7001742
Detecting cosmic rays with the LOFAR radio telescope
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.
118563003
CORRELATION OF CHANDRA PHOTONS WITH THE RADIO GIANT PULSES FROM THE CRAB PULSAR
No apparent correlation was found between giant pulses (GPs) and X-ray photons from the Crab pulsar during 5.4 hr of simultaneous observations with the Green Bank Telescope at 1.5 GHz and Chandra X-Ray Observatory primarily in the energy range of 1.5-4.5 keV. During the Crab pulsar periods with GPs, the X-ray flux in radio emission phase windows does not change more than by {+-}10% for main pulse (MP) GPs and {+-}30% for interpulse (IP) GPs. During GPs themselves, the X-ray flux does not change by more than two times for MP GPs and five times for IP GPs. All limits quoted are compatible with 2{sigma} fluctuations of the X-ray flux around the sets of false GPs with random arrival times. The results speak in favor of changes in plasma coherence as the origin of GPs. However, the results do not rule out variations in the rate of particle creation if the particles that emit coherent radio emission are mostly at the lowest Landau level.
119110851
THE PULSAR SEARCH COLLABORATORY: DISCOVERY AND TIMING OF FIVE NEW PULSARS
We present the discovery and timing solutions of five new pulsars by students involved in the Pulsar Search Collaboratory, a NSF-funded joint program between the National Radio Astronomy Observatory and West Virginia University designed to excite and engage high-school students in Science, Technology, Engineering, and Mathematics (STEM) and related fields. We encourage students to pursue STEM fields by apprenticing them within a professional scientific community doing cutting edge research, specifically by teaching them to search for pulsars. The students are analyzing 300?hr of drift-scan survey data taken with the Green Bank Telescope at 350?MHz. These data cover 2876?deg2 of the sky. Over the course of five years, more than 700 students have inspected diagnostic plots through a web-based graphical interface designed for this project. The five pulsars discovered in the data have spin periods ranging from 3.1?ms to 4.8?s. Among the new discoveries are PSR?J1926?1314, a long period, nulling pulsar; PSR?J1821+0155, an isolated, partially recycled 33?ms pulsar; and PSR?J1400?1438, a millisecond pulsar in a 9.5?day orbit whose companion is likely a white dwarf star.
16206012
Giant pulses from PSR B1937+21 with widths ≤15 nanoseconds and Tb ≥ 5 × 1039 K, the highest brightness temperature observed in the universe
Giant radio pulses of the millisecond pulsar B1937+21 were recorded with the S2 VLBI system at 1.65 GHz with NASA/JPL's 70 m radio telescope at Tidbinbilla, Australia. These pulses have been observed as strong as 65,000 Jy with widths ≤15 ns, corresponding to a brightness temperature of Tb ≥ 5 × 1039 K, the highest observed in the universe. The vast majority of these pulses occur in 5.8 and 8.2 μs windows at the very trailing edges of the regular main pulse and interpulse profiles, respectively. Giant pulses occur, in general, with a single spike. Only in one case of 309 was the structure clearly more complex. The cumulative distribution is fitted by a power law with index -1.40 ± 0.01 with a low-energy but no high-energy cutoff. We estimate that giant pulses occur frequently but are only rarely detected. When corrected for the directivity factor, 25 giant pulses are estimated to be generated in one neutron star revolution alone. The intensities of the giant pulses of the main pulses and interpulses are not correlated with each other nor with the intensities or energies of the main pulses and interpulses themselves. Their radiation energy density can exceed 300 times the plasma energy density at the surface of the neutron star and can even exceed the magnetic field energy density at that surface. We therefore do not think that the generation of giant pulses is linked to the plasma mechanisms in the magnetosphere. Instead we suggest that it is directly related to discharges in the polar cap region of the pulsar.
3353965
Calibrating high-precision Faraday rotation measurements for LOFAR and the next generation of low-frequency radio telescopes
Faraday rotation measurements using the current and next generation of low-frequency radio telescopes will provide a powerful probe of astronomical magnetic fields. However, achieving the full potential of these measurements requires accurate removal of the time-variable ionospheric Faraday rotation contribution. We present ionFR, a code that calculates the amount of ionospheric Faraday rotation for a specific epoch, geographic location, and line-of-sight. ionFR uses a number of publicly available, GPS-derived total electron content maps and the most recent release of the International Geomagnetic Reference Field. We describe applications of this code for the calibration of radio polarimetric observations, and demonstrate the high accuracy of its modeled ionospheric Faraday rotations using LOFAR pulsar observations. These show that we can accurately determine some of the highest-precision pulsar rotation measures ever achieved. Precision rotation measures can be used to monitor rotation measure variations - either intrinsic or due to the changing line-of-sight through the interstellar medium. This calibration is particularly important for nearby sources, where the ionosphere can contribute a significant fraction of the observed rotation measure. We also discuss planned improvements to ionFR, as well as the importance of ionospheric Faraday rotation calibration for the emerging generation of low-frequency radio telescopes, such as the SKA and its pathfinders.
