The Late-Time Rebrightening of Type Ia SN 2005gj in the Mid-Infrared

TL;DR

This study reports late-time mid-infrared observations of Type Ia supernovae with circumstellar interaction, revealing dust emission and rebrightening likely caused by renewed shock interaction with circumstellar material.

Contribution

It provides new archival mid-IR data showing late-time dust emission and rebrightening in SNe Ia-CSM, highlighting ongoing circumstellar interaction beyond 500 days.

Findings

Mid-IR emission indicates pre-existing dust heated by CSM interaction.

SN 2005gj's luminosity more than doubles after 1 year, suggesting renewed shock interaction.

Evidence supports a dust shell beyond the forward-shock radius, heated by optical and X-ray emission.

Abstract

A growing number of observations reveal a subset of Type Ia supernovae undergoing circumstellar interaction (SNe Ia-CSM). We present unpublished archival Spitzer Space Telescope data on SNe Ia-CSM 2002ic and 2005gj obtained > 1300 and 500 days post-discovery, respectively. Both SNe show evidence for late-time mid-infrared (mid-IR) emission from warm dust. The dust parameters are most consistent with a pre-existing dust shell that lies beyond the forward-shock radius, most likely radiatively heated by optical and X-ray emission continuously generated by late-time CSM interaction. In the case of SN 2005gj, the mid-IR luminosity more than doubles after 1 year post-discovery. While we are not aware of any late-time optical-wavelength observations at these epochs, we attribute this rebrightening to renewed shock interaction with a dense circumstellar shell.