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.
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.
We describe a 22-yr survey for variable and transient radio sources, performed with archival images taken with the Molonglo Observatory Synthesis Telescope (MOST). This survey covers 2776 deg2 of the ...sky south of δ < −30° at an observing frequency of 843 MHz, an angular resolution of 45 × 45 cosec | δ | arcsec2 and a sensitivity of 5σ≥ 14 mJy beam−1. We describe a technique to compensate for image gain error, along with statistical techniques to check and classify variability in a population of light curves, with applicability to any image-based radio variability survey. Among radio light curves for almost 30 000 sources, we present 53 highly variable sources and 15 transient sources. Only three of the transient sources, and none of the variable sources, have been previously identified as transient or variable. Many of our variable sources are suspected scintillating active galactic nuclei. We have identified three variable sources and one transient source that are likely to be associated with star-forming galaxies at z≃ 0.05, but whose implied luminosity is higher than the most luminous known radio supernova (SN1979C) by an order of magnitude. We also find a class of variable and transient source with no optical counterparts.
We present the first results of coordinated multiwavelength observations of the Galactic black hole GX 339-4 in a canonical low/hard state, obtained during its 2004 outburst. XMM-Newton observed the ...source for two revolutions, or approximately 280 ks; RXTE monitored the source throughout this long stare. The resulting data offer the best view yet obtained of the inner accretion flow geometry in the low/hard state, which is thought to be analogous to the geometry in low-luminosity active galactic nuclei. The XMM-Newton spectra clearly reveal the presence of a cool accretion disk component and a relativistic Fe K emission line. The results of fits made to both components strongly suggest that a standard thin disk remains at or near to the innermost stable circular orbit, at least in bright phases of the low/hard state. These findings indicate that potential links between the inner disk radius and the onset of a steady compact jet, and the paradigm of a radially recessed disk in the low/hard state, do not hold universally. The results of our observations can best be explained if a standard thin accretion disk fuels a corona that is closely related to, or consistent with, the base of a compact jet. In a brief examination of archival data, we show that Cygnus X-1 supports this picture of the low/hard state. We discuss our results within the context of disk-jet connections and prevailing models for accretion onto black holes.
We present a complete sample of megaparsec-sized double radio sources compiled from the Sydney University Molonglo Sky Survey. Almost complete redshift information has been obtained for the sample. ...The sample has the following defining criteria: Galactic latitude > 125, declination d < -50DG, and angular size > 5'. All the sources have a projected linear size larger than 0.7 Mpc (assuming H0 = 71 km s-1 Mpc-1). The sample is chosen from a region of the sky covering 2100 deg2. In this paper we present 843 MHz radio images of the extended radio morphologies made using the Molonglo Observatory Synthesis Telescope, higher resolution radio observations of any compact radio structures using the Australia Telescope Compact Array, and low-resolution optical spectra of the host galaxies from the 2.3 m Australian National University telescope at Siding Spring Observatory. The sample presented here is the first in the southern hemisphere and significantly enhances the database of known giant radio sources. The giant radio sources with linear size exceeding 0.7 Mpc have an abundance of (215 Mpc)-3 at the sensitivity of the survey. In the low-redshift universe, the survey may be suggesting the possibility that giant radio sources with relict lobes are more numerous than giant sources in which beams from the center currently energize the lobes.
We present the first data release from the second epoch Molonglo Galactic Plane Survey (MGPS-2). MGPS-2 was carried out with the Molonglo Observatory Synthesis Telescope at a frequency of 843 MHz and ...with a restoring beam of 45 × 45 arcsec2, making it the highest resolution large-scale radio survey of the southern Galactic plane. It covers the range |b| < 10° and 245° < l < 365°, and is the Galactic counterpart to the Sydney University Molonglo Sky Survey (SUMSS) which covers the whole southern sky with δ≤−30° (|b| > 10°). In this paper, we present the MGPS-2 compact source catalogue. The catalogue has 48 850 sources above a limiting peak brightness of 10 mJy beam−1. Positions in the catalogue are accurate to 1–2 arcsec. A full catalogue including extended sources is in preparation. We have carried out an analysis of the compact source density across the Galactic plane and find that the source density is not statistically higher than the density expected from the extragalactic source density alone. We also present version 2.0 of the SUMSS image data and catalogue which is now available online. The data consist of 629 4.3°× 4.3° mosaic images covering the 8100 deg2 of sky with δ≤−30° and |b| > 10°. The catalogue contains 210 412 radio sources to a limiting peak brightness of 6 mJy beam−1 at δ≤−50° and 10 mJy beam−1 at δ > −50°. We describe the updates and improvements made to the SUMSS cataloguing process.
