ALBERT

Description: In recent years, millisecond-duration radio signals originating in distant galaxies appear to have been discovered in the so-called fast radio bursts. These signals are dispersed according to a precise physical law and this dispersion is a key observable quantity, which, in tandem with a redshift measurement, can be used for fundamental physical investigations. Every fast radio burst has a dispersion measurement, but none before now have had a redshift measurement, because of the difficulty in pinpointing their celestial coordinates. Here we report the discovery of a fast radio burst and the identification of a fading radio transient lasting ~6 days after the event, which we use to identify the host galaxy; we measure the galaxy's redshift to be z = 0.492 +/- 0.008. The dispersion measure and redshift, in combination, provide a direct measurement of the cosmic density of ionized baryons in the intergalactic medium of OmegaIGM = 4.9 +/- 1.3 per cent, in agreement with the expectation from the Wilkinson Microwave Anisotropy Probe, and including all of the so-called 'missing baryons'. The ~6-day radio transient is largely consistent with the radio afterglow of a short gamma-ray burst, and its existence and timescale do not support progenitor models such as giant pulses from pulsars, and supernovae. This contrasts with the interpretation of another recently discovered fast radio burst, suggesting that there are at least two classes of bursts.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Keane, E F -- Johnston, S -- Bhandari, S -- Barr, E -- Bhat, N D R -- Burgay, M -- Caleb, M -- Flynn, C -- Jameson, A -- Kramer, M -- Petroff, E -- Possenti, A -- van Straten, W -- Bailes, M -- Burke-Spolaor, S -- Eatough, R P -- Stappers, B W -- Totani, T -- Honma, M -- Furusawa, H -- Hattori, T -- Morokuma, T -- Niino, Y -- Sugai, H -- Terai, T -- Tominaga, N -- Yamasaki, S -- Yasuda, N -- Allen, R -- Cooke, J -- Jencson, J -- Kasliwal, M M -- Kaplan, D L -- Tingay, S J -- Williams, A -- Wayth, R -- Chandra, P -- Perrodin, D -- Berezina, M -- Mickaliger, M -- Bassa, C -- England -- Nature. 2016 Feb 25;530(7591):453-6. doi: 10.1038/nature17140.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Square Kilometre Array Organisation, Jodrell Bank Observatory, SK11 9DL, UK. ; Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Mail H29, PO Box 218, Victoria 3122, Australia. ; Australian Research Council Centre of Excellence for All-sky Astrophysics (CAASTRO), Australia. ; Commonwealth Science and Industrial Research Organisation (CSIRO), Astronomy and Space Science, Australia Telescope National Facility, PO Box 76, Epping, New South Wales 1710, Australia. ; International Centre for Radio Astronomy Research, Curtin University, Bentley, Western Australia 6102, Australia. ; Instituto Nazionale di Astrofisica (INAF)-Osservatorio Astronomico di Cagliari, Via della Scienza 5, I-09047 Selargius (CA), Italy. ; Research School of Astronomy and Astrophysics, Australian National University, Canberra, Australian Capital Territory 2611, Australia. ; Max-Planck-Institut fur Radioastronomie (MPIfR), Auf dem Hugel 69, D-53121 Bonn, Germany. ; Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK. ; National Radio Astronomy Observatory, Socorro, New Mexico, USA. ; Department of Astronomy, the University of Tokyo, Hongo, Tokyo 113-0033, Japan. ; National Astronomical Observatory of Japan, 2 Chome-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan. ; Department of Astronomical Science, SOKENDAI (Graduate University for the Advanced Study), Osawa, Mitaka 181-8588, Japan. ; Subaru Telescope, National Astronomical Observatory of Japan, 650 North A'ohoku Place, Hilo, Hawaii 96720, USA. ; Institute of Astronomy, Graduate School of Science, University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015, Japan. ; Kavli Institute for the Physics and Mathematics of the Universe (WPI), Institutes for Advanced Study, University of Tokyo, Kashiwa, Chiba 277-8583, Japan. ; Department of Physics, Faculty of Science and Engineering, Konan University, 8-9-1 Okamoto, Kobe, Hyogo 658-8501, Japan. ; Cahill Center for Astrophysics, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, USA. ; Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin 53201, USA. ; National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, Pune University Campus, Ganeshkhind, Pune 411 007, India. ; ASTRON, the Netherlands Institute for Radio Astronomy, Postbus 2, NL-7990 AA Dwingeloo, The Netherlands.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26911781" target="_blank"〉PubMed〈/a〉

