Author: "Paas, H." / Publisher: radboud university nijmegen, the netherlands - Searchworks@Jio Institute Digital Library Search Results

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1. Imaging Jupiter’s radiation belts down to 127 MHz with LOFAR

Author: Girard, J. N., Zarka, P., Tasse, C., Hess, S., de Pater, I., Santos-Costa, D., Nenon, Q., Sicard, A., Bourdarie, S., Anderson, J., Asgekar, A., Bell, M. E., van Bemmel, I., Bentum, M. J., Bernardi, G., Best, P., Bonafede, A., Breitling, F., Breton, R. P., Broderick, J. W., Brouw, W. N., Brüggen, M., Ciardi, B., Corbel, S., Corstanje, A., de Gasperin, F., de Geus, E., Deller, A., Duscha, S., Eislöffel, J., Falcke, H., Frieswijk, W., Garrett, M. A., Grießmeier, J., Gunst, A. W., Hessels, J. W. T., Hoeft, M., Hörandel, J., Iacobelli, M., Juette, E., Kondratiev, V. I., Kuniyoshi, M., Kuper, G., van Leeuwen, J., Loose, M., Maat, P., Mann, G., Markoff, S., McFadden, R., McKay-Bukowski, D., Moldon, J., Munk, H., Nelles, A., Norden, M. J., Orru, E., Paas, H., Pandey-Pommier, M., Pizzo, R., Polatidis, A. G., Reich, W., Röttgering, H., Rowlinson, A., Schwarz, D., Smirnov, O., Steinmetz, M., Swinbank, J., Tagger, M., Thoudam, Satyendra, Toribio, M. C., Vermeulen, R., Vocks, C., van Weeren, R. J., Wijers, R. A. M. J., Wucknitz, O., Girard, J. N., Zarka, P., Tasse, C., Hess, S., de Pater, I., Santos-Costa, D., Nenon, Q., Sicard, A., Bourdarie, S., Anderson, J., Asgekar, A., Bell, M. E., van Bemmel, I., Bentum, M. J., Bernardi, G., Best, P., Bonafede, A., Breitling, F., Breton, R. P., Broderick, J. W., Brouw, W. N., Brüggen, M., Ciardi, B., Corbel, S., Corstanje, A., de Gasperin, F., de Geus, E., Deller, A., Duscha, S., Eislöffel, J., Falcke, H., Frieswijk, W., Garrett, M. A., Grießmeier, J., Gunst, A. W., Hessels, J. W. T., Hoeft, M., Hörandel, J., Iacobelli, M., Juette, E., Kondratiev, V. I., Kuniyoshi, M., Kuper, G., van Leeuwen, J., Loose, M., Maat, P., Mann, G., Markoff, S., McFadden, R., McKay-Bukowski, D., Moldon, J., Munk, H., Nelles, A., Norden, M. J., Orru, E., Paas, H., Pandey-Pommier, M., Pizzo, R., Polatidis, A. G., Reich, W., Röttgering, H., Rowlinson, A., Schwarz, D., Smirnov, O., Steinmetz, M., Swinbank, J., Tagger, M., Thoudam, Satyendra, Toribio, M. C., Vermeulen, R., Vocks, C., van Weeren, R. J., Wijers, R. A. M. J., and Wucknitz, O.
Abstract: Context. With the limited amount of in situ particle data available for the innermost region of Jupiter’s magnetosphere, Earth-based observations of the giant planets synchrotron emission remain the sole method today of scrutinizing the distribution and dynamical behavior of the ultra energetic electrons magnetically trapped around the planet. Radio observations ultimately provide key information about the origin and control parameters of the harsh radiation environment. Aims. We perform the first resolved and low-frequency imaging of the synchrotron emission with LOFAR. At a frequency as low as 127 MHz, the radiation from electrons with energies of ~1–30 MeV are expected, for the first time, to be measured and mapped over a broad region of Jupiter’s inner magnetosphere. Methods. Measurements consist of interferometric visibilities taken during a single 10-hour rotation of the Jovian system. These visibilities were processed in a custom pipeline developed for planetary observations, combining flagging, calibration, wide-field imaging, direction-dependent calibration, and specific visibility correction for planetary targets. We produced spectral image cubes of Jupiter’s radiation belts at the various angular, temporal, and spectral resolutions from which flux densities were measured. Results. The first resolved images of Jupiter’s radiation belts at 127–172 MHz are obtained with a noise level ~20–25 mJy/beam, along with total integrated flux densities. They are compared with previous observations at higher frequencies. A greater extent of the synchrotron emission source (≥4 RJ) is measured in the LOFAR range, which is the signature – as at higher frequencies – of the superposition of a “pancake” and an isotropic electron distribution. Asymmetry of east-west emission peaks is measured, as well as the longitudinal dependence of the radial distance of the belts, and the presence of a hot spot at λIII = 230° ± 25°. Spectral flux density measurements are on the low side o
Published: 2016
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2. LOFAR MSSS : detection of a low-frequency radio transient in 400 h of monitoring of the North Celestial Pole

Author: Stewart, A. J., Fender, R. P., Broderick, J. W., Hassall, T. E., Muñoz-Darias, T., Rowlinson, A., Swinbank, J. D., Staley, T. D., Molenaar, G. J., Scheers, B., Grobler, T. L., Pietka, M., Heald, G., McKean, J. P., Bell, M. E., Bonafede, A., Breton, R. P., Carbone, D., Cendes, Y., Clarke, A. O., Corbel, S., de Gasperin, F., Eislöffel, J., Falcke, H., Ferrari, C., Grießmeier, J. -M, Hardcastle, M. J., Heesen, V., Hessels, J. W. T., Horneffer, A., Iacobelli, M., Jonker, P., Karastergiou, A., Kokotanekov, G., Kondratiev, V. I., Kuniyoshi, M., Law, C. J., van Leeuwen, J., Markoff, S., Miller-Jones, J. C. A., Mulcahy, D., Orru, E., Pandey-Pommier, M., Pratley, L., Rol, E., Röttgering, H. J. A., Scaife, A. M. M., Shulevski, A., Sobey, C. A., Stappers, B. W., Tasse, C., van der Horst, A. J., van Velzen, S., van Weeren, R. J., Wijers, R. A. M. J., Wijnands, R., Wise, M., Zarka, P., Alexov, A., Anderson, J., Asgekar, A., Avruch, I. M., Bentum, M. J., Bernardi, G., Best, P., Breitling, F., Brüggen, M., Butcher, H. R., Ciardi, B., Conway, J. E., Corstanje, A., de Geus, E., Deller, A., Duscha, S., Frieswijk, W., Garrett, M. A., Gunst, A. W., van Haarlem, M. P., Hoeft, M., Hörandel, J., Juette, E., Kuper, G., Loose, M., Maat, P., McFadden, R., McKay-Bukowski, D., Moldon, J., Munk, H., Norden, M. J., Paas, H., Polatidis, A. G., Schwarz, D., Sluman, J., Smirnov, O., Steinmetz, M., Thoudam, Satyendra, Toribio, M. C., Vermeulen, R., Vocks, C., Wijnholds, S. J., Wucknitz, O., Yatawatta, S., Stewart, A. J., Fender, R. P., Broderick, J. W., Hassall, T. E., Muñoz-Darias, T., Rowlinson, A., Swinbank, J. D., Staley, T. D., Molenaar, G. J., Scheers, B., Grobler, T. L., Pietka, M., Heald, G., McKean, J. P., Bell, M. E., Bonafede, A., Breton, R. P., Carbone, D., Cendes, Y., Clarke, A. O., Corbel, S., de Gasperin, F., Eislöffel, J., Falcke, H., Ferrari, C., Grießmeier, J. -M, Hardcastle, M. J., Heesen, V., Hessels, J. W. T., Horneffer, A., Iacobelli, M., Jonker, P., Karastergiou, A., Kokotanekov, G., Kondratiev, V. I., Kuniyoshi, M., Law, C. J., van Leeuwen, J., Markoff, S., Miller-Jones, J. C. A., Mulcahy, D., Orru, E., Pandey-Pommier, M., Pratley, L., Rol, E., Röttgering, H. J. A., Scaife, A. M. M., Shulevski, A., Sobey, C. A., Stappers, B. W., Tasse, C., van der Horst, A. J., van Velzen, S., van Weeren, R. J., Wijers, R. A. M. J., Wijnands, R., Wise, M., Zarka, P., Alexov, A., Anderson, J., Asgekar, A., Avruch, I. M., Bentum, M. J., Bernardi, G., Best, P., Breitling, F., Brüggen, M., Butcher, H. R., Ciardi, B., Conway, J. E., Corstanje, A., de Geus, E., Deller, A., Duscha, S., Frieswijk, W., Garrett, M. A., Gunst, A. W., van Haarlem, M. P., Hoeft, M., Hörandel, J., Juette, E., Kuper, G., Loose, M., Maat, P., McFadden, R., McKay-Bukowski, D., Moldon, J., Munk, H., Norden, M. J., Paas, H., Polatidis, A. G., Schwarz, D., Sluman, J., Smirnov, O., Steinmetz, M., Thoudam, Satyendra, Toribio, M. C., Vermeulen, R., Vocks, C., Wijnholds, S. J., Wucknitz, O., and Yatawatta, S.
Abstract: We present the results of a four-month campaign searching for low-frequency radio transients near the North Celestial Pole with the Low-Frequency Array (LOFAR), as part of the Multifrequency Snapshot Sky Survey (MSSS). The data were recorded between 2011 December and 2012 April and comprised 2149 11-min snapshots, each covering 175 deg2. We have found one convincing candidate astrophysical transient, with a duration of a few minutes and a flux density at 60 MHz of 15–25 Jy. The transient does not repeat and has no obvious optical or high-energy counterpart, as a result of which its nature is unclear. The detection of this event implies a transient rate at 60 MHz of 3.9−3.7+14.7×10−4" style="position: relative;" tabindex="0" id="MathJax-Element-1-Frame" class="MathJax">3.9+14.7−3.7×10−4 d−1 deg−2, and a transient surface density of 1.5 × 10−5 deg−2, at a 7.9-Jy limiting flux density and ∼10-min time-scale. The campaign data were also searched for transients at a range of other time-scales, from 0.5 to 297 min, which allowed us to place a range of limits on transient rates at 60 MHz as a function of observation duration.
Published: 2016
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3. LOFAR MSSS : detection of a low-frequency radio transient in 400 h of monitoring of the North Celestial Pole

