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1. Low-frequency radio absorption in Cassiopeia A

Author

Arias, M, Vink, J, De Gasperin, F, Salas, P, Oonk, JBR, Van Weeren, RJ, Van Amesfoort, AS, Anderson, J, Beck, R, Bell, ME, Bentum, MJ, Best, P, Blaauw, R, Breitling, F, Broderick, JW, Brouw, WN, Brüggen, M, Butcher, HR, Ciardi, B, De Geus, E, Deller, A, Van Dijk, PCG, Duscha, S, Eislöffel, J, Garrett, MA, Grießmeier, JM, Gunst, AW, Van Haarlem, MP, Heald, G, Hessels, J, Hörandel, J, Holties, HA, Van Der Horst, AJ, Iacobelli, M, Juette, E, Krankowski, A, Van Leeuwen, J, Mann, G, McKay-Bukowski, D, McKean, JP, Mulder, H, Nelles, A, Orru, E, Paas, H, Pandey-Pommier, M, Pandey, VN, Pekal, R, Pizzo, R, Polatidis, AG, Reich, W, Röttgering, HJA, Rothkaehl, H, Schwarz, DJ, Smirnov, O, Soida, M, Steinmetz, M, Tagger, M, Thoudam, S, Toribio, MC, Vocks, C, Van Der Wiel, MHD, Wijers, RAMJ, Wucknitz, O, Zarka, P, Zucca, P, Arias, M, Vink, J, De Gasperin, F, Salas, P, Oonk, JBR, Van Weeren, RJ, Van Amesfoort, AS, Anderson, J, Beck, R, Bell, ME, Bentum, MJ, Best, P, Blaauw, R, Breitling, F, Broderick, JW, Brouw, WN, Brüggen, M, Butcher, HR, Ciardi, B, De Geus, E, Deller, A, Van Dijk, PCG, Duscha, S, Eislöffel, J, Garrett, MA, Grießmeier, JM, Gunst, AW, Van Haarlem, MP, Heald, G, Hessels, J, Hörandel, J, Holties, HA, Van Der Horst, AJ, Iacobelli, M, Juette, E, Krankowski, A, Van Leeuwen, J, Mann, G, McKay-Bukowski, D, McKean, JP, Mulder, H, Nelles, A, Orru, E, Paas, H, Pandey-Pommier, M, Pandey, VN, Pekal, R, Pizzo, R, Polatidis, AG, Reich, W, Röttgering, HJA, Rothkaehl, H, Schwarz, DJ, Smirnov, O, Soida, M, Steinmetz, M, Tagger, M, Thoudam, S, Toribio, MC, Vocks, C, Van Der Wiel, MHD, Wijers, RAMJ, Wucknitz, O, Zarka, P, and Zucca, P

Abstract

© ESO 2018. Context. Cassiopeia A is one of the best-studied supernova remnants. Its bright radio and X-ray emission is due to shocked ejecta. Cas A is rather unique in that the unshocked ejecta can also be studied: through emission in the infrared, the radio-active decay of 44Ti, and the low-frequency free-free absorption caused by cold ionised gas, which is the topic of this paper. Aims. Free-free absorption processes are affected by the mass, geometry, temperature, and ionisation conditions in the absorbing gas. Observations at the lowest radio frequencies can constrain a combination of these properties. Methods. We used Low Frequency Array (LOFAR) Low Band Antenna observations at 30-77 MHz and Very Large Array (VLA) L-band observations at 1-2 GHz to fit for internal absorption as parametrised by the emission measure. We simultaneously fit multiple UV-matched images with a common resolution of 17″ (this corresponds to 0.25 pc for a source t the distance of Cas A). The ample frequency coverage allows us separate the relative contributions from the absorbing gas, the unabsorbed front of the shell, and the absorbed back of the shell to the emission spectrum. We explored the effects that a temperature lower than the ~100-500 K proposed from infrared observations and a high degree of clumping can have on the derived physical properties of the unshocked material, such as its mass and density. We also compiled integrated radio flux density measurements, fit for the absorption processes that occur in the radio band, and considered their effect on the secular decline of the source. Results. We find a mass in the unshocked ejecta of M = 2.95 ± 0.48 MȮ for an assumed gas temperatureof T = 100 K. This estimate is reduced for colder gas temperatures and, most significantly, if the ejecta are clumped. We measure the reverse shock to have a radius of 114″± 6″ and be centred at 23:23:26, +58:48:54 (J2000). We also find that a decrease in the amount of mass in the unshocked eject

Published
2018

2. Tracking of an electron beam through the solar corona with LOFAR

Author

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

Abstract

© ESO 2018. The Sun's activity leads to bursts of radio emission, among other phenomena. An example is type-III radio bursts. They occur frequently and appear as short-lived structures rapidly drifting from high to low frequencies in dynamic radio spectra. They are usually interpreted as signatures of beams of energetic electrons propagating along coronal magnetic field lines. Here we present novel interferometric LOFAR (LOw Frequency ARray) observations of three solar type-III radio bursts and their reverse bursts with high spectral, spatial, and temporal resolution. They are consistent with a propagation of the radio sources along the coronal magnetic field lines with nonuniform speed. Hence, the type-III radio bursts cannot be generated by a monoenergetic electron beam, but by an ensemble of energetic electrons with a spread distribution in velocity and energy. Additionally, the density profile along the propagation path is derived in the corona. It agrees well with three-fold coronal density model by (1961, ApJ, 133, 983).

