Spectral properties of 441 radio pulsars Jankowski, F.; van Straten, W.; Keane, E. F. ...
Monthly Notices of the Royal Astronomical Society,
02/2018, Letnik:
473, Številka:
4
Journal Article
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AbstractWe present a study of the spectral properties of 441 pulsars observed with the Parkes radio telescope near the centre frequencies of 728, 1382 and 3100 MHz. The observations at 728 and 3100 ...MHz were conducted simultaneously using the dual-band 10-50 cm receiver. These high-sensitivity, multifrequency observations provide a systematic and uniform sample of pulsar flux densities. We combine our measurements with spectral data from the literature in order to derive the spectral properties of these pulsars. Using techniques from robust regression and information theory, we classify the observed spectra in an objective, robust and unbiased way into five morphological classes: simple or broken power law, power law with either low- or high-frequency cut-off and log-parabolic spectrum. While about 79 per cent of the pulsars that could be classified have simple power-law spectra, we find significant deviations in 73 pulsars, 35 of which have curved spectra, 25 with a spectral break and 10 with a low-frequency turn-over. We identify 11 gigahertz-peaked spectrum (GPS) pulsars, with 3 newly identified in this work and 8 confirmations of known GPS pulsars; 3 others show tentative evidence of GPS, but require further low-frequency measurements to support this classification. The weighted mean spectral index of all pulsars with simple power-law spectra is -1.60 ± 0.03. The observed spectral indices are well described by a shifted log-normal distribution. The strongest correlations of spectral index are with spin-down luminosity, magnetic field at the light-cylinder and spin-down rate. We also investigate the physical origin of the observed spectral features and determine emission altitudes for three pulsars.
Television viewing time, the predominant leisure-time sedentary behavior, is associated with biomarkers of cardiometabolic risk, but its relationship with mortality has not been studied. We examined ...the associations of prolonged television viewing time with all-cause, cardiovascular disease (CVD), cancer, and non-CVD/noncancer mortality in Australian adults.
Television viewing time in relation to subsequent all-cause, CVD, and cancer mortality (median follow-up, 6.6 years) was examined among 8800 adults > or =25 years of age in the Australian Diabetes, Obesity and Lifestyle Study (AusDiab). During 58 087 person-years of follow-up, there were 284 deaths (87 CVD deaths, 125 cancer deaths). After adjustment for age, sex, waist circumference, and exercise, the hazard ratios for each 1-hour increment in television viewing time per day were 1.11 (95% confidence interval CI, 1.03 to 1.20) for all-cause mortality, 1.18 (95% CI, 1.03 to 1.35) for CVD mortality, and 1.09 (95% CI, 0.96 to 1.23) for cancer mortality. Compared with a television viewing time of <2 h/d, the fully adjusted hazard ratios for all-cause mortality were 1.13 (95% CI, 0.87 to 1.36) for > or =2 to <4 h/d and 1.46 (95% CI, 1.04 to 2.05) for > or =4 h/d. For CVD mortality, corresponding hazard ratios were 1.19 (95% CI, 0.72 to 1.99) and 1.80 (95% CI, 1.00 to 3.25). The associations with both cancer mortality and non-CVD/noncancer mortality were not significant.
Television viewing time was associated with increased risk of all-cause and CVD mortality. In addition to the promotion of exercise, chronic disease prevention strategies could focus on reducing sitting time, particularly prolonged television viewing.
