Radio Events Research Articles

Radio emissions from pulsar companions: a refutable explanation for galactic transients and fast radio bursts

The six known highly dispersed fast radio bursts are attributed to extragalactic radio sources, of unknown origin but extremely energetic. We propose here a new explanation - not requiring an extreme release of energy - involving a body (planet, asteroid, white dwarf) orbiting an extragalactic pulsar. We investigate a theory of radio waves associated to such pulsar-orbiting bodies. We focus our analysis on the waves emitted from the magnetic wake of the body in the pulsar wind. After deriving their properties, we compare them with the observations of various transient radio signals in order to see if they could originate from pulsar-orbiting bodies. The analysis is based on the theory of Alfv\'en wings: for a body immersed in a pulsar wind, a system of two stationary Alfv\'en waves is attached to the body, provided that the wind is highly magnetized. When destabilized through plasma instabilities, Alfv\'en wings can be the locus of strong radio sources convected with the pulsar wind. Assuming a cyclotron maser instability operating in the Alfv\'en wings, we make predictions about the shape, frequencies and brightness of the resulting radio emissions. Because of the beaming by relativistic aberration, the signal is seen only when the companion is perfectly aligned between its parent pulsar and the observer, as for occultations. For pulsar winds with a high Lorentz factor, the whole duration of the radio event does not exceed a few seconds, and it is composed of one to four peaks lasting a few milliseconds each, detectable up to distances of several Mpc. The Lorimer burst, the three isolated pulses of PSR J1928+15, and the recently detected fast radio bursts are all compatible with our model. According to it, these transient signals should repeat periodically with the companion's orbital period. The search of pulsar-orbiting bodies could be an exploration theme for new- or next-generation radio telescopes.

TRACKING THE CME-DRIVEN SHOCK WAVE ON 2012 MARCH 5 AND RADIO TRIANGULATION OF ASSOCIATED RADIO EMISSION

We present a multiwavelength study of the 2012 March 5 solar eruptive event, with an emphasis on the radio triangulation of the associated radio bursts. The main points of the study are reconstruction of the propagation of shock waves driven by coronal mass ejections (CMEs) using radio observations and finding the relative positions of the CME, the CME-driven shock wave, and its radio signatures. For the first time, radio triangulation is applied to different types of radio bursts in the same event and performed in a detailed way using goniopolarimetric observations from STEREO/Waves and WIND/Waves spacecraft. The event on 2012 March 5 was associated with a X1.1 flare from the NOAA AR 1429 situated near the northeast limb, accompanied by a full halo CME and a radio event comprising long-lasting interplanetary type II radio bursts. The results of the three-dimensional reconstruction of the CME (using SOHO/LASCO, STEREO COR, and HI observations), and modeling with the ENLIL cone model suggest that the CME-driven shock wave arrived at 1 AU at about 12:00 UT on March 7 (as observed by SOHO/CELIAS). The results of radio triangulation show that the source of the type II radio burst was situated on the southern flankmore » of the CME. We suggest that the interaction of the shock wave and a nearby coronal streamer resulted in the interplanetary type II radio emission.« less

Optimal Index Policies for Anomaly Localization in Resource-Constrained Cyber Systems

The problem of anomaly localization in a resource-constrained cyber system is considered. Each anomalous component of the system incurs a cost per unit time until its anomaly is identified and fixed. Different anomalous components may incur different costs depending on their criticality to the system. Due to resource constraints, only one component can be probed at each given time. The observations from a probed component are realizations drawn from two different distributions depending on whether the component is normal or anomalous. The objective is a probing strategy that minimizes the total expected cost, incurred by all the components during the detection process, under reliability constraints. We consider both independent and exclusive models. In the former, each component can be abnormal with a certain probability independent of other components. In the latter, one and only one component is abnormal. We develop optimal index policies under both models. The proposed index policies apply to a more general case where a subset (more than one) of the components can be probed simultaneously. The problem under study also finds applications in spectrum scanning in cognitive radio networks and event detection in sensor networks.

