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RE: Possible supernova in Messier 51
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Title: A Binary Progenitor for the Type IIb Supernova 2011dh in M51
Authors: Omar G. Benvenuto, Melina C. Bersten, Ken'ichi Nomoto

We perform binary stellar evolutionary calculations following the simultaneous evolution of both stars in the system to study a potential progenitor system for the Type IIb supernova 2011dh. Pre-explosion photometry as well as light-curve modelling have provided constraints on the physical properties of the progenitor system. Here we present a close binary system that is compatible with such constraints. The system is formed by stars of solar composition with 16 solar masses + 10 solar masses on a circular orbit with an initial period of 125 days. The primary star ends its evolution as a yellow supergiant with a mass of \sim 4 solar masses, a final hydrogen content of \sim 3-5E-03 solar masses and with an effective temperature and luminosity in agreement with the HST pre-explosion observations of SN 2011dh. These results are nearly insensitive to the adopted accretion efficiency factor beta. At the time of explosion, the companion star has an effective temperature of 22 to 40 thousand Kelvin, depending on the value of beta, and lies near the zero age main sequence. Considering the uncertainties in the HST pre-SN photometry the secondary star is only marginally detectable in the bluest observed band. Close binary systems, as opposed to single stars, provide a natural frame to explain the properties of SN 2011dh without the need to fine tune any parameter.

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Supernova 2011dh
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Title: Photometric observations and preliminary modelling of type IIb supernova 2011dh
Authors: D. Yu. Tsvetkov, I. M. Volkov, E. I. Sorokina, S. I. Blinnikov, N. N. Pavlyuk, G. V. Borisov

CCD UBVRI photometry is presented for type IIb SN 2011dh for about 300 days. The main photometric parameters are derived and the comparison with SNe of similar types is reported. The light curves are similar to those for SN IIb 2008ax, but the initial flash is stronger and very short, and there are humps on the light curves in U and B at the onset of linear decline. Preliminary modelling is carried out, and the results are compared to the quasi-bolometric light curve and to the light curves in UBVRI bands.

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SN 2011dh
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Two images of Supernova 2011dh in the Whirlpool galaxy (Messier 51) in the constellation Canes Venatici, taken on the 5th and 8th June, 2011.
8" Schmidt Cassegrain reflector.



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Supernova 2011dh
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Title: EVLA Observations of the Radio Evolution of SN 2011dh
Authors: M. I. Krauss, A. M. Soderberg, L. Chomiuk, B. A. Zauderer, A. Brunthaler, M. F. Bietenholz, R. A. Chevalier, C. Fransson, M. Rupen

We report on Expanded Very Large Array (EVLA) 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 propagation of a self-similar spherical shockwave, generated as the supernova ejecta interact with the local circumstellar environment. Modelling this emission with a standard synchrotron self-absorption (SSA) model gives an average expansion velocity of v ~ 0.1c, supporting the classification of the progenitor as a compact star (R ~ 10^11 cm). We find that the circumstellar density is consistent with a r^-2 profile. We determine that the progenitor shed mass at a constant rate of 4 x 10^-5 solar masses/yr, assuming a wind velocity of 1000 km/s (values appropriate for a Wolf-Rayet star), or 9 x 10^-7 solar masses/yr assuming 20 km/s (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 the presence of a YSG is favoured by optical imaging, the observed rapid optical evolution and fast expansion argue for a compact progenitor. 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, or that interaction with the companion is mitigated by explosion/ejecta asymmetries. Finally, it is possible that the YSG is unrelated and is only coincidentally along the same line of sight.

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Possible supernova in Messier 51
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Title: VLBI Observations of the Nearby Type IIb Supernova 2011dh
Authors: M. F. Bietenholz, A. Brunthaler, A. M. Soderberg, M. Krauss, N. Bartel, L. Chomiuk, M. P. Rupen

We report on phase-referenced VLBI radio observations of the Type IIb supernova 2011dh at a time t = 83 d and 179 d after the explosion, at frequencies of 22.2 and 8.4 GHz, respectively. We detected SN 2011dh at both epochs. At the first epoch only an upper limit on SN 2011dh's angular size was obtained, but at the second epoch, we determine the angular radius SN 2011dh's radio emission to be 0.25 ± 0.08 mas by fitting a spherical shell model directly to the visibility measurements. At a distance of 8.4 Mpc this angular radius corresponds to a time-averaged (since t = 0) expansion velocity of the forward shock of 21000 ± 7000 km/s. Our measured values of the radius of the emission region are in excellent agreement with those derived from fitting synchrotron self-absorbed models to the radio spectral energy distribution, providing strong confirmation for the latter method of estimating the radius. We find that SN 2011dh's radius evolves in a power-law fashion, with R \propto t^(0.90 ± 0.15).

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Final moments of star caught before it explodes

Astronomers have been cataloguing star systems for three years to try to capture them as they meet their ends. Now, an international team says it has noticed one star system in the Whirlpool Galaxy, which was brightening and dimming in an unusual way, has produced a supernova.
The development could help researchers predict when a star may expire in the future as they try to determine whether the change in brightness was linked to the end of its life.