Author: Stewart, A. J., Fender, R. P., Broderick, J. W., Hassall, T. E., Muñoz-Darias, T., Rowlinson, A., Swinbank, J. D., Staley, T. D., Molenaar, G. J., Scheers, B., Grobler, T. L., Pietka, M., Heald, G., McKean, J. P., Bell, M. E., Bonafede, A., Breton, R. P., Carbone, D., Cendes, Y., Clarke, A. O., Corbel, S., de Gasperin, F., Eislöffel, J., Falcke, H., Ferrari, C., Grießmeier, J. -M, Hardcastle, M. J., Heesen, V., Hessels, J. W. T., Horneffer, A., Iacobelli, M., Jonker, P., Karastergiou, A., Kokotanekov, G., Kondratiev, V. I., Kuniyoshi, M., Law, C. J., van Leeuwen, J., Markoff, S., Miller-Jones, J. C. A., Mulcahy, D., Orru, E., Pandey-Pommier, M., Pratley, L., Rol, E., Röttgering, H. J. A., Scaife, A. M. M., Shulevski, A., Sobey, C. A., Stappers, B. W., Tasse, C., van der Horst, A. J., van Velzen, S., van Weeren, R. J., Wijers, R. A. M. J., Wijnands, R., Wise, M., Zarka, P., Alexov, A., Anderson, J., Asgekar, A., Avruch, I. M., Bentum, M. J., Bernardi, G., Best, P., Breitling, F., Brüggen, M., Butcher, H. R., Ciardi, B., Conway, J. E., Corstanje, A., de Geus, E., Deller, A., Duscha, S., Frieswijk, W., Garrett, M. A., Gunst, A. W., van Haarlem, M. P., Hoeft, M., Hörandel, J., Juette, E., Kuper, G., Loose, M., Maat, P., McFadden, R., McKay-Bukowski, D., Moldon, J., Munk, H., Norden, M. J., Paas, H., Polatidis, A. G., Schwarz, D., Sluman, J., Smirnov, O., Steinmetz, M., Thoudam, Satyendra, Toribio, M. C., Vermeulen, R., Vocks, C., Wijnholds, S. J., Wucknitz, O., Yatawatta, S., Stewart, A. J., Fender, R. P., Broderick, J. W., Hassall, T. E., Muñoz-Darias, T., Rowlinson, A., Swinbank, J. D., Staley, T. D., Molenaar, G. J., Scheers, B., Grobler, T. L., Pietka, M., Heald, G., McKean, J. P., Bell, M. E., Bonafede, A., Breton, R. P., Carbone, D., Cendes, Y., Clarke, A. O., Corbel, S., de Gasperin, F., Eislöffel, J., Falcke, H., Ferrari, C., Grießmeier, J. -M, Hardcastle, M. J., Heesen, V., Hessels, J. W. T., Horneffer, A., Iacobelli, M., Jonker, P., Karastergiou, A., Kokotanekov, G., Kondratiev, V. I., Kuniyoshi, M., Law, C. J., van Leeuwen, J., Markoff, S., Miller-Jones, J. C. A., Mulcahy, D., Orru, E., Pandey-Pommier, M., Pratley, L., Rol, E., Röttgering, H. J. A., Scaife, A. M. M., Shulevski, A., Sobey, C. A., Stappers, B. W., Tasse, C., van der Horst, A. J., van Velzen, S., van Weeren, R. J., Wijers, R. A. M. J., Wijnands, R., Wise, M., Zarka, P., Alexov, A., Anderson, J., Asgekar, A., Avruch, I. M., Bentum, M. J., Bernardi, G., Best, P., Breitling, F., Brüggen, M., Butcher, H. R., Ciardi, B., Conway, J. E., Corstanje, A., de Geus, E., Deller, A., Duscha, S., Frieswijk, W., Garrett, M. A., Gunst, A. W., van Haarlem, M. P., Hoeft, M., Hörandel, J., Juette, E., Kuper, G., Loose, M., Maat, P., McFadden, R., McKay-Bukowski, D., Moldon, J., Munk, H., Norden, M. J., Paas, H., Polatidis, A. G., Schwarz, D., Sluman, J., Smirnov, O., Steinmetz, M., Thoudam, Satyendra, Toribio, M. C., Vermeulen, R., Vocks, C., Wijnholds, S. J., Wucknitz, O., and Yatawatta, S.
Abstract: We present the results of a four-month campaign searching for low-frequency radio transients near the North Celestial Pole with the Low-Frequency Array (LOFAR), as part of the Multifrequency Snapshot Sky Survey (MSSS). The data were recorded between 2011 December and 2012 April and comprised 2149 11-min snapshots, each covering 175 deg2. We have found one convincing candidate astrophysical transient, with a duration of a few minutes and a flux density at 60 MHz of 15–25 Jy. The transient does not repeat and has no obvious optical or high-energy counterpart, as a result of which its nature is unclear. The detection of this event implies a transient rate at 60 MHz of 3.9−3.7+14.7×10−4" style="position: relative;" tabindex="0" id="MathJax-Element-1-Frame" class="MathJax">3.9+14.7−3.7×10−4 d−1 deg−2, and a transient surface density of 1.5 × 10−5 deg−2, at a 7.9-Jy limiting flux density and ∼10-min time-scale. The campaign data were also searched for transients at a range of other time-scales, from 0.5 to 297 min, which allowed us to place a range of limits on transient rates at 60 MHz as a function of observation duration.
Published: 2016
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4. Wide-band, low-frequency pulse profiles of 100 radio pulsars with LOFAR

Author: Pilia, M., Hessels, J. W. T., Stappers, B. W., Kondratiev, V. I., Kramer, M., van Leeuwen, J., Weltevrede, P., Lyne, A. G., Zagkouris, K., Hassall, T. E., Bilous, A. V., Breton, R. P., Falcke, H., Grießmeier, J. -M, Keane, E., Karastergiou, A., Kuniyoshi, M., Noutsos, A., Os\lowski, S., Serylak, M., Sobey, C., ter Veen, S., Alexov, A., Anderson, J., Asgekar, A., Avruch, I. M., Bell, M. E., Bentum, M. J., Bernardi, G., Bîrzan, L., Bonafede, A., Breitling, F., Broderick, J. W., Brüggen, M., Ciardi, B., Corbel, S., de Geus, E., de Jong, A., Deller, A., Duscha, S., Eislöffel, J., Fallows, R. A., Fender, R., Ferrari, C., Frieswijk, W., Garrett, M. A., Gunst, A. W., Hamaker, J. P., Heald, G., Horneffer, A., Jonker, P., Juette, E., Kuper, G., Maat, P., Mann, G., Markoff, S., McFadden, R., McKay-Bukowski, D., Miller-Jones, J. C. A., Nelles, A., Paas, H., Pandey-Pommier, M., Pietka, M., Pizzo, R., Polatidis, A. G., Reich, W., Röttgering, H., Rowlinson, A., Schwarz, D., Smirnov, O., Steinmetz, M., Stewart, A., Swinbank, J. D., Tagger, M., Tang, Y., Tasse, C., Thoudam, Satyendra, Toribio, M. C., van der Horst, A. J., Vermeulen, R., Vocks, C., van Weeren, R. J., Wijers, R. A. M. J., Wijnands, R., Wijnholds, S. J., Wucknitz, O., Zarka, P., Pilia, M., Hessels, J. W. T., Stappers, B. W., Kondratiev, V. I., Kramer, M., van Leeuwen, J., Weltevrede, P., Lyne, A. G., Zagkouris, K., Hassall, T. E., Bilous, A. V., Breton, R. P., Falcke, H., Grießmeier, J. -M, Keane, E., Karastergiou, A., Kuniyoshi, M., Noutsos, A., Os\lowski, S., Serylak, M., Sobey, C., ter Veen, S., Alexov, A., Anderson, J., Asgekar, A., Avruch, I. M., Bell, M. E., Bentum, M. J., Bernardi, G., Bîrzan, L., Bonafede, A., Breitling, F., Broderick, J. W., Brüggen, M., Ciardi, B., Corbel, S., de Geus, E., de Jong, A., Deller, A., Duscha, S., Eislöffel, J., Fallows, R. A., Fender, R., Ferrari, C., Frieswijk, W., Garrett, M. A., Gunst, A. W., Hamaker, J. P., Heald, G., Horneffer, A., Jonker, P., Juette, E., Kuper, G., Maat, P., Mann, G., Markoff, S., McFadden, R., McKay-Bukowski, D., Miller-Jones, J. C. A., Nelles, A., Paas, H., Pandey-Pommier, M., Pietka, M., Pizzo, R., Polatidis, A. G., Reich, W., Röttgering, H., Rowlinson, A., Schwarz, D., Smirnov, O., Steinmetz, M., Stewart, A., Swinbank, J. D., Tagger, M., Tang, Y., Tasse, C., Thoudam, Satyendra, Toribio, M. C., van der Horst, A. J., Vermeulen, R., Vocks, C., van Weeren, R. J., Wijers, R. A. M. J., Wijnands, R., Wijnholds, S. J., Wucknitz, O., and Zarka, P.
Abstract: Context. LOFAR offers the unique capability of observing pulsars across the 10−240 MHz frequency range with a fractional bandwidth of roughly 50%. This spectral range is well suited for studying the frequency evolution of pulse profile morphology caused by both intrinsic and extrinsic effects such as changing emission altitude in the pulsar magnetosphere or scatter broadening by the interstellar medium, respectively. Aims. The magnitude of most of these effects increases rapidly towards low frequencies. LOFAR can thus address a number of open questions about the nature of radio pulsar emission and its propagation through the interstellar medium. Methods. We present the average pulse profiles of 100 pulsars observed in the two LOFAR frequency bands: high band (120–167 MHz, 100 profiles) and low band (15–62 MHz, 26 profiles). We compare them with Westerbork Synthesis Radio Telescope (WSRT) and Lovell Telescope observations at higher frequencies (350 and 1400 MHz) to study the profile evolution. The profiles were aligned in absolute phase by folding with a new set of timing solutions from the Lovell Telescope, which we present along with precise dispersion measures obtained with LOFAR. Results. We find that the profile evolution with decreasing radio frequency does not follow a specific trend; depending on the geometry of the pulsar, new components can enter into or be hidden from view. Nonetheless, in general our observations confirm the widening of pulsar profiles at low frequencies, as expected from radius-to-frequency mapping or birefringence theories.
Published: 2016
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5. A large light-mass component of cosmic rays at 1017–1017.5 electronvolts from radio observations

Author: Buitink, S., Corstanje, A., Falcke, H., Hörandel, J. R., Huege, T., Nelles, A., Rachen, J. P., Rossetto, L., Schellart, P., Scholten, O., Ter Veen, S., Thoudam, Satyendra, Trinh, T. N. G., Anderson, J., Asgekar, A., Avruch, I. M., Bell, M. E., Bentum, M. J., Bernardi, G., Best, P., Bonafede, A., Breitling, F., Broderick, J. W., Brouw, W. N., Brüggen, M., Butcher, H. R., Carbone, D., Ciardi, B., Conway, J. E., de Gasperin, F., de Geus, E., Deller, A., Dettmar, R. -J, van Diepen, G., Duscha, S., Eislöffel, J., Engels, D., Enriquez, J. E., Fallows, R. A., Fender, R., Ferrari, C., Frieswijk, W., Garrett, M. A., Grießmeier, J. M., Gunst, A. W., van Haarlem, M. P., Hassall, T. E., Heald, G., Hessels, J. W. T., Hoeft, M., Horneffer, A., Iacobelli, M., Intema, H., Juette, E., Karastergiou, A., Kondratiev, V. I., Kramer, M., Kuniyoshi, M., Kuper, G., van Leeuwen, J., Loose, G. M., Maat, P., Mann, G., Markoff, S., McFadden, R., McKay-Bukowski, D., McKean, J. P., Mevius, M., Mulcahy, D. D., Munk, H., Norden, M. J., Orru, E., Paas, H., Pandey-Pommier, M., Pandey, V. N., Pietka, M., Pizzo, R., Polatidis, A. G., Reich, W., Röttgering, H. J. A., Scaife, A. M. M., Schwarz, D. J., Serylak, M., Sluman, J., Smirnov, O., Stappers, B. W., Steinmetz, M., Stewart, A., Swinbank, J., Tagger, M., Tang, Y., Tasse, C., Toribio, M. C., Vermeulen, R., Vocks, C., Vogt, C., van Weeren, R. J., Wijers, R. A. M. J., Wijnholds, S. J., Wise, M. W., Wucknitz, O., Yatawatta, S., Zarka, P., Zensus, J. A., Buitink, S., Corstanje, A., Falcke, H., Hörandel, J. R., Huege, T., Nelles, A., Rachen, J. P., Rossetto, L., Schellart, P., Scholten, O., Ter Veen, S., Thoudam, Satyendra, Trinh, T. N. G., Anderson, J., Asgekar, A., Avruch, I. M., Bell, M. E., Bentum, M. J., Bernardi, G., Best, P., Bonafede, A., Breitling, F., Broderick, J. W., Brouw, W. N., Brüggen, M., Butcher, H. R., Carbone, D., Ciardi, B., Conway, J. E., de Gasperin, F., de Geus, E., Deller, A., Dettmar, R. -J, van Diepen, G., Duscha, S., Eislöffel, J., Engels, D., Enriquez, J. E., Fallows, R. A., Fender, R., Ferrari, C., Frieswijk, W., Garrett, M. A., Grießmeier, J. M., Gunst, A. W., van Haarlem, M. P., Hassall, T. E., Heald, G., Hessels, J. W. T., Hoeft, M., Horneffer, A., Iacobelli, M., Intema, H., Juette, E., Karastergiou, A., Kondratiev, V. I., Kramer, M., Kuniyoshi, M., Kuper, G., van Leeuwen, J., Loose, G. M., Maat, P., Mann, G., Markoff, S., McFadden, R., McKay-Bukowski, D., McKean, J. P., Mevius, M., Mulcahy, D. D., Munk, H., Norden, M. J., Orru, E., Paas, H., Pandey-Pommier, M., Pandey, V. N., Pietka, M., Pizzo, R., Polatidis, A. G., Reich, W., Röttgering, H. J. A., Scaife, A. M. M., Schwarz, D. J., Serylak, M., Sluman, J., Smirnov, O., Stappers, B. W., Steinmetz, M., Stewart, A., Swinbank, J., Tagger, M., Tang, Y., Tasse, C., Toribio, M. C., Vermeulen, R., Vocks, C., Vogt, C., van Weeren, R. J., Wijers, R. A. M. J., Wijnholds, S. J., Wise, M. W., Wucknitz, O., Yatawatta, S., Zarka, P., and Zensus, J. A.
Abstract: Cosmic rays are the highest-energy particles found in nature. Measurements of the mass composition of cosmic rays with energies of 1017–1018 electronvolts are essential to understanding whether they have galactic or extragalactic sources. It has also been proposed that the astrophysical neutrino signal1 comes from accelerators capable of producing cosmic rays of these energies2. 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 maximum3 (Xmax; the depth of the air shower when it contains the most particles) or of the composition of shower particles reaching the ground4. Current measurements5 have either high uncertainty, or a low duty cycle and a high energy threshold. Radio detection of cosmic rays6, 7, 8 is a rapidly developing technique9 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 front6, 12. 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 1017–1017.5 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 1017.5 electronvolts, our measurements indicate the existence of an additional galactic component, to account for the light composition that we measured in the 1017–1017.5 electronvolt range., Corrigendum: Buitink et al. (2016) A large light-mass component of cosmic rays at 1017–1017.5 electronvolts from radio observations. Nature, 537: 572.DOI: 10.1038/nature18936
Published: 2016
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6. The peculiar radio galaxy 4C 35.06 : a case for recurrent AGN activity?