An interferometric analysis method for radio impulses from ultra-high energy particle showers

We present an interferometric technique for the reconstruction of ultra-wide band impulsive signals from point sources. This highly sensitive method was developed for the search for ultra-high energy neutrinos with the ANITA experiment but is fully generalizable to any antenna array detecting radio impulsive events. Applications of the interferometric method include event reconstruction, thermal noise and anthropogenic background rejection, and solar imaging for calibrations. We illustrate this technique with applications from the analysis of the ANITA-I and ANITA-II data in the 200–1200MHz band.

Estimation and Compensation of Non-deterministic Delays for Time Synchronization in Wireless Sensor Networks

New research opportunities are emerging as Wireless Sensor Networks (WSNs) are penetrating into the industrial domain; one such prospect is within time synchronization. For the operation of WSNs, partial or full time synchronization is needed. Time synchronization is very important in a distributed WSN for the purpose of data fusion, time interval calculation, context-free access to radio channel, coordination, event ordering and power management. This paper proposes a novel distributed time synchronization protocol for WSNs, which compensates for the nondeterministic delays by estimating the uncertainties in the synchronization packet delays. The main idea is to minimize the uncertainties in the synchronization packet delays to achieve a synchronization scheme that is accurate, efficient and has a low communication overhead. An average per hop synchronization accuracy of 2.4µs has been achieved.

BRIGHT MICROWAVE PULSES FROM PSR B0531+21 OBSERVED WITH A PROTOTYPE TRANSIENT SURVEY RECEIVER

Recent discoveries of transient radio events have renewed interest in time-variable astrophysical phenomena. Many radio transient events are rare, requiring long observing times for reliable statistical study. The National Aeronautics and Space Administration/Jet Propulsion Laboratory's Deep Space Network (DSN) tracks spacecraft nearly continuously with 13 large-aperture, low system temperature radio antennas. During normal spacecraft operations, the DSN processes only a small fraction of the pre-detection bandwidth available from these antennas; any information in the remaining bandwidth, e.g., from an astronomical source in the same antenna beam as the spacecraft, is currently ignored. As a firmware modification to the standard DSN tracking receiver, we built a prototype receiver that could be used for astronomical transient surveys. Here, we demonstrate the receiver's utility through observations of bright pulses from the Crab pulsar and describe attributes of potential transient survey observations piggybacking on operational DSN tracks.

Digital Off-Air Radio Events Archive of the Bulgarian National Radio

The paper describes the design and the system created for digital off-air radio events archive of the Bulgarian National Radio. The system provides more efficient application of modern information technologies into radio production and its presentation on different new media platforms.ACM Computing Classification System (1998): H.2.1, H.2.4, H.2.8, H.3.7, J.5.

TEMPORAL SMEARING OF TRANSIENT RADIO SOURCES BY THE INTERGALACTIC MEDIUM

The temporal smearing of impulsive radio events at cosmological redshifts probes the properties of the ionized Inter-Galactic Medium (IGM). We relate the degree of temporal smearing and the profile of a scattered source to the evolution of turbulent structure in the IGM as a function of redshift. We estimate the degree of scattering expected by analysing the contributions to the Scattering Measure (SM) of the various components of baryonic matter embedded in the IGM, including the diffuse IGM, intervening galaxies and intracluster gas. These estimates predict that the amount of temporal smearing expected at 300\,MHz is typically as low as ~1 ms and suggests that these bursts may be detectable with low frequency widefield arrays. A generalization of the DM-SM relation observed for Galactic scattering to the densities and turbulent conditions relevant to the IGM suggests that scattering measures of order 10^{-6} kpc m {-20/3} would be expected at z ~ 1. This scattering is sufficiently low that its effects would, for most lines of sight, not be manifest in existing observations of the scattering broadening in images of extragalactic compact sources. The redshift dependence of the temporal smearing discriminates between scattering that occurs in the host galaxy of the burst and the IGM, with tau_host \propto (1+z)^{-3} if the scattering probes length scales below the inner scale of the turbulence or tau_host \propto (1+z)^{-17/5} if the turbulence follows a Kolmogorov spectrum. This differs strongly from the expected IGM scaling tau_{IGM} ~ z^2 for z < 1 and (1+z)^{0.2-0.5} for z >> 1.

