The Post-LBV Supernova 2001em
Abstract
The supernova (SN) 2001em in UGC 11794 was classified early as Type Ib/c, i.e., as one arising from a hydrogen-stripped star. As part of a radio survey with the Very Large Array of SNe Ib/c at late times (Stockdale et al. 2003, BAAS, 35, 1346), SN 2001em was detected as a highly luminous radio source ∼2 years after explosion. The SN was also subsequently discovered with Chandra to be a very luminous X-ray source. The properties of both the radio and X-ray emission are more characteristic of the Type II-narrow (IIn) SNe, where the SN shock is interacting with dense, massive circumstellar matter, resulting in bright radio synchrotron emission and thermal bremsstrahlung from the interaction region. In fact, SN 2001em has shown to have spectroscopically transformed to a SN IIn. The premise that this might indicate an off-axis gamma-ray burst has been presented (Granot & Ramirez-Ruiz 2004, ApJ, 609, L9) and later, rather convincingly, refuted (e.g., Schinzel et al. 2009, ApJ, 691, 1380). Chugai & Chevalier (2006, ApJ, 641, 1051) have interpreted the spectral transformation and radio/X-ray emission as the SN shock overtaking the detached hydrogen envelope of the progenitor star, which was shed in a superwind episode many years prior to explosion. Chevalier (2007, RMxAC, 30, 41) has further pointed to the required mass-loss rate in the event being equivalent to what would occur in the eruption of a luminous blue variable (LBV). The optical (ground-based and HST) and radio/X-ray data, together with mid-infrared Spitzer observations, tend to support this scenario of a very massive star that experienced a powerful LBV outburst prior to explosion. Such an event may not be unique, with possible parallels in the cases of SNe 2005bf and 2006jc, and may provide valuable new information about massive stellar evolution.
- Publication:
-
American Astronomical Society Meeting Abstracts #214
- Pub Date:
- December 2009
- Bibcode:
- 2009AAS...21460402V