Description: We analyse dispersion measure (DM) variations in six years of radio observations of more than 160 young pulsars, all gamma-ray candidates for the Fermi gamma-ray telescope mostly located close to the Galactic plane. DMs were fitted across 256 MHz of bandwidth for observations centred at 1.4 GHz and across three frequencies – 0.7, 1.4 and 3.1 GHz – where multifrequency observations were available. Changes in dispersion measure, dDM/d t , were calculated using a weighted linear fit across all epochs of available DMs. DM variations were detected at a 3 level in 11 pulsars, four of which were above 5: PSRs J0835–4510, J0908–4913, J1824–1945 and J1833–0827. We find that after 28 years of gradual decline, the DM of PSR J0835–4510 is now increasing. The magnitude of variations in three of the four (PSRs J0835–4510, J0908–4913 and J1833–0827) are above what models would predict for an interstellar medium (ISM) dominated by Kolmogorov turbulence. We attribute this excess as likely due to the pulsar's local environment – the supernova remnants near PSRs J0835–4510 and J1833–0827 and the pulsar wind nebula around PSR J0908–4913. Upper limits were determined for all pulsars without detectable values of dDM/d t , most limits were found to lie above the levels of variations predicted by ISM theory. We find our results to be consistent with scattering estimates from the NE2001 model along these lines of sight.

Description: We present initial results from the low-latitude Galactic plane region of the High Time Resolution Universe pulsar survey conducted at the Parkes 64-m radio telescope. We discuss the computational challenges arising from the processing of the terabyte-sized survey data. Two new radio interference mitigation techniques are introduced, as well as a partially coherent segmented acceleration search algorithm which aims to increase our chances of discovering highly relativistic short-orbit binary systems, covering a parameter space including potential pulsar–black hole binaries. We show that under a constant acceleration approximation, a ratio of data length over orbital period of 0.1 results in the highest effectiveness for this search algorithm. From the 50 per cent of data processed thus far, we have redetected 435 previously known pulsars and discovered a further 60 pulsars, two of which are fast-spinning pulsars with periods less than 30 ms. PSR J1101–6424 is a millisecond pulsar whose heavy white dwarf (WD) companion and short spin period of 5.1 ms indicate a rare example of full-recycling via Case A Roche lobe overflow. PSR J1757–27 appears to be an isolated recycled pulsar with a relatively long spin period of 17 ms. In addition, PSR J1244–6359 is a mildly recycled binary system with a heavy WD companion, PSR J1755–25 has a significant orbital eccentricity of 0.09 and PSR J1759–24 is likely to be a long-orbit eclipsing binary with orbital period of the order of tens of years. Comparison of our newly discovered pulsar sample to the known population suggests that they belong to an older population. Furthermore, we demonstrate that our current pulsar detection yield is as expected from population synthesis.

Description: Several theories exist to explain the source of the bright, millisecond duration pulses known as fast radio bursts (FRBs). If the progenitors of FRBs are non-cataclysmic, such as giant pulses from pulsars, pulsar–planet binaries, or magnetar flares, FRB emission may be seen to repeat. We have undertaken a survey of the fields of eight known FRBs from the High Time Resolution Universe survey to search for repeating pulses. Although no repeat pulses were detected the survey yielded the detection of a new FRB, described in Petroff et al. ( 2015a ). From our observations we rule out periodic repeating sources with periods P  ≤ 8.6 h and rule out sources with periods 8.6 〈  P  〈 21 h at the 90 per cent confidence level. At P  ≥ 21 h our limits fall off as ~1/ P . Dedicated and persistent observations of FRB source fields are needed to rule out repetition on longer time-scales, a task well-suited to next generation wide-field transient detectors.

