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We report the X-ray detection of the Type II-plateau supernova SN 2004et inthe spiral galaxy NGC 6946, using the Chandra X-Ray Observatory. The positionof the X-ray source was found to agree with the optical position within ~0.4arcsec. Chandra also surveyed the region before the 2004 event, finding noX-ray emission at the location of the progenitor. For the post-explosionobservations, a total of 202, 151, and 158 photons were detected in threepointings, each ~29 ks in length, on 2004 October 22, November 6, and December3, respectively. The spectrum of the first observation is best fit by a thermalmodel with a temperature of kT=1.3 keV and a line-of-sight absorption ofN_H=1.0 x 10^{22} cm^{-2}. The inferred unabsorbed luminosity (0.4-8 keV) is~4x10^{38} erg/s, adopting a distance of 5.5 Mpc. A comparison between hard andsoft counts on the first and third epochs indicates a softening over this time,although there is an insufficient number of photons to constrain the variationof temperature and absorption by spectral fitting. We model the emission asarising from the reverse shock region in the interaction between the supernovaejecta and the progenitor wind. For a Type IIP supernova with an extendedprogenitor, the cool shell formed at the time of shock wave breakout from thestar can affect the initial evolution of the interaction shell and theabsorption of radiation from the reverse shock. The observed spectral softeningmight be due to decreasing shell absorption. We find a pre-supernova mass lossrate of (2-2.5)x 10^{-6} M_{\odot} /yr for a wind velocity of 10 kms, which isin line with expectations for a Type IIP supernova.

Chandra Observations of SN 2004et and the X-ray Emission of Type IIp Supernovae