Abstract
We present an overview and the first results from a large-scale pulsar timing programme that is part of the UTMOST project at the refurbished Molonglo Observatory Synthesis Radio Telescope ...(MOST) near Canberra, Australia. We currently observe more than 400 mainly bright southern radio pulsars with up to daily cadences. For 205 (8 in binaries, 4 millisecond pulsars), we publish updated timing models, together with their flux densities, flux density variability, and pulse widths at 843 MHz, derived from observations spanning between 1.4 and 3 yr. In comparison with the ATNF pulsar catalogue, we improve the precision of the rotational and astrometric parameters for 123 pulsars, for 47 by at least an order of magnitude. The time spans between our measurements and those in the literature are up to 48 yr, which allow us to investigate their long-term spin-down history and to estimate proper motions for 60 pulsars, of which 24 are newly determined and most are major improvements. The results are consistent with interferometric measurements from the literature. A model with two Gaussian components centred at 139 and 463 km s−1 fits the transverse velocity distribution best. The pulse duty cycle distributions at 50 and 10 per cent maximum are best described by lognormal distributions with medians of 2.3 and 4.4 per cent, respectively. We discuss two pulsars that exhibit spin-down rate changes and drifting subpulses. Finally, we describe the autonomous observing system and the dynamic scheduler that has increased the observing efficiency by a factor of 2–3 in comparison with static scheduling.
This paper is the second in a series describing the Sydney University Molonglo Sky Survey (SUMSS) being carried out at 843 MHz with the Molonglo Observatory Synthesis Telescope (MOST). The survey ...will consist of ∼590 4.3°× 4.3° mosaic images with 45 × 45 cosec|δ| arcsec2 resolution, and a source catalogue. In this paper we describe the initial release (version 1.0) of the source catalogue consisting of 107 765 radio sources made by fitting elliptical Gaussians in 271 SUMSS 4.3°× 4.3° mosaics to a limiting peak brightness of 6 mJy beam−1 at δ≤−50° and 10 mJy beam−1 at δ > −50°. The catalogue covers approximately 3500 deg2 of the southern sky with δ≤−30°, about 43 per cent of the total survey area. Positions in the catalogue are accurate to within 1–2 arcsec for sources with peak brightness A843≥ 20 mJy beam−1 and are always better than 10 arcsec. The internal flux density scale is accurate to within 3 per cent. Image artefacts have been classified using a decision tree, which correctly identifies and rejects spurious sources in over 96 per cent of cases. Analysis of the catalogue shows that it is highly uniform and is complete to 8 mJy at δ≤−50° and 18 mJy at δ > −50°. In this release of the catalogue about 7000 sources are found in the overlap region with the National Radio Astronomy Observatories Very Large Array Sky Survey at 1.4 GHz. We calculate a median spectral index of α=−0.83 between 1.4 GHz and 843 MHz. This version of the catalogue will be released via the World Wide Web with future updates as new mosaics are released.
Of the 228 sources in the Molonglo Southern 4 Jy sample (MS4), the 133 with angular sizes <35'' have been imaged at 5 GHz at 2''-4'' resolution with the Australia Telescope Compact Array. More than ...90% of the sample has been reliably optically identified, either on the plates of the UK Schmidt Southern Sky Survey or on R-band CCD images made with the Anglo-Australian Telescope. A subsample of 137 sources, the SMS4, defined to be a close southern equivalent of the northern 3CRR sample, was found to have global properties mostly consistent with the northern sample. Linear sizes of MS4 galaxies and quasars were found to be consistent with galaxy-quasar unification models of orientation and evolution.
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