The Use of the Digital Off-Air Radio Events Archive System EventsBNR in the Bulgarian National Radio

The paper describes the use of the system created for Digital off-air radio events archive EventsBNR in the Bulgarian National Radio. The system provides efficient application of modern information technologies in radio archiving.

A Population of Fast Radio Bursts at Cosmological Distances

Searches for transient astrophysical sources often reveal unexpected classes of objects that are useful physical laboratories. In a recent survey for pulsars and fast transients, we have uncovered four millisecond-duration radio transients all more than 40° from the Galactic plane. The bursts' properties indicate that they are of celestial rather than terrestrial origin. Host galaxy and intergalactic medium models suggest that they have cosmological redshifts of 0.5 to 1 and distances of up to 3 gigaparsecs. No temporally coincident x- or gamma-ray signature was identified in association with the bursts. Characterization of the source population and identification of host galaxies offers an opportunity to determine the baryonic content of the universe.

Unusual Solar Radio Burst Observed at Decameter Wavelengths

An unusual solar burst was observed simultaneously by two decameter radio telescopes UTR-2 (Kharkov, Ukraine) and URAN-2 (Poltava, Ukraine) on 3 June 2011 in the frequency range 16-28 MHz. The observed radio burst has some unusual properties, which are not typical for the other types of solar radio bursts. The frequency drift rate of it was positive (about 500 kHz s$^{-1}$) at frequencies higher than 22 MHz and negative (100 kHz s$^{-1}$) at lower frequencies. The full duration of this event varies from 50 s up to 80 s, depending on the frequency. The maximum radio flux of the unusual burst reaches $\approx 10^3$ s.f.u and its polarization does not exceed 10%. This burst has a fine frequency-time structure of unusual appearance. It consists of stripes with the frequency bandwidth 300-400 kHz. We consider that several accompanied radio and optical events observed by SOHO and STEREO spacecraft are possibly associated with the reported radio burst. A model that may interpret the observed unusual solar radio burst is proposed.

Topside electron density profiles observed at low latitudes by COSMIC and compared with in situ ion densities measured by C/NOFS

AbstractElectron density height profiles (EDPs) play critical roles in accurately tracing the propagation of radio frequency signals through the topside ionosphere. The Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) satellites were designed to provide this information during GPS radio occultation events. However, due to the reliance of COSMIC data reduction on inverse Abel transformations, questions persist about the accuracy of its EDP products. The Communication/Navigation Outage Forecasting System (C/NOFS) satellite in a low‐inclination orbit offers new opportunities for empirically testing the accuracy of topside EDPs from COSMIC over the altitude range 400 to 800 km. We report here on the results of a feasibility study covering the interval 24–25 October 2011 in which a large magnetic storm occurred. We identified universal times when C/NOFS passed within 6° × 60° rectangles centered at the latitudes and longitudes of the tangent line for COSMIC EDPs. We also compared COSMIC EDPs with those predicted by two widely used models. Our analysis shows that during a very large fraction of the available events, ion densities measured by C/NOFS were in closer agreement with COSMIC EDPs than were model predictions at the same altitudes. We also use the COSMIC and C/NOFS data sets to assess stormtime effects on the low‐latitude ionosphere. During the main phase of the storm both local densities and vertical total electron content rose on the dayside, but decreased on the nightside. During recovery both quantities quickly reverted toward their quiet‐time levels.

