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Heino Falcke - One of the best experts on this subject based on the ideXlab platform.
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probing atmospheric electric fields in thunderstorms through Radio Emission from cosmic ray induced air showers
Physical Review Letters, 2015Co-Authors: P Schellart, Heino Falcke, A. Nelles, S Buitink, J. E. Enriquez, T N G Trinh, A Corstanje, J R Horandel, J P Rachen, L RossettoAbstract: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.
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Measuring a Cherenkov ring in the Radio Emission from air showers at 110-190 MHz with LOFAR
Astroparticle Physics, 2015Co-Authors: A. Nelles, Heino Falcke, K. D. Vries, Pim Schellart, Stijn Buitink, Arthur Corstanje, J. E. Enriquez, Wilfred Frieswijk, Jörg R. Hörandel, Olaf ScholtenAbstract: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.
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polarized Radio Emission from extensive air showers measured with lofar
arXiv: High Energy Astrophysical Phenomena, 2014Co-Authors: P Schellart, Heino Falcke, A. Nelles, S Buitink, J. E. Enriquez, A Corstanje, J R Horandel, J P Rachen, M Krause, O ScholtenAbstract:We present LOFAR measurements of Radio Emission from extensive air showers. We find that this Emission is strongly polarized, with a median degree of polarization of nearly $99\%$, and that the angle between the polarization direction of the electric field and the Lorentz force acting on the particles, depends on the observer location in the shower plane. This can be understood as a superposition of the radially polarized charge-excess Emission mechanism, first proposed by Askaryan and the geomagnetic Emission mechanism proposed by Kahn and Lerche. We calculate the relative strengths of both contributions, as quantified by the charge-excess fraction, for $163$ individual air showers. We find that the measured charge-excess fraction is higher for air showers arriving from closer to the zenith. Furthermore, the measured charge-excess fraction also increases with increasing observer distance from the air shower symmetry axis. The measured values range from $(3.3\pm 1.0)\%$ for very inclined air showers at $25\, \mathrm{m}$ to $(20.3\pm 1.3)\%$ for almost vertical showers at $225\, \mathrm{m}$. Both dependencies are in qualitative agreement with theoretical predictions.
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Radio Emission of energetic cosmic ray air showers polarization measurements with lopes
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2009Co-Authors: P G Isar, Heino Falcke, S Buitink, L Bahren, J R Horandel, K H A Horneffer, J Kuijpers, S Lafebre, A NiglAbstract:Abstract LOPES is a Radio antenna array co-located with the Karlsruhe Shower Core and Array DEtector, KASCADE–Grande in Forschungszentrum Karlsruhe, Germany, which provides well-calibrated trigger information and air shower parameters for primary energies up to 10 18 eV . By the end of 2006, the Radio antennas were re-configured to perform polarization measurements of the Radio signal of cosmic ray air showers, recording in the same time both, the East–West and North–South polarization directions of the Radio Emission. The main goal of these measurements is to reconstruct the polarization characteristics of the emitted signal. This will allow a detailed comparison with theoretical predictions. The current status of these measurements is reported here.
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simulations of Radio Emission from cosmic ray air showers
International Journal of Modern Physics A, 2005Co-Authors: T Huege, Heino FalckeAbstract:Radio Emission from cosmic ray air showers has the potential to become an additional, cost-effective observing technique for cosmic ray research, being largely complementary to the well-established particle detector and air fluorescence techniques. We present Monte Carlo simulations of Radio Emission from extensive air showers in the scheme of coherent geosynchrotron radiation from electron-positron pairs gyrating in the earth's magnetic field. Preliminary results of our simulations are the predicted frequency, primary particle energy, shower zenith angle, shower azimuth angle and polarization dependence of the Radio Emission. These properties can be directly related to data measured by LOPES and other experiments.
T Huege - One of the best experts on this subject based on the ideXlab platform.
