| 1. |
- Andreoni, I., et al.
(författare)
-
Follow Up of GW170817 and Its Electromagnetic Counterpart by Australian-Led Observing Programmes
- 2017
-
Ingår i: Publications Astronomical Society of Australia. - : Cambridge University Press (CUP). - 1323-3580 .- 1448-6083. ; 34
-
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.
|
|
| 2. |
- Amiri, M., et al.
(författare)
-
Periodic activity from a fast radio burst source
- 2020
-
Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 582:7812, s. 351-355
-
Tidskriftsartikel (refereegranskat)abstract
- Fast radio bursts (FRBs) are bright, millisecond-duration radio transients originating from sources at extragalactic distances1, the origin of which is unknown. Some FRB sources emit repeat bursts, ruling out cataclysmic origins for those events2–4. Despite searches for periodicity in repeat burst arrival times on timescales from milliseconds to many days2,5–7, these bursts have hitherto been observed to appear sporadically and—although clustered8—without a regular pattern. Here we report observations of a 16.35 ± 0.15 day periodicity (or possibly a higher-frequency alias of that periodicity) from the repeating FRB 180916.J0158+65 detected by the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst Project4,9. In 38 bursts recorded from 16 September 2018 to 4 February 2020 utc, we find that all bursts arrive in a five-day phase window, and 50 per cent of the bursts arrive in a 0.6-day phase window. Our results suggest a mechanism for periodic modulation either of the burst emission itself or through external amplification or absorption, and disfavour models invoking purely sporadic processes.
|
|
| 3. |
- Kirsten, Franz, 1983, et al.
(författare)
-
A repeating fast radio burst source in a globular cluster
- 2022
-
Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 602:7898, s. 585-589
-
Tidskriftsartikel (refereegranskat)abstract
- Fast radio bursts (FRBs) are flashes of unknown physical origin1. The majority of FRBs have been seen only once, although some are known to generate multiple flashes2,3. Many models invoke magnetically powered neutron stars (magnetars) as the source of the emission4,5. Recently, the discovery6 of another repeater (FRB 20200120E) was announced, in the direction of the nearby galaxy M81, with four potential counterparts at other wavelengths6. Here we report observations that localized the FRB to a globular cluster associated with M81, where it is 2 parsecs away from the optical centre of the cluster. Globular clusters host old stellar populations, challenging FRB models that invoke young magnetars formed in a core-collapse supernova. We propose instead that FRB 20200120E originates from a highly magnetized neutron star formed either through the accretion-induced collapse of a white dwarf, or the merger of compact stars in a binary system7. Compact binaries are efficiently formed inside globular clusters, so a model invoking them could also be responsible for the observed bursts.
|
|
| 4. |
- Scholz, P., et al.
(författare)
-
Simultaneous X-Ray and Radio Observations of the Repeating Fast Radio Burst FRB similar to 180916.J0158+65
- 2020
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 901:2
-
Tidskriftsartikel (refereegranskat)abstract
- We report on simultaneous radio and X-ray observations of the repeating fast radio burst source FRB 180916.J0158+65 using the Canadian Hydrogen Intensity Mapping Experiment (CHIME), Effelsberg, and Deep Space Network (DSS-14 and DSS-63) radio telescopes and the Chandra X-ray Observatory. During 33 ks of Chandra observations, we detect no radio bursts in overlapping Effelsberg or Deep Space Network observations and a single burst during CHIME/FRB source transits. We detect no X-ray events in excess of the background during the Chandra observations. These non-detections imply a 5 sigma limit of <5 x 10(-10)erg cm(-2)for the 0.5-10 keV fluence of prompt emission at the time of the radio burst and 1.3 x 10(-9)erg cm(-2)at any time during the Chandra observations. Given the host-galaxy redshift of FRB 180916.J0158+65 (z similar to 0.034), these correspond to energy limits of <1.6 x 10(45)erg and <4 x 10(45)erg, respectively. We also place a 5 sigma limit of <8 x 10(-15)erg s(-1) cm(-2)on the 0.5-10 keV absorbed flux of a persistent source at the location of FRB 180916.J0158+65. This corresponds to a luminosity limit of <2 x 10(40)erg s(-1). Using an archival set of radio bursts from FRB 180916.J0158+65, we search for prompt gamma-ray emission in Fermi/GBM data but find no significant gamma-ray bursts, thereby placing a limit of 9 x 10(-9)erg cm(-2)on the 10-100 keV fluence. We also search Fermi/LAT data for periodic modulation of the gamma-ray brightness at the 16.35 days period of radio burst activity and detect no significant modulation. We compare these deep limits to the predictions of various fast radio burst models, but conclude that similar X-ray constraints on a closer fast radio burst source would be needed to strongly constrain theory.