Author: Shulevski, A., Morganti, R., Barthel, P. D., Murgia, M., van Weeren, R. J., White, G. J., Brüggen, M., Kunert-Bajraszewska, M., Jamrozy, M., Best, P. N., Röttgering, H. J. A., Chyzy, K. T., de Gasperin, F., Bîrzan, L., Brunetti, G., Brienza, M., Rafferty, D. A., Anderson, J., Beck, R., Deller, A., Zarka, P., Schwarz, D., Mahony, E., Orrú, E., Bell, M. E., Bentum, M. J., Bernardi, G., Bonafede, A., Breitling, F., Broderick, J. W., Butcher, H. R., Carbone, D., Ciardi, B., de Geus, E., Duscha, S., Eislöffel, J., Engels, D., Falcke, H., Fallows, R. A., Fender, R., Ferrari, C., Frieswijk, W., Garrett, M. A., Grießmeier, J., Gunst, A. W., Heald, G., Hoeft, M., Hörandel, J., Horneffer, A., van der Horst, A. J., Intema, H., Juette, E., Karastergiou, A., Kondratiev, V. I., Kramer, M., Kuniyoshi, M., Kuper, G., Maat, P., Mann, G., McFadden, R., McKay-Bukowski, D., McKean, J. P., Meulman, H., Mulcahy, D. D., Munk, H., Norden, M. J., Paas, H., Pandey-Pommier, M., Pizzo, R., Polatidis, A. G., Reich, W., Rowlinson, A., Scaife, A. M. M., Serylak, M., Sluman, J., Smirnov, O., Steinmetz, M., Swinbank, J., Tagger, M., Tang, Y., Tasse, C., Thoudam, Satyendra, Toribio, M. C., Vermeulen, R., Vocks, C., Wijers, R. A. M. J., Wise, M. W., Wucknitz, O., Shulevski, A., Morganti, R., Barthel, P. D., Murgia, M., van Weeren, R. J., White, G. J., Brüggen, M., Kunert-Bajraszewska, M., Jamrozy, M., Best, P. N., Röttgering, H. J. A., Chyzy, K. T., de Gasperin, F., Bîrzan, L., Brunetti, G., Brienza, M., Rafferty, D. A., Anderson, J., Beck, R., Deller, A., Zarka, P., Schwarz, D., Mahony, E., Orrú, E., Bell, M. E., Bentum, M. J., Bernardi, G., Bonafede, A., Breitling, F., Broderick, J. W., Butcher, H. R., Carbone, D., Ciardi, B., de Geus, E., Duscha, S., Eislöffel, J., Engels, D., Falcke, H., Fallows, R. A., Fender, R., Ferrari, C., Frieswijk, W., Garrett, M. A., Grießmeier, J., Gunst, A. W., Heald, G., Hoeft, M., Hörandel, J., Horneffer, A., van der Horst, A. J., Intema, H., Juette, E., Karastergiou, A., Kondratiev, V. I., Kramer, M., Kuniyoshi, M., Kuper, G., Maat, P., Mann, G., McFadden, R., McKay-Bukowski, D., McKean, J. P., Meulman, H., Mulcahy, D. D., Munk, H., Norden, M. J., Paas, H., Pandey-Pommier, M., Pizzo, R., Polatidis, A. G., Reich, W., Rowlinson, A., Scaife, A. M. M., Serylak, M., Sluman, J., Smirnov, O., Steinmetz, M., Swinbank, J., Tagger, M., Tang, Y., Tasse, C., Thoudam, Satyendra, Toribio, M. C., Vermeulen, R., Vocks, C., Wijers, R. A. M. J., Wise, M. W., and Wucknitz, O.
Abstract: Using observations obtained with the LOw Fequency ARray (LOFAR), the Westerbork Synthesis Radio Telescope (WSRT) and archival Very Large Array (VLA) data, we have traced the radio emission to large scales in the complex source 4C 35.06 located in the core of the galaxy cluster Abell 407. At higher spatial resolution (~ 4″), the source was known to have two inner radio lobes spanning 31 kpc and a diffuse, low-brightness extension running parallel to them, offset by about 11 kpc (in projection). At 62 MHz, we detect the radio emission of this structure extending out to 210 kpc. At 1.4 GHz and intermediate spatial resolution (~ 30″), the structure appears to have a helical morphology. We have derived the characteristics of the radio spectral index across the source. We show that the source morphology is most likely the result of at least two episodes of AGN activity separated by a dormant period of around 35 Myr. The outermost regions of radio emission have a steep spectral index (α< − 1), indicative of old plasma. We connect the spectral index properties of the resolved source structure with the integrated fluxdensity spectral index of 4C 35.06 and suggest an explanation for its unusual integrated flux density spectral shape (a moderately steep power law with no discernible spectral break), possibly providing a proxy for future studies of more distant radio sources through inferring their detailed spectral index properties and activity history from their integrated spectral indices. The AGN is hosted by one of the galaxies located in the cluster core of Abell 407. We propose that it is intermittently active as it moves in the dense environment in the cluster core. In this scenario, the AGN turned on sometime in the past, and has produced the helical pattern of emission, possibly a sign of jet precession/merger during that episode of activity. Using LOFAR, we can trace the relic plasma from that episode of activity out to greater distances from the core than ever be
Published: 2015
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7. Measuring a Cherenkov ring in the radio emission from air showers at 110-190 MHz with LOFAR

Author: Nelles, A., Schellart, P., Buitink, S., Corstanje, A., de Vries, K. D., Enriquez, J. E., Falcke, H., Frieswijk, W., Hörandel, J. R., Scholten, O., ter Veen, S., Thoudam, Satyendra, van den Akker, M., Anderson, J., Asgekar, A., Bell, M. E., Bentum, M. J., Bernardi, G., Best, P., Bregman, J., Breitling, F., Broderick, J., Brouw, W. N., Brüggen, M., Butcher, H. R., Ciardi, B., Deller, A., Duscha, S., Eislöffel, J., Fallows, R. A., Garrett, M. A., Gunst, A. W., Hassall, T. E., Heald, G., Horneffer, A., Iacobelli, M., Juette, E., Karastergiou, A., Kondratiev, V. I., Kramer, M., Kuniyoshi, M., Kuper, G., Maat, P., Mann, G., Mevius, M., Norden, M. J., Paas, H., Pandey-Pommier, M., Pietka, G., Pizzo, R., Polatidis, A. G., Reich, W., Röttgering, H., Scaife, A. M. M., Schwarz, D., Smirnov, O., Stappers, B. W., Steinmetz, M., Stewart, A., Tagger, M., Tang, Y., Tasse, C., Vermeulen, R., Vocks, C., van Weeren, R. J., Wijnholds, S. J., Wucknitz, O., Yatawatta, S., Zarka, P., Nelles, A., Schellart, P., Buitink, S., Corstanje, A., de Vries, K. D., Enriquez, J. E., Falcke, H., Frieswijk, W., Hörandel, J. R., Scholten, O., ter Veen, S., Thoudam, Satyendra, van den Akker, M., Anderson, J., Asgekar, A., Bell, M. E., Bentum, M. J., Bernardi, G., Best, P., Bregman, J., Breitling, F., Broderick, J., Brouw, W. N., Brüggen, M., Butcher, H. R., Ciardi, B., Deller, A., Duscha, S., Eislöffel, J., Fallows, R. A., Garrett, M. A., Gunst, A. W., Hassall, T. E., Heald, G., Horneffer, A., Iacobelli, M., Juette, E., Karastergiou, A., Kondratiev, V. I., Kramer, M., Kuniyoshi, M., Kuper, G., Maat, P., Mann, G., Mevius, M., Norden, M. J., Paas, H., Pandey-Pommier, M., Pietka, G., Pizzo, R., Polatidis, A. G., Reich, W., Röttgering, H., Scaife, A. M. M., Schwarz, D., Smirnov, O., Stappers, B. W., Steinmetz, M., Stewart, A., Tagger, M., Tang, Y., Tasse, C., Vermeulen, R., Vocks, C., van Weeren, R. J., Wijnholds, S. J., Wucknitz, O., Yatawatta, S., and Zarka, P.
Abstract: Measuring radio emission from air showers offers a novel way to determine properties of the primary cosmic rays such as their mass and energy. Theory predicts that relativistic time compression effects lead to a ring of amplified emission which starts to dominate the emission pattern for frequencies above ∼100∼100 MHz. In this article we present the first detailed measurements of this structure. Ring structures in the radio emission of air showers are measured with the LOFAR radio telescope in the frequency range of 110–190 MHz. These data are well described by CoREAS simulations. They clearly confirm the importance of including the index of refraction of air as a function of height. Furthermore, the presence of the Cherenkov ring offers the possibility for a geometrical measurement of the depth of shower maximum, which in turn depends on the mass of the primary particle.
Published: 2015
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8. Calibrating the absolute amplitude scale for air showers measured at LOFAR

Author: Nelles, A., Hörandel, J. R., Karskens, T., Krause, M., Buitink, S., Corstanje, A., Enriquez, J. E., Erdmann, M., Falcke, H., Haungs, A., Hiller, R., Huege, T., Krause, R., Link, K., Norden, M. J., Rachen, J. P., Rossetto, L., Schellart, P., Scholten, O., Schröder, F. G., ter Veen, S., Thoudam, Satyendra, Trinh, T. N. G., Weidenhaupt, K., Wijnholds, S. J., Anderson, J., Bähren, L., Bell, M. E., Bentum, M. J., Best, P., Bonafede, A., Bregman, J., Brouw, W. N., Brüggen, M., Butcher, H. R., Carbone, D., Ciardi, B., de Gasperin, F., Duscha, S., Eislöffel, J., Fallows, R. A., Frieswijk, W., Garrett, M. A., van Haarlem, M. P., Heald, G., Hoeft, M., Horneffer, A., Iacobelli, M., Juette, E., Karastergiou, A., Kohler, J., Kondratiev, V. I., Kuniyoshi, M., Kuper, G., van Leeuwen, J., Maat, P., McFadden, R., McKay-Bukowski, D., Orru, E., Paas, H., Pandey-Pommier, M., Pandey, V. N., Pizzo, R., Polatidis, A. G., Reich, W., Röttgering, H., Schwarz, D., Serylak, M., Sluman, J., Smirnov, O., Tasse, C., Toribio, M. C., Vermeulen, R., van Weeren, R. J., Wijers, R. A. M. J., Wucknitz, O., Zarka, P., Nelles, A., Hörandel, J. R., Karskens, T., Krause, M., Buitink, S., Corstanje, A., Enriquez, J. E., Erdmann, M., Falcke, H., Haungs, A., Hiller, R., Huege, T., Krause, R., Link, K., Norden, M. J., Rachen, J. P., Rossetto, L., Schellart, P., Scholten, O., Schröder, F. G., ter Veen, S., Thoudam, Satyendra, Trinh, T. N. G., Weidenhaupt, K., Wijnholds, S. J., Anderson, J., Bähren, L., Bell, M. E., Bentum, M. J., Best, P., Bonafede, A., Bregman, J., Brouw, W. N., Brüggen, M., Butcher, H. R., Carbone, D., Ciardi, B., de Gasperin, F., Duscha, S., Eislöffel, J., Fallows, R. A., Frieswijk, W., Garrett, M. A., van Haarlem, M. P., Heald, G., Hoeft, M., Horneffer, A., Iacobelli, M., Juette, E., Karastergiou, A., Kohler, J., Kondratiev, V. I., Kuniyoshi, M., Kuper, G., van Leeuwen, J., Maat, P., McFadden, R., McKay-Bukowski, D., Orru, E., Paas, H., Pandey-Pommier, M., Pandey, V. N., Pizzo, R., Polatidis, A. G., Reich, W., Röttgering, H., Schwarz, D., Serylak, M., Sluman, J., Smirnov, O., Tasse, C., Toribio, M. C., Vermeulen, R., van Weeren, R. J., Wijers, R. A. M. J., Wucknitz, O., and Zarka, P.
Abstract: Air showers induced by cosmic rays create nanosecond pulses detectable at radio frequencies. These pulses have been measured successfully in the past few years at the LOw-Frequency ARray (LOFAR) and are used to study the properties of cosmic rays. For a complete understanding of this phenomenon and the underlying physical processes, an absolute calibration of the detecting antenna system is needed. We present three approaches that were used to check and improve the antenna model of LOFAR and to provide an absolute calibration of the whole system for air shower measurements. Two methods are based on calibrated reference sources and one on a calibration approach using the diffuse radio emission of the Galaxy, optimized for short data-sets. An accuracy of 19% in amplitude is reached. The absolute calibration is also compared to predictions from air shower simulations. These results are used to set an absolute energy scale for air shower measurements and can be used as a basis for an absolute scale for the measurement of astronomical transients with LOFAR.
Published: 2015
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9. Probing Atmospheric Electric Fields in Thunderstorms through Radio Emission from Cosmic-Ray-Induced Air Showers

