53656326
The LOFAR pilot surveys for pulsars and fast radio transients
We have conducted two pilot surveys for radio pulsars and fast transients with the Low-Frequency Array (LOFAR) around 140 MHz and here report on the first low-frequency fast-radio burst limit and the discovery of two new pulsars. The first survey, the LOFAR Pilot Pulsar Survey (LPPS), observed a large fraction of the northern sky, ~1.4 x 10^4 sq. deg, with 1-hr dwell times. Each observation covered ~75 sq. deg using 7 independent fields formed by incoherently summing the high-band antenna fields. The second pilot survey, the LOFAR Tied-Array Survey (LOTAS), spanned ~600 sq. deg, with roughly a 5-fold increase in sensitivity compared with LPPS. Using a coherent sum of the 6 LOFAR "Superterp" stations, we formed 19 tied-array beams, together covering 4 sq. deg per pointing. From LPPS we derive a limit on the occurrence, at 142 MHz, of dispersed radio bursts of 107 Jy for the narrowest searched burst duration of 0.66 ms. In LPPS, we re-detected 65 previously known pulsars. LOTAS discovered two pulsars, the first with LOFAR or any digital aperture array. LOTAS also re-detected 27 previously known pulsars. These pilot studies show that LOFAR can efficiently carry out all-sky surveys for pulsars and fast transients, and they set the stage for further surveying efforts using LOFAR and the planned low-frequency component of the Square Kilometer Array.
16224154
The brightness and spatial distributions of terrestrial radio sources
Faint undetected sources of radio-frequency interference (RFI) might become visible in long radio observations when they are consistently present over time. Thereby, they might obstruct the detection of the weak astronomical signals of interest. This issue is especially important for Epoch of Reionization (EoR) projects that try to detect the faint redshifted H i signals from the time of the earliest structures in the Universe. We explore the RFI situation at 30–163 MHz by studying brightness histograms of visibility data observed with Low-Frequency Array (LOFAR), similar to radio-source-count analyses that are used in cosmology. An empirical RFI distribution model is derived that allows the simulation of RFI in radio observations. The brightness histograms show an RFI distribution that follows a power-law distribution with an estimated exponent around −1.5. With several assumptions, this can be explained with a uniform distribution of terrestrial radio sources whose radiation follows existing propagation models. Extrapolation of the power law implies that the current LOFAR EoR observations should be severely RFI limited if the strength of RFI sources remains strong after time integration. This is in contrast with actual observations, which almost reach the thermal noise and are thought not to be limited by RFI. Therefore, we conclude that it is unlikely that there are undetected RFI sources that will become visible in long observations. Consequently, there is no indication that RFI will prevent an EoR detection with LOFAR.
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.
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.
121572324
Results of in-beam tests of an MCP-based vacuum sector prototype of the T0/centrality detector for ALICE
AbstractWereportonresultsofeﬃciencytestsforMIPsandtimingresolutionstudiesobtainedwithdiﬀerentlayoutsofmicro-channelplate(MCP)detectorprototypesatCERNPStestbeams.ThedetectoriscomposedofanMCPstackand multipad readout anodes integrated with a passive isochronal summator. Several types of setups were tested,includingMCPswithdiﬀerentgain.Also,averyﬁrsttestoftheMicroSpherePlatesdetectorwasperformed.TheperformanceoffastelectronicsincludingDoubleThresholdDiscriminatorsandafastmultiplicitydiscriminatorforshort2nssignalswasstudied.Currently,thebestexperimentalresultsforMCPdetectorsshow75pstimingresolutionobtainedat75%eﬃciencyfortheregistrationofasinglemuon.Weexpectfurtherenhancements,mostlythroughimprovementsinthefastelectronics.r 2002ElsevierScienceB.V.Allrightsreserved. 1. IntroductionA Micro-Channel Plate (MCP) disk detectorsystem with integrated isochronal signal readoutandprecisetimingcapabilitiesisconsideredasoneof the options for the ALICE pre-trigger T0/centralitydetector.MCPsareawell-knowndevicefor the registration of charged particles due totheir excellent timing properties (20–50ps), highinternalgain(10