13221938
Multifrequency Study of Giant Radio Pulses from the Crab Pulsar with the K5 VLBI Recording Terminal
AbstractSimultaneous multifrequency observations of the Crab pulsar giant pulses (GPs)were performed with the 64-m Kalyazin radio telescope at four frequencies ν = 0.6,1.4, 2.2 and 8.3 GHz, using the K5 VLBI recording terminal. The K5 terminal pro-vided continuous recording in 16 4-MHz wide frequency channels distributed over 4frequency bands. Several thousand GPs were detected during about 6 hours of obser-vations in two successive days in July 2005. Radio spectra of single GPs were analysedat separate frequencies and over the whole frequency range. These spectra mani-fest notable modulation over frequency ranges, ∆ν, both on large (∆ν/ν ≈ 0.5) andsmall (∆ν/ν ≈ 0.01) frequency scales. Cross-correlation analysis of GPs at 2.2 GHzshowed that their pulse shapes can be interpreted as an ensemble of unresolved burstsgrouped together at time scales of ≈1 µs being well-correlated over a 60-MHz band.The corresponding GP cross-correlation functions do not obey the predictions of theamplitude-modulated noise model of Rickett (1975), thus indicating that unresolvedcomponents represent a small number of elementary emitters.Key words: Pulsars — giant pulses, Crab pulsar, PSR B0531+21 — e-VLBI1
17757265
Correlation of fermi photons with high-frequency radio giant pulses from the crab pulsar
To constrain the giant pulse (GP) emission mechanism and test the model of Lyutikov for GP emission, we have carried out a campaign of simultaneous observations of the Crab pulsar at ?-ray (Fermi) and radio (Green Bank Telescope) wavelengths. Over 10 hr of simultaneous observations we obtained a sample of 2.1 ? 104 GPs, observed at a radio frequency of 9?GHz, and 77 Fermi photons, with energies between 100?MeV and 5?GeV. The majority of GPs came from the interpulse (IP) phase window. We found no change in the GP generation rate within 10-120?s windows at lags of up to ?40?minutes of observed ?-ray photons. The 95% upper limit for a ?-ray flux enhancement in pulsed emission phase window around all GPs is four times the average pulsed ?-ray flux from the Crab. For the subset of IP GPs, the enhancement upper limit, within the IP emission window, is 12 times the average pulsed ?-ray flux. These results suggest that GPs, at least high-frequency IP GPs, are due to changes in coherence of radio emission rather than an overall increase in the magnetospheric particle density.
7628453
Pulsar microstructure and its quasi-periodicities with the S2 VLBI system at a resolution of 62.5 nanoseconds
We report a study of microstructure and its quasi-periodicities of three pulsars at 1.65 GHz with the S2 VLBI system at a resolution of 62.5 ns, by far the highest for any such statistical study yet. For PSR B1929+10 we found in the average cross-correlation function (CCF) broad microstructure with a characteristic timescale of 95 ± 10 µs and confirmed microstructure with characteristic timescales between 100 and 450 µs for PSRs B0950+08 and B1133+16. On a finer scale PSRs B0950+08, B1133+16 (component II) and B1929+10 show narrow microstructure with a characteristic timescale in the CCFs of ∼10 µs, the shortest found in the average CCF or autocorrelation function (ACF) for any pulsar, apart perhaps for the Crab pulsar. Histograms of microstructure widths are skewed heavily toward shorter timescales but display a sharp cutoff. The shortest micropulses have widths between 2 and 7 µs. There is some indication that the timescales of the broad, narrow, and shortest micropulses are, at least partly, related to the widths of the components of the integrated profiles and the subpulse widths. If the shortest micropulses observed are indeed due to beaming then the ratio, γ, of the relativistic energy of the emitting particles to the rest energy is about 20000, independent of the pulsar period. We predict an observable lower limit for the width of micropulses from these pulsars at 1.65 GHz of 0.5 µs. If the short micropulses are instead interpreted as a radial modulation of the radiation pattern, then the associated emitting sources have dimensions of about 3 km in the observer's frame. For PSRs B0950+08 and B1133+16 (both components) the micropulses had a residual dispersion delay over a 16-MHz frequency difference of ∼2 µs when compared to that of average pulse profiles over a much larger relative and absolute frequency range. This residual delay is likely the result of propagation effects in the pulsar magnetosphere that contribute to limiting the width of micropulses. No nanopulses or unresolved pulse spikes were detected. Cross-power spectra of single pulses show a large range of complexity with single spectral features representing classic quasi-periodicities and broad and overlapping features with essentially no periodicities at all. Significant differences were found for the two components of PSR B1133+16 in every aspect of our statistical analysis of micropulses and their quasi-periodicities. Asymmetries in the magnetosphere and the hollow cone of emission above the polar cap of the neutron star may be responsible for these differences. the observed intensity fluctuations can be either caused by a longitudinal modulation of the radiation pattern over the cross section of the polar magnetic field lines or by a radial modula- tion of the radiation pattern along the opening polar magnetic field lines, or, again, by a combination of both. The longitudi- nal modulation is most likely related to the stationary geome- try of the emission beam fixed to each of the poles of the ro- tating neutron star. The radial modulation is likely related to plasma bunching and linked to the elementary emission mech- anism. In this model the spectrum of the radio emission is a function of the radial distance from the neutron star, and the beam width is frequency dependent. High frequency radiation is emitted closer to the neutron star and the beam is narrower, low frequency radiation is emitted further out and the beam is broader, reflecting the opening of the polar magnetic field