Abstract
We present the first interferometric detections of fast radio bursts (FRBs), an enigmatic new class of astrophysical transient. In a 180-d survey of the Southern sky, we discovered three ...FRBs at 843 MHz with the UTMOST array, as a part of commissioning science during a major ongoing upgrade. The wide field of view of UTMOST (≈9 deg2) is well suited to FRB searches. The primary beam is covered by 352 partially overlapping fan-beams, each of which is searched for FRBs in real time with pulse widths in the range 0.655–42 ms, and dispersion measures ≤2000 pc cm−3. Detections of FRBs with the UTMOST array place a lower limit on their distances of ≈104 km (limit of the telescope near-field) supporting the case for an astronomical origin. Repeating FRBs at UTMOST or an FRB detected simultaneously with the Parkes radio telescope and UTMOST would allow a few arcsec localization, thereby providing an excellent means of identifying FRB host galaxies, if present. Up to 100 h of followup for each FRB has been carried out with the UTMOST, with no repeating bursts seen. From the detected position, we present 3σ error ellipses of 15 arcsec × 8
${^{\circ}_{.}}$
4 on the sky for the point of origin for the FRBs. We estimate an all-sky FRB rate at 843 MHz above a fluence
$\cal F_\mathrm{lim}$
of 11 Jy ms of ∼78 events sky−1 d−1 at the 95 per cent confidence level. The measured rate of FRBs at 843 MHz is two times higher than we had expected, scaling from the FRB rate at the Parkes radio telescope, assuming that FRBs have a flat spectral index and a uniform distribution in Euclidean space. We examine how this can be explained by FRBs having a steeper spectral index and/or a flatter logN–log
$\mathcal {F}$
distribution than expected for a Euclidean Universe.
Aims/hypothesis Hyperglycaemia is a risk factor for cardiovascular disease (CVD) and all-cause mortality in individuals without diabetes. We investigated: (1) whether the risk of all-cause and CVD ...mortality extended continuously throughout the range of fasting plasma glucose (FPG), 2 h plasma glucose (2hPG) and HbA₁c values; and (2) the ability of these measures to improve risk prediction for mortality. Methods Data on 10,026 people aged >=25 years without diagnosed diabetes were obtained from the population-based Australian Diabetes, Obesity and Lifestyle study. Between 1999 and 2000, FPG, 2hPG and HbA₁c were assessed and all-cause (332 deaths) and CVD (88 deaths) mortality were obtained after 7 years. Results Both 2hPG and HbA₁c exhibited linear relationships with all-cause and CVD mortality, whereas FPG showed J-shaped relationships. The adjusted HR (95% CI) for all-cause mortality per SD increase was 1.2 (1.1-1.3) for 2hPG and 1.1 (1.0-1.2) for HbA₁c. The HR for FPG <5.1 mmol/l (per SD decrease) was 2.0 (1.3-3.0); for FPG >=5.1 mmol/l (per SD increase) the HR was 1.1 (1.0-1.2). Corresponding HRs for CVD mortality were 1.2 (1.0-1.4), 1.2 (1.0-1.3), 4.0 (2.1-7.6) and 1.3 (1.1-1.4). The discriminative ability of each measure was similar; no measure substantially improved individual risk identification over traditional risk factors. Conclusions/interpretation In individuals without diagnosed diabetes, 2hPG and FPG, but not HbA₁c were significant predictors of all-cause mortality, whereas all measures were significant predictors of CVD mortality. However, these glucose measures did not substantially improve individual risk identification.
Weyl points are the crossings of linearly dispersing energy bands of three-dimensional crystals, providing the opportunity to explore a variety of intriguing phenomena such as topologically protected ...surface states and chiral anomalies. However, the lack of an ideal Weyl system in which the Weyl points all exist at the same energy and are separated from any other bands, poses a serious limitation to the further development of Weyl physics and potential applications. By experimentally characterizing a microwave photonic crystal of saddle-shaped metallic coils, we observe ideal Weyl points that are related to each other through symmetry operations. Topological surface states exhibiting helicoidal structure have also been demonstrated. Our system provides a photonic platform for exploring ideal Weyl systems and developing possible topological devices.
