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Date:
 Supernova 1993J Permalink Cosmic detectives discover missing star in ultimate of dead endsAstronomers have solved a 21-year-old cosmic mystery with the discovery of a star whose companion exploded, confirming that the surviving star was partly responsible for the resulting supernova. A team of 12 scientists, including the University of Chicagos Vikram Dwarkadas, recently published the discovery in the Astrophysical Journal. Read more __________________

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 SN 1993J companion star Permalink Hubble Finds Companion Star Hidden for 21 Years in a Supernova's GlareAstronomers using NASA's Hubble Space Telescope have discovered a companion star to a rare type of supernova. This observation confirms the theory that the explosion originated in a double-star system where one star fueled the mass-loss from the aging primary star. This detection is the first time astronomers have been able to put constraints on the properties of the companion star in an unusual class of supernova called Type IIb. They were able to estimate the surviving star's luminosity and mass, which provide insight into the conditions that preceded the explosion. Read more __________________

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Date:
 Supernova 1993J Permalink Title: X-rays from the explosion site: Fifteen years of light curves of SN 1993JAuthors: Poonam Chandra, Vikram V. Dwarkadas, Alak Ray, Stefan Immler, David PooleyWe present a comprehensive analysis of the X-ray light curves of SN 1993J in a nearby galaxy M81. This is the only supernova other than SN 1987A, which is so extensively followed in the X-ray bands.Here we report on SN 1993J observations with the Chandra in the year 2005 and 2008, and Swift observations in 2005, 2006 and 2008. We combined these observations with all available archival data of SN 1993J, which includes ROSAT, ASCA, Chandra, and XMM-Newton observations from 1993 April to 2006 August. In this paper we report the X-ray light curves of SN 1993J, extending up to fifteen years, in the soft (0.3--2.4 keV), hard (2--8 keV) and combined (0.3--8 keV) bands. The hard and soft-band fluxes decline at different rates initially, but after about 5 years they both undergo a t^{-1} decline. The soft X-rays, which are initially low, start dominating after a few hundred days. We interpret that most of the emission below 8 keV is coming from the reverse shock which is radiative initially for around first 1000-2000 days and then turn into adiabatic shock. Our hydrodynamic simulation also confirms the reverse shock origin of the observed light curves. We also compare the H \alpha line luminosity of SN 1993J with its X-ray light curve and note that the H$\alpha$ line luminosity has a fairly high fraction of the X-ray emission, indicating presence of clumps in the emitting plasma. Read more  (138kb, PDF) __________________

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 RE: SN1993J Permalink Title: SN 1993J VLBI (IV): A Geometric Determination of the Distance to M81 with the Expanding Shock Front MethodAuthors: N. Bartel, M. F. Bietenholz (York Univ.), M. P. Rupen (NRAO), V. V. Dwarkadas (Univ. of Chicago)We compare the angular expansion velocities, determined with VLBI, with the linear expansion velocities measured from optical spectra for supernova 1993J in the galaxy M81, over the period from 7 d to ~9 yr after shock breakout. We estimate the distance to SN 1993J using the Expanding Shock Front Method (ESM). We find the best distance estimate is obtained by fitting the angular velocity of a point halfway between the contact surface and outer shock front to the maximum observed hydrogen gas velocity. We obtain a direct, geometric, distance estimate for M81 of D=3.96 ±0.05 ±0.29 Mpc with statistical and systematic error contributions, respectively, corresponding to a total standard error of ±0.29 Mpc. The upper limit of 4.25 Mpc corresponds to the hydrogen gas with the highest observed velocity reaching no farther out than the contact surface a few days after shock breakout. The lower limit of 3.67 Mpc corresponds to this hydrogen gas reaching as far out as the forward shock for the whole period, which would mean that Rayleigh-Taylor fingers have grown to the forward shock already a few days after shock breakout. Our distance estimate is 9 ±13 % larger than that of 3.63 ±0.34 Mpc from the HST Key Project, which is near our lower limit but within the errors. Read more  (521kb, PDF) __________________

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 Permalink Beginning with a full view of beautiful spiral galaxy M81, follow the insets (left, bottom, then right) to zoom in on a real survivor. Seen at the centre of the final field on the right is a star identified as the survivor of a cosmic cataclysm - the supernova explosion of its companion star. Light from the cosmic blast, likely triggered by the core collapse of a star initially more than 10 times as massive as the Sun, first reached Earth over 10 years ago and was catalogued as supernova SN 1993J. Expand (1326kb, 2239 x 1716)Though the supernova itself is no longer visible, light-echoes from dust in the region can still be seen near the companion, the first known survivor of a supernova in a binary star system. Astronomers believe that a substantial transfer of material to the surviving companion star during the last few hundred years before the stellar explosion can explain peculiarities seen in this supernova. After supernova SN 1987A in the Large Magellanic Cloud, SN 1993J in nearby M81 is the brightest supernova seen in modern times. __________________
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