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determination of the absolute energy scale of extensive air showers via Radio Emission systematic uncertainty of underlying first principle calculations
Astroparticle Physics, 2018Co-Authors: Marvin Gottowik, T Huege, C Glaser, Julian RautenbergAbstract:Abstract Recently, the energy determination of extensive air showers using Radio Emission has been shown to be both precise and accurate. In particular, Radio detection offers the opportunity for an independent measurement of the absolute energy scale of cosmic rays, since the radiation energy (the energy radiated in the form of Radio signals) can be predicted using first-principle calculations involving no free parameters, and the measurement of Radio waves is not subject to any significant absorption or scattering in the atmosphere. To quantify the uncertainty associated with such an approach, we collate the various contributions to the uncertainty, and we verify the consistency of radiation-energy calculations from microscopic simulation codes by comparing Monte Carlo simulations made with the two codes CoREAS and ZHAireS. We compare a large set of simulations with different primary energies and shower directions and observe differences in the radiation energy prediction for the 30–80 MHz band of 5.2%. This corresponds to an uncertainty of 2.6% for the determination of the absolute cosmic-ray energy scale. Our result has general validity and can be built upon directly by experimental efforts for the calibration of the cosmic-ray energy scale on the basis of Radio Emission measurements.
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simulating Radio Emission from air showers with coreas
5TH INTERNATIONAL WORKSHOP ON ACOUSTIC AND RADIO EEV NEUTRINO DETECTION ACTIVITIES: ARENA 2012, 2013Co-Authors: T Huege, Marianne Ludwig, C W JamesAbstract:CoREAS is a Monte Carlo code for the simulation of Radio Emission from extensive air showers. It implements the endpoint formalism for the calculation of electromagnetic radiation directly in CORSIKA. As such, it is parameter-free, makes no assumptions on the Emission mechanism for the Radio signals, and takes into account the complete complexity of the electron and positron distributions as simulated by CORSIKA. In this article, we illustrate the capabilities of CoREAS with simulations carried out in different frequency ranges from tens of MHz up to GHz frequencies, and describe in particular the Emission characteristics at high frequencies due to Cherenkov effects arising from the varying refractive index of the atmosphere.
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reas3 monte carlo simulations of Radio Emission from cosmic ray air showers using an end point formalism
Astroparticle Physics, 2011Co-Authors: Marianne Ludwig, T HuegeAbstract:Abstract In recent years, the freely available Monte Carlo code REAS for modelling Radio Emission from cosmic ray air showers has evolved to include the full complexity of air shower physics. However, it turned out that in REAS2 and all other time-domain models which calculate the Radio Emission by superposing the radiation of the single air shower electrons and positrons, the calculation of the Emission contributions was not fully consistent. In this article, we present a revised implementation in REAS3, which incorporates the missing Radio Emission due to the variation of the number of charged particles during the air shower evolution using an “end-point formalism”. With the inclusion of these Emission contributions, the structure of the simulated Radio pulses changes from unipolar to bipolar, and the azimuthal Emission pattern becomes nearly symmetric. Remaining asymmetries can be explained by Radio Emission due to the variation of the net charge excess in air showers, which is automatically taken into account in the new implementation. REAS3 constitutes the first self-consistent time-domain implementation based on single particle Emission taking the full complexity of air shower physics into account, and is freely available for all interested users.
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simulations and theory of Radio Emission from cosmic ray air showers
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2009Co-Authors: T HuegeAbstract:In the last few years, interest in Radio detection of cosmic ray air showers has risen continuously. By now, large-scale application of the Radio technique is under investigation in the framework of LOFAR and the Pierre Auger Observatory. The experimental efforts are accompanied by new approaches to describe and model the underlying radiation mechanisms, to lay the foundation for an interpretation of the experimental data. In this article, I review the current Radio Emission theory and simulations, with slight focus on the geosynchrotron model and its predictions for the information content of the Radio signals.
