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We describe the design and deployment of GREENBURST, a commensal Fast Radio Burst (FRB) search system at the Green Bank Telescope. GREENBURST uses the dedicated L-band receiver tap to search over the 960–1 920 MHz frequency range for pulses with dispersion measures out to
. Due to its unique design, GREENBURST is capable of conducting searches for FRBs when the L-band receiver is not being used for scheduled observing. This makes it a sensitive single pixel detector capable of reaching deeper in the radio sky. While single pulses from Galactic pulsars and rotating radio transients will be detectable in our observations, and will form part of the database we archive, the primary goal is to detect and study FRBs. Based on recent determinations of the all-sky rate, we predict that the system will detect approximately one FRB for every 2–3 months of continuous operation. The high sensitivity of GREENBURST means that it will also be able to probe the slope of the FRB fluence distribution, which is currently uncertain in this observing band.
Phased Array Feed (PAF) technology is the next major advancement in radio astronomy in terms of combining high sensitivity and large field of view. The Focal L-band Array for the Green Bank Telescope (FLAG) is one of the most sensitive PAFs developed so far. It consists of 19 dual-polarization elements mounted on a prime focus dewar resulting in seven beams on the sky. Its unprecedented system temperature of ~17 K will lead to a 3 fold increase in pulsar survey speeds as compared to contemporary single pixel feeds. Early science observations were conducted in a recently concluded commissioning phase of the FLAG where we clearly demonstrated its science capabilities. We observed a selection of normal and millisecond pulsars and detected giant pulses from PSR B1937+21.
PSR J0337+1715 is a millisecond radio pulsar in a hierarchical stellar triple system with two white dwarfs. This system is a unique and excellent laboratory in which to test the strong equivalence principle (SEP) of general relativity. An initial SEP-violation test was performed using direct 3-body numerical integration of the orbit in order to model the more than 25000 pulse times of arrival (TOAs) from three radio telescopes: Arecibo, Green Bank and Westerbork. In this work I present our efforts to quantify the effects of systematics in the TOAs and timing residuals, which limit the precision of an SEP test. In particular, we apply Fourier-based techniques to the timing residuals in order to isolate the effects of systematics that can masquerade as an SEP violation.
The millisecond pulsar PSR J0337+1715 is in a mildly relativistic hierarchical triple system with two white dwarfs. This offers the possibility of testing the universality of free fall: does the neutron star fall with the same acceleration as the inner white dwarf in the gravity of the outer white dwarf? We have carried out an intensive pulsar timing campaign, yielding some 27000 pulse time-of-arrival (TOA) measurements with a median uncertainty of 1.2 μs. Here we describe our analysis procedure and timing model.
PSR B1828–11 is a young pulsar once thought to be undergoing free precession and recently found instead to be switching magnetospheric states in tandem with spin-down changes. Here we show the two extreme states of the mode-changing found for this pulsar and comment briefly on its interpretation.
Multi-decade observing campaigns of the globular clusters 47 Tucanae and M15 have led to an outstanding number of discoveries. Here, we report on the latest results of the long-term observations of the pulsars in these two clusters. For most of the pulsars in 47 Tucanae we have measured, among other things, their higher-order spin period derivatives, which have in turn provided stringent constraints on the physical parameters of the cluster, such as its distance and gravitational potential. For M15, we have studied the relativistic spin precession effect in PSR B2127+11C. We have used full-Stokes observations to model the precession effect, and to constrain the system geometry. We find that the visible beam of the pulsar is swiftly moving away from our line of sight and may very soon become undetectable. On the other hand, we expect to see the opposite emission beam sometime between 2041 and 2053.
Here, we present initial results from the ALFABURST radio transient survey, which is currently running in a commensal mode with the ALFA receiver at the Arecibo telescope. We observed for a total of 1400 hours and have detected single pulses from known pulsars but did not detect any FRBs. The non-detection of FRBs is consistent with the current FRB sky rates.
We review current understanding of the underlying, as opposed to the observed, pulsar population. The observed sample is heavily biased by selection effects, so that surveys see less than 10% of all potentially observable pulsars. We compare various techniques used to correct the sample for these biases. By far the most significant recent development has been the discovery of over 700 pulsars in the Parkes Multibeam (PM) survey. This new sample is far less affected by selection effects and we use it to make a preliminary analysis of the Galactic pulsar distribution, finding further evidence for a deficit of pulsars in the inner Galaxy.
We report on new pulsars discovered in Arecibo drift-scan datA. Processing of 2200 deg2 of data has resulted in the detection of 41 known and 12 new pulsars. New pulsars include two millisecond pulsars, one solitary and one binary recycled pulsar, and one pulsar with very unusual pulse profile morphology and complex drifting subpulse behavior.
We are conducting deep searches for radio pulsations at L-band (∼ 20 cm) towards more than 30 globular clusters (GCs) using the 305 m Arecibo telescope in Puerto Rico and the 100 m Green Bank Telescope in West VirginiA. With roughly three quarters of our search data analyzed, we have discovered 12 new millisecond pulsars (MSPs), 11 of which are in binary systems, and at least three of which eclipse. We have timing solutions for several of these systems.
