Constraints on Circumstellar Material Around the Type Ia Supernova 2007af

TL;DR

This study uses high-resolution spectroscopy of SN 2007af to investigate circumstellar material, finding no evidence of variable Na I D absorption lines, thus constraining the presence and properties of circumstellar matter around this Type Ia supernova.

Contribution

It provides the first detailed constraints on circumstellar material around SN 2007af, challenging previous detections and suggesting possible differences in progenitor systems.

Findings

No variable Na D absorption lines detected in SN 2007af.

Limits placed on circumstellar shell mass and Na ionization fraction.

SN 2007af is confirmed as a normal Type Ia supernova.

Abstract

Patat et al. recently inferred the existence of circumstellar material around a normal Type Ia supernova (SN) for the first time, finding time-variable Na I D absorption lines in the spectrum of SN 2006X. We present high-resolution spectroscopy of the bright SN Ia 2007af at three epochs and search for variability in any of the Na D absorption components. Over the time range from 4 days before to 24 days after maximum light, we find that the host-galaxy Na D lines appear to be of interstellar rather than circumstellar origin and do not vary down to the level of 18 mA (column density of 2 x 10^11 cm^-2). We limit any circumstellar absorption lines to be weaker than ~10 mA (6 x 10^10 cm^-2). For the case of material distributed in spherically symmetric shells of radius ~10^16 cm surrounding the progenitor system, we place an upper limit on the shell mass of ~(3 x 10^-8)/X Msun, where X is the Na ionization fraction. We also show that SN 2007af is a photometrically and spectroscopically normal SN Ia. Assuming that the variable Na D lines in SN 2006X came from circumstellar matter, we therefore conclude that either there is a preferred geometry for the detection of variable absorption components in Type Ia supernovae, or SN 2007af and SN 2006X had different types of progenitor systems.