An Extremely Bright Echo Associated With SN 2002hh

TL;DR

This paper reports the discovery of an extremely bright light echo around SN 2002hh, which dominates its late-time optical emission and challenges previous understanding of supernova echoes.

Contribution

It presents the first detailed optical spectroscopic and photometric analysis of a supernova with a dominant light echo at late times, revealing unusual brightness persistence.

Findings

The supernova's brightness remains nearly constant over two years.

The observed brightness is dominated by a dust echo, not the supernova itself.

The echo's brightness is only 4 magnitudes below the supernova's peak.

Abstract

We present new, very late-time optical photometry and spectroscopy of the interesting Type II-P supernova, SN 2002hh, in NGC 6946. Gemini/GMOS-N has been used to acquire visible spectra at six epochs between 2004 August and 2006 July, following the evolution of the SN from age 661 to 1358 days. Few optical spectra of Type II supernovae with ages greater than one year exist. In addition, g'r'i' images were acquired at all six epochs. The spectral and photometric evolution of SN 2002hh has been very unusual. Measures of the brightness of this SN, both in the R and I bands as well as in the H-alpha emission flux, show no significant fading over an interval of nearly two years. The most straightforward explanation for this behavior is that the light being measured comes not only from the SN itself but also from an echo off of nearby dust. Echoes have been detected previously around several SNe but these echoes, at their brightest, were ~8 mag below the maximum brightness of the SN. At V~21 mag, the putative echo dominates the light of SN 2002hh and is only ~4 mag below the outburst's peak brightness. There is an estimated 6 magnitudes of total extinction in V towards SN 2002hh. The proposed explanation of a differential echo/SN absorption is inconsistent with the observed BVRI colors.