Author: Schellart, P., Trinh, T. N. G., Buitink, S., Corstanje, A., Enriquez, J. E., Falcke, H., Hörandel, J. R., Nelles, A., Rachen, J. P., Rossetto, L., Scholten, O., ter Veen, S., Thoudam, Satyendra, Ebert, U., Koehn, C., Rutjes, C., Alexov, A., Anderson, J. M., Avruch, I. M., Bentum, M. J., Bernardi, G., Best, P., Bonafede, A., Breitling, F., Broderick, J. W., Brüggen, M., Butcher, H. R., Ciardi, B., de Geus, E., de Vos, M., Duscha, S., Eislöffel, J., Fallows, R. A., Frieswijk, W., Garrett, M. A., Grießmeier, J., Gunst, A. W., Heald, G., Hessels, J. W. T., Hoeft, M., Holties, H. A., Juette, E., Kondratiev, V. I., Kuniyoshi, M., Kuper, G., Mann, G., McFadden, R., McKay-Bukowski, D., McKean, J. P., Mevius, M., Moldon, J., Norden, M. J., Orru, E., Paas, H., Pandey-Pommier, M., Pizzo, R., Polatidis, A. G., Reich, W., Röttgering, H., Scaife, A. M. M., Schwarz, D. J., Serylak, M., Smirnov, O., Steinmetz, M., Swinbank, J., Tagger, M., Tasse, C., Toribio, M. C., van Weeren, R. J., Vermeulen, R., Vocks, C., Wise, M. W., Wucknitz, O., Zarka, P., Schellart, P., Trinh, T. N. G., Buitink, S., Corstanje, A., Enriquez, J. E., Falcke, H., Hörandel, J. R., Nelles, A., Rachen, J. P., Rossetto, L., Scholten, O., ter Veen, S., Thoudam, Satyendra, Ebert, U., Koehn, C., Rutjes, C., Alexov, A., Anderson, J. M., Avruch, I. M., Bentum, M. J., Bernardi, G., Best, P., Bonafede, A., Breitling, F., Broderick, J. W., Brüggen, M., Butcher, H. R., Ciardi, B., de Geus, E., de Vos, M., Duscha, S., Eislöffel, J., Fallows, R. A., Frieswijk, W., Garrett, M. A., Grießmeier, J., Gunst, A. W., Heald, G., Hessels, J. W. T., Hoeft, M., Holties, H. A., Juette, E., Kondratiev, V. I., Kuniyoshi, M., Kuper, G., Mann, G., McFadden, R., McKay-Bukowski, D., McKean, J. P., Mevius, M., Moldon, J., Norden, M. J., Orru, E., Paas, H., Pandey-Pommier, M., Pizzo, R., Polatidis, A. G., Reich, W., Röttgering, H., Scaife, A. M. M., Schwarz, D. J., Serylak, M., Smirnov, O., Steinmetz, M., Swinbank, J., Tagger, M., Tasse, C., Toribio, M. C., van Weeren, R. J., Vermeulen, R., Vocks, C., Wise, M. W., Wucknitz, O., and Zarka, P.
Abstract: We present measurements of radio emission from cosmic ray air showers that took place during thunderstorms. The intensity and polarization patterns of these air showers are radically different from those measured during fair-weather conditions. With the use of a simple two-layer model for the atmospheric electric field, these patterns can be well reproduced by state-of-the-art simulation codes. This in turn provides a novel way to study atmospheric electric fields.
Published: 2015
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10. The LOFAR long baseline snapshot calibrator survey

Author: Moldón, J., Deller, A. T., Wucknitz, O., Jackson, N., Drabent, A., Carozzi, T., Conway, J., Kapinska, A. D., McKean, J. P., Morabito, L., Varenius, E., Zarka, P., Anderson, J., Asgekar, A., Avruch, I. M., Bell, M. E., Bentum, M. J., Bernardi, G., Best, P., Bîrzan, L., Bregman, J., Breitling, F., Broderick, J. W., Brüggen, M., Butcher, H. R., Carbone, D., Ciardi, B., de Gasperin, F., de Geus, E., Duscha, S., Eislöffel, J., Engels, D., Falcke, H., Fallows, R. A., Fender, R., Ferrari, C., Frieswijk, W., Garrett, M. A., Grießmeier, J., Gunst, A. W., Hamaker, J. P., Hassall, T. E., Heald, G., Hoeft, M., Juette, E., Karastergiou, A., Kondratiev, V. I., Kramer, M., Kuniyoshi, M., Kuper, G., Maat, P., Mann, G., Markoff, S., McFadden, R., McKay-Bukowski, D., Morganti, R., Munk, H., Norden, M. J., Offringa, A. R., Orru, E., Paas, H., Pandey-Pommier, M., Pizzo, R., Polatidis, A. G., Reich, W., Röttgering, H., Rowlinson, A., Scaife, A. M. M., Schwarz, D., Sluman, J., Smirnov, O., Stappers, B. W., Steinmetz, M., Tagger, M., Tang, Y., Tasse, C., Thoudam, Satyendra, Toribio, M. C., Vermeulen, R., Vocks, C., van Weeren, R. J., White, S., Wise, M. W., Yatawatta, S., Zensus, A., Moldón, J., Deller, A. T., Wucknitz, O., Jackson, N., Drabent, A., Carozzi, T., Conway, J., Kapinska, A. D., McKean, J. P., Morabito, L., Varenius, E., Zarka, P., Anderson, J., Asgekar, A., Avruch, I. M., Bell, M. E., Bentum, M. J., Bernardi, G., Best, P., Bîrzan, L., Bregman, J., Breitling, F., Broderick, J. W., Brüggen, M., Butcher, H. R., Carbone, D., Ciardi, B., de Gasperin, F., de Geus, E., Duscha, S., Eislöffel, J., Engels, D., Falcke, H., Fallows, R. A., Fender, R., Ferrari, C., Frieswijk, W., Garrett, M. A., Grießmeier, J., Gunst, A. W., Hamaker, J. P., Hassall, T. E., Heald, G., Hoeft, M., Juette, E., Karastergiou, A., Kondratiev, V. I., Kramer, M., Kuniyoshi, M., Kuper, G., Maat, P., Mann, G., Markoff, S., McFadden, R., McKay-Bukowski, D., Morganti, R., Munk, H., Norden, M. J., Offringa, A. R., Orru, E., Paas, H., Pandey-Pommier, M., Pizzo, R., Polatidis, A. G., Reich, W., Röttgering, H., Rowlinson, A., Scaife, A. M. M., Schwarz, D., Sluman, J., Smirnov, O., Stappers, B. W., Steinmetz, M., Tagger, M., Tang, Y., Tasse, C., Thoudam, Satyendra, Toribio, M. C., Vermeulen, R., Vocks, C., van Weeren, R. J., White, S., Wise, M. W., Yatawatta, S., and Zensus, A.
Abstract: Aims. An efficient means of locating calibrator sources for international LOw Frequency ARray (LOFAR) is developed and used to determine the average density of usable calibrator sources on the sky for subarcsecond observations at 140 MHz. Methods. We used the multi-beaming capability of LOFAR to conduct a fast and computationally inexpensive survey with the full international LOFAR array. Sources were preselected on the basis of 325 MHz arcminute-scale flux density using existing catalogues. By observing 30 different sources in each of the 12 sets of pointings per hour, we were able to inspect 630 sources in two hours to determine if they possess a sufficiently bright compact component to be usable as LOFAR delay calibrators. Results. More than 40% of the observed sources are detected on multiple baselines between international stations and 86 are classified as satisfactory calibrators. We show that a flat low-frequency spectrum (from 74 to 325 MHz) is the best predictor of compactness at 140 MHz. We extrapolate from our sample to show that the sky density of calibrators that are sufficiently bright to calibrate dispersive and non-dispersive delays for the international LOFAR using existing methods is 1.0 per square degree. Conclusions. The observed density of satisfactory delay calibrator sources means that observations with international LOFAR should be possible at virtually any point in the sky provided that a fast and efficient search, using the methodology described here, is conducted prior to the observation to identify the best calibrator.
Published: 2015
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11. LOFAR discovery of a quiet emission mode in PSR B0823+26

Author: Sobey, C., Young, N. J., Hessels, J. W. T., Weltevrede, P., Noutsos, A., Stappers, B. W., Kramer, M., Bassa, C., Lyne, A. G., Kondratiev, V. I., Hassall, T. E., Keane, E. F., Bilous, A. V., Breton, R. P., Grießmeier, J. -M, Karastergiou, A., Pilia, M., Serylak, M., Veen, S. t., van Leeuwen, J., Alexov, A., Anderson, J., Asgekar, A., Avruch, I. M., Bell, M. E., Bentum, M. J., Bernardi, G., Best, P., Bîrzan, L., Bonafede, A., Breitling, F., Broderick, J., Brüggen, M., Corstanje, A., Carbone, D., de Geus, E., de Vos, M., van Duin, A., Duscha, S., Eislöffel, J., Falcke, H., Fallows, R. A., Fender, R., Ferrari, C., Frieswijk, W., Garrett, M. A., Gunst, A. W., Hamaker, J. P., Heald, G., Hoeft, M., Hörandel, J., Jütte, E., Kuper, G., Maat, P., Mann, G., Markoff, S., McFadden, R., McKay-Bukowski, D., McKean, J. P., Mulcahy, D. D., Munk, H., Nelles, A., Norden, M. J., Orrù, E., Paas, H., Pandey-Pommier, M., Pandey, V. N., Pietka, G., Pizzo, R., Polatidis, A. G., Rafferty, D., Renting, A., Röttgering, H., Rowlinson, A., Scaife, A. M. M., Schwarz, D., Sluman, J., Smirnov, O., Steinmetz, M., Stewart, A., Swinbank, J., Tagger, M., Tang, Y., Tasse, C., Thoudam, Satyendra, Toribio, C., Vermeulen, R., Vocks, C., van Weeren, R. J., Wijers, R. A. M. J., Wise, M. W., Wucknitz, O., Yatawatta, S., Zarka, P., Sobey, C., Young, N. J., Hessels, J. W. T., Weltevrede, P., Noutsos, A., Stappers, B. W., Kramer, M., Bassa, C., Lyne, A. G., Kondratiev, V. I., Hassall, T. E., Keane, E. F., Bilous, A. V., Breton, R. P., Grießmeier, J. -M, Karastergiou, A., Pilia, M., Serylak, M., Veen, S. t., van Leeuwen, J., Alexov, A., Anderson, J., Asgekar, A., Avruch, I. M., Bell, M. E., Bentum, M. J., Bernardi, G., Best, P., Bîrzan, L., Bonafede, A., Breitling, F., Broderick, J., Brüggen, M., Corstanje, A., Carbone, D., de Geus, E., de Vos, M., van Duin, A., Duscha, S., Eislöffel, J., Falcke, H., Fallows, R. A., Fender, R., Ferrari, C., Frieswijk, W., Garrett, M. A., Gunst, A. W., Hamaker, J. P., Heald, G., Hoeft, M., Hörandel, J., Jütte, E., Kuper, G., Maat, P., Mann, G., Markoff, S., McFadden, R., McKay-Bukowski, D., McKean, J. P., Mulcahy, D. D., Munk, H., Nelles, A., Norden, M. J., Orrù, E., Paas, H., Pandey-Pommier, M., Pandey, V. N., Pietka, G., Pizzo, R., Polatidis, A. G., Rafferty, D., Renting, A., Röttgering, H., Rowlinson, A., Scaife, A. M. M., Schwarz, D., Sluman, J., Smirnov, O., Steinmetz, M., Stewart, A., Swinbank, J., Tagger, M., Tang, Y., Tasse, C., Thoudam, Satyendra, Toribio, C., Vermeulen, R., Vocks, C., van Weeren, R. J., Wijers, R. A. M. J., Wise, M. W., Wucknitz, O., Yatawatta, S., and Zarka, P.
Abstract: PSR B0823+26, a 0.53-s radio pulsar, displays a host of emission phenomena over time-scales of seconds to (at least) hours, including nulling, subpulse drifting, and mode-changing. Studying pulsars like PSR B0823+26 provides further insight into the relationship between these various emission phenomena and what they might teach us about pulsar magnetospheres. Here we report on the LOFAR (Low-Frequency Array) discovery that PSR B0823+26 has a weak and sporadically emitting ‘quiet’ (Q) emission mode that is over 100 times weaker (on average) and has a nulling fraction forty-times greater than that of the more regularly-emitting ‘bright’ (B) mode. Previously, the pulsar has been undetected in the Q mode, and was assumed to be nulling continuously. PSR B0823+26 shows a further decrease in average flux just before the transition into the B mode, and perhaps truly turns off completely at these times. Furthermore, simultaneous observations taken with the LOFAR, Westerbork, Lovell, and Effelsberg telescopes between 110 MHz and 2.7 GHz demonstrate that the transition between the Q mode and B mode occurs within one single rotation of the neutron star, and that it is concurrent across the range of frequencies observed.
Published: 2015
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12. LOFAR sparse image reconstruction

