Variable sodium absorption in a low-extinction type Ia supernova

Joshua D. Simon, Avishay Gal-Yam, Orly Gnat, Robert M. Quimby, Mohan Ganeshalingam, Jeffrey M. Silverman, Stephane Blondin, Weidong Li, Alexei V. Filippenko, J. Craig Wheeler, Robert P. Kirshner, Ferdinando Patat, Peter Nugent, Ryan J. Foley, Steven S. Vogt, R. Paul Butler, Kathryn M.G. Peek, Erik Rosolowsky, Gregory J. Herczeg, Daniel N. SauerPaolo A. Mazzali

Research output: Contribution to journalArticlepeer-review

Abstract

Recent observations have revealed that some Type Ia supernovae exhibit narrow, time-variable NaI D absorption features. The origin of the absorbing material is controversial, but it may suggest the presence of circumstellar gas in the progenitor system prior to the explosion, with significant implications for the nature of the supernova (SN) progenitors. We present the third detection of such variable absorption, based on six epochs of high-resolution spectroscopy of the Type Ia supernova SN 2007le from the Keck I Telescope and the Hobby-Eberly Telescope. The data span a time frame of approximately three months, from 5 days before maximum light to 90 days after maximum. We find that one component of the NaI D absorption lines strengthened significantly with time, indicating a total column density increase of 2.5 × 1012 cm-2. The data limit the typical timescale for the variability to be more than 2 days but less than 10 days. The changes appear to be most prominent after maximum light rather than at earlier times when the ultraviolet flux from the SN peaks. As with SN 2006X, we detect no change in the CaII H and K absorption lines over the same time period, rendering line-of-sight effects improbable and suggesting a circumstellar origin for the absorbing material. Unlike the previous two supernovae exhibiting variable absorption, SN 2007le is not highly reddened (E B - V = 0.27 mag), also pointing toward circumstellar rather than interstellar absorption. Photoionization calculations show that the data are consistent with a dense (107 cm-3) cloud or clouds of gas located 0.1 pc (3 × 1017 cm) from the explosion. These results broadly support the single-degenerate scenario previously proposed to explain the variable absorption, with mass loss from a nondegenerate companion star responsible for providing the circumstellar gas. We also present possible evidence for narrow Hα emission associated with the SN, which will require deep imaging and spectroscopy at late times to confirm.

Original languageEnglish (US)
Pages (from-to)1157-1170
Number of pages14
JournalAstrophysical Journal
Volume702
Issue number2
DOIs
StatePublished - 2009

Keywords

  • Circumstellar matter
  • Supernovae: general
  • Supernovae: individual (SN 1999cl, SN 2006X, SN 2007le)

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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