| 1. |
- 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.
|
|
| 2. |
- Baes, Maarten, et al.
(författare)
-
Composite biasing in Monte Carlo radiative transfer
- 2016
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 590, s. Art. no. A55-
-
Tidskriftsartikel (refereegranskat)abstract
- Biasing or importance sampling is a powerful technique in Monte Carlo radiative transfer, and can be applied in different forms to increase the accuracy and efficiency of simulations. One of the drawbacks of the use of biasing is the potential introduction of large weight factors. We discuss a general strategy, composite biasing, to suppress the appearance of large weight factors. We use this composite biasing approach for two different problems faced by current state-of-the-art Monte Carlo radiative transfer codes: the generation of photon packages from multiple components, and the penetration of radiation through high optical depth barriers. In both cases, the implementation of the relevant algorithms is trivial and does not interfere with any other optimisation techniques. Through simple test models, we demonstrate the general applicability, accuracy and efficiency of the composite biasing approach. In particular, for the penetration of high optical depths, the gain in efficiency is spectacular for the specific problems that we consider: in simulations with composite path length stretching, high accuracy results are obtained even for simulations with modest numbers of photon packages, while simulations without biasing cannot reach convergence, even with a huge number of photon packages.
|
|
| 3. |
- Camps, Peter, et al.
(författare)
-
Benchmarking the calculation of stochastic heating and emissivity of dust grains in the context of radiative transfer simulations
- 2015
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 580
-
Tidskriftsartikel (refereegranskat)abstract
- Context. Thermal emission by stochastically heated dust grains (SHGs) plays an important role in the radiative transfer (RT) problem for a dusty medium. It is therefore essential to verify that RT codes properly calculate the dust emission before studying the effects of spatial distribution and other model parameters on the simulated observables. Aims. We define an appropriate problem for benchmarking dust emissivity calculations in the context of RT simulations, specifically including the emission from SHGs. Our aim is to provide a self-contained guide for implementors of such functionality and to offer insight into the effects of the various approximations and heuristics implemented by the participating codes to accelerate the calculations. Methods. The benchmark problem definition includes the optical and calorimetric material properties and the grain size distributions for a typical astronomical dust mixture with silicate, graphite, and PAH components. It also includes a series of analytically defined radiation fields to which the dust population is to be exposed and instructions for the desired output. We processed this problem using six RT codes participating in this benchmark effort and compared the results to a reference solution computed with the publicly available dust emission code DustEM. Results. The participating codes implement different heuristics to keep the calculation time at an acceptable level.We study the effects of these mechanisms on the calculated solutions and report on the level of (dis)agreement between the participating codes. For all but the most extreme input fields, we find agreement within 10% across the important wavelength range 3 μm ≤1000 μm. Conclusions. We conclude that the relevant modules in RT codes can and do produce fairly consistent results for the emissivity spectra of SHGs. This work can serve as a reference for implementors of dust RT codes, and it will pave the way for a more extensive benchmark effort focusing on the RT aspects of the various codes.
|
|
| 4. |
- Gordon, K. D., et al.
(författare)
-
I. A 3D externally illuminated slab benchmark for dust radiative transfer
- 2017
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 603, s. A114-
-
Tidskriftsartikel (refereegranskat)abstract
- Context. The radiative transport of photons through arbitrary three-dimensional (3D) structures of dust is a challenging problem due to the anisotropic scattering of dust grains and strong coupling between different spatial regions. The radiative transfer problem in 3D is solved using Monte Carlo or Ray Tracing techniques as no full analytic solution exists for the true 3D structures. Aims. We provide the first 3D dust radiative transfer benchmark composed of a slab of dust with uniform density externally illuminated by a star. This simple 3D benchmark is explicitly formulated to provide tests of the different components of the radiative transfer problem including dust absorption, scattering, and emission. Methods. The details of the external star, the slab itself, and the dust properties are provided. This benchmark includes models with a range of dust optical depths fully probing cases that are optically thin at all wavelengths to optically thick at most wavelengths. The dust properties adopted are characteristic of the diffuse Milky Way interstellar medium. This benchmark includes solutions for the full dust emission including single photon (stochastic) heating as well as two simplifying approximations: One where all grains are considered in equilibrium with the radiation field and one where the emission is from a single effective grain with size-distribution-averaged properties. A total of six Monte Carlo codes and one Ray Tracing code provide solutions to this benchmark. Results. The solution to this benchmark is given as global spectral energy distributions (SEDs) and images at select diagnostic wavelengths from the ultraviolet through the infrared. Comparison of the results revealed that the global SEDs are consistent on average to a few percent for all but the scattered stellar flux at very high optical depths. The image results are consistent within 10%, again except for the stellar scattered flux at very high optical depths. The lack of agreement between different codes of the scattered flux at high optical depths is quantified for the first time. Convergence tests using one of the Monte Carlo codes illustrate the sensitivity of the solutions to various model parameters. Conclusions. We provide the first 3D dust radiative transfer benchmark and validate the accuracy of this benchmark through comparisons between multiple independent codes and detailed convergence tests.