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dependence of geosynchrotron Radio Emission on the energy and depth of maximum of cosmic ray showers
Astroparticle Physics, 2008Co-Authors: T Huege, Ralf Ulrich, R EngelAbstract:Abstract Based on CORSIKA and REAS2 simulations, we investigate the dependence of geosynchrotron Radio Emission from extensive air showers on the energy of the primary cosmic ray and the depth of the shower maximum. It is found that at a characteristic lateral distance, the amplitude of the bandpass-filtered Radio signal is directly proportional to the energy deposited in the atmosphere by the electromagnetic cascade, with an RMS uncertainty due to shower-to-shower fluctuations of less than 3%. In addition, the ratio of this Radio amplitude and that at a larger lateral distance is directly related to the atmospheric depth of the shower maximum, with an RMS uncertainty of ∼15–20 g cm −2 . By measuring these quantities, geosynchrotron Radio Emission from cosmic ray air showers can be used to infer the energy of the primary particle and the depth of the air shower maximum on a shower-to-shower basis.
Gregg Hallinan - One of the best experts on this subject based on the ideXlab platform.
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a first search for prompt Radio Emission from a gravitational wave event
The Astrophysical Journal, 2019Co-Authors: T A Callister, Gregg Hallinan, Marin M Anderson, Larry Daddario, Jayce Dowell, Namir E Kassim, Joseph T W Lazio, Danny C Price, Frank SchinzelAbstract:Multimessenger observations of the binary neutron star merger GW170817 have enabled the discovery of a diverse array of electromagnetic counterparts to compact binary mergers, including an unambiguous kilonova, a short gamma-ray burst, and a late-time Radio jet. Beyond these counterparts, compact binary mergers are additionally predicted to be accompanied by prompt low-frequency Radio Emission. The successful observation of a prompt Radio counterpart would be immensely valuable, but is made difficult by the short delay between the gravitational-wave and prompt electromagnetic signals, as well as by the poor localization of gravitational-wave sources. Here, we present the first search for prompt Radio Emission accompanying a gravitational-wave event, targeting the binary black hole merger GW170104 detected by the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo during their second (O2) observing run. Using the Owens Valley Radio Observatory Long Wavelength Array, we search a ~900 deg^2 region for transient Radio Emission within approximately one hour of GW170104, obtaining an upper limit of 2.5 × 10^(41) erg s^(−1) on its equivalent isotropic luminosity between 27 and 84 MHz. We additionally discuss plans to target binary neutron star mergers in Advanced LIGO and Virgo's upcoming O3 observing run.
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a first search for prompt Radio Emission from a gravitational wave event
arXiv: High Energy Astrophysical Phenomena, 2019Co-Authors: T A Callister, Gregg Hallinan, Marin M Anderson, Larry Daddario, Jayce Dowell, Namir E Kassim, Joseph T W Lazio, Danny C Price, Frank SchinzelAbstract:Multimessenger observations of the binary neutron star merger GW170817 have enabled the discovery of a diverse array of electromagnetic counterparts to compact binary mergers, including an unambiguous kilonova, a short gamma-ray burst, and a late-time Radio jet. Beyond these counterparts, compact binary mergers are additionally predicted to be accompanied by prompt low-frequency Radio Emission. The successful observation of a prompt Radio counterpart would be immensely valuable, but is made difficult by the short delay between the gravitational-wave and prompt electromagnetic signals as well as the poor localization of gravitational-wave sources. Here, we present the first search for prompt Radio Emission accompanying a gravitational-wave event, targeting the binary black hole merger GW170104 detected by the Advanced LIGO and Virgo gravitational-wave observatories during their second (O2) observing run. Using the Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA), we search a $\sim900\,\mathrm{deg}^2$ region for transient Radio Emission within approximately one hour of GW170104, obtaining an upper limit of $2.5\times10^{41}\,\mathrm{erg}\,\mathrm{s}^{-1}$ on its equivalent isotropic luminosity between 27-84 MHz. We additionally discuss plans to target binary neutron star mergers in Advanced LIGO and Virgo's upcoming O3 observing run.
