


Depot Dependent Effects of Dexamethasone on Gene Expression in Human Omental and Abdominal Subcutaneous Adipose Tissues from Obese Women

PLOS ONE 11 (2016) e0167337-e0167337

RT Pickering, M-J Lee, K Karastergiou, A Gower, SK Fried


A LOFAR census of millisecond pulsars

ASTRONOMY & ASTROPHYSICS 585 (2016) ARTN A128

VI Kondratiev, JPW Verbiest, JWT Hessels, AV Bilous, BW Stappers, M Kramer, EF Keane, A Noutsos, S Oslowski, RP Breton, TE Hassall, A Alexov, S Cooper, H Falcke, J-M Griessmeier, A Karastergiou, M Kuniyoshi, M Pilia, C Sobey, S ter Veen, J van Leeuwen, P Weltevrede, ME Bell, JW Broderick, S Corbel, J Eisloeffel, S Markoff, A Rowlinson, JD Swinbank, RAMJ Wijers, R Wijnands, P Zarka


LOFAR imaging of Cygnus A - direct detection of a turnover in the hotspot radio spectra

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 463 (2016) 3143-3150

JP McKean, LEH Godfrey, S Vegetti, MW Wise, R Morganti, MJ Hardcastle, D Rafferty, J Anderson, IM Avruch, R Beck, ME Bell, I van Bemmel, MJ Bentum, G Bernardi, P Best, R Blaauw, A Bonafede, F Breitling, JW Broderick, M Brueggen, L Cerrigone, B Ciardi, F de Gasperin, A Deller, S Duscha, D Engels, H Falcke, RA Fallows, W Frieswijk, MA Garrett, JM Griessmeier, MP van Haarlem, G Heald, M Hoeft, AJ van der Horst, M Iacobelli, H Intema, E Juette, A Karastergiou, VI Kondratiev, LVE Koopmans, M Kuniyoshi, G Kuper, J van Leeuwen, P Maat, G Mann, S Markoff, R McFadden, D McKay-Bukowski, DD Mulcahy, H Munk, A Nelles, E Orru, H Paas, M Pandey-Pommier, M Pietka, R Pizzo, AG Polatidis, W Reich, HJA Rottgering, A Rowlinson, AMM Scaife, M Serylak, A Shulevski, J Sluman, O Smirnov, M Steinmetz, A Stewart, J Swinbank, M Tagger, S Thoudam, MC Toribio, R Vermeulen, C Vocks, RJ van Weeren, O Wucknitz, S Yatawatta, P Zarka


Wide-band, low-frequency pulse profiles of 100 radio pulsars with LOFAR

ASTRONOMY & ASTROPHYSICS 586 (2016) ARTN A92

M Pilia, JWT Hessels, BW Stappers, VI Kondratiev, M Kramer, J van Leeuwen, P Weltevrede, AG Lyne, K Zagkouris, TE Hassall, AV Bilous, RP Breton, H Falcke, J-M Griessmeier, E Keane, A Karastergiou, M Kuniyoshi, A Noutsos, S Oslowski, M Serylak, C Sobey, S ter Veen, A Alexov, J Anderson, A Asgekar, IM Avruch, ME Bell, MJ Bentum, G Bernardi, L Birzan, A Bonafede, F Breitling, JW Broderick, M Brueggen, B Ciardi, S Corbel, E de Geus, A de Jong, A Deller, S Duscha, J Eisloeffel, RA Fallows, R Fender, C Ferrari, W Frieswijk, MA Garrett, AW Gunst, JP Hamaker, G Heald, A Horneffer, P Jonker, E Juette, G Kuper, P Maat, G Mann, S Markoff, R McFadden, D McKay-Bukowski, JCA Miller-Jones, A Nelles, H Paas, M Pandey-Pommier, M Pietka, R Pizzo, AG Polatidis, W Reich, H Roettgering, A Rowlinson, D Schwarz, O Smirnov, M Steinmetz, A Stewart, JD Swinbank, M Tagger, Y Tang, C Tasse, S Thoudam, MC Toribio, AJ van der Horst, R Vermeulen, C Vocks, RJ van Weeren, RAMJ Wijers, R Wijnands, SJ Wijnholds, O Wucknitz, P Zarka


A large light-mass component of cosmic rays at 10(17)-10(17.5) electronvolts from radio observations.

