The Dual-Axis Circumstellar Environment of SN 1997egJennifer L. Hoffman, Douglas C. Leonard, and Alexei V. Filippenko2007 AAS, 209, 25402 PDF (442 K) |
| SN 1997eg is a Type IIn (“narrow-line”) supernova; its spectral line profiles indicate an intense interaction between the SN ejecta and surrounding dense circumstellar material. We use multi-epoch Keck spectropolarimetry to probe the configuration of this CSM. In polarized light, the complex Balmer lines are broader than in direct light and have enhanced blue line wings, suggesting that the receding side of the scattering region is blocked from our view. The broad Hα, Hβ, and He I λ5876 lines also produce intriguing “loops” in the Stokes q–u plane reminiscent of those arising from the rotating disks around Herbig Ae/Be stars and AGN central sources. These loops are distinct from the patterns formed by line depolarization or expansion of the scattering region, and indicate the presence of two distinct axes within the system. Our picture for SN 1997eg consists of an aspherical broad-line emission region and a nearly edge-on equatorially flattened circumstellar scattering region whose axes are misaligned with respect to one another. Such a scenario may arise from multiple asymmetric mass-loss episodes of the supernova progenitor; spectropolarimetry provides a way to probe these circumstellar shells and constrain the nature and mass-loss history of the progenitor. Although our model for SN 1997eg is similar to that proposed for the Type IIn SN 1998S, the two supernovae differ substantially in their polarimetric signatures. This suggests that part of the diversity of this heterogeneous subclass may be due to variations in viewing angle, a possibility that can also be explored with broader application of spectropolarimetric observational techniques in the study of core-collapse supernovae. J.L. Hoffman acknowledges the support of an NSF Astronomy & Astrophysics Postdoctoral Fellowship under award AST-0302123. |
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For more information, please send email to Jennifer. May 10, 2007 |