Author: Garsden, H., Girard, J. N., Starck, J. L., Corbel, S., Tasse, C., Woiselle, A., McKean, J. P., van Amesfoort, A. S., Anderson, J., Avruch, I. M., Beck, R., Bentum, M. J., Best, P., Breitling, F., Broderick, J., Brüggen, M., Butcher, H. R., Ciardi, B., de Gasperin, F., de Geus, E., de Vos, M., Duscha, S., Eislöffel, J., Engels, D., Falcke, H., Fallows, R. A., Fender, R., Ferrari, C., Frieswijk, W., Garrett, M. A., Grießmeier, J., Gunst, A. W., Hassall, T. E., Heald, G., Hoeft, M., Hörandel, J., van der Horst, A., Juette, E., Karastergiou, A., Kondratiev, V. I., Kramer, M., Kuniyoshi, M., Kuper, G., Mann, G., Markoff, S., McFadden, R., McKay-Bukowski, D., Mulcahy, D. D., Munk, H., Norden, M. J., Orru, E., Paas, H., Pandey-Pommier, M., Pandey, V. N., Pietka, G., Pizzo, R., Polatidis, A. G., Renting, A., Röttgering, H., Rowlinson, A., Schwarz, D., Sluman, J., Smirnov, O., Stappers, B. W., Steinmetz, M., Stewart, A., Swinbank, J., Tagger, M., Tang, Y., Thoudam, Satyendra, Toribio, C., Vermeulen, R., Vocks, C., van Weeren, R. J., Wijnholds, S. J., Wise, M. W., Wucknitz, O., Yatawatta, S., Zarka, P., Zensus, A., Garsden, H., Girard, J. N., Starck, J. L., Corbel, S., Tasse, C., Woiselle, A., McKean, J. P., van Amesfoort, A. S., Anderson, J., Avruch, I. M., Beck, R., Bentum, M. J., Best, P., Breitling, F., Broderick, J., Brüggen, M., Butcher, H. R., Ciardi, B., de Gasperin, F., de Geus, E., de Vos, M., Duscha, S., Eislöffel, J., Engels, D., Falcke, H., Fallows, R. A., Fender, R., Ferrari, C., Frieswijk, W., Garrett, M. A., Grießmeier, J., Gunst, A. W., Hassall, T. E., Heald, G., Hoeft, M., Hörandel, J., van der Horst, A., Juette, E., Karastergiou, A., Kondratiev, V. I., Kramer, M., Kuniyoshi, M., Kuper, G., Mann, G., Markoff, S., McFadden, R., McKay-Bukowski, D., Mulcahy, D. D., Munk, H., Norden, M. J., Orru, E., Paas, H., Pandey-Pommier, M., Pandey, V. N., Pietka, G., Pizzo, R., Polatidis, A. G., Renting, A., Röttgering, H., Rowlinson, A., Schwarz, D., Sluman, J., Smirnov, O., Stappers, B. W., Steinmetz, M., Stewart, A., Swinbank, J., Tagger, M., Tang, Y., Thoudam, Satyendra, Toribio, C., Vermeulen, R., Vocks, C., van Weeren, R. J., Wijnholds, S. J., Wise, M. W., Wucknitz, O., Yatawatta, S., Zarka, P., and Zensus, A.
Abstract: Context. The LOw Frequency ARray (LOFAR) radio telescope is a giant digital phased array interferometer with multiple antennas distributed in Europe. It provides discrete sets of Fourier components of the sky brightness. Recovering the original brightness distribution with aperture synthesis forms an inverse problem that can be solved by various deconvolution and minimization methods. Aims. Recent papers have established a clear link between the discrete nature of radio interferometry measurement and the “compressed sensing” (CS) theory, which supports sparse reconstruction methods to form an image from the measured visibilities. Empowered by proximal theory, CS offers a sound framework for efficient global minimization and sparse data representation using fast algorithms. Combined with instrumental direction-dependent effects (DDE) in the scope of a real instrument, we developed and validated a new method based on this framework. Methods. We implemented a sparse reconstruction method in the standard LOFAR imaging tool and compared the photometric and resolution performance of this new imager with that of CLEAN-based methods (CLEAN and MS-CLEAN) with simulated and real LOFAR data. Results. We show that i) sparse reconstruction performs as well as CLEAN in recovering the flux of point sources; ii) performs much better on extended objects (the root mean square error is reduced by a factor of up to 10); and iii) provides a solution with an effective angular resolution 2−3 times better than the CLEAN images. Conclusions. Sparse recovery gives a correct photometry on high dynamic and wide-field images and improved realistic structures of extended sources (of simulated and real LOFAR datasets). This sparse reconstruction method is compatible with modern interferometric imagers that handle DDE corrections (A- and W-projections) required for current and future instruments such as LOFAR and SKA.
Published: 2015
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13. The shape of the radio wavefront of extensive air showers as measured with LOFAR

Author: Corstanje, A., Schellart, P., Nelles, A., Buitink, S., Enriquez, J. E., Falcke, H., Frieswijk, W., Hörandel, J. R., Krause, M., Rachen, J. P., Scholten, O., ter Veen, S., Thoudam, Satyendra, Trinh, T. N. G., van den Akker, M., Alexov, A., Anderson, J., Avruch, I. M., Bell, M. E., Bentum, M. J., Bernardi, G., Best, P., Bonafede, A., Breitling, F., Broderick, J., Brüggen, M., Butcher, H. R., Ciardi, B., de Gasperin, F., de Geus, E., de Vos, M., Duscha, S., Eislöffel, J., Engels, D., Fallows, R. A., Ferrari, C., Garrett, M. A., Grießmeier, J., Gunst, A. W., Hamaker, J. P., Hoeft, M., Horneffer, A., Iacobelli, M., Juette, E., Karastergiou, A., Kohler, J., Kondratiev, V. I., Kuniyoshi, M., Kuper, G., Maat, P., Mann, G., McFadden, R., McKay-Bukowski, D., Mevius, M., Munk, H., Norden, M. J., Orru, E., Paas, H., Pandey-Pommier, M., Pandey, V. N., Pizzo, R., Polatidis, A. G., Reich, W., Röttgering, H., Scaife, A. M. M., Schwarz, D., Smirnov, O., Stewart, A., Steinmetz, M., Swinbank, J., Tagger, M., Tang, Y., Tasse, C., Toribio, C., Vermeulen, R., Vocks, C., van Weeren, R. J., Wijnholds, S. J., Wucknitz, O., Yatawatta, S., Zarka, P., Corstanje, A., Schellart, P., Nelles, A., Buitink, S., Enriquez, J. E., Falcke, H., Frieswijk, W., Hörandel, J. R., Krause, M., Rachen, J. P., Scholten, O., ter Veen, S., Thoudam, Satyendra, Trinh, T. N. G., van den Akker, M., Alexov, A., Anderson, J., Avruch, I. M., Bell, M. E., Bentum, M. J., Bernardi, G., Best, P., Bonafede, A., Breitling, F., Broderick, J., Brüggen, M., Butcher, H. R., Ciardi, B., de Gasperin, F., de Geus, E., de Vos, M., Duscha, S., Eislöffel, J., Engels, D., Fallows, R. A., Ferrari, C., Garrett, M. A., Grießmeier, J., Gunst, A. W., Hamaker, J. P., Hoeft, M., Horneffer, A., Iacobelli, M., Juette, E., Karastergiou, A., Kohler, J., Kondratiev, V. I., Kuniyoshi, M., Kuper, G., Maat, P., Mann, G., McFadden, R., McKay-Bukowski, D., Mevius, M., Munk, H., Norden, M. J., Orru, E., Paas, H., Pandey-Pommier, M., Pandey, V. N., Pizzo, R., Polatidis, A. G., Reich, W., Röttgering, H., Scaife, A. M. M., Schwarz, D., Smirnov, O., Stewart, A., Steinmetz, M., Swinbank, J., Tagger, M., Tang, Y., Tasse, C., Toribio, C., Vermeulen, R., Vocks, C., van Weeren, R. J., Wijnholds, S. J., Wucknitz, O., Yatawatta, S., and Zarka, P.
Abstract: Extensive air showers, induced by high energy cosmic rays impinging on the Earth’s atmosphere, produce radio emission that is measured with the LOFAR radio telescope. As the emission comes from a finite distance of a few kilometers, the incident wavefront is non-planar. A spherical, conical or hyperbolic shape of the wavefront has been proposed, but measurements of individual air showers have been inconclusive so far. For a selected high-quality sample of 161 measured extensive air showers, we have reconstructed the wavefront by measuring pulse arrival times to sub-nanosecond precision in 200 to 350 individual antennas. For each measured air shower, we have fitted a conical, spherical, and hyperboloid shape to the arrival times. The fit quality and a likelihood analysis show that a hyperboloid is the best parameterization. Using a non-planar wavefront shape gives an improved angular resolution, when reconstructing the shower arrival direction. Furthermore, a dependence of the wavefront shape on the shower geometry can be seen. This suggests that it will be possible to use a wavefront shape analysis to get an additional handle on the atmospheric depth of the shower maximum, which is sensitive to the mass of the primary particle.
Published: 2015
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14. Discovery of carbon radio recombination lines in absorption towards Cygnus A

Author: Oonk, J. B. R., van Weeren, R. J., Salgado, F., Morabito, L. K., Tielens, A. G. G. M., Rottgering, H. J. A., Asgekar, A., White, G. J., Alexov, A., Anderson, J., Avruch, I. M., Batejat, F., Beck, R., Bell, M. E., van Bemmel, I., Bentum, M. J., Bernardi, G., Best, P., Bonafede, A., Breitling, F., Brentjens, M., Broderick, J., Brüggen, M., Butcher, H. R., Ciardi, B., Conway, J. E., Corstanje, A., de Gasperin, F., de Geus, E., de Vos, M., Duscha, S., Eislöffel, J., Engels, D., van Enst, J., Falcke, H., Fallows, R. A., Fender, R., Ferrari, C., Frieswijk, W., Garrett, M. A., Grießmeier, J., Hamaker, J. P., Hassall, T. E., Heald, G., Hessels, J. W. T., Hoeft, M., Horneffer, A., van der Horst, A., Iacobelli, M., Jackson, N. J., Juette, E., Karastergiou, A., Klijn, W., Kohler, J., Kondratiev, V. I., Kramer, M., Kuniyoshi, M., Kuper, G., van Leeuwen, J., Maat, P., Macario, G., Mann, G., Markoff, S., McKean, J. P., Mevius, M., Miller-Jones, J. C. A., Mol, J. D., Mulcahy, D. D., Munk, H., Norden, M. J., Orru, E., Paas, H., Pandey-Pommier, M., Pandey, V. N., Pizzo, R., Polatidis, A. G., Reich, W., Scaife, A. M. M., Schoenmakers, A., Schwarz, D., Shulevski, A., Sluman, J., Smirnov, O., Sobey, C., Stappers, B. W., Steinmetz, M., Swinbank, J., Tagger, M., Tang, Y., Tasse, C., Veen, S. t., Thoudam, Satyendra, Toribio, C., van Nieuwpoort, R., Vermeulen, R., Vocks, C., Vogt, C., Wijers, R. A. M. J., Wise, M. W., Wucknitz, O., Yatawatta, S., Zarka, P., Zensus, A., Oonk, J. B. R., van Weeren, R. J., Salgado, F., Morabito, L. K., Tielens, A. G. G. M., Rottgering, H. J. A., Asgekar, A., White, G. J., Alexov, A., Anderson, J., Avruch, I. M., Batejat, F., Beck, R., Bell, M. E., van Bemmel, I., Bentum, M. J., Bernardi, G., Best, P., Bonafede, A., Breitling, F., Brentjens, M., Broderick, J., Brüggen, M., Butcher, H. R., Ciardi, B., Conway, J. E., Corstanje, A., de Gasperin, F., de Geus, E., de Vos, M., Duscha, S., Eislöffel, J., Engels, D., van Enst, J., Falcke, H., Fallows, R. A., Fender, R., Ferrari, C., Frieswijk, W., Garrett, M. A., Grießmeier, J., Hamaker, J. P., Hassall, T. E., Heald, G., Hessels, J. W. T., Hoeft, M., Horneffer, A., van der Horst, A., Iacobelli, M., Jackson, N. J., Juette, E., Karastergiou, A., Klijn, W., Kohler, J., Kondratiev, V. I., Kramer, M., Kuniyoshi, M., Kuper, G., van Leeuwen, J., Maat, P., Macario, G., Mann, G., Markoff, S., McKean, J. P., Mevius, M., Miller-Jones, J. C. A., Mol, J. D., Mulcahy, D. D., Munk, H., Norden, M. J., Orru, E., Paas, H., Pandey-Pommier, M., Pandey, V. N., Pizzo, R., Polatidis, A. G., Reich, W., Scaife, A. M. M., Schoenmakers, A., Schwarz, D., Shulevski, A., Sluman, J., Smirnov, O., Sobey, C., Stappers, B. W., Steinmetz, M., Swinbank, J., Tagger, M., Tang, Y., Tasse, C., Veen, S. t., Thoudam, Satyendra, Toribio, C., van Nieuwpoort, R., Vermeulen, R., Vocks, C., Vogt, C., Wijers, R. A. M. J., Wise, M. W., Wucknitz, O., Yatawatta, S., Zarka, P., and Zensus, A.
Abstract: We present the first detection of carbon radio recombination line absorption along the line of sight to Cygnus A. The observations were carried out with the Low Frequency Array in the 33–57 MHz range. These low-frequency radio observations provide us with a new line of sight to study the diffuse, neutral gas in our Galaxy. To our knowledge this is the first time that foreground Milky Way recombination line absorption has been observed against a bright extragalactic background source. By stacking 48 carbon α lines in the observed frequency range we detect carbon absorption with a signal-to-noise ratio of about 5. The average carbon absorption has a peak optical depth of 2 × 10−4, a line width of 10 km s−1 and a velocity of +4 km s−1 with respect to the local standard of rest. The associated gas is found to have an electron temperature Te ∼ 110 K and density ne ∼ 0.06 cm−3. These properties imply that the observed carbon α absorption likely arises in the cold neutral medium of the Orion arm of the Milky Way. Hydrogen and helium lines were not detected to a 3σ peak optical depth limit of 1.5 × 10−4 for a 4 km s−1 channel width. Radio recombination lines associated with Cygnus A itself were also searched for, but are not detected. We set a 3σ upper limit of 1.5 × 10−4 for the peak optical depth of these lines for a 4 km s−1 channel width.
Published: 2014
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15. LOFAR Low-band Antenna Observations of the 3C 295 and Boötes Fields : Source Counts and Ultra-steep Spectrum Sources