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Astrónomos de la UV fotografían la supernova más joven, captada nada más explotar

Un equipo internacional de astrónomos, liderado por el valenciano Iván Martí Vidal, ha conseguido tomar una imagen radioastronómica de la supernova más joven nunca obtenida. Catorce días tras la explosión de una estrella en la Galaxia del Remolino (M51) el pasado mes de junio, telescopios coordinados en toda Europa han fotografiado el estallido cósmico con un detalle equivalente al que supondría ver una pelota de golf en la superficie de la Luna.
Los resultados de esta investigación, en la que participan la Universitat de València y el Instituto de Astrofísica de Andalucía, se publican esta semana en la revista Astronomy & Astrophysics. En las observaciones han participado los telescopios de la NASA en Robledo de Chavela (Madrid) y del Instituto Geográfico Nacional en Yebes (Guadalajara).

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Title: VLBI observations of SN 2011dh: imaging of the youngest radio supernova
Authors: I. Martí-Vidal, V. Tudose, Z. Paragi, J. Yang, J. M. Marcaide, J. C. Guirado, E. Ros, A. Alberdi, M. A. Pérez-Torres, M. K. Argo, A. J. van der Horst, M. A. Garrett, C. J. Stockdale and K. W. Weiler

We report on the VLBI detection of supernova SN 2011dh at 22 GHz using a subset of the EVN array. The observations took place 14 days after the discovery of the supernova, thus resulting in a VLBI image of the youngest radio-loud supernova ever. We provide revised coordinates for the supernova with milli-arcsecond precision, linked to the ICRF. The recovered flux density is a factor ~2 below the EVLA flux density reported by other authors at the same frequency and epoch of our observations. This discrepancy could be due to extended emission detected with the EVLA or to calibration problems in the VLBI and/or EVLA observations.

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Posts: 131433
Date:
SN2011dh
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Title: VLBI observations of SN2011dh: imaging of the youngest radio supernova
Authors: I. Marti-Vidal, V. Tudose, Z. Paragi, J. Yang, J. M. Marcaide, J. C. Guirado, E. Ros, A. Alberdi, M. A. Perez-Torres, M. K. Argo, A. J. van der Horst, M. A. Garrett, C. J. Stockdale, K. W. Weiler

We report on the VLBI detection of supernova SN2011dh at 22GHz using a subset of the EVN array. The observations took place 14 days after the discovery of the supernova, thus resulting in a VLBI image of the youngest radio-loud supernova ever. We provide revised coordinates for the supernova with milli-arcsecond precision, linked to the ICRF. The recovered flux density is a factor 2 below the EVLA flux density reported by other authors at the same frequency and epoch of our observations. This discrepancy could be due to extended emission detected with the EVLA or to calibration problems in the VLBI and/or EVLA observations.

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Posts: 131433
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Supernova 2011dh
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Title: Discovery of Variability of the Progenitor of SN 2011dh in M51 Using the Large Binocular Telescope
Authors: D. M. Szczygie, J. R. Gerke, C. S. Kochanek, K. Z. Stanek

We show that the candidate progenitor of the core-collapse SN 2011dh in M51 (8 Mpc away) was fading by 0.039 ± 0.006 mag/year during the three years prior to the supernova, and that this level of variability is moderately unusual for other similar stars in M 51. While there are uncertainties about whether the true progenitor was a blue companion to this candidate, the result illustrates that there are no technical challenges to obtaining fairly high precision light curves of supernova progenitors using ground based observations of nearby (<10 Mpc) galaxies with wide field cameras on 8m-class telescopes. While other sources of variability may dominate, it is even possible to reach into the range of evolution rates required by the quasi-static evolution of the stellar envelope. For M 81, where we have many more epochs and a slightly longer time baseline, our formal 3 sigma sensitivity to slow changes is presently 3 millimag/year for a M_V ~= -8 mag star. In short, there is no observational barrier to determining whether the variability properties of stars in their last phases of evolution (post Carbon ignition) are different from earlier phases.

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SN 2011dh
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Title: The Progenitor Mass of SN 2011dh from Stellar Populations Analysis
Authors: Jeremiah W. Murphy (1), Zachary G. Jennings (1), Benjamin Williams (1), Julianne J. Dalcanton (1), Andrew E. Dolphin (2), ((1) Department of Astronomy, University of Washington, (2) Raytheon)

Using Hubble Space Telescope (HST) photometry, we characterise the age of the stellar association in the vicinity of supernova (SN) 2011dh and use it to infer the zero-age main sequence mass (M_{ZAMS}) of the progenitor star. We find two distinct and significant star formation events with ages of <6 and 17^{+3}_{-1} Myrs, and the corresponding M_{ZAMS} are >29 and 13±1 solar masses, respectively. These two bursts represent 18^{+4}_{-9}% (young) and 64^{+10}_{-14}% (old) of the total star formation in the last 50 Myrs. Adopting these fractions as probabilities suggests that the most probable progenitor mass is M_{ZAMS}=13±1 solar masses. Further information about the progenitor will help to identify the appropriate population. However, the exact nature of the progenitor is currently debated, and the range of scenarios permits either population. Using precise astrometry, others have identified a yellow supergiant as the progenitor candidate and have compared the photometry of this progenitor candidate with stellar evolution models to estimate M_{ZAMS}. These efforts have resulted in two discrepant estimates: 13±3 solar masses and 18-21 solar masses. The lower mass estimate is most consistent with our results. Adding yet another interpretation, panchromatic SN light curves suggest that a more compact star was the progenitor, and the yellow supergiant may not be associated with the SN at all. This scenario is consistent with either population, in which case we simply adopt our most probable mass estimate. To further constrain the age, we predict the post SN observations for each scenario.

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