Astronomy & Astrophysics

Free access article

Issue		A&A Volume 386, Number 3, May II 2002
Page(s)		944 - 956
Section		Formation, structure and evolution of stars
DOI		10.1051/0004-6361:20020326

A&A 386, 944-956 (2002)
DOI: 10.1051/0004-6361:20020326

Supernova 1998bw - the final phases

J. Sollerman^{1, 2}, S. T. Holland³, P. Challis⁴, C. Fransson², P. Garnavich³, R. P. Kirshner⁴, C. Kozma², B. Leibundgut¹, P. Lundqvist², F. Patat¹, A. V. Filippenko⁵, N. Panagia⁶ and J. C. Wheeler⁷

¹ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
² Stockholm Observatory, Department of Astronomy, SCFAB, 106 91 Stockholm, Sweden
³ Physics Department, University of Notre Dame, Notre Dame, IN, USA
⁴ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, USA
⁵ Department of Astronomy, University of California, Berkeley, CA, USA
⁶ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD, USA
⁷ Department of Astronomy, University of Texas, Austin, TX, USA

(Received 3 January 2002 / Accepted 28 February 2002 )

Abstract
The probable association with GRB 980425 immediately put SN 1998bw at the forefront of supernova research. Here, we present revised late-time BVRI light curves of the supernova, based on template images taken at the VLT. To follow the supernova to the very last observable phases we have used HST/STIS. Deep images taken in June and November 2000 are compared to images taken in August 2001. The identification of the supernova is firmly established. This allows us to measure the light curve to ~ 1000 days past explosion. The main features are a rapid decline up to more than 500 days after explosion, with no sign of complete positron trapping from the $\element[][56]$ decay. Thereafter, the light curve flattens out significantly. One possible explanation is powering by more long lived radioactive isotopes, if they are abundantly formed in this energetic supernova.

Key words: supernovae: individual (SN 1998bw) -- nuclear reactions, nucleosynthesis, abundances -- Gamma rays: bursts

Offprint request: J. Sollerman, jesper@astro.su.se

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