Author: van Weeren, R. J., Williams, W. L., Tasse, C., Röttgering, H. J. A., Rafferty, D. A., van der Tol, S., Heald, G., White, G. J., Shulevski, A., Best, P., Intema, H. T., Bhatnagar, S., Reich, W., Steinmetz, M., van Velzen, S., Enßlin, T. A., Prandoni, I., de Gasperin, F., Jamrozy, M., Brunetti, G., Jarvis, M. J., McKean, J. P., Wise, M. W., Ferrari, C., Harwood, J., Oonk, J. B. R., Hoeft, M., Kunert-Bajraszewska, M., Horellou, C., Wucknitz, O., Bonafede, A., Mohan, N. R., Scaife, A. M. M., Klöckner, H. -R, van Bemmel, I. M., Merloni, A., Chyzy, K. T., Engels, D., Falcke, H., Pandey-Pommier, M., Alexov, A., Anderson, J., Avruch, I. M., Beck, R., Bell, M. E., Bentum, M. J., Bernardi, G., Breitling, F., Broderick, J., Brouw, W. N., Brüggen, M., Butcher, H. R., Ciardi, B., de Geus, E., de Vos, M., Deller, A., Duscha, S., Eislöffel, J., Fallows, R. A., Frieswijk, W., Garrett, M. A., Grießmeier, J., Gunst, A. W., Hamaker, J. P., Hassall, T. E., Hörandel, J., van der Horst, A., Iacobelli, M., Jackson, N. J., Juette, E., Kondratiev, V. I., Kuniyoshi, M., Maat, P., Mann, G., McKay-Bukowski, D., Mevius, M., Morganti, R., Munk, H., Offringa, A. R., Orrù, E., Paas, H., Pandey, V. N., Pietka, G., Pizzo, R., Polatidis, A. G., Renting, A., Rowlinson, A., Schwarz, D., Serylak, M., Sluman, J., Smirnov, O., Stappers, B. W., Stewart, A., Swinbank, J., Tagger, M., Tang, Y., Thoudam, Satyendra, Toribio, C., Vermeulen, R., Vocks, C., Zarka, P., van Weeren, R. J., Williams, W. L., Tasse, C., Röttgering, H. J. A., Rafferty, D. A., van der Tol, S., Heald, G., White, G. J., Shulevski, A., Best, P., Intema, H. T., Bhatnagar, S., Reich, W., Steinmetz, M., van Velzen, S., Enßlin, T. A., Prandoni, I., de Gasperin, F., Jamrozy, M., Brunetti, G., Jarvis, M. J., McKean, J. P., Wise, M. W., Ferrari, C., Harwood, J., Oonk, J. B. R., Hoeft, M., Kunert-Bajraszewska, M., Horellou, C., Wucknitz, O., Bonafede, A., Mohan, N. R., Scaife, A. M. M., Klöckner, H. -R, van Bemmel, I. M., Merloni, A., Chyzy, K. T., Engels, D., Falcke, H., Pandey-Pommier, M., Alexov, A., Anderson, J., Avruch, I. M., Beck, R., Bell, M. E., Bentum, M. J., Bernardi, G., Breitling, F., Broderick, J., Brouw, W. N., Brüggen, M., Butcher, H. R., Ciardi, B., de Geus, E., de Vos, M., Deller, A., Duscha, S., Eislöffel, J., Fallows, R. A., Frieswijk, W., Garrett, M. A., Grießmeier, J., Gunst, A. W., Hamaker, J. P., Hassall, T. E., Hörandel, J., van der Horst, A., Iacobelli, M., Jackson, N. J., Juette, E., Kondratiev, V. I., Kuniyoshi, M., Maat, P., Mann, G., McKay-Bukowski, D., Mevius, M., Morganti, R., Munk, H., Offringa, A. R., Orrù, E., Paas, H., Pandey, V. N., Pietka, G., Pizzo, R., Polatidis, A. G., Renting, A., Rowlinson, A., Schwarz, D., Serylak, M., Sluman, J., Smirnov, O., Stappers, B. W., Stewart, A., Swinbank, J., Tagger, M., Tang, Y., Thoudam, Satyendra, Toribio, C., Vermeulen, R., Vocks, C., and Zarka, P.
Abstract: We present Low Frequency Array (LOFAR) Low Band observations of the Boötes and 3C 295 fields. Our images made at 34, 46, and 62 MHz reach noise levels of 12, 8, and 5 mJy beam–1, making them the deepest images ever obtained in this frequency range. In total, we detect between 300 and 400 sources in each of these images, covering an area of 17-52 deg2. From the observations, we derive Euclidean-normalized differential source counts. The 62 MHz source counts agree with previous GMRT 153 MHz and Very Large Array 74 MHz differential source counts, scaling with a spectral index of –0.7. We find that a spectral index scaling of –0.5 is required to match up the LOFAR 34 MHz source counts. This result is also in agreement with source counts from the 38 MHz 8C survey, indicating that the average spectral index of radio sources flattens toward lower frequencies. We also find evidence for spectral flattening using the individual flux measurements of sources between 34 and 1400 MHz and by calculating the spectral index averaged over the source population. To select ultra-steep spectrum (α < –1.1) radio sources that could be associated with massive high-redshift radio galaxies, we compute spectral indices between 62 MHz, 153 MHz, and 1.4 GHz for sources in the Boötes field. We cross-correlate these radio sources with optical and infrared catalogs and fit the spectral energy distribution to obtain photometric redshifts. We find that most of these ultra-steep spectrum sources are located in the 0.7 z 2.5 range.
Published: 2014
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16. The LOFAR pilot surveys for pulsars and fast radio transients

Author: Coenen, T., van Leeuwen, J., Hessels, J. W. T., Stappers, B. W., Kondratiev, V. I., Alexov, A., Breton, R. P., Bilous, A., Cooper, S., Falcke, H., Fallows, R. A., Gajjar, V., Grießmeier, J. -M, Hassall, T. E., Karastergiou, A., Keane, E. F., Kramer, M., Kuniyoshi, M., Noutsos, A., Os\lowski, S., Pilia, M., Serylak, M., Schrijvers, C., Sobey, C., ter Veen, S., Verbiest, J., Weltevrede, P., Wijnholds, S., Zagkouris, K., van Amesfoort, A. S., Anderson, J., Asgekar, A., Avruch, I. M., Bell, M. E., Bentum, M. J., Bernardi, G., Best, P., Bonafede, A., Breitling, F., Broderick, J., Brüggen, M., Butcher, H. R., Ciardi, B., Corstanje, A., Deller, A., Duscha, S., Eislöffel, J., Fender, R., Ferrari, C., Frieswijk, W., Garrett, M. A., de Gasperin, F., de Geus, E., Gunst, A. W., Hamaker, J. P., Heald, G., Hoeft, M., van der Horst, A., Juette, E., Kuper, G., Law, C., Mann, G., McFadden, R., McKay-Bukowski, D., McKean, J. P., Munk, H., Orru, E., Paas, H., Pandey-Pommier, M., Polatidis, A. G., Reich, W., Renting, A., Röttgering, H., Rowlinson, A., Scaife, A. M. M., Schwarz, D., Sluman, J., Smirnov, O., Swinbank, J., Tagger, M., Tang, Y., Tasse, C., Thoudam, Satyendra, Toribio, C., Vermeulen, R., Vocks, C., van Weeren, R. J., Wucknitz, O., Zarka, P., Zensus, A., Coenen, T., van Leeuwen, J., Hessels, J. W. T., Stappers, B. W., Kondratiev, V. I., Alexov, A., Breton, R. P., Bilous, A., Cooper, S., Falcke, H., Fallows, R. A., Gajjar, V., Grießmeier, J. -M, Hassall, T. E., Karastergiou, A., Keane, E. F., Kramer, M., Kuniyoshi, M., Noutsos, A., Os\lowski, S., Pilia, M., Serylak, M., Schrijvers, C., Sobey, C., ter Veen, S., Verbiest, J., Weltevrede, P., Wijnholds, S., Zagkouris, K., van Amesfoort, A. S., Anderson, J., Asgekar, A., Avruch, I. M., Bell, M. E., Bentum, M. J., Bernardi, G., Best, P., Bonafede, A., Breitling, F., Broderick, J., Brüggen, M., Butcher, H. R., Ciardi, B., Corstanje, A., Deller, A., Duscha, S., Eislöffel, J., Fender, R., Ferrari, C., Frieswijk, W., Garrett, M. A., de Gasperin, F., de Geus, E., Gunst, A. W., Hamaker, J. P., Heald, G., Hoeft, M., van der Horst, A., Juette, E., Kuper, G., Law, C., Mann, G., McFadden, R., McKay-Bukowski, D., McKean, J. P., Munk, H., Orru, E., Paas, H., Pandey-Pommier, M., Polatidis, A. G., Reich, W., Renting, A., Röttgering, H., Rowlinson, A., Scaife, A. M. M., Schwarz, D., Sluman, J., Smirnov, O., Swinbank, J., Tagger, M., Tang, Y., Tasse, C., Thoudam, Satyendra, Toribio, C., Vermeulen, R., Vocks, C., van Weeren, R. J., Wucknitz, O., Zarka, P., and Zensus, A.
Abstract: We have conducted two pilot surveys for radio pulsars and fast transients with the Low-Frequency Array (LOFAR) around 140 MHz and here report on the first low-frequency fast-radio burst limit and the discovery of two new pulsars. The first survey, the LOFAR Pilot Pulsar Survey (LPPS), observed a large fraction of the northern sky, ~ 1.4 × 104 deg2, with 1 h dwell times. Each observation covered ~75 deg2 using 7 independent fields formed by incoherently summing the high-band antenna fields. The second pilot survey, the LOFAR Tied-Array Survey (LOTAS), spanned ~600 deg2, with roughly a 5-fold increase in sensitivity compared with LPPS. Using a coherent sum of the 6 LOFAR “Superterp” stations, we formed 19 tied-array beams, together covering 4 deg2 per pointing. From LPPS we derive a limit on the occurrence, at 142 MHz, of dispersed radio bursts of < 150 day-1 sky-1, for bursts brighter than S> 107 Jy for the narrowest searched burst duration of 0.66 ms. In LPPS, we re-detected 65 previously known pulsars. LOTAS discovered two pulsars, the first with LOFAR or any digital aperture array. LOTAS also re-detected 27 previously known pulsars. These pilot studies show that LOFAR can efficiently carry out all-sky surveys for pulsars and fast transients, and they set the stage for further surveying efforts using LOFAR and the planned low-frequency component of the Square Kilometer Array.
Published: 2014
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17. LOFAR tied-array imaging of Type III solar radio bursts