Description: We present the discovery of a further five recycled pulsar systems in the mid-Galactic latitude portion of the High Time Resolution Universe survey. The pulsars have rotational periods ranging from 2 to 66 ms, and four are in binary systems with orbital periods between 10.8 h and 9 d. Three of these binary systems are particularly interesting; PSR J1227–6208 has a pulse period of 34.5 ms and the highest mass function of all pulsars with near-circular orbits. The circular orbit suggests that the companion is not another neutron star, so future timing experiments may reveal one of the heaviest white dwarfs ever found (〉1.3 M ). Timing observations of PSR J1431–4715 indicate that it is eclipsed by its companion which has a mass indicating it belongs to the redback class of eclipsing millisecond pulsars. PSR J1653–2054 has a companion with a minimum mass of only 0.08 M , placing it among the class of pulsars with low-mass companions. Unlike the majority of such systems, however, no evidence of eclipses is seen at 1.4 GHz.

Description: In this paper we identify some sub-optimal performance in algorithms that search for fast radio bursts (FRBs), which can reduce the cosmological volume probed by over 20 per cent, and result in missed discoveries and incorrect flux density and sky rate determinations. Re-calculating parameters for all of the FRBs discovered with the Parkes telescope (i.e. all of the reported FRBs bar one), we find some inconsistencies with previously determined values, e.g. FRB 010125 was approximately twice as bright as previously reported. We describe some incompleteness factors not previously considered which are important in determining accurate population statistics, e.g. accounting for fluence incompleteness the Thornton et al. all-sky rate can be re-phrased as ~2500 FRBs per sky per day above a 1.4-GHz fluence of ~2 Jy ms. Finally we make data for the FRBs easily available, along with software to analyse these.

Description: The detection of five new fast radio bursts (FRBs) found in the 1.4-GHz High Time Resolution Universe high-latitude survey at Parkes, is presented. The rate implied is 7 $^{+5}_{-3}\times 10^3$ (95 per cent) FRBs sky –1 d –1 above a fluence of 0.13 Jy ms for an FRB of 0.128 ms duration to 1.5 Jy ms for 16 ms duration. One of these FRBs has a two-component profile, in which each component is similar to the known population of single component FRBs and the two components are separated by 2.4 ± 0.4 ms. All the FRB components appear to be unresolved following deconvolution with a scattering tail and accounting for intrachannel smearing. The two-component burst, FRB 121002, also has the highest dispersion measure (1629 pc cm –3 ) of any FRB to-date. Many of the proposed models to explain FRBs use a single high-energy event involving compact objects (such as neutron-star mergers) and therefore cannot easily explain a two-component FRB. Models that are based on extreme versions of flaring, pulsing, or orbital events, however, could produce multiple component profiles. The compatibility of these models and the FRB rate implied by these detections is discussed.

Description: We present observations made with the Australia Telescope Compact Array (ATCA), the Jansky Very Large Array (JVLA) and the Giant Metre-Wave Telescope of the radio source within the galaxy WISE J071634.59–190039.2, claimed to be host of FRB 150418 by Keane et al. We have established a common flux density scale between the ATCA and JVLA observations, the main result of which is to increase the flux densities obtained by Keane et al. At a frequency of 5.5 GHz, the source has a mean flux density of 140 μJy and is variable on short time-scales with a modulation index of 0.36. Statistical analysis of the flux densities shows that the variations seen are consistent with the refractive interstellar scintillation of the weak active galactic nucleus at the centre of the galaxy. It may therefore be the case that the fast radio burst (FRB) and the galaxy are not associated. However, taking into account the rarity of highly variable sources in the radio sky, and our lack of knowledge of the progenitors of FRBs as a class, the association between WISE J071634.59–190039.2 and FRB 150418 remains a possibility.