Hint of 150 MHz radio emission from the Neptune-mass extrasolar transiting planet HAT-P-11b

Since the radio-frequency emission from planets is expected to be strongly influenced by their interaction with the magnetic field and corona of the host star, the physics of this process can be effectively constrained by making sensitive measurements of the planetary radio emission. Up to now, however, numerous searches for radio emission from extrasolar planets at radio wavelengths have only yielded negative results. Here we report deep radio observations of the nearby Neptune-mass extrasolar transiting planet HAT-P-11b at 150 MHz, using the Giant Meterwave Radio Telescope (GMRT). On July 16, 2009, we detected a 3-sigma emission whose light curve is consistent with an eclipse when the planet passed behind the star. This emission is at a position 14 arcsec from the transiting exoplanet's coordinates; thus, with a synthetized beam of FWHM~16 arcsec, the position uncertainty of this weak radio signal encompasses the location of HAT-P-11. We estimate a 5% false positive probability that the observed radio light curve mimics the planet's eclipse light curve. If the faint signature is indeed a radio eclipse event associated with the planet, then its flux would be 3.87 mJy +/- 1.29 mJy at 150 MHz. However, our equally sensitive repeat observations of the system on November 17, 2010 did not detect a significant signal in the radio light curve near the same position. This lack of confirmation leaves us with the possibility of either a variable planetary emission, or a chance occurrence of a false positive signal in our first observation. Deeper observations are required to confirm this hint of 150 MHz radio emission from HAT-P-11b.

All Work and No Play: British Leisure Culture and the 1947 Fuel Crisis

The impact that the 1947 fuel crisis and the subsequent drive to increase industrial output had on the standing of Clement Attlee's first Labour government has often been understood in primarily economic terms. This article demonstrates that for many Britons these events were not only the cause of daytime power cuts and short-term unemployment, but also the source of restrictions on a host of leisure pursuits that altered the established rhythms of everyday social and cultural life. Such restrictions, which affected, amongst other things, the cinema, theatre, radio and sporting events, helped to determine the experience of the fuel crisis and thereby shaped attitudes towards the government, not least because of the emotive way in which they were reported in the press.

Fast Magnetoacoustic Waves in a Fan Structure Above a Coronal Magnetic Null Point

We analyze the 26 November 2005 solar radio event observed interferometrically at frequencies of 244 and 611 MHz by the Giant Metrewave Radio Telescope (GMRT) in Pune, India. These observations are used to make interferometric maps of the event at both frequencies with the time cadence of 1 s from 06:50 to 07:12 UT. These maps reveal several radio sources. The light curves of these sources show that only two sources at 244 MHz and 611 MHz are well correlated in time. The EUV flare is more localized with flare loops located rather away from the radio sources. Using SoHO/MDI observations and potential magnetic field extrapolation we demonstrate that both the correlated sources are located in the fan structure of magnetic field lines starting from a coronal magnetic null point. Wavelet analysis of the light curves of the radio sources detects tadpoles with periods in the range P=10 – 83 s. These wavelet tadpoles indicate the presence of fast magnetoacoustic waves that propagate in the fan structure of the coronal magnetic null point. We estimate the plasma parameters in the studied radio sources and find them consistent with the presented scenario involving the coronal magnetic null point.

Constraints on Blazar Jet Conditions During Gamma-Ray Flaring from Radiative Transfer Modeling

As part of a program to investigate jet flow conditions during GeV gamma-ray flares detected by Fermi, we are using UMRAO multi-frequency, centimeter-band total flux density and linear polarization monitoring observations to constrain radiative transfer models incorporating propagating shocks orientated at an arbitrary angle to the flow direction. We describe the characteristics of the model, illustrate how the data are used to constrain the models, and present results for three program sources with diverse characteristics: PKS 0420-01, OJ 287, and 1156+295. The modeling of the observed spectral behavior yields information on the sense, strength and orientation of the shocks producing the radio-band flaring; on the energy distribution of the radiating particles; and on the observer's viewing angle with respect to the jet independent of VLBI data. We present evidence that, while a random component dominates the jet magnetic field, a distinguishing feature of those radio events with an associated gamma-ray flare is the presence of a weak but non-negligible ordered magnetic field component along the jet axis.

