The Type IIn Supernova 2002kg: The Outburst of a Luminous Blue Variable Star in NGC 2403

Van Dyk, Schuyler D.; Li, Weidong; Filippenko, Alexei V.; Humphreys, Roberta M.; Chornock, Ryan; Foley, Ryan; Challis, Peter M.

The Type IIn Supernova 2002kg: The Outburst of a Luminous Blue Variable Star in NGC 2403

Authors

Van Dyk, Schuyler D.

Li, Weidong

Filippenko, Alexei V.

Humphreys, Roberta M.

Chornock, Ryan

Foley, Ryan

Challis, Peter M.

Description

We show that Supernova (SN) 2002kg in NGC 2403, initially classified as Type II-narrow (IIn), has photometric and spectroscopic properties unlike those of normal SNe. Its behavior, instead, is more typical of highly massive stars which experience the short-lived luminous blue variable (LBV) phase toward the end of their lives. The star, in fact, most resembles the LBV S Doradus in outburst. The precursor of SN 2002kg is the irregular, bright blue variable star 37 (V37), catalogued by Tammann & Sandage in 1968. Using high-quality ground-based, multi-band images we can constrain the initial mass of V37 to be M_ini >~ 40 M_sun. We find that, although the spectra indicate a nitrogen enhancement, possibly revealing the products of CNO processing by V37 in the ejecta, the star lacks a substantial LBV nebula. The outburst from SN 2002kg/V37 is not nearly as energetic as the giant eruptions of the eta Carinae-like variables, such as SN 1954J/V12, also in NGC 2403. SN 2002kg/V37, however, is among a growing number of ``SN impostors'' exhibiting a broad range of outburst energetics during a pre-SN phase of massive-star evolution.
22 pages, 15 figures, submitted to PASP