Nature 531 (2016) 70-73

S Buitink, A Corstanje, H Falcke, JR Hörandel, T Huege, A Nelles, JP Rachen, L Rossetto, P Schellart, O Scholten, S ter Veen, S Thoudam, TNG Trinh, J Anderson, A Asgekar, IM Avruch, ME Bell, MJ Bentum, G Bernardi, P Best, A Bonafede, F Breitling, JW Broderick, WN Brouw, M Brüggen, HR Butcher, D Carbone, B Ciardi, JE Conway, F de Gasperin, E de Geus, A Deller, R-J Dettmar, G van Diepen, S Duscha, J Eislöffel, D Engels, JE Enriquez, RA Fallows, R Fender, C Ferrari, W Frieswijk, MA Garrett, JM Grießmeier, AW Gunst, MP van Haarlem, TE Hassall, G Heald, JWT Hessels, M Hoeft, A Horneffer, M Iacobelli, H Intema, E Juette, A Karastergiou, VI Kondratiev, M Kramer, M Kuniyoshi, G Kuper, J van Leeuwen, GM Loose, P Maat, G Mann, S Markoff, R McFadden, D McKay-Bukowski, JP McKean, M Mevius, DD Mulcahy, H Munk, MJ Norden, E Orru, H Paas, M Pandey-Pommier, VN Pandey, M Pietka, R Pizzo, AG Polatidis, W Reich, HJA Röttgering, AMM Scaife, DJ Schwarz, M Serylak, J Sluman, O Smirnov, BW Stappers, M Steinmetz, A Stewart, J Swinbank, M Tagger, Y Tang, C Tasse, MC Toribio, R Vermeulen, C Vocks, C Vogt, RJ van Weeren, RAMJ Wijers, SJ Wijnholds, MW Wise, O Wucknitz, S Yatawatta, P Zarka, JA Zensus

Cosmic rays are the highest-energy particles found in nature. Measurements of the mass composition of cosmic rays with energies of 10(17)-10(18) electronvolts are essential to understanding whether they have galactic or extragalactic sources. It has also been proposed that the astrophysical neutrino signal comes from accelerators capable of producing cosmic rays of these energies. Cosmic rays initiate air showers--cascades of secondary particles in the atmosphere-and their masses can be inferred from measurements of the atmospheric depth of the shower maximum (Xmax; the depth of the air shower when it contains the most particles) or of the composition of shower particles reaching the ground. Current measurements have either high uncertainty, or a low duty cycle and a high energy threshold. Radio detection of cosmic rays is a rapidly developing technique for determining Xmax (refs 10, 11) with a duty cycle of, in principle, nearly 100 per cent. The radiation is generated by the separation of relativistic electrons and positrons in the geomagnetic field and a negative charge excess in the shower front. Here we report radio measurements of Xmax with a mean uncertainty of 16 grams per square centimetre for air showers initiated by cosmic rays with energies of 10(17)-10(17.5) electronvolts. This high resolution in Xmax enables us to determine the mass spectrum of the cosmic rays: we find a mixed composition, with a light-mass fraction (protons and helium nuclei) of about 80 per cent. Unless, contrary to current expectations, the extragalactic component of cosmic rays contributes substantially to the total flux below 10(17.5) electronvolts, our measurements indicate the existence of an additional galactic component, to account for the light composition that we measured in the 10(17)-10(17.5) electronvolt range.