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a simultaneous search for prompt Radio Emission associated with the short grb 170112a using the all sky imaging capability of the ovro lwa
The Astrophysical Journal, 2018Co-Authors: Marin M Anderson, Gregg Hallinan, Michael Eastwood, Ryan M Monroe, H K Vedantham, S Bourke, L J Greenhill, Jonathon Kocz, Joseph T W LazioAbstract:We have conducted the most sensitive low-frequency (below 100 MHz) search to date for prompt, low-frequency Radio Emission associated with short-duration gamma-ray bursts (GRBs), using the Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA). The OVRO-LWA's nearly full-hemisphere field of view (~20,000 square degrees) allows us to search for low-frequency (sub-100 MHz) counterparts for a large sample of the subset of GRB events for which prompt Radio Emission has been predicted. Following the detection of short GRB 170112A by Swift, we used all-sky OVRO-LWA images spanning one hour prior to and two hours following the GRB event to search for a transient source coincident with the position of GRB 170112A. We detect no transient source to within a 3σ flux density limit of 4.5 Jy at 13 s timescales for frequencies spanning 27–84 MHz. We place constraints on a number of models predicting prompt, low-frequency Radio Emission accompanying short GRBs and their potential binary neutron star merger progenitors, and place an upper limit of L_(Radio)/ L_γ ≾ 3.5 × 10^(−6) on the fraction of energy released in the prompt Radio Emission, under the assumptions of negligible scattering of the Radio pulse and beaming of Emission along the line of sight. These observations serve as a pilot effort for a program targeting a wider sample of both short and long GRBs with the OVRO-LWA, including bursts with confirmed redshift measurements that are critical to placing constraining limits on prompt Radio Emission models, as well as a program for the follow-up of gravitational wave compact binary coalescence events detected by advanced LIGO and Virgo.
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simulating Radio Emission from low mass stars
The Astrophysical Journal, 2018Co-Authors: Joe Llama, M Jardine, Kenneth Wood, Gregg Hallinan, J MorinAbstract:Understanding the origins of stellar Radio Emission can provide invaluable insight into the strength and geometry of stellar magnetic fields and the resultant space weather environment experienced by exoplanets. Here, we present the first model capable of predicting Radio Emission through the electron cyclotron maser instability using observed stellar magnetic maps of low-mass stars. We determine the structure of the coronal magnetic field and plasma using spectropolarimetric observations of the surface magnetic fields and the X-ray Emission measure. We then model the Emission of photons from the locations within the corona that satisfy the conditions for electron cyclotron maser Emission. Our model predicts the frequency and intensity of Radio photons from within the stellar corona. We have benchmarked our model against the low-mass star V374 Peg. This star has both Radio observations from the Very Large Array and a nearly simultaneous magnetic map. Using our model we are able to fit the Radio observations of V374 Peg, providing additional evidence that the Radio Emission observed from low-mass stars may originate from the electron cyclotron maser instability. Our model can now be extended to all stars with observed magnetic maps to predict the expected frequency and variability of stellar Radio Emission in an effort to understand and guide future Radio observations of low-mass stars.
