| 1. |
- Horesh, Assaf, et al.
(författare)
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A Non-equipartition Shock Wave Traveling in a Dense Circumstellar Environment around SN 2020oi
- 2020
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 903:2
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Tidskriftsartikel (refereegranskat)abstract
- We report the discovery and panchromatic follow-up observations of the young Type Ic supernova (SN Ic) SN 2020oi in M100, a grand-design spiral galaxy at a mere distance of 14 Mpc. We followed up with observations at radio, X-ray, and optical wavelengths from only a few days to several months after explosion. The optical behavior of the supernova is similar to those of other normal SNe Ic. The event was not detected in the X-ray band but our radio observations revealed a bright mJy source (L-nu approximate to 1.2 x 10(27) erg s(-1) Hz(-1)). Given the relatively small number of stripped envelope SNe for which radio emission is detectable, we used this opportunity to perform a detailed analysis of the comprehensive radio data set we obtained. The radio-emitting electrons initially experience a phase of inverse Compton cooling, which leads to steepening of the spectral index of the radio emission. Our analysis of the cooling frequency points to a large deviation from equipartition at the level of epsilon(e)/epsilon(B) greater than or similar to 200, similar to a few other cases of stripped envelope SNe. Our modeling of the radio data suggests that the shock wave driven by the SN ejecta into the circumstellar matter (CSM) is moving at similar to 3 x 10(4) km s(-1). Assuming a constant mass loss from the stellar progenitor, we find that the mass-loss rate is (M)over dot approximate to 1.4 x 10(-4) M-circle dot yr(-1) for an assumed wind velocity of 1000 km s(-1). The temporal evolution of the radio emission suggests a radial CSM density structure steeper than the standard r(-2).
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| 2. |
- Kool, Erik C., et al.
(författare)
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A radio-detected type Ia supernova with helium-rich circumstellar material
- 2023
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Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 617:7961, s. 477-482
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Tidskriftsartikel (refereegranskat)abstract
- Type Ia supernovae (SNe Ia) are thermonuclear explosions of degenerate white dwarf stars destabilized by mass accretion from a companion star1, but the nature of their progenitors remains poorly understood. A way to discriminate between progenitor systems is through radio observations; a non-degenerate companion star is expected to lose material through winds2 or binary interaction3 before explosion, and the supernova ejecta crashing into this nearby circumstellar material should result in radio synchrotron emission. However, despite extensive efforts, no type Ia supernova (SN Ia) has ever been detected at radio wavelengths, which suggests a clean environment and a companion star that is itself a degenerate white dwarf star4,5. Here we report on the study of SN 2020eyj, a SN Ia showing helium-rich circumstellar material, as demonstrated by its spectral features, infrared emission and, for the first time in a SN Ia to our knowledge, a radio counterpart. On the basis of our modelling, we conclude that the circumstellar material probably originates from a single-degenerate binary system in which a white dwarf accretes material from a helium donor star, an often proposed formation channel for SNe Ia (refs. 6,7). We describe how comprehensive radio follow-up of SN 2020eyj-like SNe Ia can improve the constraints on their progenitor systems.
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| 3. |
- Lundqvist, Peter, et al.
(författare)
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The Deepest Radio Observations of Nearby SNe Ia : Constraining Progenitor Types and Optimizing Future Surveys
- 2020
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 890:2
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Tidskriftsartikel (refereegranskat)abstract
- We report deep radio observations of nearby Type Ia supernovae (SNe Ia) with the electronic Multi-Element Radio Linked Interferometer Network and the Australia Telescope Compact Array. No detections were made. With standard assumptions for the energy densities of relativistic electrons going into a power-law energy distribution and the magnetic field strength (epsilon(e) = epsilon(B)=.0.1), we arrive at upper limits on mass-loss rate for the progenitor system of SN.2013dy.(SN 2016coj, SN 2018gv, SN 2018pv, SN 2019np) of M less than or similar to 12 (2.8, 1.3, 2.1, 1.7) x 10(-8) M-circle dot yr(-1) (v(w)/100 km s-(1)), where v(w) is the wind speed of the mass loss. To SN.2016coj, SN 2018gv, SN 2018pv, and SN 2019np we add radio data for 17 other nearby SNe.Ia and model their nondetections. With the same model as described, all 21 SNe Ia have M less than or similar to 4 x 10(-8) M-circle dot yr(-1) (v(w)/ 100 km s(-1)). We compare those limits with the expected mass-loss rates in different single-degenerate progenitor scenarios. We also discuss how information on oe and oB can be obtained from late observations of SNe.Ia and the youngest SN.Ia remnant detected in radio, G1.9+0.3, as well as strippedenvelope core-collapse SNe. We highlight SN.2011dh and argue for epsilon e approximate to 0.1 and epsilon(B) approximate to 0.0033. Finally, we discuss strategies to observe at radio frequencies to maximize the chance of detection, given the time since explosion, the distance to the SN, and the telescope sensitivity.
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| 4. |
- Venkattu, Deepika, et al.
(författare)
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Subarcsecond-resolution Imaging of M51 with the International LOFAR Telescope
- 2023
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 953:2
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Tidskriftsartikel (refereegranskat)abstract
- We present an International LOFAR Telescope (ILT) subarcsecond-resolution image of the nearby galaxy M51 with a beam size of 0436 × 0366 and rms of 46 μJy. We compare this image with a European VLBI Network study of M51 and discuss the supernovae in this galaxy, which have not yet been probed at these low radio frequencies. We find a flux density of 0.97 mJy for SN 2011dh in the ILT image, which is about five times smaller than the flux density reported by the LOFAR Two-metre Sky Survey (LoTSS) at 6'' resolution using the same data set without the international stations. This difference makes evident the need for LOFAR international baselines to reliably obtain flux density measurements of compact objects in nearby galaxies. Our LOFAR flux density measurement of SN 2011dh directly translates into fitting the radio light curves for the supernova and constraining the mass-loss rates of the progenitor star. We do not detect two other supernovae in the same galaxy, SN 1994I and SN 2005cs, and our observations place limits on the evolution of both supernovae at radio wavelengths. We also discuss the radio emission from the center of M51, in which we detect the active galactic nucleus and other parts of the nuclear emission in the galaxy, with a possible detection of Component N. We discuss a few other sources, including the detection of a high-mass X-ray binary not detected by LoTSS but with a flux density in the ILT image that matches well with higher-frequency catalogs.
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