| 1. |
- Andreoni, I., et al.
(författare)
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Follow Up of GW170817 and Its Electromagnetic Counterpart by Australian-Led Observing Programmes
- 2017
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Ingår i: Publications Astronomical Society of Australia. - : Cambridge University Press (CUP). - 1323-3580 .- 1448-6083. ; 34
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Forskningsöversikt (refereegranskat)abstract
- The discovery of the first electromagnetic counterpart to a gravitational wave signal has generated follow-up observations by over 50 facilities world-wide, ushering in the new era of multi-messenger astronomy. In this paper, we present follow-up observations of the gravitational wave event GW170817 and its electromagnetic counterpart SSS17a/DLT17ck (IAU label AT2017gfo) by 14 Australian telescopes and partner observatories as part of Australian-based and Australian-led research programs. We report early- to late-time multi-wavelength observations, including optical imaging and spectroscopy, mid-infrared imaging, radio imaging, and searches for fast radio bursts. Our optical spectra reveal that the transient source emission cooled from approximately 6 400 K to 2 100 K over a 7-d period and produced no significant optical emission lines. The spectral profiles, cooling rate, and photometric light curves are consistent with the expected outburst and subsequent processes of a binary neutron star merger. Star formation in the host galaxy probably ceased at least a Gyr ago, although there is evidence for a galaxy merger. Binary pulsars with short (100 Myr) decay times are therefore unlikely progenitors, but pulsars like PSR B1534+12 with its 2.7 Gyr coalescence time could produce such a merger. The displacement (similar to 2.2 kpc) of the binary star system from the centre of the main galaxy is not unusual for stars in the host galaxy or stars originating in the merging galaxy, and therefore any constraints on the kick velocity imparted to the progenitor are poor.
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| 2. |
- Bhat, N. D. R., et al.
(författare)
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Observations of Low-frequency Radio Emission from Millisecond Pulsars and Multipath Propagation in the Interstellar Medium
- 2018
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Ingår i: Astrophysical Journal, Supplement Series. - : American Astronomical Society. - 1538-4365 .- 0067-0049. ; 238:1
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Tidskriftsartikel (refereegranskat)abstract
- Studying the gravitational-wave sky with pulsar timing arrays (PTAs) is a key science goal for the Square Kilometre Array (SKA) and its pathfinder telescopes. With current PTAs reaching sub-microsecond timing precision, making accurate measurements of interstellar propagation effects and mitigating them effectively has become increasingly important to realize PTA goals. As these effects are much stronger at longer wavelengths, low-frequency observations are most appealing for characterizing the interstellar medium (ISM) along the sight lines toward PTA pulsars. The Murchison Widefield Array (MWA) and the Engineering Development Array (EDA), which utilizes MWA technologies, present promising opportunities for undertaking such studies, particularly for PTA pulsars located in the southern sky. Such pulsars are also the prime targets for PTA efforts planned with the South African MeerKAT, and eventually with the SKA. In this paper we report on observations of two bright southern millisecond pulsars, PSR J0437-4715 and PSR J2145-0750, made with these facilities; MWA observations sampled multiple frequencies across the 80-250 MHz frequency range, while the EDA provided direct-sampled baseband data to yield a large instantaneous usable bandwidth of similar to 200 MHz. Using these exploratory observations, we investigate various aspects relating to pulsar emission and ISM properties, such as spectral evolution of the mean pulse shape, scintillation as a function of frequency, chromaticity in interstellar dispersion, and flux density spectra at low frequencies. Systematic and regular monitoring observations will help ascertain the role of low-frequency measurements in PTA experiments, while simultaneously providing a detailed characterization of the ISM toward the pulsars, which will be useful in devising optimal observing strategies for future PTA experiments.
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| 3. |
- Pallot, J., et al.
(författare)
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Is Parkinson's disease associated with worse outcomes following hip replacement for treatment of acute hip fracture?
- 2021
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Ingår i: Acta Orthopaedica Belgica. - 0001-6462. ; 86:S 3, s. 94-101
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Tidskriftsartikel (refereegranskat)abstract
- The prevalence of Parkinson's disease (PD) is increasing. Targeted research evaluating clinical outcomes following hip arthroplasty (HR) for acute hip fractures in this high-risk group of patients is lacking. This study evaluates whether PD is associated with worse outcomes with regards to revision rate and mortality in patients who sustain hip fractures treated with total or hemiarthroplasty. Between 2005 and 2012, 1,204 patients with PD who underwent HR surgery following acute hip fracture were identified in the Swedish Hip Arthroplasty Register (SHAR). A control group was generated, with 1 :1 exact matching for potentially confounding variables. Risks of revision and mortality were compared at predetermined intervals over a six-year study period, using Kaplan-Meier and Log-rank testing. No significant differences were detected in revision rates between PD and control groups at 30 days (p=0.71), 90 days (p=0.85), one-year (p=0.51) and sixyears (p=0.40). Increased mortality was observed in the PD group at all time periods assessed. Log-rank testing identified these differences to be significantly higher at 90 days (p<0.01) and on completion of the six-year study period (p<0.001). Differences in mortality rates observed at interim periods of 30 days (p=0.06) and one year (p=0.07) were not shown to be of statistical significance. Patients with PD had increased risk for mortality following total or hemiarthroplasty after a hip fracture, however we were unable to identify an increased risk of revision. As increased incidence of hip fracture sustained by PD patients is predicted, multidisciplinary care must be prioritised to improve outcomes.
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