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a simultaneous search for prompt Radio Emission associated with the short grb 170112a using the all sky imaging capability of the ovro lwa
arXiv: High Energy Astrophysical Phenomena, 2017Co-Authors: Marin M Anderson, Gregg Hallinan, Michael Eastwood, Ryan M Monroe, H K Vedantham, S Bourke, L J Greenhill, Jonathon Kocz, Joseph T W LazioAbstract:We have conducted the most sensitive low frequency (below 100 MHz) search to date for prompt, low-frequency Radio Emission associated with short-duration gamma-ray bursts (GRBs), using the Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA). The OVRO-LWA's nearly full-hemisphere field-of-view ($\sim20$,$000$ square degrees) allows us to search for low-frequency (sub-$100$ MHz) counterparts for a large sample of the subset of GRB events for which prompt Radio Emission has been predicted. Following the detection of short GRB 170112A by Swift, we used all-sky OVRO-LWA images spanning one hour prior to and two hours following the GRB event to search for a transient source coincident with the position of GRB 170112A. We detect no transient source, with our most constraining $1\sigma$ flux density limit of $650~\text{mJy}$ for frequencies spanning $27~\text{MHz}-84~\text{MHz}$. We place constraints on a number of models predicting prompt, low-frequency Radio Emission accompanying short GRBs and their potential binary neutron star merger progenitors, and place an upper limit of $L_\text{Radio}/L_\gamma \lesssim 7\times10^{-16}$ on the fraction of energy released in the prompt Radio Emission. These observations serve as a pilot effort for a program targeting a wider sample of both short and long GRBs with the OVRO-LWA, including bursts with confirmed redshift measurements which are critical to placing the most constraining limits on prompt Radio Emission models, as well as a program for the follow-up of gravitational wave compact binary coalescence events detected by advanced LIGO and Virgo.
R Engel - One of the best experts on this subject based on the ideXlab platform.
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Radio Emission from extensive air showers as a method for cosmic ray detection
Physics of Atomic Nuclei, 2010Co-Authors: N N Kalmykov, A A Konstantinov, R EngelAbstract:At the present time, Radio Emission from extensive air showers (EASs) is being considered as a new promising method for detecting cosmic rays of energy in the region E0 > 5 × 1016 eV. Radio Emission from an EAS whose development is simulated by the Monte Carlo method is calculated here. The field of Radio Emission from an EAS is calculated on the basis of two representations of a shower: that as a set of individual particles and that as a continuous set of currents. The sensitivity of Radio Emission to EAS parameters in the frequency range 10–100 MHz is investigated. The results can be used to analyze experiments that being presently performed (CODALEMA and LOPES) and those that are being planned for the future.
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dependence of geosynchrotron Radio Emission on the energy and depth of maximum of cosmic ray showers
Astroparticle Physics, 2008Co-Authors: T Huege, Ralf Ulrich, R EngelAbstract:Abstract Based on CORSIKA and REAS2 simulations, we investigate the dependence of geosynchrotron Radio Emission from extensive air showers on the energy of the primary cosmic ray and the depth of the shower maximum. It is found that at a characteristic lateral distance, the amplitude of the bandpass-filtered Radio signal is directly proportional to the energy deposited in the atmosphere by the electromagnetic cascade, with an RMS uncertainty due to shower-to-shower fluctuations of less than 3%. In addition, the ratio of this Radio amplitude and that at a larger lateral distance is directly related to the atmospheric depth of the shower maximum, with an RMS uncertainty of ∼15–20 g cm −2 . By measuring these quantities, geosynchrotron Radio Emission from cosmic ray air showers can be used to infer the energy of the primary particle and the depth of the air shower maximum on a shower-to-shower basis.
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monte carlo simulations of geosynchrotron Radio Emission from corsika simulated air showers
Astroparticle Physics, 2007Co-Authors: T Huege, R Ulrich, R EngelAbstract:Abstract We present simulations performed with REAS2, a new Monte Carlo code for the calculation of geosynchrotron Radio Emission from extensive air showers. The code uses thoroughly tested time-domain Radio Emission routines in conjunction with a realistic air shower model based on per-shower multi-dimensional CORSIKA-generated histograms. We assess in detail how the transition from simpler, parametrised, to realistic, CORSIKA-based particle distributions affects the predicted Radio Emission from a typical 10 17 eV air shower. The effects of eliminating a previously needed free parameter and adopting realistic electron to positron ratios are also discussed. Compared with earlier calculations based on parametrised showers, REAS2 simulations predict slightly weaker and in some cases narrower pulses. In addition, a pronounced east–west versus north–south asymmetry arises in the Emission pattern, and the Radio pulses become generally unipolar. Finally, we demonstrate how REAS2 can be used to study Radio pulse shapes and their relation to shower characteristics such as the longitudinal air shower development.