|
|
| 5. |
- Meixner, Margaret, et al.
(författare)
-
Herschel and ALMA measurements of dust and molecules in supernova 1987A
- 2013
-
Ingår i: Proceedings of Science. - 1824-8039. ; Part F113823
-
Konferensbidrag (refereegranskat)abstract
- Dust production by supernovae is important in the dust life cycle of a galaxy. The explosion of SN 1987A was the nearest SN detected in the last 400 years, allowing us detailed studies of contemporary evolution of a supernova for the first time. In 2011, Matsuura et al. reported 0.4-0.7 M of dust in SN 1987A based on Herschel HERITAGE survey data, which is surprisingly large compared to prior measurements of supernovae. In this paper, we present our follow-up studies of this important discovery about SN 1987A using the Herschel Space Observatory and the Atacama Large Millimeter Array (ALMA). We highlight two important results, the detection of cold molecular gas and dust in the ejected material of SN 1987A. Our results suggest that SNe are significant producers of dust and molecules, as well as heavy elements, driving chemical evolution of galaxies.
|
|
| 6. |
- Murphy, T., et al.
(författare)
-
VAST: An ASKAP Survey for Variables and Slow Transients
- 2013
-
Ingår i: Publications of the Astronomical Society of Australia. - : Cambridge University Press (CUP). - 1323-3580 .- 1448-6083. ; 30
-
Tidskriftsartikel (refereegranskat)abstract
- The Australian Square Kilometre Array Pathfinder (ASKAP) will give us an unprecedented opportunity to investigate the transient sky at radio wavelengths. In this paper we present VAST, an ASKAP survey for Variables and Slow Transients. VAST will exploit the wide-field survey capabilities of ASKAP to enable the discovery and investigation of variable and transient phenomena from the local to the cosmological, including flare stars, intermittent pulsars, X-ray binaries, magnetars, extreme scattering events, interstellar scintillation, radio supernovae, and orphan afterglows of gamma-ray bursts. In addition, it will allow us to probe unexplored regions of parameter space where new classes of transient sources may be detected. In this paper we review the known radio transient and variable populations and the current results from blind radio surveys. We outline a comprehensive program based on a multi-tiered survey strategy to characterise the radio transient sky through detection and monitoring of transient and variable sources on the ASKAP imaging timescales of 5 s and greater. We also present an analysis of the expected source populations that we will be able to detect with VAST.
|
|
| 7. |
- Heald, G., et al.
(författare)
-
Magnetism science with the square kilometre array
- 2020
-
Ingår i: Galaxies. - : MDPI AG. - 2075-4434. ; 8:8
-
Tidskriftsartikel (refereegranskat)abstract
- The Square Kilometre Array (SKA) will answer fundamental questions about the origin, evolution, properties, and influence of magnetic fields throughout the Universe. Magnetic fields can illuminate and influence phenomena as diverse as star formation, galactic dynamics, fast radio bursts, active galactic nuclei, large-scale structure, and dark matter annihilation. Preparations for the SKA are swiftly continuing worldwide, and the community is making tremendous observational progress in the field of cosmic magnetism using data from a powerful international suite of SKA pathfinder and precursor telescopes. In this contribution, we revisit community plans for magnetism research using the SKA, in light of these recent rapid developments. We focus in particular on the impact that new radio telescope instrumentation is generating, thus advancing our understanding of key SKA magnetism science areas, as well as the new techniques that are required for processing and interpreting the data. We discuss these recent developments in the context of the ultimate scientific goals for the SKA era.
|
|
| 8. |
- Weltman, A., et al.