Author: Morosan, D. E., Gallagher, P. T., Zucca, P., Fallows, R., Carley, E. P., Mann, G., Bisi, M. M., Kerdraon, A., Konovalenko, A. A., MacKinnon, A. L., Rucker, H. O., Thidé, B., Magdalenić, J., Vocks, C., Reid, H., Anderson, J., Asgekar, A., Avruch, I. M., Bentum, M. J., Bernardi, G., Best, P., Bonafede, A., Bregman, J., Breitling, F., Broderick, J., Brüggen, M., Butcher, H. R., Ciardi, B., Conway, J. E., de Gasperin, F., de Geus, E., Deller, A., Duscha, S., Eislöffel, J., Engels, D., Falcke, H., Ferrari, C., Frieswijk, W., Garrett, M. A., Grießmeier, J., Gunst, A. W., Hassall, T. E., Hessels, J. W. T., Hoeft, M., Hörandel, J., Horneffer, A., Iacobelli, M., Juette, E., Karastergiou, A., Kondratiev, V. I., Kramer, M., Kuniyoshi, M., Kuper, G., Maat, P., Markoff, S., McKean, J. P., Mulcahy, D. D., Munk, H., Nelles, A., Norden, M. J., Orru, E., Paas, H., Pandey-Pommier, M., Pandey, V. N., Pietka, G., Pizzo, R., Polatidis, A. G., Reich, W., Röttgering, H., Scaife, A. M. M., Schwarz, D., Serylak, M., Smirnov, O., Stappers, B. W., Stewart, A., Tagger, M., Tang, Y., Tasse, C., Thoudam, Satyendra, Toribio, C., Vermeulen, R., van Weeren, R. J., Wucknitz, O., Yatawatta, S., Zarka, P., Morosan, D. E., Gallagher, P. T., Zucca, P., Fallows, R., Carley, E. P., Mann, G., Bisi, M. M., Kerdraon, A., Konovalenko, A. A., MacKinnon, A. L., Rucker, H. O., Thidé, B., Magdalenić, J., Vocks, C., Reid, H., Anderson, J., Asgekar, A., Avruch, I. M., Bentum, M. J., Bernardi, G., Best, P., Bonafede, A., Bregman, J., Breitling, F., Broderick, J., Brüggen, M., Butcher, H. R., Ciardi, B., Conway, J. E., de Gasperin, F., de Geus, E., Deller, A., Duscha, S., Eislöffel, J., Engels, D., Falcke, H., Ferrari, C., Frieswijk, W., Garrett, M. A., Grießmeier, J., Gunst, A. W., Hassall, T. E., Hessels, J. W. T., Hoeft, M., Hörandel, J., Horneffer, A., Iacobelli, M., Juette, E., Karastergiou, A., Kondratiev, V. I., Kramer, M., Kuniyoshi, M., Kuper, G., Maat, P., Markoff, S., McKean, J. P., Mulcahy, D. D., Munk, H., Nelles, A., Norden, M. J., Orru, E., Paas, H., Pandey-Pommier, M., Pandey, V. N., Pietka, G., Pizzo, R., Polatidis, A. G., Reich, W., Röttgering, H., Scaife, A. M. M., Schwarz, D., Serylak, M., Smirnov, O., Stappers, B. W., Stewart, A., Tagger, M., Tang, Y., Tasse, C., Thoudam, Satyendra, Toribio, C., Vermeulen, R., van Weeren, R. J., Wucknitz, O., Yatawatta, S., and Zarka, P.
Abstract: Context. The Sun is an active source of radio emission which is often associated with energetic phenomena such as solar flares and coronal mass ejections (CMEs). At low radio frequencies (<100 MHz), the Sun has not been imaged extensively because of the instrumental limitations of previous radio telescopes. Aims. Here, the combined high spatial, spectral, and temporal resolution of the LOw Frequency ARray (LOFAR) was used to study solar Type III radio bursts at 30–90 MHz and their association with CMEs. Methods. The Sun was imaged with 126 simultaneous tied-array beams within ≤5 R⊙ of the solar centre. This method offers benefits over standard interferometric imaging since each beam produces high temporal (~83 ms) and spectral resolution (12.5 kHz) dynamic spectra at an array of spatial locations centred on the Sun. LOFAR’s standard interferometric output is currently limited to one image per second. Results. Over a period of 30 min, multiple Type III radio bursts were observed, a number of which were found to be located at high altitudes (~4 R⊙ from the solar center at 30 MHz) and to have non-radial trajectories. These bursts occurred at altitudes in excess of values predicted by 1D radial electron density models. The non-radial high altitude Type III bursts were found to be associated with the expanding flank of a CME. Conclusions. The CME may have compressed neighbouring streamer plasma producing larger electron densities at high altitudes, while the non-radial burst trajectories can be explained by the deflection of radial magnetic fields as the CME expanded in the low corona.
Published: 2014
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18. Initial LOFAR observations of epoch of reionization windows : II. Diffuse polarized emission in the ELAIS-N1 field

Author: Jelić, V., de Bruyn, A. G., Mevius, M., Abdalla, F. B., Asad, K. M. B., Bernardi, G., Brentjens, M. A., Bus, S., Chapman, E., Ciardi, B., Daiboo, S., Fernandez, E. R., Ghosh, A., Harker, G., Jensen, H., Kazemi, S., Koopmans, L. V. E., Labropoulos, P., Martinez-Rubi, O., Mellema, G., Offringa, A. R., Pandey, V. N., Patil, A. H., Thomas, R. M., Vedantham, H. K., Veligatla, V., Yatawatta, S., Zaroubi, S., Alexov, A., Anderson, J., Avruch, I. M., Beck, R., Bell, M. E., Bentum, M. J., Best, P., Bonafede, A., Bregman, J., Breitling, F., Broderick, J., Brouw, W. N., Brüggen, M., Butcher, H. R., Conway, J. E., de Gasperin, F., de Geus, E., Deller, A., Dettmar, R. -J, Duscha, S., Eislöffel, J., Engels, D., Falcke, H., Fallows, R. A., Fender, R., Ferrari, C., Frieswijk, W., Garrett, M. A., Grießmeier, J., Gunst, A. W., Hamaker, J. P., Hassall, T. E., Haverkorn, M., Heald, G., Hessels, J. W. T., Hoeft, M., Hörandel, J., Horneffer, A., van der Horst, A., Iacobelli, M., Juette, E., Karastergiou, A., Kondratiev, V. I., Kramer, M., Kuniyoshi, M., Kuper, G., van Leeuwen, J., Maat, P., Mann, G., McKay-Bukowski, D., McKean, J. P., Munk, H., Nelles, A., Norden, M. J., Paas, H., Pandey-Pommier, M., Pietka, G., Pizzo, R., Polatidis, A. G., Reich, W., Röttgering, H., Rowlinson, A., Scaife, A. M. M., Schwarz, D., Serylak, M., Smirnov, O., Steinmetz, M., Stewart, A., Tagger, M., Tang, Y., Tasse, C., ter Veen, S., Thoudam, Satyendra, Toribio, C., Vermeulen, R., Vocks, C., van Weeren, R. J., Wijers, R. A. M. J., Wijnholds, S. J., Wucknitz, O., Zarka, P., Jelić, V., de Bruyn, A. G., Mevius, M., Abdalla, F. B., Asad, K. M. B., Bernardi, G., Brentjens, M. A., Bus, S., Chapman, E., Ciardi, B., Daiboo, S., Fernandez, E. R., Ghosh, A., Harker, G., Jensen, H., Kazemi, S., Koopmans, L. V. E., Labropoulos, P., Martinez-Rubi, O., Mellema, G., Offringa, A. R., Pandey, V. N., Patil, A. H., Thomas, R. M., Vedantham, H. K., Veligatla, V., Yatawatta, S., Zaroubi, S., Alexov, A., Anderson, J., Avruch, I. M., Beck, R., Bell, M. E., Bentum, M. J., Best, P., Bonafede, A., Bregman, J., Breitling, F., Broderick, J., Brouw, W. N., Brüggen, M., Butcher, H. R., Conway, J. E., de Gasperin, F., de Geus, E., Deller, A., Dettmar, R. -J, Duscha, S., Eislöffel, J., Engels, D., Falcke, H., Fallows, R. A., Fender, R., Ferrari, C., Frieswijk, W., Garrett, M. A., Grießmeier, J., Gunst, A. W., Hamaker, J. P., Hassall, T. E., Haverkorn, M., Heald, G., Hessels, J. W. T., Hoeft, M., Hörandel, J., Horneffer, A., van der Horst, A., Iacobelli, M., Juette, E., Karastergiou, A., Kondratiev, V. I., Kramer, M., Kuniyoshi, M., Kuper, G., van Leeuwen, J., Maat, P., Mann, G., McKay-Bukowski, D., McKean, J. P., Munk, H., Nelles, A., Norden, M. J., Paas, H., Pandey-Pommier, M., Pietka, G., Pizzo, R., Polatidis, A. G., Reich, W., Röttgering, H., Rowlinson, A., Scaife, A. M. M., Schwarz, D., Serylak, M., Smirnov, O., Steinmetz, M., Stewart, A., Tagger, M., Tang, Y., Tasse, C., ter Veen, S., Thoudam, Satyendra, Toribio, C., Vermeulen, R., Vocks, C., van Weeren, R. J., Wijers, R. A. M. J., Wijnholds, S. J., Wucknitz, O., and Zarka, P.
Abstract: Aims. This study aims to characterise the polarized foreground emission in the ELAIS-N1 field and to address its possible implications for extracting of the cosmological 21 cm signal from the LOw-Frequency ARray – Epoch of Reionization (LOFAR-EoR) data. Methods. We used the high band antennas of LOFAR to image this region and RM-synthesis to unravel structures of polarized emission at high Galactic latitudes. Results. The brightness temperature of the detected Galactic emission is on average ~4 K in polarized intensity and covers the range from –10 to + 13 rad m-2 in Faraday depth. The total polarized intensity and polarization angle show a wide range of morphological features. We have also used the Westerbork Synthesis Radio Telescope (WSRT) at 350 MHz to image the same region. The LOFAR and WSRT images show a similar complex morphology at comparable brightness levels, but their spatial correlation is very low. The fractional polarization at 150 MHz, expressed as a percentage of the total intensity, amounts to ≈1.5%. There is no indication of diffuse emission in total intensity in the interferometric data, in line with results at higher frequencies Conclusions. The wide frequency range, high angular resolution, and high sensitivity make LOFAR an exquisite instrument for studying Galactic polarized emission at a resolution of ~1–2 rad m-2 in Faraday depth. The different polarized patterns observed at 150 MHz and 350 MHz are consistent with different source distributions along the line of sight wring in a variety of Faraday thin regions of emission. The presence of polarized foregrounds is a serious complication for epoch of reionization experiments. To avoid the leakage of polarized emission into total intensity, which can depend on frequency, we need to calibrate the instrumental polarization across the field of view to a small fraction of 1%.
Published: 2014
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19. LOFAR : The LOw-Frequency ARray