S Bourke - One of the best experts on this subject based on the ideXlab platform.
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a simultaneous search for prompt Radio Emission associated with the short grb 170112a using the all sky imaging capability of the ovro lwa
The Astrophysical Journal, 2018Co-Authors: Marin M Anderson, Gregg Hallinan, Michael Eastwood, Ryan M Monroe, H K Vedantham, S Bourke, L J Greenhill, Jonathon Kocz, Joseph T W LazioAbstract:We have conducted the most sensitive low-frequency (below 100 MHz) search to date for prompt, low-frequency Radio Emission associated with short-duration gamma-ray bursts (GRBs), using the Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA). The OVRO-LWA's nearly full-hemisphere field of view (~20,000 square degrees) allows us to search for low-frequency (sub-100 MHz) counterparts for a large sample of the subset of GRB events for which prompt Radio Emission has been predicted. Following the detection of short GRB 170112A by Swift, we used all-sky OVRO-LWA images spanning one hour prior to and two hours following the GRB event to search for a transient source coincident with the position of GRB 170112A. We detect no transient source to within a 3σ flux density limit of 4.5 Jy at 13 s timescales for frequencies spanning 27–84 MHz. We place constraints on a number of models predicting prompt, low-frequency Radio Emission accompanying short GRBs and their potential binary neutron star merger progenitors, and place an upper limit of L_(Radio)/ L_γ ≾ 3.5 × 10^(−6) on the fraction of energy released in the prompt Radio Emission, under the assumptions of negligible scattering of the Radio pulse and beaming of Emission along the line of sight. These observations serve as a pilot effort for a program targeting a wider sample of both short and long GRBs with the OVRO-LWA, including bursts with confirmed redshift measurements that are critical to placing constraining limits on prompt Radio Emission models, as well as a program for the follow-up of gravitational wave compact binary coalescence events detected by advanced LIGO and Virgo.
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a simultaneous search for prompt Radio Emission associated with the short grb 170112a using the all sky imaging capability of the ovro lwa
arXiv: High Energy Astrophysical Phenomena, 2017Co-Authors: Marin M Anderson, Gregg Hallinan, Michael Eastwood, Ryan M Monroe, H K Vedantham, S Bourke, L J Greenhill, Jonathon Kocz, Joseph T W LazioAbstract:We have conducted the most sensitive low frequency (below 100 MHz) search to date for prompt, low-frequency Radio Emission associated with short-duration gamma-ray bursts (GRBs), using the Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA). The OVRO-LWA's nearly full-hemisphere field-of-view ($\sim20$,$000$ square degrees) allows us to search for low-frequency (sub-$100$ MHz) counterparts for a large sample of the subset of GRB events for which prompt Radio Emission has been predicted. Following the detection of short GRB 170112A by Swift, we used all-sky OVRO-LWA images spanning one hour prior to and two hours following the GRB event to search for a transient source coincident with the position of GRB 170112A. We detect no transient source, with our most constraining $1\sigma$ flux density limit of $650~\text{mJy}$ for frequencies spanning $27~\text{MHz}-84~\text{MHz}$. We place constraints on a number of models predicting prompt, low-frequency Radio Emission accompanying short GRBs and their potential binary neutron star merger progenitors, and place an upper limit of $L_\text{Radio}/L_\gamma \lesssim 7\times10^{-16}$ on the fraction of energy released in the prompt Radio Emission. These observations serve as a pilot effort for a program targeting a wider sample of both short and long GRBs with the OVRO-LWA, including bursts with confirmed redshift measurements which are critical to placing the most constraining limits on prompt Radio Emission models, as well as a program for the follow-up of gravitational wave compact binary coalescence events detected by advanced LIGO and Virgo.