(författare)
-
Fundamental physics with the Square Kilometre Array
- 2020
-
Ingår i: Publications Astronomical Society of Australia. - : CAMBRIDGE UNIV PRESS. - 1323-3580 .- 1448-6083. ; 37
-
Forskningsöversikt (refereegranskat)abstract
- The Square Kilometre Array (SKA) is a planned large radio interferometer designed to operate over a wide range of frequencies, and with an order of magnitude greater sensitivity and survey speed than any current radio telescope. The SKA will address many important topics in astronomy, ranging from planet formation to distant galaxies. However, in this work, we consider the perspective of the SKA as a facility for studying physics. We review four areas in which the SKA is expected to make major contributions to our understanding of fundamental physics: cosmic dawn and reionisation; gravity and gravitational radiation; cosmology and dark energy; and dark matter and astroparticle physics. These discussions demonstrate that the SKA will be a spectacular physics machine, which will provide many new breakthroughs and novel insights on matter, energy, and spacetime.
|
|
| 9. |
- Indebetouw, R., et al.
(författare)
-
DUST PRODUCTION AND PARTICLE ACCELERATION IN SUPERNOVA 1987A REVEALED WITH ALMA
- 2014
-
Ingår i: The Astrophysical Journal Letters. - : Institute of Physics (IOP). - 2041-8205. ; 782:1, s. L2-
-
Tidskriftsartikel (refereegranskat)abstract
- Supernova (SN) explosions are crucial engines driving the evolution of galaxies by shock heating gas, increasing the metallicity, creating dust, and accelerating energetic particles. In 2012 we used the Atacama Large Millimeter/Submillimeter Array to observe SN 1987A, one of the best-observed supernovae since the invention of the telescope. We present spatially resolved images at 450 mu m, 870 mu m, 1.4 mm, and 2.8 mm, an important transition wavelength range. Longer wavelength emission is dominated by synchrotron radiation from shock-accelerated particles, shorter wavelengths by emission from the largest mass of dust measured in a supernova remnant (>0.2 M-circle dot). For the first time we show unambiguously that this dust has formed in the inner ejecta (the cold remnants of the exploded star's core). The dust emission is concentrated at the center of the remnant, so the dust has not yet been affected by the shocks. If a significant fraction survives, and if SN 1987A is typical, supernovae are important cosmological dust producers.
|
|
| 10. |
- Indebetouw, R., et al.
(författare)
-
DUST PRODUCTION AND PARTICLE ACCELERATION IN SUPERNOVA 1987A REVEALED WITH ALMA
- 2014
-
Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 782:1, s. 6-
-
Tidskriftsartikel (refereegranskat)abstract
- Supernova (SN) explosions are crucial engines driving the evolution of galaxies by shock heating gas, increasing the metallicity, creating dust, and accelerating energetic particles. In 2012 we used the Atacama Large Millimeter/Submillimeter Array to observe SN 1987A, one of the best-observed supernovae since the invention of the telescope. We present spatially resolved images at 450 mu m, 870 mu m, 1.4 mm, and 2.8 mm, an important transition wavelength range. Longer wavelength emission is dominated by synchrotron radiation from shock-accelerated particles, shorter wavelengths by emission from the largest mass of dust measured in a supernova remnant (>0.2 M-circle dot). For the first time we show unambiguously that this dust has formed in the inner ejecta (the cold remnants of the exploded star's core). The dust emission is concentrated at the center of the remnant, so the dust has not yet been affected by the shocks. If a significant fraction survives, and if SN 1987A is typical, supernovae are important cosmological dust producers.
|
|
| 11. |
- Oppermann, N., et al.