Published
2018

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

Author

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

Subjects
General Science & Technology, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics::Instrumentation and Methods for Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics
Abstract

© 2016 Macmillan Publishers Limited. All rights reserved. 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 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 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.

Published
2015

4. The association of a J -burst with a solar jet

Author

Morosan, DE, Gallagher, PT, Fallows, RA, Reid, H, Mann, G, Bisi, MM, Magdalenić, J, Rucker, HO, Thidé, B, Vocks, C, Anderson, J, Asgekar, A, Avruch, IM, Bell, ME, Bentum, MJ, Best, P, Blaauw, R, Bonafede, A, Breitling, F, Broderick, JW, Brüggen, M, Cerrigone, L, Ciardi, B, De Geus, E, Duscha, S, Eislöffel, J, Falcke, H, Garrett, MA, Grießmeier, JM, Gunst, AW, Hoeft, M, Iacobelli, M, Juette, E, Kuper, G, McFadden, R, McKay-Bukowski, D, McKean, JP, Mulcahy, DD, Munk, H, Nelles, A, Orru, E, Paas, H, Pandey-Pommier, M, Pandey, VN, Pizzo, R, Polatidis, AG, Reich, W, Schwarz, DJ, Sluman, J, Smirnov, O, Steinmetz, M, Tagger, M, Ter Veen, S, Thoudam, S, Toribio, MC, Vermeulen, R, Van Weeren, RJ, Wucknitz, O, Zarka, P, Morosan, DE, Gallagher, PT, Fallows, RA, Reid, H, Mann, G, Bisi, MM, Magdalenić, J, Rucker, HO, Thidé, B, Vocks, C, Anderson, J, Asgekar, A, Avruch, IM, Bell, ME, Bentum, MJ, Best, P, Blaauw, R, Bonafede, A, Breitling, F, Broderick, JW, Brüggen, M, Cerrigone, L, Ciardi, B, De Geus, E, Duscha, S, Eislöffel, J, Falcke, H, Garrett, MA, Grießmeier, JM, Gunst, AW, Hoeft, M, Iacobelli, M, Juette, E, Kuper, G, McFadden, R, McKay-Bukowski, D, McKean, JP, Mulcahy, DD, Munk, H, Nelles, A, Orru, E, Paas, H, Pandey-Pommier, M, Pandey, VN, Pizzo, R, Polatidis, AG, Reich, W, Schwarz, DJ, Sluman, J, Smirnov, O, Steinmetz, M, Tagger, M, Ter Veen, S, Thoudam, S, Toribio, MC, Vermeulen, R, Van Weeren, RJ, Wucknitz, O, and Zarka, P

Abstract

© ESO, 2017. Context. The Sun is an active star that produces large-scale energetic events such as solar flares and coronal mass ejections, and numerous smaller scale events such as solar jets. These events are often associated with accelerated particles that can cause emission at radio wavelengths. The reconfiguration of the solar magnetic field in the corona is believed to be the cause of the majority of solar energetic events and accelerated particles. Aims. Here, we investigate a bright J-burst that was associated with a solar jet and the possible emission mechanism causing these two phenomena. Methods. We used data from the Solar Dynamics Observatory (SDO) to observe a solar jet and radio data from the Low Frequency Array (LOFAR) and the Nançay Radioheliograph (NRH) to observe a J-burst over a broad frequency range (33-173 MHz) on 9 July 2013 at ~11:06 UT. Results. The J-burst showed fundamental and harmonic components and was associated with a solar jet observed at extreme ultraviolet wavelengths with SDO. The solar jet occurred in the northern hemisphere at a time and location coincident with the radio burst and not inside a group of complex active regions in the southern hemisphere. The jet occurred in the negative polarity region of an area of bipolar plage. Newly emerged positive flux in this region appeared to be the trigger of the jet. Conclusions. Magnetic reconnection between the overlying coronal field lines and the newly emerged positive field lines is most likely the cause of the solar jet. Radio imaging provides a clear association between the jet and the J-burst, which shows the path of the accelerated electrons. These electrons travelled from a region in the vicinity of the solar jet along closed magnetic field lines up to the top of a closed magnetic loop at a height of ~360 Mm. Such small-scale complex eruptive events arising from magnetic reconnection could facilitate accelerated electrons to produce continuously the large numbers of Type III

Published
2017

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

Abstract

© 2016 Macmillan Publishers Limited. All rights reserved. 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 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 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.