The frequency dependence of scattering imprints on pulsar observations

Monthly Notices of the Royal Astronomical Society 462 (2016) 2587-2602

M Geyer, A Karastergiou

© 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Observations of pulsars across the radio spectrum are revealing a dependence of the characteristic scattering time (τ) on frequency, which is more complex than the simple power law with a theoretically predicted power-law index. In this paper, we investigate these effects using simulated pulsar data at frequencies below 300 MHz. We investigate different scattering mechanisms, namely isotropic and anisotropic scattering, by thin screens along the line of sight, and the particular frequency-dependent impact on pulsar profiles and scattering time-scales of each. We also consider how the screen shape, location and offset along the line of sight lead to specific observable effects. We evaluate how well forward fitting techniques perform in determining τ. We investigate the systematic errors in τ associated with the use of an incorrect fitting method and with the determination of an off-pulse baseline. Our simulations provide examples of average pulse profiles at various frequencies. Using these, we compute spectra of τ and mean flux for different scattering setups. We identify setups that lead to deviations from the simple theoretical picture. This work provides a framework for interpretation of upcoming low-frequency data, both in terms of modelling the interstellar medium and understanding intrinsic emission properties of pulsars.


A LOFAR census of non-recycled pulsars: average profiles, dispersion measures, flux densities, and spectra

ASTRONOMY & ASTROPHYSICS 591 (2016) ARTN A134

AV Bilous, VI Kondratiev, M Kramer, EF Keane, JWT Hessels, BW Stappers, VM Malofeev, C Sobey, RP Breton, S Cooper, H Falcke, A Karastergiou, D Michilli, S Oslowski, S Sanidas, S ter Veen, J van Leeuwen, JPW Verbiest, P Weltevrede, P Zarka, J-M Griessmeier, M Serylak, ME Bell, JW Broderick, J Eisloeffel, S Markoff, A Rowlinson


Emission-rotation correlation in pulsars: new discoveries with optimal techniques

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 456 (2016) 1374-1393

PR Brook, A Karastergiou, S Johnston, M Kerr, RM Shannon, SJ Roberts


HIRAX : A Probe of Dark Energy and Radio Transients

GROUND-BASED AND AIRBORNE TELESCOPES VI 9906 (2016)

LB Newburgh, K Bandura, MA Bucher, T-C Chang, HC Chiang, JF Cliche, R Dave, M Dobbs, C Clarkson, KM Ganga, T Gogo, A Gumba, N Gupta, M Hilton, B Johnstone, A Karastergiou, M Kunz, D Lokhorst, R Maartens, S Macpherson, M Mdlalose, K Moodley, L Ngwenya, JM Parra, J Peterson, O Recnik, B Saliwanchik, MG Santos, JL Sievers, O Smirnov, P Stronkhorst, R Taylor, K Vanderlinde, G Van Vuuren, A Weltman, A Witzemann


Corrigendum: A large light-mass component of cosmic rays at 1017-1017.5 electronvolts from radio observations.

Nature 537 (2016) 572-572

S Buitink, A Corstanje, H Falcke, JR Hörandel, T Huege, A Nelles, JP Rachen, L Rossetto, P Schellart, O Scholten, S Ter Veen, S Thoudam, TNG Trinh, J Anderson, A Asgekar, IM Avruch, ME Bell, MJ Bentum, G Bernardi, P Best, A Bonafede, F Breitling, JW Broderick, WN Brouw, M Brüggen, HR Butcher, D Carbone, B Ciardi, JE Conway, F de Gasperin, E de Geus, A Deller, R-J Dettmar, G van Diepen, S Duscha, J Eislöffel, D Engels, JE Enriquez, RA Fallows, R Fender, C Ferrari, W Frieswijk, MA Garrett, JM Grießmeier, AW Gunst, MP van Haarlem, TE Hassall, G Heald, JWT Hessels, M Hoeft, A Horneffer, M Iacobelli, H Intema, E Juette, A Karastergiou, VI Kondratiev, M Kramer, M Kuniyoshi, G Kuper, J van Leeuwen, GM Loose, P Maat, G Mann, S Markoff, R McFadden, D McKay-Bukowski, JP McKean, M Mevius, DD Mulcahy, H Munk, MJ Norden, E Orru, H Paas, M Pandey-Pommier, VN Pandey, M Pietka, R Pizzo, AG Polatidis, W Reich, HJA Röttgering, AMM Scaife, DJ Schwarz, M Serylak, J Sluman, O Smirnov, BW Stappers, M Steinmetz, A Stewart, J Swinbank, M Tagger, Y Tang, C Tasse, MC Toribio, R Vermeulen, C Vocks, C Vogt, RJ van Weeren, RAMJ Wijers, SJ Wijnholds, MW Wise, O Wucknitz, S Yatawatta, P Zarka, JA Zensus


