| 1. |
- Marcote, B., et al.
(författare)
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A repeating fast radio burst source localized to a nearby spiral galaxy
- 2020
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 577:7789, s. 190-194
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Tidskriftsartikel (refereegranskat)abstract
- Fast radio bursts (FRBs) are brief, bright, extragalactic radio flashes1,2. Their physical origin remains unknown, but dozens of possible models have been postulated3. Some FRB sources exhibit repeat bursts4–7. Although over a hundred FRB sources have been discovered8, only four have been localized and associated with a host galaxy9–12, and just one of these four is known to emit repeating FRBs9. The properties of the host galaxies, and the local environments of FRBs, could provide important clues about their physical origins. The first known repeating FRB, however, was localized to a low-metallicity, irregular dwarf galaxy, and the apparently non-repeating sources were localized to higher-metallicity, massive elliptical or star-forming galaxies, suggesting that perhaps the repeating and apparently non-repeating sources could have distinct physical origins. Here we report the precise localization of a second repeating FRB source6, FRB 180916.J0158+65, to a star-forming region in a nearby (redshift 0.0337 ± 0.0002) massive spiral galaxy, whose properties and proximity distinguish it from all known hosts. The lack of both a comparably luminous persistent radio counterpart and a high Faraday rotation measure6 further distinguish the local environment of FRB 180916.J0158+65 from that of the single previously localized repeating FRB source, FRB 121102. This suggests that repeating FRBs may have a wide range of luminosities, and originate from diverse host galaxies and local environments.
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| 2. |
- Chomiuk, Laura, et al.
(författare)
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Classical Novae at Radio Wavelengths
- 2021
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Ingår i: Astrophysical Journal Supplement Series. - : American Astronomical Society. - 0067-0049 .- 1538-4365. ; 257:2
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Tidskriftsartikel (refereegranskat)abstract
- We present radio observations (1-40 GHz) for 36 classical novae, representing data from over five decades compiled from the literature, telescope archives, and our own programs. Our targets display a striking diversity in their optical parameters (e.g., spanning optical fading timescales, t (2) = 1-263 days), and we find a similar diversity in the radio light curves. Using a brightness temperature analysis, we find that radio emission from novae is a mixture of thermal and synchrotron emission, with nonthermal emission observed at earlier times. We identify high brightness temperature emission (T ( B ) > 5 x 10(4) K) as an indication of synchrotron emission in at least nine (25%) of the novae. We find a class of synchrotron-dominated novae with mildly evolved companions, exemplified by V5589 Sgr and V392 Per, that appear to be a bridge between classical novae with dwarf companions and symbiotic binaries with giant companions. Four of the novae in our sample have two distinct radio maxima (the first dominated by synchrotron and the later by thermal emission), and in four cases the early synchrotron peak is temporally coincident with a dramatic dip in the optical light curve, hinting at a common site for particle acceleration and dust formation. We publish the light curves in a machine-readable table and encourage the use of these data by the broader community in multiwavelength studies and modeling efforts.
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| 3. |
- Finzell, Thomas, et al.
(författare)
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A Detailed Observational Analysis of V1324 Sco, the Most Gamma-Ray-luminous Classical Nova to Date
- 2018
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 852:2
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Tidskriftsartikel (refereegranskat)abstract
- It has recently been discovered that some, if not all, classical novae emit GeV gamma-rays during outburst, but the mechanisms involved in the production ofgamma-rays are still not well understood. We present here a comprehensive multiwavelength data set - from radio to X-rays - for the most gamma-ray-luminous classical nova to date, V1324 Sco. Using this data set, we show that V1324 Sco is a canonical dusty Fe ii-type nova, with a maximum ejecta velocity of 2600 km s-1 and an ejecta mass of a few × 10-5 M⊙. There is also evidence for complex shock interactions, including a double-peaked radio light curve which shows high brightness temperatures at early times. To explore why V1324 Sco was so gamma-ray luminous, we present a model of the nova ejecta featuring strong internal shocks and find that higher gamma-ray luminosities result from higher ejecta velocities and/or mass-loss rates. Comparison of V1324 Sco with other gamma-ray-detected novae does not show clear signatures of either, and we conclude that a larger sample of similarly well-observed novae is needed to understand the origin and variation of gamma-rays in novae.
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| 4. |
- Chomiuk, L., et al.
(författare)
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Binary orbits as the driver of gamma-ray emission and mass ejection in classical novae
- 2014
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 514:7522, s. 339-
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Tidskriftsartikel (refereegranskat)abstract
- Classical novae are the most common astrophysical thermonuclear explosions, occurring on the surfaces of white dwarf stars accreting gas from companions in binary star systems(1). Novae typically expel about 10(-4) solar masses of material at velocities exceeding 1,000 kilometres per second. However, the mechanism of mass ejection in novae is poorly understood, and could be dominated by the impulsive flash of thermonuclear energy(2), prolonged optically thick winds(3) or binary interaction with the nova envelope(4). Classical novae are now routinely detected at gigaelectronvolt gamma-ray wavelengths(5), suggesting that relativistic particles are accelerated by strong shocks in the ejecta. Here we report high-resolution radio imaging of the gamma-ray-emitting nova V959 Mon. We find that its ejecta were shaped by the motion of the binary system: some gas was expelled rapidly along the poles as a wind from the white dwarf, while denser material drifted out along the equatorial plane, propelled by orbital motion(6,7). At the interface between the equatorial and polar regions, we observe synchrotron emission indicative of shocks and relativistic particle acceleration, thereby pinpointing the location of gamma-ray production. Binary shaping of the nova ejecta and associated internal shocks are expected to be widespread among novae(8), explaining why many novae are gamma-ray emitters(5).
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| 5. |
- Yang, Jun, 1979, et al.
(författare)
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VLBI detection of the internal shocks in nova V959 Mon
- 2015
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Ingår i: Proceedings of Science. - Trieste, Italy : Sissa Medialab. - 1824-8039.
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Konferensbidrag (refereegranskat)abstract
- V959 Mon is a classical nova detected at GeV γ-ray wavelengths on 2012 June 19. While classicalnovae are now routinely detected in gamma-rays, the origin of the shocks that produce relativisticparticles has remained unknown. We carried out electronic European VLBI Network (e-EVN)observations that revealed a pair of compact synchrotron emission features in V959 Mon on 2012Sep 18. Since synchrotron emission requires strong shocks as well, we identify these features asthe location where the gamma rays were produced. We also detected the extended ejecta in thefollow-up EVN observations. They expanded much faster in East-West direction than the compact knots detected in the aforementioned e-EVN measurements. By comparing the VLBI results with lower resolution images obtained using e-MERLIN and the VLA – as reported by Chomiuk et al.[4] – it appears that 1) influenced by the binary orbit, the nova ejecta was highly asymmetric with a dense and slow outflow in the equatorial plane and low-density and faster ejecta along the poles; and 2) the VLBI knots were related to shocks formed in the interaction region of these outflows.
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