(författare)
-
Estimating extragalactic Faraday rotation
- 2015
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 575
-
Tidskriftsartikel (refereegranskat)abstract
- Observations of Faraday rotation for extragalactic sources probe magnetic fields both inside and outside the Milky Way. Building on our earlier estimate of the Galactic contribution, we set out to estimate the extragalactic contributions. We discuss the problems involved; in particular, we point out that taking the difference between the observed values and the Galactic foreground reconstruction is not a good estimate for the extragalactic contributions. We point out a degeneracy between the contributions to the observed values due to extragalactic magnetic fields and observational noise and comment on the dangers of over-interpreting an estimate without taking into account its uncertainty information. To overcome these difficulties, we develop an extended reconstruction algorithm based on the assumption that the observational uncertainties are accurately described for a subset of the data, which can overcome the degeneracy with the extragalactic contributions. We present a probabilistic derivation of the algorithm and demonstrate its performance using a simulation, yielding a high quality reconstruction of the Galactic Faraday rotation foreground, a precise estimate of the typical extragalactic contribution, and a well-defined probabilistic description of the extragalactic contribution for each data point. We then apply this reconstruction technique to a catalog of Faraday rotation observations for extragalactic sources. The analysis is done for several different scenarios, for which we consider the error bars of different subsets of the data to accurately describe the observational uncertainties. By comparing the results, we argue that a split that singles out only data near the Galactic poles is the most robust approach. We find that the dispersion of extragalactic contributions to observed Faraday depths is most likely lower than 7 rad/m(2), in agreement with earlier results, and that the extragalactic contribution to an individual data point is poorly constrained by the data in most cases.
|
|
| 12. |
- Zanardo, G., et al.
(författare)
-
Spectral and Morphological Analysis of the Remnant of Supernova 1987A with ALMA and ATCA
- 2014
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 796:2, s. Art. no. 82-
-
Tidskriftsartikel (refereegranskat)abstract
- We present a comprehensive spectral and morphological analysis of the remnant of supernova (SN) 1987A with the Australia Telescope Compact Array (ATCA) and the Atacama Large Millimeter/submillimeter Array (ALMA). The non-thermal and thermal components of the radio emission are investigated in images from 94 to 672 GHz (lambda 3.2 mm to 450 mu m), with the assistance of a high-resolution 44 GHz synchrotron template from the ATCA, and a dust template from ALMA observations at 672 GHz. An analysis of the emission distribution over the equatorial ring in images from 44 to 345 GHz highlights a gradual decrease of the east-to-west asymmetry ratio with frequency. We attribute this to the shorter synchrotron lifetime at high frequencies. Across the transition from radio to far infrared, both the synchrotron/dust-subtracted images and the spectral energy distribution (SED) suggest additional emission beside the main synchrotron component (S-nu proportional to nu(-0.73)) and the thermal component originating from dust grains at T similar to 22 K. This excess could be due to free-free flux or emission from grains of colder dust. However, a second flat-spectrum synchrotron component appears to better fit the SED, implying that the emission could be attributed to a pulsar wind nebula (PWN). The residual emission is mainly localized west of the SN site, as the spectral analysis yields -0.4 less than or similar to alpha less than or similar to -0.1 across the western regions, with alpha similar to 0 around the central region. If there is a PWN in the remnant interior, these data suggest that the pulsar may be offset westward from the SN position.
|
|
| 13. |
- Abellán, F. J., et al.
(författare)
-
Very Deep inside the SN 1987A Core Ejecta : Molecular Structures Seen in 3D
- 2017
-
Ingår i: Astrophysical Journal Letters. - : Institute of Physics Publishing. - 2041-8205 .- 2041-8213. ; 842:2
-
Tidskriftsartikel (refereegranskat)abstract
- Most massive stars end their lives in core-collapse supernova explosions and enrich the interstellar medium with explosively nucleosynthesized elements. Following core collapse, the explosion is subject to instabilities as the shock propagates outward through the progenitor star. Observations of the composition and structure of the innermost regions of a core-collapse supernova provide a direct probe of the instabilities and nucleosynthetic products. SN 1987A in the Large Magellanic Cloud is one of very few supernovae for which the inner ejecta can be spatially resolved but are not yet strongly affected by interaction with the surroundings. Our observations of SN 1987A with the Atacama Large Millimeter/submillimeter Array are of the highest resolution to date and reveal the detailed morphology of cold molecular gas in the innermost regions of the remnant. The 3D distributions of carbon and silicon monoxide (CO and SiO) emission differ, but both have a central deficit, or torus-like distribution, possibly a result of radioactive heating during the first weeks ("nickel heating"). The size scales of the clumpy distribution are compared quantitatively to models, demonstrating how progenitor and explosion physics can be constrained.