PSRs J1847–0130 and J1718–37184 have inferred surface dipole magnetic fields greater than those of any other known pulsars and well above the “quantum critical field” above which some models predict radio emission should not occur. These fields are similar to those of the anomalous X-ray pulsars (AXPs), which growing evidence suggests are “magnetars”. The lack of AXP-like X-ray emission from these radio pulsars (and the non-detection of radio emission from the AXPs) creates new challenges for understanding pulsar emission physics and the relationship between these classes of apparently young neutron stars.
The recent shift of opinion concerning the distribution of pulsar velocities at birth with a mean value of 400-500 km/s has several ramifications for our understanding of the origin and evolution of pulsars. From the present data, there is no convincing evidence for a causal correlation between velocity and magnetic field, any magnetic field evolution in neutron stars or that galactic neutron stars once active as radio pulsars are the sources of γ-ray bursts. Asymmetric kicks seem the most plausible origin for the high velocities.
To study the structure of emission beam, we have analysed the single pulse data of PSR B0329+54 at 325 and 606 MHz. In order to unambiguously detect the weak emission components, we have developed a new data analysis technique, which we term “window-thresholding”. By applying this technique to the data, we have detected three new emission components, and also confirmed the presence of a component which was proposed earlier. Hence our analysis indicates that PSR B0329+54 has nine components, which is among the highest of all the known pulsars. The symmetric distribution of pulse components about the pulse centre, indicates that the emission beam is conal.
We report the status of a search for pulsars in the Galactic Centre, using a completely revised and improved high-sensitivity double-horn system at 4.85-GHz. We also present calculations about the success rate of periodicity searches for such a survey, showing that in contrast to conclusions in recent literature pulsars can be indeed detected at the chosen search frequency.
The graphics processing unit has become an integral part of astronomical instrumentation, enabling high-performance online data reduction and accelerated online signal processing. In this paper, we describe a wide-band reconfigurable spectrometer built using an off-the-shelf graphics processing unit card. This spectrometer, when configured as a polyphase filter bank, supports a dual-polarisation bandwidth of up to 1.1 GHz (or a single-polarisation bandwidth of up to 2.2 GHz) on the latest generation of graphics processing units. On the other hand, when configured as a direct fast Fourier transform, the spectrometer supports a dual-polarisation bandwidth of up to 1.4 GHz (or a single-polarisation bandwidth of up to 2.8 GHz).
The Parkes pulsar data archive currently provides access to 144044 data files obtained from observations carried out at the Parkes observatory since the year 1991. Around 105 files are from surveys of the sky, the remainder are observations of 775 individual pulsars and their corresponding calibration signals. Survey observations are included from the Parkes 70 cm and the Swinburne Intermediate Latitude surveys. Individual pulsar observations are included from young pulsar timing projects, the Parkes Pulsar Timing Array and from the PULSE@Parkes outreach program. The data files and access methods are compatible with Virtual Observatory protocols. This paper describes the data currently stored in the archive and presents ways in which these data can be searched and downloaded.
The luminosity distribution of Galactic radio pulsars is believed to be log-normal in form. Applying this functional form to populations of pulsars in globular clusters, we employ Bayesian methods to explore constraints on the mean and standard deviation of the function, as well as the total number of pulsars in the cluster. Our analysis is based on an observed number of pulsars down to some limiting flux density, measurements of flux densities of individual pulsars, as well as diffuse emission from the direction of the cluster. We apply our analysis to Terzan 5 and demonstrate, under reasonable assumptions, that the number of potentially observable pulsars is in a 95.45% credible interval of 133+101−58. Beaming considerations would increase the true population size by approximately a factor of two.
Optical luminescence in porous silicon induced by soft X-ray and vacuum UV excitation with energies in the vicinity of the Si K-edge (1838 eV) and the Si L-edge (99 eV) has been observed. The luminescence has been used, together with total electron yield, to record X-ray absorption fine structure (XAFS) in the near-edge region of both Si edges. The near- edge spectra recorded simultaneously with either luminescence or total electron yield were compared, and the implications of these measurements for the structure of porous silicon are discussed.
A total of 69 species of lichens have been collected from various locations around New Zealand. Screening of extracts of these species for antimicrobial, antiviral and cytotoxic activity showed a high proportion with biological activity. Active extracts were generally from species known to contain phenolic compounds. Bioactivity-directed isolation work on Cladia retipora, Pseudocyphellaria glabra and P. homoeophylla led to the identification of usnic acid as the main antimicrobial, cytotoxic and antiviral component in these three species.
Psychiatric day care has expanded considerably over the past 20 years. Day hospitals may serve as alternatives to short-stay in-patient units or speed discharge from them. Day services are also necessary to ensure appropriate support for patients with chronic disability, especially chronic functional psychosis, if they are to remain in a community setting (these are often called day hospitals to ensure NHS support). The present paper focuses on this latter group and describes the characteristics of day attenders in a service that has developed a multi-facility approach to community support.