| 1. |
- Soderberg, A. M., et al.
(författare)
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PANCHROMATIC OBSERVATIONS OF SN 2011dh POINT TO A COMPACT PROGENITOR STAR
- 2012
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 752:2, s. 78-
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Tidskriftsartikel (refereegranskat)abstract
- We report the discovery and detailed monitoring of X-ray emission associated with the Type IIb SN 2011dh using data from the Swift and Chandra satellites, placing it among the best-studied X-ray supernovae (SNe) to date. We further present millimeter and radio data obtained with the Submillimeter Array, the Combined Array for Research in Millimeter-wave Astronomy, and the Expanded Very Large Array during the first three weeks after explosion. Combining these observations with early optical photometry, we show that the panchromatic data set is well described by non-thermal synchrotron emission (radio/mm) with inverse Compton scattering (X-ray) of a thermal population of optical photons. In this scenario, the shock partition fractions deviate from equipartition by a factor, (epsilon(e)/epsilon(B)) similar to 30. We derive the properties of the shock wave and the circumstellar environment and find a time-averaged shock velocity of (v) over bar approximate to 0.1c and a progenitor mass-loss rate of (M) over dot approximate to 6x10(-5) M-circle dot yr(-1) (for an assumed wind velocity, v(w) = 1000 km s(-1)). We show that these properties are consistent with the sub-class of Type IIb SNe characterized by compact progenitors (Type cIIb) and dissimilar from those with extended progenitors (Type eIIb). Furthermore, we consider the early optical emission in the context of a cooling envelope model to estimate a progenitor radius of R-* approximate to 10(11) cm, in line with the expectations for a Type cIIb SN. Together, these diagnostics are difficult to reconcile with the extended radius of the putative yellow supergiant progenitor star identified in archival Hubble Space Telescope observations, unless the stellar density profile is unusual. Finally, we searched for the high-energy shock breakout pulse using X-ray and gamma-ray observations obtained during the purported explosion date range. Based on the compact radius of the progenitor, we estimate that the shock breakout pulse was detectable with current instruments but likely missed due to their limited temporal/spatial coverage. Future all-sky missions will regularly detect shock breakout emission from compact SN progenitors enabling prompt follow-up observations with sensitive multi-wavelength facilities.
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| 2. |
- Krauss, M. I., et al.
(författare)
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EXPANDED VERY LARGE ARRAY OBSERVATIONS OF THE RADIO EVOLUTION OF SN 2011dh
- 2012
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Ingår i: ASTROPHYSICAL JOURNAL LETTERS. - 2041-8205. ; 750:2, s. L40-
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Tidskriftsartikel (refereegranskat)abstract
- We report on Expanded Very Large Array observations of the Type IIb supernova 2011dh, performed over the first 100 days of its evolution and spanning 1-40 GHz in frequency. The radio emission is well described by the self-similar propagation of a spherical shockwave, generated as the supernova ejecta interact with the local circumstellar environment. Modeling this emission with a standard synchrotron self-absorption (SSA) model gives an average expansion velocity of v approximate to 0.1c, supporting the classification of the progenitor as a compact star (R-star approximate to 10(11) cm). We find that the circumstellar density is consistent with a rho proportional to r(-2) profile. We determine that the progenitor shed mass at a constant rate of approximate to 3 x 10(-5) M-circle dot yr(-1), assuming a wind velocity of 1000 km s(-1) (values appropriate for a Wolf-Rayet star), or approximate to 7 x 10(-7) M-circle dot yr(-1) assuming 20 km s(-1) (appropriate for a yellow supergiant [YSG] star). Both values of the mass-loss rate assume a converted fraction of kinetic to magnetic energy density of epsilon(B) = 0.1. Although optical imaging shows the presence of a YSG, the rapid optical evolution and fast expansion argue that the progenitor is a more compact star-perhaps a companion to the YSG. Furthermore, the excellent agreement of the radio properties of SN 2011dh with the SSA model implies that any YSG companion is likely in a wide, non-interacting orbit.
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