|
|
| 14. |
- Heald, G., et al.
(författare)
-
Magnetic Field Tomography in Nearby Galaxies with the Square Kilometre Array
- 2015
-
Ingår i: Proceedings of Science. - 1824-8039. ; 9-13-June-2014
-
Konferensbidrag (refereegranskat)abstract
- Magnetic fields play an important role in shaping the structure and evolution of the interstellarmedium (ISM) of galaxies, but the details of this relationship remain unclear. With SKA1, the 3Dstructure of galactic magnetic fields and its connection to star formation will be revealed. A highlysensitive probe of the internal structure of the magnetoionized ISM is the partial depolarizationof synchrotron radiation from inside the volume. Different configurations of magnetic field andionized gas within the resolution element of the telescope lead to frequency-dependent changesin the observed degree of polarization. The results of spectro-polarimetric observations are tiedto physical structure in the ISM through comparison with detailed modeling, supplemented withthe use of new analysis techniques that are being actively developed and studied within the communitysuch as Rotation Measure Synthesis. The SKA will enable this field to come into its ownand begin the study of the detailed structure of the magnetized ISM in a sample of nearby galaxies,thanks to its extraordinary wideband capabilities coupled with the combination of excellentsurface brightness sensitivity and angular resolution.
|
|
| 15. |
- Alp, Dennis, et al.
(författare)
-
The 30 Year Search for the Compact Object in SN 1987A
- 2018
-
Ingår i: Astrophysical Journal. - : Institute of Physics Publishing (IOPP). - 0004-637X .- 1538-4357. ; 864:2
-
Tidskriftsartikel (refereegranskat)abstract
- Despite more than 30 years of searching, the compact object in Supernova (SN) 1987A has not yet been detected. We present new limits on the compact object in SN 1987A using millimeter, near-infrared, optical, ultraviolet, and X-ray observations from ALMA, VLT, HST, and Chandra. The limits are approximately 0.1 mJy (0.1 x 10(-26) erg s(-1) cm(-2) Hz(-1)) at 213 GHz, 1 L-circle dot (6 x 10(-29) erg s(-1) cm(-2) Hz(-1)) in the optical if our line of sight is free of ejecta dust, and 10(36) erg s(-1) (2 x 10(-30) erg s(-1) cm(-2) Hz(-1) ) in 2-10 keV X-rays. Our X-ray limits are an order of magnitude less constraining than previous limits because we use a more realistic ejecta absorption model based on three-dimensional neutrino-driven SN explosion models. The allowed bolometric luminosity of the compact object is 22 L-circle dot if our line of sight is free of ejecta dust, or 138L(circle dot) if dust-obscured. Depending on assumptions, these values limit the effective temperature of a neutron star (NS) to <4-8 MK and do not exclude models, which typically are in the range 3-4 MK. For the simplest accretion model, the accretion rate for an efficiency 77 is limited to <10(-11) eta(-1) M-circle dot yr(-1), which excludes most predictions. For pulsar activity modeled by a rotating magnetic dipole in vacuum, the limit on the magnetic field strength (B) for a given spin period (P) is B less than or similar to 10(14) P-2 G s(-2), which firmly excludes pulsars comparable to the Crab. By combining information about radiation reprocessing and geometry, we infer that the compact object is a dust-obscured thermally emitting NS, which may appear as a region of higher-temperature ejecta dust emission.
|
|