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confirmation of the electron cyclotron maser instability as the dominant source of Radio Emission from very low mass stars and brown dwarfs
The Astrophysical Journal, 2008Co-Authors: Gregg Hallinan, S Bourke, A Antonova, J G Doyle, C Lane, A GoldenAbstract:We report on Radio observations of the M8.5 dwarf LSR J1835+3259 and the L3.5 dwarf 2MASS J00361617+1821104, which provide the strongest evidence to date that the electron cyclotron maser instability is the dominant mechanism producing Radio Emission in the magnetospheres of ultracool dwarfs. As has previously been reported for the M9 dwarf TVLM 513–46546, periodic pulses of 100% circularly polarized, coherent Radio Emission are detected from both dwarfs with periods of 2.84 ± 0.01 and 3.08 ± 0.05 hr, respectively, for LSR J1835+3259 and 2MASS J00361617+1821104. Importantly, periodic unpolarized Radio Emission is also detected from 2MASS J00361617+1821104, and brightness temperature limitations rule out gyrosynchrotron radiation as a source of this Radio Emission. The unpolarized Emission from this and other ultracool dwarfs is also attributed to electron cyclotron maser Emission, which has become depolarized on traversing the ultracool dwarf magnetosphere, possibly due to propagations effects such as scattering. Based on available v sin i data in the literature and rotation periods derived from the periodic Radio data for the three confirmed sources of electron cyclotron maser Emission, TVLM 513–46546, LSR J1835+3259, and 2MASS J00361617+1821104, we determine that the rotation axes of all three dwarfs are close to perpendicular to our line of sight. This suggests a possible geometrical selection effect due to the inherent directivity of electron cyclotron maser Emission, that may account for the previously reported relationship between Radio activity and v sin i observed for ultracool dwarfs. We also determine the radius of the dwarf LSR J1835+3259 to be ≥0.117 ± 0.012 R_☉. The implied size of the radius, together with the bolometric luminosity of the dwarf, suggests that either LSR J1835 is a young- or intermediate-age brown dwarf, or that current theoretical models underestimate the radii of ultracool dwarfs.
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confirmation of the electron cyclotron maser instability as the dominant source of Radio Emission from very low mass stars and brown dwarfs
arXiv: Astrophysics, 2008Co-Authors: Gregg Hallinan, S Bourke, A Antonova, J G Doyle, C Lane, A GoldenAbstract:We report on Radio observations of the M8.5 dwarf LSR J1835+3259 and the L3.5 dwarf 2MASS J00361617+1821104, which provide the strongest evidence to date that the electron cyclotron maser instability is the dominant mechanism producing Radio Emission in the magnetospheres of ultracool dwarfs. As has previously been reported for the M9 dwarf TVLM 513-46546, periodic pulses of 100% circularly polarized, coherent Radio Emission are detected from both dwarfs with periods of 2.84 +/- 0.01 and 3.08 +/- 0.05 hours respectively for LSR J1835+3259 and 2MASS J00361617+1821104. Importantly, periodic unpolarized Radio Emission is also detected from 2MASS J00361617+1821104, and brightness temperature limitations rule out gyrosynchrotron radiation as a source of this Radio Emission. The unpolarized Emission from this and other ultracool dwarfs is also attributed to electron cyclotron maser Emission, which has become depolarized on traversing the ultracool dwarf magnetosphere, possibly due to propagations effects such as scattering. Based on available v sin i data in the literature and rotation periods derived from the periodic Radio data for the three confirmed sources of electron cyclotron maser Emission, TVLM 513-46546, LSR J1835+3259 and 2MASS J00361617+1821104, we determine that the rotation axes of all three dwarfs are close to perpendicular to our line of sight. This suggests a possible geometrical selection effect due to the inherent directivity of electron cyclotron maser Emission, that may account for the previously reported relationship between Radio activity and v sin i observed for ultracool dwarfs. We also determine the radius of the dwarf LSR J1835+3259 to be > 0.117 +/- 0.012 R_Sol. (abridged)
