TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1243 SUBJECT: SN 2002ap in M74 DATE: 02/02/04 23:19:06 GMT FROM: Lifan Wang at U.Texas SUPERNOVA 2002ap IN M74 L. Wang, Lawrence Berkeley National Laboratory (LBNL); D. Baade, European Southern Observatory (ESO); C. Fransson, Stockholm Observatory; P. Hoeflich, University of Texas; P. Lundqvist, Stockholm Observatory; and J. C. Wheeler, University of Texas, communicate: "High-quality spectropolarimetry (range 417-860 nm; spectral resolution 1.27 nm and 0.265 nm/pixel) of SN 2002ap was obtained with the ESO Very Large Telescope UT3 (+ FORS1) on Feb. 3 UT. A sharp change of the degree of polarization by more than 1 percent in the wavelength region from 650 nm to 800 nm relative to other wavelength regions is detected. The FWHM of the feature is 60.3 nm with centroid at 735.1 nm. The highest observed degree of polarization is 2.1 percent. The polarized feature corresponds to an absorption minimum in the flux spectrum. The polarization of this particular feature may provide important clues of the structure of the supernova envelope. Such large variation across spectral lines is quite unusual for supernovae, and further spectropolarimetric observations are encouraged. "