Observation of the powerful solar flare of October 27, 2002 on the far side of the sun

Observations of the hard X-ray and radio event of October 27, 2002 are analyzed. This flare was observed from near-Martian orbit by the HEND instrument developed at the Space Research Institute of the Russian Academy of Sciences and installed on the Mars Odyssey satellite. Although this powerful flare was observed far over the eastern solar limb, the extended source associated with the flare was detected by RHESSI at energies up to about 60 keV. The eruptive event was observed in the radio at the Nobeyama Radio Observatory. The properties of the X-ray radiation are used to calculate the spectrum of the accelerated electrons responsible for the observed radiation, assuming that the target is thick for a Martian observer and thin for a terrestrial observer. The results are compared with the results of radio observations. The conditions for electron propagation in the corona are discussed.

Radio astronomy with the European Lunar Lander: Opening up the last unexplored frequency regime

The Moon is a unique location in our solar system and provides important information regarding the exposure to free space that is essential for future human space exploration to mars and beyond. The active broadband (100kHz–100MHz) tripole antenna now envisaged to be placed on the European Lunar Lander located at the Lunar South Pole allows for sensitive measurements of the exosphere and ionosphere, and their interaction with the Earths magnetosphere, solar particles, wind and CMEs and studies of radio communication on the Moon, that are essential for future lunar human and science exploration. In addition, the Lunar South Pole provides an excellent opportunity for radio astronomy. Placing a single radio antenna in an eternally dark crater or behind a mountain at the South (or North) pole would potentially provide perfect shielding from man-made radio interference (RFI), absence of ionospheric distortions, and high temperature and antenna gain stability that allows detection of the 21cm wave emission from pristine hydrogen formed after the Big Bang and into the period where the first stars formed. A detection of the 21cm line from the Moon at these frequencies would allow for the first time a clue on the distribution and evolution on mass in the early universe between the Epoch of Recombination and Epoch of Reionization (EoR). Next to providing a cosmological breakthrough, a single lunar radio antenna would allow for studies of the effect of solar flares and coronal mass ejections (CMEs) on the solar wind at distances close to Earth (space weather) and would open up the study of low frequency radio events (flares and pulses) from planets such as Jupiter and Saturn, which are known to emit bright (kJy–MJy) radio emission below 30MHz (Jester and Falcke, 2009). Finally, a single radio antenna on the lunar lander would pave the way for a future large lunar radio interferometer; not only will it demonstrate the possibilities for lunar radio science and open up the last unexplored radio regime, but it will also allow a determination of the limitations of lunar radio science by measuring the local radio background noise.

Zooming into radio events by bus snooping

In this position paper, we advocate the use of bus snooping to trace radio events. Highly precise and unintrusive, the technique leads to potentially more efficient code and enables more insightful protocol analysis than conventional code instrumentation techniques.

Type II solar radio bursts: 2. Detailed comparison of theory with observations

In this paper, the second in a two paper series, we quantitatively compare a detailed theory for type II solar radio bursts with observations and extract the parameters of the associated shocks. We use the techniques and assessment parameters developed and demonstrated in the companion paper for artificial data sets and solar wind models. Here we investigate three relatively well‐observed type II events with estimates of shock parameters from LASCO/SOHO observations of coronal mass ejections (CMEs) or other data. Using these parameters we obtain reasonable qualitative and semiquantitative agreement (25–40% correlations) between the theory and observed dynamic spectra. Then, using an iterative downhill simplex method with two assessment parameters, we extract model shock parameters that increase the agreement between theory and observation in terms of relative flux levels, spectral intensifications and drift rates. The extracted parameters agree qualitatively and semiquantitatively with the parameters (speed, size and expansion index) estimated from CME observations for one of the studied events. The extracted parameters agree qualitatively with the remaining two events and yield new initial shock speeds. The agreement between this multiprocess theory and observations is promising for these first quantitative comparisons performed here. Quantitatively, the bulk of the radio emission agrees to within 5 to 10 dB with observations, with the theory typically overpredicting the intensity of bright spots in the dynamic spectra. The methods and analyses presented here show potential for the remote inference of CME‐driven shock parameters and the prediction of radio and space weather events.