LOFAR discovery of a quiet emission mode in PSR B0823+26

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 451 (2015) 2493-2506

C Sobey, NJ Young, JWT Hessels, P Weltevrede, A Noutsos, BW Stappers, M Kramer, C Bassa, AG Lyne, VI Kondratiev, TE Hassall, EF Keane, AV Bilous, RP Breton, J-M Griessmeier, A Karastergiou, M Pilia, M Serylak, S ter Veen, J van Leeuwen, A Alexov, J Anderson, A Asgekar, IM Avruch, ME Bell, MJ Bentum, G Bernardi, P Best, L Birzan, A Bonafede, F Breitling, J Broderick, M Brueggen, A Corstanje, D Carbone, E de Geus, M de Vos, A van Duin, S Duscha, J Eisloeffel, H Falcke, RA Fallows, R Fender, C Ferrari, W Frieswijk, MA Garrett, AW Gunst, JP Hamaker, G Heald, M Hoeft, J Horandel, E Juette, G Kuper, P Maat, G Mann, 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, G Pietka, R Pizzo, AG Polatidis, D Rafferty, A Renting, H Rottgering, A Rowlinson, AMM Scaife, D Schwarz, J Sluman, O Smirnov, M Steinmetz, A Stewart, J Swinbank, M Tagger, Y Tang, C Tasse, S Thoudam, C Toribio, R Vermeulen, C Vocks, RJ van Weeren, RAMJ Wijers, MW Wise, O Wucknitz, S Yatawatta, P Zarka


Calibrating high-precision Faraday rotation measurements for LOFAR and the next generation of low-frequency radio telescopes (vol 552, A58, 2013)

ASTRONOMY & ASTROPHYSICS 581 (2015) ARTN C4

C Sotomayor-Beltran, C Sobey, JWT Hesselsa, G de Bruyn, A Noutsos, A Alexov, J Anderson, A Asgekar, IM Avruch, R Beck, ME Bell, MR Bell, MJ Bentum, G Bernardi, P Best, L Birzan, A Bonafede, F Breitling, J Broderick, WN Brouw, M Bruggen, B Ciardi, E de Gasperin, R-J Dettmar, A van Duin, S Duscha, J Eisloffel, H Falcke, RA Fallows, R Fender, C Ferrari, W Frieswijk, MA Garrett, J Griessmeier, T Grit, AW Gunst, TE Hassall, G Heald, M Hoeft, A Horneffer, M Iacobelli, E Juette, A Karastergiou, E Keane, J Koher, M Kramer, VI Kondratiev, LVE Koopmans, M Kuniyoshi, G Kuper, J van Leeuwen, P Maat, G Macario, S Markoff, JP McKean, DD Mulcalty, H Munk, E Orru, H Paas, M Pandey-Pommier, M Pilia, R Pizzo, AG Polatidis, W Reich, H Rottering, M Serylak, J Sluman, BW Stappers, M Tagger, Y Tang, C Tasse, S ter Veen, R Vermeulen, RJ van Weeren, RAMJ Wijers, SJ Wijnholds, MW Wise, O Wucknitz, S Yatawatta, P Zarka


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

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