Author: van Haarlem, M. P., Wise, M. W., Gunst, A. W., Heald, G., McKean, J. P., Hessels, J. W. T., de Bruyn, A. G., Nijboer, R., Swinbank, J., Fallows, R., Brentjens, M., Nelles, A., Beck, R., Falcke, H., Fender, R., Hörandel, J., Koopmans, L. V. E., Mann, G., Miley, G., Röttgering, H., Stappers, B. W., Wijers, R. A. M. J., Zaroubi, S., van den Akker, M., Alexov, A., Anderson, J., Anderson, K., van Ardenne, A., Arts, M., Asgekar, A., Avruch, I. M., Batejat, F., Bähren, L., Bell, M. E., Bell, M. R., van Bemmel, I., Bennema, P., Bentum, M. J., Bernardi, G., Best, P., Bîrzan, L., Bonafede, A., Boonstra, A. -J, Braun, R., Bregman, J., Breitling, F., van de Brink, R. H., Broderick, J., Broekema, P. C., Brouw, W. N., Brüggen, M., Butcher, H. R., van Cappellen, W., Ciardi, B., Coenen, T., Conway, J., Coolen, A., Corstanje, A., Damstra, S., Davies, O., Deller, A. T., Dettmar, R. -J, van Diepen, G., Dijkstra, K., Donker, P., Doorduin, A., Dromer, J., Drost, M., van Duin, A., Eislöffel, J., van Enst, J., Ferrari, C., Frieswijk, W., Gankema, H., Garrett, M. A., de Gasperin, F., Gerbers, M., de Geus, E., Grießmeier, J. -M, Grit, T., Gruppen, P., Hamaker, J. P., Hassall, T., Hoeft, M., Holties, H. A., Horneffer, A., van der Horst, A., van Houwelingen, A., Huijgen, A., Iacobelli, M., Intema, H., Jackson, N., Jelic, V., de Jong, A., Juette, E., Kant, D., Karastergiou, A., Koers, A., Kollen, H., Kondratiev, V. I., Kooistra, E., Koopman, Y., Koster, A., Kuniyoshi, M., Kramer, M., Kuper, G., Lambropoulos, P., Law, C., van Leeuwen, J., Lemaitre, J., Loose, M., Maat, P., Macario, G., Markoff, S., Masters, J., McFadden, R. A., McKay-Bukowski, D., Meijering, H., Meulman, H., Mevius, M., Middelberg, E., Millenaar, R., Miller-Jones, J. C. A., Mohan, R. N., Mol, J. D., Morawietz, J., Morganti, R., Mulcahy, D. D., Mulder, E., Munk, H., Nieuwenhuis, L., van Nieuwpoort, R., Noordam, J. E., Norden, M., Noutsos, A., Offringa, A. R., Olofsson, H., Omar, A., Orrú, E., Overeem, R., Paas, H., Pandey-Pommier, M., Pandey, V. N., Pizzo, R., Polatidis, A., Rafferty, D., Rawlings, S., Reich, W., de Reijer, J. -P, Reitsma, J., Renting, G. A., Riemers, P., Rol, E., Romein, J. W., Roosjen, J., Ruiter, M., Scaife, A., van der Schaaf, K., Scheers, B., Schellart, P., Schoenmakers, A., Schoonderbeek, G., Serylak, M., Shulevski, A., Sluman, J., Smirnov, O., Sobey, C., Spreeuw, H., Steinmetz, M., Sterks, C. G. M., Stiepel, H. -J, Stuurwold, K., Tagger, M., Tang, Y., Tasse, C., Thomas, I., Thoudam, Satyendra, Toribio, M. C., van der Tol, B., Usov, O., van Veelen, M., van der Veen, A. -J, ter Veen, S., Verbiest, J. P. W., Vermeulen, R., Vermaas, N., Vocks, C., Vogt, C., de Vos, M., van der Wal, E., van Weeren, R., Weggemans, H., Weltevrede, P., White, S., Wijnholds, S. J., Wilhelmsson, T., Wucknitz, O., Yatawatta, S., Zarka, P., Zensus, A., van Zwieten, J., van Haarlem, M. P., Wise, M. W., Gunst, A. W., Heald, G., McKean, J. P., Hessels, J. W. T., de Bruyn, A. G., Nijboer, R., Swinbank, J., Fallows, R., Brentjens, M., Nelles, A., Beck, R., Falcke, H., Fender, R., Hörandel, J., Koopmans, L. V. E., Mann, G., Miley, G., Röttgering, H., Stappers, B. W., Wijers, R. A. M. J., Zaroubi, S., van den Akker, M., Alexov, A., Anderson, J., Anderson, K., van Ardenne, A., Arts, M., Asgekar, A., Avruch, I. M., Batejat, F., Bähren, L., Bell, M. E., Bell, M. R., van Bemmel, I., Bennema, P., Bentum, M. J., Bernardi, G., Best, P., Bîrzan, L., Bonafede, A., Boonstra, A. -J, Braun, R., Bregman, J., Breitling, F., van de Brink, R. H., Broderick, J., Broekema, P. C., Brouw, W. N., Brüggen, M., Butcher, H. R., van Cappellen, W., Ciardi, B., Coenen, T., Conway, J., Coolen, A., Corstanje, A., Damstra, S., Davies, O., Deller, A. T., Dettmar, R. -J, van Diepen, G., Dijkstra, K., Donker, P., Doorduin, A., Dromer, J., Drost, M., van Duin, A., Eislöffel, J., van Enst, J., Ferrari, C., Frieswijk, W., Gankema, H., Garrett, M. A., de Gasperin, F., Gerbers, M., de Geus, E., Grießmeier, J. -M, Grit, T., Gruppen, P., Hamaker, J. P., Hassall, T., Hoeft, M., Holties, H. A., Horneffer, A., van der Horst, A., van Houwelingen, A., Huijgen, A., Iacobelli, M., Intema, H., Jackson, N., Jelic, V., de Jong, A., Juette, E., Kant, D., Karastergiou, A., Koers, A., Kollen, H., Kondratiev, V. I., Kooistra, E., Koopman, Y., Koster, A., Kuniyoshi, M., Kramer, M., Kuper, G., Lambropoulos, P., Law, C., van Leeuwen, J., Lemaitre, J., Loose, M., Maat, P., Macario, G., Markoff, S., Masters, J., McFadden, R. A., McKay-Bukowski, D., Meijering, H., Meulman, H., Mevius, M., Middelberg, E., Millenaar, R., Miller-Jones, J. C. A., Mohan, R. N., Mol, J. D., Morawietz, J., Morganti, R., Mulcahy, D. D., Mulder, E., Munk, H., Nieuwenhuis, L., van Nieuwpoort, R., Noordam, J. E., Norden, M., Noutsos, A., Offringa, A. R., Olofsson, H., Omar, A., Orrú, E., Overeem, R., Paas, H., Pandey-Pommier, M., Pandey, V. N., Pizzo, R., Polatidis, A., Rafferty, D., Rawlings, S., Reich, W., de Reijer, J. -P, Reitsma, J., Renting, G. A., Riemers, P., Rol, E., Romein, J. W., Roosjen, J., Ruiter, M., Scaife, A., van der Schaaf, K., Scheers, B., Schellart, P., Schoenmakers, A., Schoonderbeek, G., Serylak, M., Shulevski, A., Sluman, J., Smirnov, O., Sobey, C., Spreeuw, H., Steinmetz, M., Sterks, C. G. M., Stiepel, H. -J, Stuurwold, K., Tagger, M., Tang, Y., Tasse, C., Thomas, I., Thoudam, Satyendra, Toribio, M. C., van der Tol, B., Usov, O., van Veelen, M., van der Veen, A. -J, ter Veen, S., Verbiest, J. P. W., Vermeulen, R., Vermaas, N., Vocks, C., Vogt, C., de Vos, M., van der Wal, E., van Weeren, R., Weggemans, H., Weltevrede, P., White, S., Wijnholds, S. J., Wilhelmsson, T., Wucknitz, O., Yatawatta, S., Zarka, P., Zensus, A., and van Zwieten, J.
Abstract: LOFAR, the LOw-Frequency ARray, is a new-generation radio interferometer constructed in the north of the Netherlands and across europe. Utilizing a novel phased-array design, LOFAR covers the largely unexplored low-frequency range from 10–240 MHz and provides a number of unique observing capabilities. Spreading out from a core located near the village of Exloo in the northeast of the Netherlands, a total of 40 LOFAR stations are nearing completion. A further five stations have been deployed throughout Germany, and one station has been built in each of France, Sweden, and the UK. Digital beam-forming techniques make the LOFAR system agile and allow for rapid repointing of the telescope as well as the potential for multiple simultaneous observations. With its dense core array and long interferometric baselines, LOFAR achieves unparalleled sensitivity and angular resolution in the low-frequency radio regime. The LOFAR facilities are jointly operated by the International LOFAR Telescope (ILT) foundation, as an observatory open to the global astronomical community. LOFAR is one of the first radio observatories to feature automated processing pipelines to deliver fully calibrated science products to its user community. LOFAR’s new capabilities, techniques and modus operandi make it an important pathfinder for the Square Kilometre Array (SKA). We give an overview of the LOFAR instrument, its major hardware and software components, and the core science objectives that have driven its design. In addition, we present a selection of new results from the commissioning phase of this new radio observatory.
Published: 2013
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20. Detecting cosmic rays with the LOFAR radio telescope

Author: Schellart, P., Nelles, A., Buitink, S., Corstanje, A., Enriquez, J. E., Falcke, H., Frieswijk, W., Hörandel, J. R., Horneffer, A., James, C. W., Krause, M., Mevius, M., Scholten, O., ter Veen, S., Thoudam, Satyendra, van den Akker, M., Alexov, A., Anderson, J., Avruch, I. M., Bähren, L., Beck, R., Bell, M. E., Bennema, P., Bentum, M. J., Bernardi, G., Best, P., Bregman, J., Breitling, F., Brentjens, M., Broderick, J., Brüggen, M., Ciardi, B., Coolen, A., de Gasperin, F., de Geus, E., de Jong, A., de Vos, M., Duscha, S., Eislöffel, J., Fallows, R. A., Ferrari, C., Garrett, M. A., Grießmeier, J., Grit, T., Hamaker, J. P., Hassall, T. E., Heald, G., Hessels, J. W. T., Hoeft, M., Holties, H. A., Iacobelli, M., Juette, E., Karastergiou, A., Klijn, W., Kohler, J., Kondratiev, V. I., Kramer, M., Kuniyoshi, M., Kuper, G., Maat, P., Macario, G., Mann, G., Markoff, S., McKay-Bukowski, D., McKean, J. P., Miller-Jones, J. C. A., Mol, J. D., Mulcahy, D. D., Munk, H., Nijboer, R., Norden, M. J., Orru, E., Overeem, R., Paas, H., Pandey-Pommier, M., Pizzo, R., Polatidis, A. G., Renting, A., Romein, J. W., Röttgering, H., Schoenmakers, A., Schwarz, D., Sluman, J., Smirnov, O., Sobey, C., Stappers, B. W., Steinmetz, M., Swinbank, J., Tang, Y., Tasse, C., Toribio, C., van Leeuwen, J., van Nieuwpoort, R., van Weeren, R. J., Vermaas, N., Vermeulen, R., Vocks, C., Vogt, C., Wijers, R. A. M. J., Wijnholds, S. J., Wise, M. W., Wucknitz, O., Yatawatta, S., Zarka, P., Zensus, A., Schellart, P., Nelles, A., Buitink, S., Corstanje, A., Enriquez, J. E., Falcke, H., Frieswijk, W., Hörandel, J. R., Horneffer, A., James, C. W., Krause, M., Mevius, M., Scholten, O., ter Veen, S., Thoudam, Satyendra, van den Akker, M., Alexov, A., Anderson, J., Avruch, I. M., Bähren, L., Beck, R., Bell, M. E., Bennema, P., Bentum, M. J., Bernardi, G., Best, P., Bregman, J., Breitling, F., Brentjens, M., Broderick, J., Brüggen, M., Ciardi, B., Coolen, A., de Gasperin, F., de Geus, E., de Jong, A., de Vos, M., Duscha, S., Eislöffel, J., Fallows, R. A., Ferrari, C., Garrett, M. A., Grießmeier, J., Grit, T., Hamaker, J. P., Hassall, T. E., Heald, G., Hessels, J. W. T., Hoeft, M., Holties, H. A., Iacobelli, M., Juette, E., Karastergiou, A., Klijn, W., Kohler, J., Kondratiev, V. I., Kramer, M., Kuniyoshi, M., Kuper, G., Maat, P., Macario, G., Mann, G., Markoff, S., McKay-Bukowski, D., McKean, J. P., Miller-Jones, J. C. A., Mol, J. D., Mulcahy, D. D., Munk, H., Nijboer, R., Norden, M. J., Orru, E., Overeem, R., Paas, H., Pandey-Pommier, M., Pizzo, R., Polatidis, A. G., Renting, A., Romein, J. W., Röttgering, H., Schoenmakers, A., Schwarz, D., Sluman, J., Smirnov, O., Sobey, C., Stappers, B. W., Steinmetz, M., Swinbank, J., Tang, Y., Tasse, C., Toribio, C., van Leeuwen, J., van Nieuwpoort, R., van Weeren, R. J., Vermaas, N., Vermeulen, R., Vocks, C., Vogt, C., Wijers, R. A. M. J., Wijnholds, S. J., Wise, M. W., Wucknitz, O., Yatawatta, S., Zarka, P., and Zensus, A.
Abstract: The low frequency array (LOFAR), is the first radio telescope designed with the capability to measure radio emission from cosmic-ray induced air showers in parallel with interferometric observations. In the first ~2 years of observing, 405 cosmic-ray events in the energy range of 1016−1018 eV have been detected in the band from 30−80 MHz. Each of these air showers is registered with up to ~1000 independent antennas resulting in measurements of the radio emission with unprecedented detail. This article describes the dataset, as well as the analysis pipeline, and serves as a reference for future papers based on these data. All steps necessary to achieve a full reconstruction of the electric field at every antenna position are explained, including removal of radio frequency interference, correcting for the antenna response and identification of the pulsed signal.
Published: 2013
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20 results on '"Paas, H."'

1. Imaging Jupiter’s radiation belts down to 127 MHz with LOFAR

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

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

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

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

6. The peculiar radio galaxy 4C 35.06 : a case for recurrent AGN activity?

7. Measuring a Cherenkov ring in the radio emission from air showers at 110-190 MHz with LOFAR

8. Calibrating the absolute amplitude scale for air showers measured at LOFAR

9. Probing Atmospheric Electric Fields in Thunderstorms through Radio Emission from Cosmic-Ray-Induced Air Showers

10. The LOFAR long baseline snapshot calibrator survey

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

12. LOFAR sparse image reconstruction

13. The shape of the radio wavefront of extensive air showers as measured with LOFAR

14. Discovery of carbon radio recombination lines in absorption towards Cygnus A

15. LOFAR Low-band Antenna Observations of the 3C 295 and Boötes Fields : Source Counts and Ultra-steep Spectrum Sources

16. The LOFAR pilot surveys for pulsars and fast radio transients

17. LOFAR tied-array imaging of Type III solar radio bursts

18. Initial LOFAR observations of epoch of reionization windows : II. Diffuse polarized emission in the ELAIS-N1 field

19. LOFAR : The LOw-Frequency ARray

20. Detecting cosmic rays with the LOFAR radio telescope

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