Supernova 1998bw - the final phases

The probable association with GRB 980425 immediately put SN 1998bw at the forefront of supernova research. Here, we present revised late-time BV RI 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 56 Co 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.

[1]  M. Phillips,et al.  The High-Z Supernova Search: Measuring Cosmic Deceleration and Global Curvature of the Universe Using Type Ia Supernovae , 1998, astro-ph/9805200.

[2]  J. Baldwin,et al.  Photometric and spectroscopic observations of SN 1990E in NGC 1035 - Observational constraints for models of type II supernovae , 1993 .

[3]  G. Helou,et al.  The Infrared Spectral Energy Distribution of Normal Star-forming Galaxies: Calibration at Far-Infrared and Submillimeter Wavelengths , 2000, astro-ph/0011014.

[4]  C. Fransson,et al.  Late Spectral Evolution of SN 1987A. I. Temperature and Ionization , 1997, astro-ph/9712223.

[5]  D. Schlegel,et al.  Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds , 1997, astro-ph/9710327.

[6]  P. Stetson.  DAOPHOT: A COMPUTER PROGRAM FOR CROWDED-FIELD STELLAR PHOTOMETRY , 1987 .

[7]  G. Neugebauer,et al.  Infrared stars with strong 1665/1667-MHz OH microwave emission. , 1972 .

[8]  M. Leising,et al.  The Co-57 Abundance in SN 1987A , 1992 .

[9]  P. A. Mazzali,et al.  The Nebular Spectra of the Hypernova SN 1998bw and Evidence for Asymmetry , 2001, astro-ph/0106095.

[10]  Puragra Guhathakurta,et al.  The Type Ic SN 1990B in NGC 4568 , 2001 .

[11]  D. Schlegel,et al.  Maps of Dust Infrared Emission for Use in Estimation of Reddening and Cosmic Microwave Background Radiation Foregrounds , 1998 .

[12]  D. Schneider,et al.  The optical light curve of SN 1985f in NGC 4618 , 1986 .

[13]  Explosive Nucleosynthesis in Aspherical Hypernova Explosions and Late-Time Spectra of SN 1998bw , 2000 .

[14]  Explosive Nucleosynthesis in Hypernovae , 2000, astro-ph/0011184.

[15]  Michael S. Bessell,et al.  UBVRI PHOTOMETRY II: THE COUSINS VRI SYSTEM, ITS TEMPERATURE AND ABSOLUTE FLUX CALIBRATION, AND RELEVANCE FOR TWO-DIMENSIONAL PHOTOMETRY. , 1979 .

[16]  Filippo Frontera,et al.  Accepted for publication in the Astrophysical Journal 2001, v. 555 Preprint typeset using L ATEX style emulateapj v. 14/09/00 THE METAMORPHOSIS OF SN 1998BW ‡ , 1999 .

[17]  C. Fransson,et al.  The Freeze-out Phase of SN 1987A: Implications for the Light Curve , 1993 .

[18]  D. Frail,et al.  Radio emission from the unusual supernova 1998bw and its association with the γ-ray burst of 25 April 1998 , 1998, Nature.

[19]  Felix Ryde,et al.  SN 1998bw at late phases , 2000 .

[20]  M. C. Begam,et al.  An unusual supernova in the error box of the γ-ray burst of 25 April 1998 , 1998, Nature.

[21]  Jonathan C. Tan,et al.  Trans-Relativistic Blast Waves in Supernovae as Gamma-Ray Burst Progenitors , 2000, astro-ph/0012003.

[22]  J. Sollerman,et al.  Why did Supernova 1054 shine at late times , 2000, astro-ph/0012347.

[23]  S. Woosley,et al.  Hard emission at late times from SN 1987A , 1989 .

[24]  P. Schechter,et al.  DOPHOT, A CCD PHOTOMETRY PROGRAM: DESCRIPTION AND TESTS , 1993 .

[25]  Deep Hubble Space Telescope STIS Color-Magnitude Diagrams of the Dwarf Irregular Galaxy WLM: Detection of the Horizontal Branch , 2000, astro-ph/0004231.

[26]  M. Montes,et al.  SN 1998bw/GRB 980425 and Radio Supernovae , 2001, astro-ph/0106131.

[27]  A. S. Fruchter,et al.  Drizzle: A Method for the Linear Reconstruction of Undersampled Images , 1998 .

[28]  L. Wang,et al.  Aspherical Explosion Models for SN 1998bw/GRB 980425 , 1998, astro-ph/9808086.

[29]  B. Leibundgut.  Circumstellar Media in the Late Stages of Stellar Evolution: Supernovae and their circumstellar environment , 1994 .

[30]  Peter B. Stetson,et al.  CCD photometry of the globular cluster M92 , 1988 .

[31]  P. Vreeswijk,et al.  A hypernova model for the supernova associated with the γ-ray burst of 25 April 1998 , 1998, Nature.

[32]  A. S. Fruchter,et al.  The Hubble Deep Field South: STIS Imaging* , 1998 .

[33]  S. Woosley,et al.  Gamma-Ray Bursts and Type Ic Supernova SN 1998bw , 1998, astro-ph/9806299.

[34]  Bradley E. Schaefer,et al.  The Late‐Time Light Curve of SN 1998bw Associated with GRB 980425 , 1999, astro-ph/9904397.

[35]  Edward L. Fitzpatrick,et al.  Correcting for the Effects of Interstellar Extinction , 1998, astro-ph/9809387.

[36]  Paolo A. Mazzali,et al.  Light Curve and Spectral Models for the Hypernova SN 1998bw Associated with GRB 980425 , 2000, astro-ph/0007010.