Properties of Two Hypernovae Entering the Nebular Phase: SN 1997ef and SN 1997dq

The two peculiar Type Ic supernovae (SNe) 1997ef and 1997dq are shown to have very similar photometric and spectral evolution in the epochs when both SNe are observed (i.e., beyond ~80 days after the explosion). The early light curves and spectra of SN 1997ef suggested that this was a "hypernova," or "SN 1998bw-like Type Ic supernova." The fact that the two SNe are very similar allows us to extend the time coverage of this type of event, since SN 1997dq, unlike SN 1997ef, was observed well into the nebular phase. In contrast to SN 1998bw, the spectra of these two SNe did not become fully nebular until almost 1 yr after the explosion. During a long transition phase, lasting at least 6 months, the SNe developed nebular emission in lines of [O I] and [Ca II], but at the same time they retained an underlying, photospheric-type spectrum, originating at very low velocities. Spectral synthesis techniques are used to model the spectrum of SN 1997dq, suggesting that it produced ~0.16 M☉ of 56Ni, and that a significant fraction of this is located in a dense, low-velocity inner region.

[1]  E. Cappellaro,et al.  The Rates of hypernovae and gamma-ray bursts: Implications for their progenitors , 2004 .

[2]  Mamoru Doi,et al.  THE TYPE IC HYPERNOVA SN 2002AP , 2002 .

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

[4]  P. Mazzali,et al.  The Properties of SN 2002ap and Other Type Ic Hypernovae , 2003 .

[5]  Lifan Wang,et al.  The supernova-gamma-ray burst connection , 1998, astro-ph/9806212.

[6]  Ryan Chornock,et al.  Optical Photometry and Spectroscopy of the SN 1998bw–like Type Ic Supernova 2002ap , 2003, astro-ph/0307136.

[7]  J. Wheeler Supernovae and Gamma-Ray Bursts , 2000 .

[8]  P. A. Mazzali,et al.  The Type Ic Hypernova SN 2003dh/GRB 030329 , 2003, astro-ph/0309555.

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

[10]  Shiomi Kumagai,et al.  Theoretical light curves for the type IC supernova SN 1994I , 1994 .

[11]  Warren R. Brown,et al.  Spectroscopic Discovery of the Supernova 2003dh Associated with GRB 030329 , 2003, astro-ph/0304173.

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

[13]  Stellar Collapse and Gravitational Waves , 2002, astro-ph/0211609.

[14]  Thomas Matheson,et al.  Optical Spectroscopy of Type Ib/c Supernovae , 2001, astro-ph/0101119.

[15]  R. Foley,et al.  Photospheric‐Phase Spectropolarimetry and Nebular‐Phase Spectroscopy of the Peculiar Type Ic Supernova 2002ap , 2002, astro-ph/0206368.

[16]  Paolo A. Mazzali,et al.  A Spectroscopic Analysis of the Energetic Type Ic Hypernova SN 1997ef , 2000, astro-ph/0007222.

[17]  D. Bersier,et al.  Photometry and Spectroscopy of GRB 030329 and Its Associated Supernova 2003dh: The First Two Months , 2003, astro-ph/0307435.

[18]  L. A. Antonelli,et al.  SN 2003lw and GRB 031203: A Bright Supernova for a Faint Gamma-Ray Burst , 2004, astro-ph/0405449.

[19]  Yuji Shirasaki,et al.  On the Spectrum and Spectropolarimetry of Type Ic Hypernova SN 2003dh/GRB 030329* , 2003 .

[20]  J. Thorstensen,et al.  The Peculiar Type Ic Supernova 1997ef: Another Hypernova , 2000 .

[21]  K. Pedersen,et al.  A very energetic supernova associated with the γ-ray burst of 29 March 2003 , 2003, Nature.

[22]  Y. Yoshii,et al.  A Two-Component Model for the Light Curves of Hypernovae , 2003, astro-ph/0305182.

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

[24]  Alexei V. Filippenko,et al.  Optical spectra of supernovae , 1997 .