|
|
| 5. |
- 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.
|
|
| 6. |
- Jarvis, M.J., et al.
(författare)
-
The discovery of a z = 0.7092 OH megamaser with the MIGHTEE survey
- 2024
-
Ingår i: Monthly Notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 529:4, s. 3484-3494
-
Tidskriftsartikel (refereegranskat)abstract
- We present the discovery of the most distant OH megamaser (OHM) to be observed in the main lines, using data from the MeerKAT International Giga-Hertz Tiered Extragalactic Exploration (MIGHTEE) survey. At a newly measured redshift of z = 0.7092, the system has strong emission in both the 1665 MHz (L ≈ 2500 L-) and 1667 MHz (L ≈ 4.5 × 104 L-) transitions, with both narrow and broad components. We interpret the broad line as a high-velocity-dispersion component of the 1667 MHz transition, with velocity v ∼330 km s-1 with respect to the systemic velocity. The host galaxy has a stellar mass of M = 2.95 × 1010 M- and a star formation rate of SFR = 371 M- yr-1, placing it ∼1.5 dex above the main sequence for star-forming galaxies at this redshift, and can be classified as an ultraluminous infrared galaxy. Alongside the optical imaging data, which exhibit evidence for a tidal tail, this suggests that the OHM arises from a system that is currently undergoing a merger, which is stimulating star formation and providing the necessary conditions for pumping the OH molecule to saturation. The OHM is likely to be lensed, with a magnification factor of ∼2.5, and perhaps more if the maser emitting region is compact and suitably offset relative to the centroid of its host galaxy's optical light. This discovery demonstrates that spectral line mapping with the new generation of radio interferometers may provide important information on the cosmic merger history of galaxies.
|
|
| 7. |
- Kamenetzky, J., et al.
(författare)
-
CARBON MONOXIDE IN THE COLD DEBRIS OF SUPERNOVA 1987A
- 2013
-
Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 773:2
-
Tidskriftsartikel (refereegranskat)abstract
- We report spectroscopic and imaging observations of rotational transitions of cold CO and SiO in the ejecta of SN1987A, the first such emission detected in a supernova remnant. In addition to line luminosities for the CO J = 1-0, 2-1, 6-5, and 7-6 transitions, we present upper limits for all other transitions up to J = 13-12, collectively measured from the Atacama Large Millimeter Array, the Atacama Pathfinder EXperiment, and the Herschel Spectral and Photometric Imaging REceiver. Simple models show the lines are emitted from at least 0.01 M-circle dot of CO at a temperature >14 K, confined within at most 35% of a spherical volume expanding at similar to 2000 km s(-1). Moreover, we locate the emission within 1 '' of the central debris. These observations, along with a partial observation of SiO, confirm the presence of cold molecular gas within supernova remnants and provide insight into the physical conditions and chemical processes in the ejecta. Furthermore, we demonstrate the powerful new window into supernova ejecta offered by submillimeter observations.
|
|
| 8. |
- 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.
|
|
| 9. |
- Zanardo, Giovanna, et al.
(författare)
-
SPECTRAL AND MORPHOLOGICAL ANALYSIS OF THE REMNANT OF SUPERNOVA 1987A WITH ALMA AND ATCA
- 2014
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 796:2
-
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.
|
|
| 10. |
- 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.
|
|