Published
2016

7. A dynamically cold disk galaxy in the early Universe.

Author

Rizzo F, Vegetti S, Powell D, Fraternali F, McKean JP, Stacey HR, and White SDM

Abstract

The extreme astrophysical processes and conditions that characterize the early Universe are expected to result in young galaxies that are dynamically different from those observed today 1-5 . This is because the strong effects associated with galaxy mergers and supernova explosions would lead to most young star-forming galaxies being dynamically hot, chaotic and strongly unstable 1,2 . Here we report the presence of a dynamically cold, but highly star-forming, rotating disk in a galaxy at redshift 6 z = 4.2, when the Universe was just 1.4 billion years old. Galaxy SPT-S J041839-4751.9 is strongly gravitationally lensed by a foreground galaxy at z = 0.263, and it is a typical dusty starburst, with global star-forming 7 and dust properties 8 that are in agreement with current numerical simulations 9 and observations 10 . Interferometric imaging at a spatial resolution of about 60 parsecs reveals a ratio of rotational to random motions of 9.7 ± 0.4, which is at least four times larger than that expected from any galaxy evolution model at this epoch 1-5 but similar to the ratios of spiral galaxies in the local Universe 11 . We derive a rotation curve with the typical shape of nearby massive spiral galaxies, which demonstrates that at least some young galaxies are dynamically akin to those observed in the local Universe, and only weakly affected by extreme physical processes.

Published
2020
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8. Corrigendum: A large light-mass component of cosmic rays at 10 17 -10 17.5 electronvolts from radio observations.

Author

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

Published
2016
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9. A large light-mass component of cosmic rays at 10(17)-10(17.5) electronvolts from radio observations.

Author

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

Abstract

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.

Published
2016
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10. Probing Atmospheric Electric Fields in Thunderstorms through Radio Emission from Cosmic-Ray-Induced Air Showers.

Author

Schellart P, Trinh TN, Buitink S, Corstanje A, Enriquez JE, Falcke H, Hörandel JR, Nelles A, Rachen JP, Rossetto L, Scholten O, Ter Veen S, Thoudam S, Ebert U, Koehn C, Rutjes C, Alexov A, Anderson JM, Avruch IM, Bentum MJ, Bernardi G, Best P, Bonafede A, Breitling F, Broderick JW, Brüggen M, Butcher HR, Ciardi B, de Geus E, de Vos M, Duscha S, Eislöffel J, Fallows RA, Frieswijk W, Garrett MA, Grießmeier J, Gunst AW, Heald G, Hessels JW, Hoeft M, Holties HA, Juette E, Kondratiev VI, Kuniyoshi M, Kuper G, Mann G, McFadden R, McKay-Bukowski D, McKean JP, Mevius M, Moldon J, Norden MJ, Orru E, Paas H, Pandey-Pommier M, Pizzo R, Polatidis AG, Reich W, Röttgering H, Scaife AM, Schwarz DJ, Serylak M, Smirnov O, Steinmetz M, Swinbank J, Tagger M, Tasse C, Toribio MC, van Weeren RJ, Vermeulen R, Vocks C, Wise MW, 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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11. Synchronous x-ray and radio mode switches: a rapid global transformation of the pulsar magnetosphere.

Author

Hermsen W, Hessels JW, Kuiper L, van Leeuwen J, Mitra D, de Plaa J, Rankin JM, Stappers BW, Wright GA, Basu R, Alexov A, Coenen T, Grießmeier JM, Hassall TE, Karastergiou A, Keane E, Kondratiev VI, Kramer M, Kuniyoshi M, Noutsos A, Serylak M, Pilia M, Sobey C, Weltevrede P, Zagkouris K, Asgekar A, Avruch IM, Batejat F, Bell ME, Bell MR, Bentum MJ, Bernardi G, Best P, Bîrzan L, Bonafede A, Breitling F, Broderick J, Brüggen M, Butcher HR, Ciardi B, Duscha S, Eislöffel J, Falcke H, Fender R, Ferrari C, Frieswijk W, Garrett MA, de Gasperin F, de Geus E, Gunst AW, Heald G, Hoeft M, Horneffer A, Iacobelli M, Kuper G, Maat P, Macario G, Markoff S, McKean JP, Mevius M, Miller-Jones JC, Morganti R, Munk H, Orrú E, Paas H, Pandey-Pommier M, Pandey VN, Pizzo R, Polatidis AG, Rawlings S, Reich W, Röttgering H, Scaife AM, Schoenmakers A, Shulevski A, Sluman J, Steinmetz M, Tagger M, Tang Y, Tasse C, ter Veen S, Vermeulen R, van de Brink RH, van Weeren RJ, Wijers RA, Wise MW, Wucknitz O, Yatawatta S, and Zarka P