We describe SPINN (Straightforward Pulsar Identification using Neural Networks), a high-performance machine learning solution developed to process increasingly large data outputs from pulsar surveys. ...SPINN has been cross-validated on candidates from the southern High Time Resolution Universe (HTRU) survey and shown to identify every known pulsar found in the survey data while maintaining a false positive rate of 0.64 per cent. Furthermore, it ranks 99 per cent of pulsars among the top 0.11 per cent of candidates, and 95 per cent among the top 0.01 per cent. In conjunction with the peasoup pipeline, it has already discovered four new pulsars in a re-processing of the intermediate Galactic latitude area of HTRU, three of which have spin periods shorter than 5 ms. SPINN's ability to reduce the amount of candidates to visually inspect by up to four orders of magnitude makes it a very promising tool for future large-scale pulsar surveys. In an effort to provide a common testing ground for pulsar candidate selection tools and stimulate interest in their development, we also make publicly available the set of candidates on which SPINN was cross-validated.
‘Perytons’ are millisecond-duration transients of terrestrial origin, whose frequency-swept emission mimics the dispersion of an astrophysical pulse that has propagated through tenuous cold plasma. ...In fact, their similarity to FRB 010724 had previously cast a shadow over the interpretation of ‘fast radio bursts’ (FRBs), which otherwise appear to be of extragalactic origin. Until now, the physical origin of the dispersion-mimicking perytons had remained a mystery. We have identified strong out-of-band emission at 2.3–2.5 GHz associated with several peryton events. Subsequent tests revealed that a peryton can be generated at 1.4 GHz when a microwave oven door is opened prematurely and the telescope is at an appropriate relative angle. Radio emission escaping from microwave ovens during the magnetron shut-down phase neatly explains all of the observed properties of the peryton signals. Now that the peryton source has been identified, we furthermore demonstrate that the microwave ovens on site could not have caused FRB 010724. This and other distinct observational differences show that FRBs are excellent candidates for genuine extragalactic transients.
We report the first radio interferometric search at 843 MHz for fast transients, particularly Fast Radio Bursts (FRBs). The recently recommissioned Swinburne University of Technology's digital ...backend for the Molonglo Observatory Synthesis Telescope array (the UTMOST) with its large collecting area (18 000 m2) and wide instantaneous field of view (7.80 deg2) is expected to be an efficient tool to detect FRBs. As an interferometer it will be capable of discerning whether the FRBs are truly a celestial population. We show that UTMOST at full design sensitivity can detect an event approximately every few days. We report on two preliminary FRB surveys at about 7 per cent and 14 per cent, respectively, of the array's final sensitivity. Several pulsars have been detected via single pulses and no FRBs were discovered with pulse widths (W), in the range 655.36 μs < W < 41.9 ms and dispersion measures (DMs) in the range 100 < DM < 2000 pc cm−3. This non-detection sets a 2σ upper limit of the sky rate of not more than 1000 events sky−1 d−1 at 843 MHz down to a flux limit of 11 Jy for 1 ms FRBs. We show that this limit is consistent with previous survey limits at 1.4 GHz and 145 MHz and set a lower limit on the mean spectral index of FRBs of α > −3.2.
The discovery of topological phases has introduced new perspectives and platforms for various interesting physics originally investigated in quantum contexts and then, on an equal footing, in classic ...wave systems. As a characteristic feature, nontrivial Fermi arcs, connecting between topologically distinct Fermi surfaces, play vital roles in the classification of Dirac and Weyl semimetals, and have been observed in quantum materials very recently. However, in classical systems, no direct experimental observation of Fermi arcs in momentum space has been reported so far. Here, using near-field scanning measurements, we show the observation of photonic topological surface-state arcs connecting topologically distinct bulk states in a chiral hyperbolic metamaterial. To verify the topological nature of this system, we further observe backscattering-immune propagation of a nontrivial surface wave across a three-dimension physical step. Our results demonstrate a metamaterial approach towards topological photonics and offer a deeper understanding of topological phases in three-dimensional classical systems.Topological effects known from condensed matter physics have recently also been explored in photonic systems. Here, the authors directly observe topological surface-state arcs in momentum space by near-field scanning the surface of a chiral hyperbolic metamaterial.
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