Abstract

Pulsars emit from low-frequency radio waves up to high-energy gamma-rays, generated anywhere from the stellar surface out to the edge of the magnetosphere. Detecting correlated mode changes across the electromagnetic spectrum is therefore key to understanding the physical relationship among the emission sites. Through simultaneous observations, we detected synchronous switching in the radio and x-ray emission properties of PSR B0943+10. When the pulsar is in a sustained radio-"bright" mode, the x-rays show only an unpulsed, nonthermal component. Conversely, when the pulsar is in a radio-"quiet" mode, the x-ray luminosity more than doubles and a 100% pulsed thermal component is observed along with the nonthermal component. This indicates rapid, global changes to the conditions in the magnetosphere, which challenge all proposed pulsar emission theories.

Published
2013
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12. Gravitational detection of a low-mass dark satellite galaxy at cosmological distance.

Author

Vegetti S, Lagattuta DJ, McKean JP, Auger MW, Fassnacht CD, and Koopmans LV

Abstract

The mass function of dwarf satellite galaxies that are observed around Local Group galaxies differs substantially from simulations based on cold dark matter: the simulations predict many more dwarf galaxies than are seen. The Local Group, however, may be anomalous in this regard. A massive dark satellite in an early-type lens galaxy at a redshift of 0.222 was recently found using a method based on gravitational lensing, suggesting that the mass fraction contained in substructure could be higher than is predicted from simulations. The lack of very low-mass detections, however, prohibited any constraint on their mass function. Here we report the presence of a (1.9 ± 0.1) × 10(8) M dark satellite galaxy in the Einstein ring system JVAS B1938+666 (ref. 11) at a redshift of 0.881, where M denotes the solar mass. This satellite galaxy has a mass similar to that of the Sagittarius galaxy, which is a satellite of the Milky Way. We determine the logarithmic slope of the mass function for substructure beyond the local Universe to be 1.1(+0.6)(-0.4), with an average mass fraction of 3.3(+3.6)(-1.8) per cent, by combining data on both of these recently discovered galaxies. Our results are consistent with the predictions from cold dark matter simulations at the 95 per cent confidence level, and therefore agree with the view that galaxies formed hierarchically in a Universe composed of cold dark matter.

Published
2012
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13. A gravitationally lensed water maser in the early Universe.

Author

Impellizzeri CM, McKean JP, Castangia P, Roy AL, Henkel C, Brunthaler A, and Wucknitz O

Abstract

Water masers are found in dense molecular clouds closely associated with supermassive black holes at the centres of active galaxies. On the basis of the understanding of the local water-maser luminosity function, it was expected that masers at intermediate and high redshifts would be extremely rare. However, galaxies at redshifts z > 2 might be quite different from those found locally, not least because of more frequent mergers and interaction events. Here we use gravitational lensing to search for masers at higher redshifts than would otherwise be possible, and find a water maser at redshift 2.64 in the dust- and gas-rich, gravitationally lensed type-1 quasar MG J0414+0534 (refs 6-13). The isotropic luminosity is 10,000 (, solar luminosity), which is twice that of the most powerful local water maser and half that of the most distant maser previously known. Using the locally determined luminosity function, the probability of finding a maser this luminous associated with any single active galaxy is 10(-6). The fact that we see such a maser in the first galaxy we observe must mean that the volume densities and luminosities of masers are higher at redshift 2.64.

Published
2008
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14. Constraints on cosmological parameters from the analysis of the cosmic lens all sky survey radio-selected gravitational lens statistics.

Author

Chae KH, Biggs AD, Blandford RD, Browne IW, De Bruyn AG, Fassnacht CD, Helbig P, Jackson NJ, King LJ, Koopmans LV, Mao S, Marlow DR, McKean JP, Myers ST, Norbury M, Pearson TJ, Phillips PM, Readhead AC, Rusin D, Sykes CM, Wilkinson PN, Xanthopoulos E, and York T

Abstract

We derive constraints on cosmological parameters and the properties of the lensing galaxies from gravitational lens statistics based on the final Cosmic Lens All Sky Survey data. For a flat universe with a classical cosmological constant, we find that the present matter fraction of the critical density is Omega(m)=0.31(+0.27)(-0.14) (68%)+0.12-0.10 (syst). For a flat universe with a constant equation of state for dark energy w=p(x)(pressure)/rho(x)(energy density), we find w<-0.55(+0.18)(-0.11) (68%).

Published
2002
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